Colorado Geological Survey

Colorado
Geological
Survey

COLORADO GEOLOGICAL SURVEY
BOULDER
R. D. GEORGE, State Geologist
BULLETIN 30
G E O L O G Y A N D O R E DEPOSITS
OF THE
R E D C L I F F D I S T R I C T
COLORADO
By
R. D. CRAWFORD and RUSSELL GIBSON
BOULDER, COLORADO
CAMERA PRINT
1925

GEOLOGICAL BOARD
His Excellency, "William E. Sweet , i .Governor of Colorado
George Norlin President University of Colorado
Victor C Alderson President State School of Mines
Charles A. Lory President State Agricultural College
LETTER OF TRANSMITTAL
State Geological Survey,
University of Colorado, July 8, 1924
Governor William E. Street, Chairman, and Members of the Advisory Board
of the. State Geological Survey.
Gentlemen: I have the honor to transmit herewith Bulletin 30 of the
Colorado Geological Survey.
Very respectfully,
R. D. George,
State Geologist.

CONTENTS
Page
Introduction 7
Geographic position 7
Field work and acknowledgments , , 3
History of mining , 9
Bibliography ,_. 11
Chapter I. Physiography 16
Topography 16
Influence of structure , 16
Glaciation , 16
Landslides , , , 18
Vegetation 18
Alluvium and soil--. 19
Chapter II. Pre-Cambrian metamorphic rocks 20
Granite gneiss , , 20
Quartz-diorite gneiss 21
Granitic gneiss 21
Mica gneiss , , 21
Pyroxene gneiss , , 21
Slllimanite gneiss , 21
Mica schist 22
Garnet-mica schist 22
Quartzite 22
Marble 22
Chapter III. Igneous rocks , 24
Granite , 24
Quartz monzonite 25
Quartz diorite 26
Quartz-hornblende diorite : 26
Quartz-mica diorite (without essential hornblende) 27
Gneissoid quartz-mica diorite 28
Syenite , , 28
Hornblendite ,- 28
Peridotite , 29
Porphyry and felsite 29
Quartz-monzonite porphyry , 31
Quartz-diorite porphyry 32
Chapter IV. Paleozoic sedimentary rocks 33
Cambrian and Ordovician or Devonian sediments 33
Sawatch quartzite 33
Description , 33
Age 35
Cambrian 35
Ordovician or Devonian 35
Devonian-Mississippian sediments.- 35
Leadvill© limestone 35
Description 35
Age
Chapter Pennsylvanian General Minerals Faulting Description Age Aluminum Sulphide V. VI. Structural character of Mineral the enrichment , sediments ore of deposits geology the deposits ores , ,
37
, 38 46 47
40 43
46
47 38

4 CONTENTS
Chapter VI (Continued) •
Alunite
Page
47
Arsenic 47
Arsenopyrite - , 47
Copper 47
Bornite , 47
Chalcanthite 47
Chalcocite 47
Chalcopyrite 47
Covellite , 48
Tetrahedrite 48
Gold 48
Iron. , 4S
Coquimbite 48
Limonite 49
Pyrite 49
Pyrrhotite , , 49
Siderite , 49
Turgite 49
Lead 50
Anglesite 50
Cerussite , 50
Galena 50
Manganese 50
Silver 50
Zinc 50
Goslarite , 50
Smithsonite , 51
Zinc blende, or sphalerite 51
Exclusively gangue minerals , , 51
Barite , 51
Calcite • , 51
Dolomite 51
Gypsum ^ 52
Kaolin , 52
Quartz * 52
Classes of mineral deposits 52
Fissure veins 52
Replacement ore deposits 53
Shape of ore bodies 53
Unsupported rock masses in ore 53
Crystals in country rock 53
Preservation of rock structures by ore 54
Size of replacement ore bodies 54
Sideritic and dolomitic replacement 55
Jasperoid replacement 56
Description of the jasperoid 56
Occurrence of jasperoid 57
Crystallized quartz replacement 59
Stratigraphic position of ore bodies , 59
Relation of ore bodies to faults , 60
Source of the ores . 62
Future possibilities
Chapter VII. Descriptions of mines 67
65
Mabel Ground Faulting Production mine Cleveland Doddridge Hog mline fault 73
71 72 70 71 67

CONTENTS O
Chapter VII (Continued)
Bedding faults
Page
73
Character of wall rock 73
Ore deposits-., 73
Fissure deposits 73
Replacement deposits 74
Character of the ore 74
Eagle mines 75
Geologic features 76
Size and range of ore bodies 77
Character of the ores , 78
Mineral relationships in ore bodies 7S
Mining methods and equipment 79
Evening Star mine 79
Ben Butler mine , 80
Tip Top tunnel , 80
Star of the West incline 80
Pursey Chester mine , 81
Potvin mine and F. C. Garbutt mine 81
Alpine mine 81
Pine Martin mine 82
Champion mine 82
Body mine 82
Silurian and Ovee mines 83
Henrietta mine 83
Little May mine 83
Foster Combination mine , 84
First National and Eighty Four mines . 84
Wyoming Valley mine 85
Liberty mine 85
Horn Silver mine 86
Index 87

ILLUSTRATIONS
Page
Plate I. Topographic and geologic map of the Red Cliff
district, Colorado In pocket
Plate II. Mining claims of the Red Cliff district , In pocket
Plate III. Section of Eagle No. 2 ore body In pocket
Figure 1. Index map of Colorado, showing position of the Red Cliff
district 7
2. Redi Cliff, looking toward Turkey Creek 8
3. Gilman from the southeast 9
4. Gilman from the northwest , 10
5. Glaciated valley connecting Eagle and Homestake valleys,
looking northwest 17
6. A hanging valley, Yoder Falls 18
7. Eagle River, looking south from near Silver Creek 19
8. Pennsylvanian sediments, looking north from Rex 39
9. Columnar section of the Paleozoic sediments in the Red Cliff
district 42
10. Jasperoid outcrop north of Coal Creek 58
11. Jasperoid outcrop south of Elk Creek 59
12. Map showing positions of post-Paleozoic quartz monzonite
and related quartz diorite 64
13. Plan of the Mabel mine 68
14. Section through the Mabel vein 69
15. Map showing faults and fissures in the Ground Hog mine 72

GEOLOGY A N D ORE DEPOSITS
OP THE
R E D CLIFF DISTRICT, COLORADO
INTRODUCTION
GEOGRAPHIC POSITION
The Red Cliff, or Battle Mountain, mining district is in the southeastern
part of Eagle County, Colorado, west of the Continental Divide. An area
of about 58 square miles has been mapped, and is described in this report.
Gilman, Bell's Camp, and Red Cliff are in the productive part of the district.
The main line of the Denver and Rio Grande Western Railroad
Figure 1. Index map of Colorado, snowing position of the Red Cliff district
passes through all the present settlements of the district except Gilman and
Bell's Camp. These two are near the railroad, but high above the bottom
of Eagle Canyon through which the railroad runs. Gilman is connected with
Belden, at the bottom of the canyon, by a tramway of the Empire Zinc
Company. The Pikes Peak Ocean to Ocean Highway runs through Pando,
Red Cliff, Bell's Camp, and Gilman.

& RED cliff mining district
FIELD WORK AND ACKNOWLEDGMENTS
The field work for this report was done in the summers of 1921,
1922, and 1923 by a party that varied in number from two to five. Each
man regularly employed spent from two to six months in the field. In
the productive area and much of the outlying territory topography and
geology were mapped at the same time. In this work a plane-table and
telescopic alidade were used, and distances and elevations determined by
stadia. One instrument man platted on a single plane-table sheet the data
obtained by two or three rodmen, together with the data obtained by
himself at and near the plane-table stations. Each rodman platted on
tracing paper the topography, geology, and cultural features at and near
the stadia stations. These data were transferred to the plane-table sheet
at convenient intervals,—at the end of the day when instrument man and
rodman were working on opposite sides of a canyon. In many places timber
or high relief made extensive linear traverses impracticable; in consequence,
sights were taken to many stadia stations from a single plane-
Figure 2. Bed Cliff, looking- toward Turkey Creek
table station. Part of the area was mapped topographically by means of
paced traverses with traverse plane-table, open-sight alidade, and aneroid
barometer. The entire map was controlled by triangulation with planetable
and telescopic alidade, beginning at the ends of a measured base line
in Eagle Park. The control was tied to Holy Cross and Homestake mountains
whose latitude and longitude had been determined by the United States
Geological Survey. A large-scale topographic map of part of Battle Mountain
made by Messrs. Piatt and Kleff for the Empire Zinc Company, was
reduced, and is included in the accompanying map (PI. I, in pocket).
The personnel of the field party changed each season. The topographic
map and the greater part of the geologic map were made by H. E. Alexander,
E. P. Andrews, H. C. Fuller, Russell Gibson, E. A. Hall, J. W. Hunter,
J. E. Hupp, A. N. Murray, and W. O. Thompson. Mr. Gibson was in the

INTRODUCTION »
field about six months, and spent most of his time in geologic work. R. D.
Crawford was in the district about ten weeks, and was engaged in geologic
work exclusively. Most of the necessary laboratory work, except the fossil
determinations and quantitative analyses, has been done by Mr. Hall and
the writers, who, in preparing this report, have used the notes of all the
field men.
The writers gratefully acknowledge the uniformly generous spirit of
cooperation shown by mine operators, miners, and others, many of whom
gave much time to further the survey of the district. Thanks are especially
due Messrs. R. B. Paul and A. H. Buck of the Empire Zinc Company, as
well as other members of their staff, for their many courtesies; Messrs. J.
M. and R. V. Dismant and Mr. B. A. Hart for maps, information concerning
production, and other assistance; Mr. Arthur Ridgway of the Denver and
Rio Grande Western Railroad for a large-scale map of the right-of-way of
the railroad, and Mr. C. W. Henderson of the United States Geological
Survey for the table (p. 12) showing the production of the district in
detail.
Figure 3. Gilman from the southeast
HISTORY OF MINING
Ore was discovered in the Gilman and Red Cliff region in 1879 when
it was part of Summit County. First known as the Eagle River mining
district the area has in recent years been called the Red Cliff district or,
•possibly more often, the Battle Mountain mining district. Eagle County
was organized in 1883.
A series of well written and interesting articles by W. B. Thorn, published
by "The Eagle Valley Enterprise," of Eagle, in 1921, gives much information
concerning the early history of mining and the mining camps of Eagle
County. Mr. Thorn states that among the earliest locations on Battle
Mountain, mostly in 1879, "were the Little Ollie, by James Deming, William

10 RED CLIFF MINING DISTRICT
Barney, and William Helmer; the Eagle Bird, by J. T. McGrew, William
and Henry Helmer and D. C. Collier; the Silver Wave, by Helmer brothers;
the Black Iron, by Dr. Bell and B. S. Morgan. Other properties were the
Ida May, Little Duke, May Queen, Kingfisher, Little Chief and Crown Point.
Robert Baney and William Travis feathered their nests from the Ben Butler.
In 1880 A. W. Maxfield represented Council Bluffs mine owners on Battle
Mountain. He was followed by J. T. Hart of Council Bluffs Among
the first locations at Red Cliff were the Henrietta, by Frank Bowland & Co.,
July 4, 1879; the Horn Silver, by Wm. Greiner and G. J. DaLee, July 7, 1879,
and the Wyoming, by Dugan, Jenkins and others, July 26, 1879 "
The foregoing list of mining claims includes some that afterward became
heavy producers. According to Mr. Thorn the first important ore
discovery was made in the Belden mine, located May 5, 1879. He also
states that the Battle Mountain smelter was "built in 1880, only to be
abandoned when the Denver and Rio Grande Railway entered Red Cliff,
November 20, 1881."
Figure 4. Gilman from the northwest
In the 80s much development work was done at Taylor Hill, a short
distance south of the area mapped, and at Holy Cross City, a few miles
west of the Red Cliff district. Each of these localities produced several
thousand dollars worth of ore, but the returns were small in proportion to
the invested capital. Near Two Elk Creek, a short distance north of the
mapped area, some prospecting has been done, and ore minerals have
been found.
The metal production of Eagle County by years is shown in Table I.
This table was prepared by C. W. Henderson, Mineral Geographer of the
United States Geological Survey, for his "History of Mining in Colorado,"
and was generously furnished by Mr. Henderson for this bulletin. According
to Mr. Henderson the Red Cliff district should be credited with all this
production excepting 200,000 ounces of silver produced by the Brush Creek

INTRODUCTION 11
district, in the years 1913-1918, and the several thousand dollars worth of
ore produced in the early days by the Taylor Hill and Holy Cross localities.
At the end of 1923 the Red Cliff district had therefore produced ore
to the value of $28,000,000 or more. The average values of the metals for
each year are shown in Table II which, down to and including 1922, is taken
from a larger table in "Mineral Resources of the United States, 1922,"
published by the United States Geological Survey; Mr. Henderson kindly
supplied the average values for 1923.
Several mills have been built in the district, and formerly much ore
was concentrated in the Iron Mask mill at Belden. This mill has been
idle for several years, and nearly or quite all the ore mined in recent years
has been shipped directly from the mines—part to the smelters, and part
to the Empire Zinc Company's plant at Canon City, Colorado.
BIBLIOGRAPHY
Peale, A. C, Report of geologist of Middle Division: Hayden S*urvey, 8th
Annual Report, 1876, pp. 73-180.
Bechler, G. R., Geographical report on the Middle and South parks,
Colorado, and adjacent country: Hayden Survey, 9th Annual Report, 1877,
pp. 371-440.
Emmons, S. F., Notes on some Colorado ore deposits: Colorado Scientific
Society Proceedings, vol. 2, 1886, pp. 85-105.
Tilden, G. C, Mining notes from Eagle County—The quartzite deposits
of Red Cliff; Taylor, Eagle County: Colo. School of Mines, Biennial Report,
1886, pp. 129-133.
Olcutt, E. E., Battle Mountain mining district, Eagle County, Colorado:
Engineering and Mining Journal, vol. 43, 1887, pp. 418-419, 436-437.
Guiterman, F., Gold deposits in the quartzite formation of Battle Mountain,
Colorado: Colorado Scientific Society Proceedings, Vol. 3, 1890, pp.
264-268.
Rosenberg, Leo von, The mines of Battle Mountain, Eagle County,
Colorado: Engineering and Mining Journal, vol. 53, 1892, p. 545, cross-section
on p. 544.
Lakes, Arthur, Redcliff ore deposits; Mines and Minerals, vol. 23, 1903,
pp. 252-253.
Lakes, Arthur, The Red Cliff ore deposits: Geology of Western Ore
Deposits, 1905, pp. 242-244.
Nicholson, H. H., Low grade sulphides of Eagle County, Colorado-
Mining Science, vol. 64, 1911, pp. 127-128.
Hoskin, A. J., Revival of mining at Red Cliff: Mines and Minerals, vol
33, 1912, pp. 147-151.
Means, A. H., Geology and ore deposits of Red Cliff, Colorado: Economic
Geology, vol. 10, 1915, pp. 1-27.

12 RED CLIFF MINING DISTRICT
TABLE I—TOTAL PRODUCTION OP GOLD, SILVER, COPPER, LEAD, AND
Year
Short Tons
Ore
Fine
Ounces
Gold
Value
Fine
Ounces
Silver
Value
Recoverable
Copper, Pounds
al879
1880 1,000
C % 2,000 38,672 44,473
dl881 2,000
4,000 79,344 89,659
el882 2,500
5.000 98,680 112,495
1883 19,859
70,000 232,031 257,554
1884 10,000
30,000 154,687 171,703
1885 11,000
33,000 170,156 182,067
1886
423,517 569,637 563,941
1887
219,594 254,078 248,996
1888
142,002 193,489 181,880
1889
92,220 170,551 160,318
1890
68,862 75,265 79,028
2,044
1891
153,453 280,168 277,366
2,200
1892
139,299 347,954 302,720
71,049
1893
168,867 187,658 146,373
5,876
1894
55,521 62,543 39,402 359,054
1895
1,866
30,900 53,421 34,724 157,914
1896
12,049
16,472 65,824 44,760 150,134
1897
15,986
34,767 46,046 27,628
32,863
1898
4,191
30,571 70,783 41,762
32,409
1899
3,009
46,094 44,393 26,636
29,331
1900
11,526
103,598 234.674 145,498 130,233
1901
27,761
97,376 175,181 105,109
14,270
1902
33,177
4,645.74
31,956 45,336 24,028
66,141
1903
34,16.4
1,992.42
16,040 27,054 14,609 286,885
1904
47,488
1,740.29
30,075 27,348 15,862 209,551
1905
49,377
964.36
46,891 46,487 28,357
66,608
1906
74,197
1,233.37
51,561 94,912 64,540 147,176
1907
105,149
3,130.98
53,641 70,586 46,587
41,368
1908
100,875
3,488.37
58,131 86,715 45,959
28,105
' 1909
89,675
$3,06,302
2,060.69
53,308 7,648,315 125,214 $6,561,612 65,111 | 6,723.485 60.086
1910
22,248
25,231 88,313 47,689 I 112,610
1911
32,635 FOOTNOTES 41,160 FOR TABLE 116,109 I 61,538
53,136
By Chari.es
1912
39,785 W. Henderson
49,294 163,735 100,697 353,041
a Director
1913
71,892 of the Mint Report for 1883, 41,220 pp. 240, 301,380 290-294 :— 182,034 123,306
"Eagle County was formerly a
1914
47,194 part of Summit, 127,080 and embraces 70,275 what 517,109 were
known as Eagle River and Holy Cross
1915
95,426 mining districts 177,550 90,018 The chief 1,833,078 camp
is Red Cliff, in the vicinity of which
1916
96,036 are the largest 222,126 producers 146,159 in the county, 1,330,296 viz.,
the Eagle Bird group, Belden, Clinton,
1917
41,187 Little Chief, 136,023 Crown 112,083 Point, Spirit, 507,612 King
Fisher, Discovery, Silver Age, and
1918
35,975 a few minor 241,406 properties. 241,406 These are located
on Battle Mountain. . . . The Belden
1919
19,935 [was] located 72,159 in 1879. 80,818 . . . Eagle Bird
Consolidated Mining Company. . . . consists
1920
25,496 of 25 279,667 claims, among 304,837 which are ....
the Silver Wave, Eagle Bird, Indian
1921
64,723 Girl, May Queen, 682.550 Cleveland, 682,550 Black Iron. . . ."
1922
72,111 1880 583,737 583,737
b Director of the Mint for 1880, p.
1923
42,598 152, gives, 327,593 under Summit 268,626 County $50 000
silver (38,672 ounces at $1.29 + ) as production of Eagle River district. . . .'"Several
promising contacts, notably the Belden group, have been opened the past summer."
1880-1882
c Estimated by Chas. "W. Henderson.

Copper
Value
$980,802
PRODUCTION
ZIN'C IN EAGLE COUNTY, COLORADO, 1879-1923
Recoverable Lead
Pounds
87,824,155
Value
$3,964,633
Recoverable
Pounds
155,093,129
Zinc
Value
$13,830,573
Value
$28,343,922
13
Year
1879
800,000 $ 40,000
$ 86,473 1880
1,600,000 76,800
170,459 1881
a 2,000,000
98,000 ::::::::::::::
215,495 1882
1 688,000 i
1,015,554 1883
16,000,000 244,200
445,903 1884
!
6,600,000 232,050
447,117 1885
3
92,000
1,079,458 1886
5,950,000 50,081
518,671 1887
rl J
104,284
428,166 1888
I 2,000,000 82,379
334,917 1889
] 1,000,000
] 1,112,905 45,000
192,390 1890
162,378
593,197 1891
f 3,776,230 2,370,090
rl
210,371
652,390 1892
5,259,280
500,240 1893
cl 2,112,280 185,000
160,923 1894
5,000,000
S 221 t
66,000
1,144,013 2,000,000
<
122,271 1895
67,775 1896
8,810
56,647
103,843 1897
1,851,512 1,770,215
151,500 1898
1,005
6,322
127,192 1899
m 1,187,930 210 717
59,603 26,372 3,679,828 2,775,291
41,184
cm 20,000 $ 880 471,491 1900
119,338
348.195 1901
18,316 832,846
70,357
108,447 1902
34,147 28,465
63,616 1903
4,502
n
677,730
53,457
16,134
66,219 1904
25,135 4,148 n 375,207
161,912 m 605,612 35.731 122,921 1905
307,755 17,542 7,366 m 1,426,029 86,988 245,766 1906
4,576 2,854 n
8,731
156,723 193,690 10,266 m 429,198 25,323 138,671 1907
11,204
n
6,548 471
113,292 1908
n 740,408 39,982 202,244 1909
37,295 26,613 n 152,280 397,409 17,486 n 4,147,945 223,989 341,008 1910
8,326 n 855,889 38,515 n 5,097,597 290,563 440.102 1911
24,284 n 1,240,156 55,807 n 5,659,261 390,489 620,571 1912
6,412 n 1,351,205 59,453 n 6,683,643 374,284 663,403 1913
3,738 n 1,177,385 45,918 n 7,522,098 383,627 550,752 1914
10,515 n 1,394,043 65,520 n 11,141,750 1,381,577 1,643,056 1915
27,702 1,517,362 104,698 28,438,052 3,810,699 4,185,294 1916
14,506 2,426,988 208,721 23,715,412 2,418,972 2,795,469 1917
87,201 2,927,099 207,824 14,845,341 1,350,926 1,923,332 1918
22,935 378,113 20,040 3,367,548 245,831 389,559 1919
95,148 282,538 22,603 6,653,235 538,912 986,996 1920
236,467 12,578 566
984,306 1921
179,590 322,818 17,755 ii,ooo,666 627,000 1,480,193 1922
35,533 632,846 93,028 23,600,000 1,604,800 2,044,585 1923
1881
d Director of the Mint for 1881, p. 435, under Summit County, says: "On Eagle
River, at Red Cliff, the Belden Mining Company and the Battle Mountain smelter
have produced a large quantity of base bullion. . . . No ore is being snipped
except from the Belden Company's mine, and from this but four car-loads per
day. The ore, containing as it does a large percentage of lead, forms an excellent
flux for the dry ores and will aid materially in smelting. In Gold Park, near the
Mount of the Holy Cross, a considerable camp has been established, and a large
stamp-mill erected to crush the gold ores found there. The veins are quite strong,
the quartz at the surface to a depth of 12 under to 15 Summit feet, much County, decomposed, says, "At and Red
the
yield $10 to $25 per ton under stamps. Below the decomposition the ores are mainly
white iron pyrites. This section is scarcely more than a year old "
1882
e Director of the Mint for 1832, p. 559,
Cliff, the Belden is the principal mine."
1883
/ Director of the Mint for 1883, p. 240.

14 BED CLIFF MINING DISTRICT
1884
h Director of the Mint for 1884, pp. 177, 207-209
which returned
. The Belden shipped during the year 1,640 tons of ore,
as follows
Ores
Lead, tons
Silver, ounces
Gold, ounces
".... The Eagle Bird shipped 2,090 tons of ore, assaying 31 per cent lead
and 8% ounces silver, giving 647 tons of lead and 17,765 ounces of silver. Black
Iron produced 378 tons of ore, assaying 41 per cent lead and 9 ounces silver
giving 154.98 tons lead and 3,402 ounces silver. The May Queen forwarded SO
tons which returned 39 per cent lead and 8 ounces silver, giving 11 tons ieaa ana
240 ounces silver. The total of these mines comprising the Cheeseman and Clayton
group was as follows:
Quantity Price Value
Ores
814.58
21,407
i 157
$72.00
1.10
20.00
$58,659.76
23,547.70
3,140.00
85,347.46
The shipments from the Little Chief, Crown Point, Kingfisher, Iron Mask,
Spirit, Clinton, Cleopatra, Great Western, and Potvin have amounted to some
597 car-loads of mineral, averaging 10 tons to the car; 32 per cent lead and 8
ounces silver per ton would give 5,970 tons of mineral yielding as follows :
Ores
Quantity Price Value
Gold, ounces
1,910.4
4,776
250
1
$72.00
1.10
20.00
$137,548.88
52,536.00
5,000.00
195,084.88
On the lower end of Battle Mountain is found what is now termed the Quartzite,
which extends on the west side of Rock Creek and on the north side of Eagle
River. The most promising of its mines are the Ground Hog group, Combined
Discovery, Uncle Sam, Horn Silver and Highland Mary The total yield
of Red Cliff Camp has been stated to be, from the Carbonate mines, $339,798.26;
from other mines, $125,000; total, $464,798.26 (which includes the value of lead).
"In the vicinity of Taylor Hill much work is being done in the way af development,
and McClelland's stamp-mill has been running most of the year on ore
from this locality. It is claimed about 1884 $12,000 was turned out during this time.
At
i Mineral
Holy Cross
Resources
exploitation
for 1834,
only
p.
has
422.
been done; bodies of ore have been developed,
but the actual yield has been almost
1885
nothing. The production of the camp, reported
j Mineral
from
Resources
ore treated,
for
was
1885,
$6,400."
p. 257, gives 11,000 tons of ore containing 3,500
tons lead gross ; deducting 15 per cent gives 2,975 tons lead.
k Interpolated by Chas. W. Henderson, to correspond with total production of
the state.
1886-1896
I From reports of the agents of the Mint, in annual reports of the Director of
the Mint, prorating the gold and silver to correspond with the corrected figures of
the total production of the State by the Director of the Mint, and prorating the
lead production to correspond with the total production of lead for the State in
annual volumes of Mineral Resources, and distributing any "unknown production"
of the State proportionately to the various counties. Similarly with copper as
with lead, but as Mineral Resources figures for copper include copper from matte
and ores treated in Colorado smelters from other states, the copper figures are
subject to revision.
1897-1907
m Colorado State Bureau of Mines figures being smelter and Mint receipts.

PRODUCTION
1905-1918
n Mineral Resources of the United States, U. S. Geological Survey, figures collected
from the mines.
TABLE II. PRICES OF SILVER, COPPER, LEAD AND ZINC, 1880-1923
Year
1880
1881
1882
1883
1884
1885
1886
1887
1888
1389
1890
1891
1892
1893
1894
1895
1396
1897
1898
1899
1900
1901
Silver
Per Fine
Ounce
$1.15
1.13
1.14
1.11
1.11
1.07
.99
.98
.94
.94
1.05
.99
.87
.78
.63
.65
.68
.60
.59
.60
.62
.60
Copper
Per
Pound
$0,214
.182
.191
.165
.13
.108
.111
.138
.168
.135
.156
.128
.116
.108
.095
.107
.108
.12
.124
.171
.166
.167
Lead
Per
Pound
$0.05
.048
.049
.043
.037
.040
.046
.045
.044
.039
.045
.043
.041
.037
.033
.032
.03
.036
.033
.045
.044
.043
Zinc
Per
Pound
$0,055
.052
.053
.045
.044
.043
.044
.046
.049
.05
.055
.05
.046
.04
.035
.036
.039
.041
.046
.058
.044
.041
Year
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
Silver
Per Fine
Ounce
$0.53
.54
.58
.61
.68
.66
.53
.52
.54
.53
.615
.604
.553
.507
.658
.824
1.00
1.12
1.09
1.00
1.00
.82
Copper
Per
Pound
$0,122
.137
.128
.156
.193
.20
.132
.13
.127
.125
.165
.155
.133
.175
.246
.273
.247
.186
.184
.129
.135
.147
Lead
Per
Pound
$0,041
.042
.043
.047
.057
.053
.042
.043
.044
.045
.045
.044
.039
.047
.069
.086
.071
.053
.08
.045
.055
.07
15
Zinc
Per
Pound
$0,048
.054
.051
.059
.061
.059
.047
.054
.054
.057
.069
.056
.051
.124
.134
.102
.091
.073
.081
.05
.057
.068

PHYSIOGRAPHY
CHAPTER I
By R. D. Crawford
TOPOGRAPHY
The Red Cliff district is in a region of steep slopes and deep gulches
and canyons. The vertical range within the area mapped is approximately
3,500 feet—from about 8,400 to 11,900 feet above sea level. A few miles
southwest is Holy Cross Mountain with an altitude of nearly 14,000
feet. The district is drained by Eagle River and its branches, several of
which carry large volumes of water throughout the summer. Homestake
Creek, which joins Eagle River below Red Cliff, is longer and probably
carries more water than that part of Eagle River above the mouth of
Homestake Creek. This creek has an advantage in heading near the top
ot the Sawatch Range where glacial lakes are numerous and snow is found
almost or quite throughout the year. Aside from ordinary stream erosion
factors that have had part in shaping the relief include geologic structure
and character of the rocks, glaciation, landslides, and vegetation.
INFLUENCE OF STRUCTURE
By reference to the geologic map (PI. I, in pocket) it will be seen that
Eagle River flows in general nearly in the direction of strike of the Sawatch
quartzite, but a little to the right of this direction, that is, inclining slightly
toward the dip of the beds. West of the river the uniformity of slope
is well shown by the contours between Pando and Camp Bryan on the map,
and is very striking when seen from points in the field. (See fig. 5.)
This slope is nearly parallel to the bedding planes of the quartzite which
extends about two miles west of the river. Promi this slope the soft beds
of the Sawatch formation and all overlying beds have been removed. Beyond
the border of the quartzite the slope of the surface of pre-Cambrian
rocks is similar. This uniformity of slope suggests planation by lateral
migration of the stream to its present position. A few local bends eastward
may have been brought about by greater erosion of rocks weakened by faulting,
with or without subsequent mineralizaton. The positions of several
gullies in the quartzite have been determined by faults. While it is probable
that some of the larger gullies in the higher formation were so determined,
efforts to prove this relationship have been unsuccessful. The fault
nearly midway between Pando and Red Cliff (PI. I) strikes southwest toward
Homestake Gulch, and may have determined the position of the
gulch which is notably straight for a distance of 8 or 9 miles southwestward.
GLACIATION
Within the area mapped glacial boulders are very common on both
sides of Eagle River, and thick moraines cover the bedrock in many places.
The positions of the largest morainal patches are shown on the geologic
map. East of the river the moraines are mostly less than 800 feet verti-

PHYSIOGRAPHY
cally from the valley bottom; west of the river glacial boulders are found
at practically all, elevations between the river land the cirques near the
top of the Sawatch Range. Many glacial lakes are found between the valley
and the crest of the range. Near Pando rocks show smoothing bymoving
ice, and roches moutonnees are very common in Homestake Gulch.
Two large glaciers have moved through the region, and converged or
followed nearly the same path at and from a point about two miles northwest
of Pando. One started near Fremont Pass in the Tenmile district,
moved westward north of Chalk Mountain, and down the valley of Eagle
River. There is good evidence that the greater part of the ice moved
northwestward through the valley now followed by the highway north of
Pando (Fig. 5), and not through the present valley of Eagle River where
it bends to the right between Coal and Silver creeks. However, nearly
Figure 5. Glaciated valley connecting Eagle and Homestake valleys, looking
northwest; shows also dip slope of Sawatch quartzite in background
all the hill between Eagle River and Homestake Creek nas been glaciated,
and considerable morainal material is found close to Eagle River south of
Red Cliff. A larger glacier headed high on the slopes of the S'awatch
Range, moved down through Homestake Gulch, and scoured out the gulch
to a depth of about 1,000 feet and to a width of a quarter of a mile. Midway
between Pando and Red Cliff it joined the Eagle glacier, or followed
the path of the Eagle glacier from this point northward. Other glaciers
came into Eagle Valley north of the Homestake glacier. Both the Homestake
and Eagle glaciers eroded their valleys to a depth considerably below
the pre-glacial level. This is shown by the many hanging valleys, of which
one is Yoder Gulch Where the creek forms a waterfall near the railroad
(Fig. 6). Eagle Canyon between Homestake Creek and Rock Creek
has evidently been much deepened by stream erosion since the glaciers
melted. (See also interpretation by M. R. Campbell in Bulletin 707, U. S.
Geological Survey, p. 115.) i
17

18 RED CLIFF MINING DISTRICT
LANDSLIDES
Several landslides are found east of Eagle River on the escarpment
slope, and a few of the largest are represented on the geologic map. Faults
can be seen in the quartzite opposite some of these landslides; it is probable
that steep-walled gullies formed in the limestone and shale along
the same faults east of the stream, thus facilitating the slump of the
shale cliffs. One of the largest areas covered by a landslide is south of
Silver Creek. In this vicinity Eagle River evidently was formerly east
Figure 6. A hanging valley, Voder Falls
of its present position, and gradually undercut the shale beds until they
formed a steep cliff which slid down and forced the stream westward.
About half a mile north of the ranger station the stream was dammed
by the landslide, and the slow-running ponded water has earned the local
name Stillwater for this part of the stream and its surroundings. Between
the south border of the slump dam and the mouth of Silver Creek the
stream is still flowing in rapids over its new bed of surficial material
(Fig. 7.)
VEGETATION
Outcrops of the more resistant rocks and steep escarpment slopes above
landslides are practically the only surfaces free from grass or trees. Great

PHYSIOGRAPHY
volumes of water from heavy rains or cloudbursts carry large quantities
of mud and boulders down the streams, but the vegetation prevents general
rapid erosion during the season when the ground is not covered with snow.
When the streams are fed chiefly by springs and melting snow the water
is clear. Many steep escarpment slopes and others are covered by grass
or timber, excepting a few bare outcrops of limestone and sandstone. The
trees are principally pine, spruce, fir and aspen. Much of the timber has
been cut for lumber, stulls, and lagging; but there still remain many trees
large enough to cut for lumber and mine timber.
Figure 7. Eagle River, looking south from near Silver Creek
The stream has been forced westward by a geologically recent
landslide over which the water still flows in rapids. Note in the left
background the trees that have grown since the surface rock slid to
its present position. The area covered by this landslide is shown on the
geologic map in pocket.
ALLUVIUM AND SOIL
Owing to the generally high gradient of the streams and the steep
valley walls a relatively small amount of alluvium has accumulated. A few
alluvial cones and areas of comparatively flat grass-covered alluvium, in part
a re-worked glacial deposit, are found in the Eagle and Homestake valleys.
Though the soil of these flats is fertile the growing season is short and the
nights are cold. Consequently the land has been used chiefly for pastures
and meadows; a few vegetables have been raised for home use. In 1923
head lettuce for outside markets was successfully grown in Eagle Valley
in the southeast part of Eagle Park.
19

CHAPTER II
PRE-CAMBRIAN METAMORPHIC ROCKS
By R. D. Crawford
The oldest rocks in the region include gneiss, schist, quartzite, and
marble. The gneiss and schist alternate with each other and intergrade;
within the gneiss and schist area as small patches of quartzite and marble.
No attempt has been made to map any one of the kinds of metamorphic
rocks separately.
Near the border of certain gneiss areas granite, in streaks, has been
injected along the foliation planes, forming either a small or a large proportion
of the rock volume. These relationships of the two kinds of rock
make impossible an exact placing of the boundary between them. Where
these conditions are found the aim has been to represent on the map as
granite the rock that is dominantly granite, and to represent as gneiss and
schist those areas in which gneiss and schist form more than half the
rock mass. The same procedure was followed where the granite was intruded
as dikes or small stocks in the gneiss and schist, and where the
granite incloses large masses of the older rocks. Good illustrations of
granite intrusions along the structure planes of the older rocks may be
seen near the mouth of Homestake Creek. Farther south, east of the same
creek, granite cuts across the foliation planes as dikes and stocks.
The foliation planes of the gneiss and schist strike in a general northeast
direction, and are usually nearly vertical or dip northwestward at a
high angle. In general there has not been intense folding, though locally
the bands are considerably contorted.
Part of the gneiss is evidently of igneous origin. In rock of this type
the gneissic structure may be in part a fluxional arrangement of the
minerals, but the structure was probably more generally imposed by pressure
during the process of metamorphism. The high proportion of quartz
and the comparatively low feldspar content, with not infrequently high
mica content, indicate that some of the gneisses and schists are metamorphosed
sediments. This is to be expected in a region that contains the
metamorphic equivalents of sandstone and limestone. Though no very
unusual types of metamorphic rocks have been observed pre-Cambrian marble—
found here in two localities—seems to be rare in Colorado.1 Varieties of
the metamorphic rocks examined in thin sections and described below should
be considered only as types; intergradations are common.
GRANITE GNEISS
Granite gneiss is here taken as a gneissic rock of igneous origin and
granitic composition whether the structure was effected by flow when the
magma was viscous or by metamorphic processes after solidification. Good
examples may he seen a mile west of Red Cliff and about 1.5 miles south-
doctor Cross has reported an occurrence of marble with schist near
Tincup, Gunnison County, Colorado, in the Proceedings of the Colorado Scientific
Society, vol. 4, 1893, pp. 286-293.

METAMORPHIC ROCKS -1
east of Pando. The gneiss varies from coarse to fine grain in different
localities. Essential component minerals are orthoclase, microcline, quartz,
and biotite.
QUARTZ-DIORITE GNEISS
A small exposure of quartz-diorite gneiss is found west of the mouth
oz Homestake Creek. The rock has a coarse texture and rough gneissic
structure. Probably half the rock mass is composed of hornblende and
biotite in nearly equal quantities. The feldspar, insofar as determinable,
is plagioclase. Quartz forms about 15 per cent of the rock.
GRANITIC GNEISS
Gneiss that resembles granite in mineral composition, and of uncertain
or mixed origin, may be called granitic gneiss. One variety is pinkishgray,
and composed chiefly of quartz and feldspar. It also carries an appreciable
quantity of muscovite and very little biotite. The rock may be
a metamorphosed arkose or feldspathic sandstone. The proportion of
feldspar is a little low for typical granite. Another vlariety bears a resemblance
to the biotite gneiss described below, but contains a higher
proportion of injected igneous material. A phase of this rock carries much
soda-lime feldspar, and approaches granodiorite in mineral composition.
MICA GNEISS
The mica gneiss differs from the granitio gneiss chiefly in the much
higher proportion of mjica or quartz or both. The feldspar content is low.
Part or all of the rock here called mica gneiss is of sedimentary origin.
The rock is dark gray or reddish-gray, and has pronounced gneissic structure.
Quartz in most specimens makes up 50 to 80 per cent of the rock.
The highly quartzose variety might be called a quartzite, but the pronounced
banding is more characteristic of gneiss. Biotite composes about
15 to 30 per cent of the rock mass. Muscovite is present in some specimens.
PYROXENE GNEISS
North of Yoder Gulch, about 200 feet above the railroad, is a small
exposure of fine-grained pyroxene gneiss. The rock is dark in color, and
contains thin veinlike streaks and lenslike patches of quartz. The most
abundant mineral is pyroxene determinable only in thin section. It is
grass-green to greenish-gray, monoclinic, and has a birefringence of about
.028 or .029. It is probably ferriferous diopside or common pyroxene.
Quartz, orthoclase, microcline, soda-lime feldspar, and a little titanite and
zircon are present.
SILLIMANITE GNEISS
South of Eagle River, west of the mouth of Homestake Creek, is a
small exposure of peculiar rock whose weathered surface shows many bluish
patches of a mineral with a splintery fracture. This mineral is shown by
the microscope and chemical tests to be sillimanite. Other minerals present
are quartz, andesine, and biotite. Any one of the minerals may be bunched,
and associated with smaller amounts of the others. That part of the rock
rich in sillimanite is about one-half sillimanite in grains up to three-

22 RED CLIFF MINING DISTRICT
rourths of an inch in diameter. The rock is probably metamorphosed clay
or shale with injected igneous material.
MICA SCHIST
The mica schist differs from the mica gneiss described in that it is
finely laminated. The mica, forming one-third to one-half the rock, is
mostly biotite, though muscovite is sometimes seen. Quartz is the dominant
mineral in some specimens; in others, potash feldspar or soda-lime
feldspar may exceed the quartz. Magnetite and apatite are present in
small quantity. Near the south border of the mapped area is a small exposure
of la peculiar mica schist with microcrystalline texture. It shows
blocky jointing, and breaks with a conchoidal fracture. It is composed essentially
of biotite and quartz.
The highly quartzose varieties of mica schist were probably derived
from sediments, but the high feldspar content of some specimens indicates a
possible igneous origin for part of the schist.
GARNET-MICA SCHIST
West of the railroad, less than a mile south of Been Station, is found
a garnet-bearing mica schist. Biotite makes up about three-fourths of the
rock. Garnet and quartz are the only other essential components of the
specimen examined. The garnet is red, and is probably almandite. It is in
roundish anhedral grains that inclose microcrystalline grains of quartz
and flakes of biotite.
QUARTZITE
Small patches of quartzite have been found in several places between
Red Cliff and Pando. Quartzite composed almost entirely of quartz grains
is in contact with marble high on the slope west of Homestake Creek, about
1.5 miles south of Red Cliff. A micaceous quartzite is found near Eagle
River less than 2 mjiles south of Red Cliff. About 10 to 15 per cent of this
rock is biotite; the rest is mostly quartz. About a quarter of a mile south
of the mouth of Homestake Creek is a small outcrop of very fine-grained
greenish-gray pyrite-bearing quartzite. As seen under the microscope about
half of the rock is quartz in irregular grains; the rest is chiefly epidote
in minute grains. The rock was probably once a calcareous sandstone.
MARBLE
Two different kinds of marble are found in the district: (1) a dense
variety, finer in texture than much of the Paleozoic limestone and dolomite
of the region; (2) a normal granular variety.
The first is found in a lenticular mass 4 or 5 feet thick about half a
mile S. 10° E. of the mouth of Rule Creek. The marble is inclosed by
gneiss, and can be traced along the strike 100 feet or more. Traces of the
bedding of the original limestone are preserved on the weathered surface
by small nodular masses and individual grains of resistant minerals. On
fresh surfaces the marble is bluish-gray. About 80 per cent of the rock
is soluble calcite with practically no magnesium. In thin section the
microgranular calcite shows very few traces of cleavage and no twinning.
Other minerals scattered throughout the slide in small grains are quartz
orthoclase, plagioclase, and monocliDic pyroxene, probably diopside.

METAMORPHIC ROCKS
The granular marble is exposed in an area about 50 by 150 feet a mile
and a half south of Red Cliff high on the slope west of Homestake Creek.
A small amount of quartzite is in contact with the marble. The marble
is white and fine grained, yet coarse enough to show many calcite cleavage
faces. The rock retains traces of the original bedding. Large patches
of wollastonite or related mineral are found in the marble. In thin section
the calcite grains show the characteristic multiple twinning. Scattered
throughout the slide and composing nearly one-fourth of the rock is
monoclinic pyroxene with high extinction angle. Qualitative wet tests
show this mineral to be iron-bearing diopside. The wollastonitic material
has the chemical and physical properties of normal wollastonite. The optical
properties in thin section are those of wollastonite, excepting part of
the material which shows extinction inclined to traces of the cleavage.
23

IGNEOUS ROCKS
CHAPTER III
By R. D. Crawford
The large body of granite and other plutonic rocks of the Red Cliff
district and nearby areas may represent successive intrusions widely
separated in time. Yet all the granite, quartz monzonite, quartz diorite,
gneiss, and schist were long exposed to erosion before the deposition of
the Sawatch formation of Cambrian age. This is shown by the peneplaned
surface of contact between the pre-Cambrian rocks and overlying quartzite.
Owing largely to the presence of extensive sediments only small exposures
of granite are found within the area mapped.
GRANITE
Though the granite varies considerably in composition, texture, and
structure no attempt has been made to map separately the different varieties.
They are mainly massive in structure, but locally, and especially near the
mouth of Homestake Creek, the granite is strongly gneissoid. Near the
border of the intrusion in this locality the granite is interlayered with the
older rocks, and it is impossible to place the exact contact between granite
and gneiss. The normal granite is mostly of even and medium-sized grain.
However, fine-grained and very coarse-grained varieties are found. Though
a small amount of pegmatite is present strong dikes of pegmatite
having large masses of quartz and feldspar are apparently absent from the
Red Cliff district, and aplite dikes are unimportant here.
Biotite, feldspar, and quartz can be megascopically determined in most
of the unaltered granite. In a few hand specimens albite twin striations
on cleavage faces show part of the feldspar to be plagioclase. Locally, especially
near ore veins, kaolin replaces part or all of the feldspar, and a
limonite stain is common.
Under the microscope the following minerals can be seen: apatite, zircon,
magnetite, pyrite, biotite, muscovite, soda-lime feldspar, alkali feldspar, and
quartz, beside several secondary minerals. Three thin sections carry hairlike
microlites of an indeterminable mineral that is probably rutile.
Apatite is found in only minute quantity and in small crystals in a few
specimens. Zircon is likewise rare, and occurs in miinute stout crystals.
Magnetite is found in small anhedral grains in about half the specimens;
it has probably been derived in part from biotite. Pyrite is very rare.
Biotite, or chlorite that has replaced biotite, is present in nearly every
thin section examined. The biotite content is commonly below 10 per cent,
though one specimen examined carries about 15 per cent of biotite. Chlorite
is a common alteration product, and in some specimens replaces nearly or
quite all the biotite. A small amount of muscovite is present in most of
the thin sections, and is probably in part a pyrogenetic component.
In some specimens, particularly those from Camp Bryan, the feldspar
is nearly all microcline. In others orthoclase occurs in considerable quantity,
and the two feldspars may intergrade in the same grain. In a few
specimens albite or oligoclase is perthitically intergrown with the potash

IGNEOUS ROCKS 25
feldspar. Independent grains of albite have been definitely determined
in only one specimen—that from a narrow dike in quartz diorite about
2 miles northwest of Pando. The soda-lime feldspar, which varies from a
negligible component in certain varieties of the rock to a quantitatively
important component in the alkalicalcic granite that approaches quartz
monzonite in composition, is mostly a low-calcium andesine. Kaolin and
finely-flaked white mlica are common alteration products of the feldspars.
A few micrographic intergrowths of quartz and feldspar may be seen, but
the quartz is found chiefly in independent grains as the last product of
crystallization fromt the magma. The quartz which commonly shows undulatory
extinction, makes up about 15 to 30 per cent of the rock, and will
probably average at least 25 per cent.
QUARTZ MONZONITE
In appearance and texture quartz monzonite resembles granite, but
it differs from granite in chemical and mineral composition. Typical
granite carries alkali feldspar (most commonly potash feldspar) in excess
of soda-lime feldspar, while quartz monzonite carries the two kinds
of feldspar in nearly equal amounts. Since the identity of most of the
feldspar grains and their relative abundance can be determined only with
the aid of the microscope quartz monzonite is ordinarily called granite in
the field.
In Eagle Canyon, at and near Belden, is a considerable exposure of
porphyritic quartz monzonite whose relation to the granite is difficult to
determine. A short distance east of Belden the two rocks seem to intergrade,
and it is probable that they are different phases of a single intrusion.
That both had solidified and suffered erosion long before the sand of the
Cambrian quartzite was deposited is shown by the nearly plane contact
between the igneous rocks and overlying quartzite. Because of the indistinct
boundary between granite and quartz monzonite the latter has not
been mapped separately.
The typical quartz monzonite of this area contains reddish feldspar
phenocrysts which have a maximum length of about 2 inches, though the
average length is probably less than an inch. In places the phenocrystic
feldspar composes nearly one-third of the rock mass. Locally the phenocrysts
are fewer or absent. Some phenocrysts inclose crystals of biotite and
plagioclase, readily seen on cleavage faces. A few phenocrysts are twinned
according to the Carlsbad law. The fairly coarse groundmass is composed
essentially of biotite, quartz, and bluish feldspar. Under a lens some blue
feldspar grains show albite twin striations on cleavage faces. Individual
grains of the groundmiass are mostly less than a quarter of an inch in
diameter. A few small grains of pyrite may be seen in some specimens.
Thin sections contain apatite, zircon, magnetite, pyrite, biotite, muscovite,
soda-lime feldspar, potash feldspar, quartz, and several secondary
minerals. Apatite is rare in minute prismatic crystals. Zircon occurs
sparingly in well shaped crystals. Magnetite is a common accessory in well
formed crystals and formless grains. Very few small anhedrons of pyrite
are present.
Biotite is the ordinary variety, and forms an average of 10 per cent

26 RED CLIFF MINING DISTRICT
or less of the rock mass. With the biotite is a small amount of muscovite
which is probably in part primary. A small quantity of epidote occurs as
an alteration product. The potash feldspar is largely microcline, though
many individual grains or crystals are partly microcline and partly
orthoclase. With the potash feldspar is a very small quantity of microperthitically
intergrown albite or oligoclase. The soda-lime feldspar is
andesine having medium or low lime content. A common alteration product
of this feldspar is a finely flaked mica, probably paragonite. The
granular groundmass carries far more soda-lime feldspar than alkali feldspar,
but the two kinds are nearly equal in quantity when the rock as a
whole—phenocrysts and groundmass—is considered. The quartz content
of the rock will run nearly 30 per cent. The quartz shows undulatory
extinction and carries numerous liquid and gas inclusions.
West of Eagle River, southwest of the mouth of Rock Creek, the quartz
monzonite (here with few phenocrysts) incloses a fine-grained dark-colored
rock in masses from a few inches to 5 feet across. An inclusion may show
a sharp contact with the coarser rock on one side and grade into the
coarser rock on the other side. The fine-grained rock is fissured and
faulted and crossed by thin dikes of granite or pegmatite. Thin sections
show less quartz, more andesine, and more biotite than the inclosing rock.
The inclusions are probably secretions formed from the quartz-monzonite
magma in an early stage of consolidation.
QUARTZ DIORITE
Several varieties of quartz diorite are found in the district, but they
fall into two general classes: (a) those in which hornblende is an essential
component, and (b) those carrying little or no hornblende.
QUARTZ-HORNBLENDE DIORITE
Northwest of Pando this variety of diorite is exposed on both slopes of
the valley. Within the valley, throughout a considerable area the same
rock is covered by soil and glacial material. Farther west the quartz
diorite is overlain by the Camibrian quartzite. The igneous rock was intruded
as a stock into the gneiss evidently in pre-Cambrian time. This
stock is in turn cut by dikes of pegmatite, aplite, and ordinary red granite.
The dikes range from a few inches to several feet in width, and seem to be
confined to areas near the border of the stock.
A smaller stock of the same kind of diorite is found on the west side
of Eagle Canyon below Red Cliff. Boulders of the same rock may be seen
near the southeast rim of Homestake Gulch several miles southwest
of Pando.
On fresh surfaces the rock is dark gray, in places almost black. It
weathers to lighter and, locally, brownish gray. Though the ratio of light
to dark minerals is variable, more than half of some specimens is composed
of black hornblende and biotite. These two minerals likewise bear
no constant relation to each other; here one, there the other is in excess.
The light colored minerals are feldspar and quartz. Under a lens some
feldspar cleavage faces show albite twin striations. The quartz diorite is
appreciably, though not strikingly, gneissoid in structure.

IGNEOUS ROCKS 27
In thin section zircon, apatite, titanite, magnetite, hornblende, biotite,
plagioclase, orthoclase, and quartz are present.
The zircon is partly in minute barrel-shaped crystals, and partly in
well shaped prismatic crystals with length five or six times the thickness.
Apatite is fairly plentiful, for an accessory component, and in unusually
large, though mlicroscopic, crystals. Titanite is rare in formless grains.
Magnetite occurs in anhedrons of considerable size in some specimens;
a few minute octahedrons can be seen. The apparent practically unaltered
character of the hornblende and biotite indicates that the magnetite is
mostly an original constituent.
Hornblende is the common green variety, and ranges from about 5 to
50 per cent of the rock volume in specimens examined. The mica is ordinary
brown biotite. It varies from a few per cent of the rock volume
in specimens having much hornblende to about 20 per cent where the
hornblende content is low.
Plagioclase is an important component of all the specimens examined.
It is commonly twinned after both albite and pericline laws, and occasional
Carlsbad twins are present. Interference colors and extinction angles
indicate that the feldspar is andesine. The mineral shows considerable
alteration. Orthoclase is present in very small quantity. Quartz varies
from 10 or 15 per cent of the rock volume to an almost negligible component.
A small intrusion of somewhat similar rock is found about seveneighths
of a mile southeast of Pando. Common green hornblende composes
more than half of the rock mass, and monoclinic pyroxene is an important
constituent. The other essential components are orthoclase and plagioclase.
The rock is a basic monzonite-diorite which in the proportion of component
hornblende lies between the quartz-hornblende diorite and the
hornblendite described farther on.
Quartz-Mica Diorite (Without Essential Hornblende)
Beginning several hundred feet west of the Red Cliff depot and extending
down Eagle Canyon on both walls, is a quartz-mica diorite almost
free from hornblende and texturally and structurally unlike the rock described
above. Near the north border of the quartz diorite the rock becomes
somewhat monzonitic owing to a considerable content of orthoclase.
The quartz diorite has a dark gray color, massive structure commonly,
and medium to very coarse texture. Near the east border of the exposure
cleavage faces of black mica throughout the rock reach a diameter of
nearly half and inch; at the same place are segregations of almost pure
biotite whose leaves are nearly an inch across. Here also are small patches
of pyrite that probably crystallized from the molten rock magma. Near
this border also narrow dikes of aplite and pegmatite cut the quartz
diorite.
Throughout the exposure biotite is an important constituent of the
rock. It ranges perhaps from 15 to 30 per cent of the rock volume and
averages probably about 25 per cent. Aside from biotite and the small
amount of pyrite mentioned, bluish-gray quartz and feldspar are the only
minerals identifiable in hand specimens. Some feldspar cleavage faces

28 RED CLIFF MINING DISTRICT
show albite twin striations. Individual grains of quartz and feldspar are
commonly less than a quarter of an inch in diameter.
Under the microscope may be seen zircon, apatite, magnetite, biotite,
feldspar, and quartz; a few small grains of hornblende were noted in
only one specimen. Zircon and apatite are very rare. Magnetite is
present in every thin section examined, and for an accessory component is
plentiful. It occurs in both euhedrons and anhedrons, and may be in part
secondary.
Biotite is the ordinary variety, brown in thin section. In some sections
it shows alteration to epidote or muscovite. Part of the magnetite observed
is probably an alteration product from biotite.
In nearly every thin section examined- the feldspar is exclusively
plagioclase. Not infrequently pericline or Carlsbad twinning is combined
with the universal albite twinning. A few determinations by the Michel-
Levy method show the feldspar to be andesine. It is mostly a highly calcic
variety having a composition of approximately AbtAni, though in some
specimens the andesine has a higher soda content. This feldspar shows
common alteration to a finely flaked mica, probably paragonite. Epidote,
calcite, and kaolin are less common alteration products. One specimen
from near the northwest border of quartz diorite is quartz-monzonitic in
composition, having potash feldspar only slightly subordinate' to the andesine.
In this specimen both orthoclase and microcline are present.
Quartz is abundant and composes about 25 to 30 per cent of most of
the specimens examined. It commonly shows slight to moderate undulatory
extinction. In some specimens the quartz is intergrown with andesine.
Gneissoid quartz-mica diorite.—A small intrusion of quartz diorite north
of Petersons Gulch megascopically resemlbles the hornblende-bearing quartz
diorite, but no hornblende is seen in the one thin section examined. It also
carries a high content of quartz and biotite. The rock is somewhat porphyritic
in texture, but probably should be included with the pre-Cambrian
granular intrusive rocks.
SYENITE
Less than a fourth of a mile southwest of the dense marble mentioned
in the preceding chapter is a dike of basic syenite. The rock is of dark
color and very fine grain. Only biotite and reddish-gray feldspar can be
identified in the hand specimen.
Nearly half the volume of a thin section is orthoclase which incloses
numerous small apatite crystals. A very little plagioclase is present. Biotite
and hornblende are abundant in nearly equal quantity. The rock carries
much epidote.
HORNBLENDITE
About 2 miles N. 70° W, of Pando, on the east side of Homestake Gulch,
is a small exposure of hornblendite. Probably 80 per cent or more of the
rock is hornblende. Pyrite, light brown miica, and andesine are the other components.
A short dike of similar hornblendite having a larger proportion of
hornblende is found about 2.5 miles northwest of Pando, east of the highway.
Near the last mentioned occurrence is a small irregularly shaped intrusion of

IGNEOUS ROCKS
hornblendite in the gneiss. It is cut pegmatite dikes, and incloses a few
quartz lenses 2 or 3 inches in diameter. Greenish-black hornblende, in grains
one-half to three-fourths inch in diameter, forms the bulk of this variety
of hornblendite. A noticeable feature is the large number of small biotite
flakes that cut across the hornblende cleavage planes at a high angle. Other
small flakes, singly and in aggregates roughly parallel to the hornblende
cleavage faces, are inclosed by hornblende. A third occurrence of biotite
shows this mineral in large grains intergrown with the hornblende in a
manner that gives a mottled luster to the mica cleavage faces. The microscope
discloses small quantities of titanite, magnetite, feldspar, and quart?.
PERIDOTITE
Near the last named locality, east of the highway and in line with
Homestake Gulch, are many boulders of a peculiar peridotite. They are
evidently boulders of weathering that have traveled little if at all; similar
boulders have not been found elsewhere by the Survey party.
The peridotite is a heavy, tough, grayish-black rock with striking mottled
luster. The peculiar luster is best shown by turning a freshly broken surface
toward the sun, when it is seen that nearly half the surface is covered
by patches of reddish-brown mica whose cleavage faces reflect the light. The
mica grains will average an inch in diameter while individual patches are
less than a sixteenth of an inch across. The mica is intergrown with or incloses
other minerals that interrupt the reflection. This, taken with the
different orientation of different mica grains, explains a large part of the
peculiar luster. In the same rock large pyroxene grains with their cleavage
faces interrupted by intergrown minenals show similar mottling and duller
luster.
Magnetite, olivine, pyroxene, phlogopite, and serpentine are seen under
the microscope. The magnetite is fairly plentiful in small grains; it may
be in part secondary. Olivine perhaps originally exceeded any other component
and is still abundant; it is in part replaced by serpentine. Part of the pyroxene
is monoclinic, but some grains with parallel extinction may be an
orthorhombic variety. The phlogopite is reddish-brown and different from
ordinary biotite; it reacts strongly for fluorine. Both phlogopite and pyroxene
poikilitically inclose olivine and serpentine.
PORPHYRY AND FELSITE
In this report the names porphyry and felsite are used for dense igneous
rocks as textural terms without reference to mineral composition. Porphyry
is accordingly a dense rock in which part of the material of the original
magma solidified as crystals large enough to be seen by the naked eye. These
crystals, called phenocrysts, may in their aggregate form either a small
fraction or the greater part of the rock mass. The rest of the rock, called
groundmass, is dense or microcrystalline. Felsite is a light colored rock
composed essentially of dense material like the groundmass of porphyry. It
contains few or no phenocrysts. Obviously porphyry and felsite mlay grade
into each other.
In many parts of central Colorado dikes or sheets of porphyry are common.
They are of comparatively late age, and some of them were almost cer-
29

30 RED CLIFF MINING DISTRICT
tainly intruded in Tertiary time. In the Red Cliff district the porphyries
were intruded into the youngest Paleozoic sediments, but there are no relationships
by which the exact age of the intrusions can be determined.
In this district exposed surfaces of porphyry and felsite are relatively
small. For the most part these rocks occur as intrusive sheets seen only
on their outcropping edges. In the vicinity of Gilman and Red Cliff a
porphyry sheet is found a few feet above the top of the Leadville limestone
where it was intruded nearly parallel to the bedding of the inclosing rocks.
This sheet is exposed at intervals through a distance of about 10 miles; it
is evidently continuous below the surface from the southeast part of the
mapped area to a point a mile or more north of Gilman. The thickness
varies: in the Wjilkesbarre shaft of the Eagle mines, at Gilman, the sheet is
said to be about 55 feet thick; in places it is much thicker or thinner.
Locaily the sheet passes from one horizon to another only a few feet higher
oi' lower, but it is generally underlain by black shale. In the Liberty incline,
near Red Cliff, the intrusion is split by about 5 feet of shale. A mile or two
southeast of Red Cliff this prophyry forms three sheets for a short distance
instead of one.
South of Yoder Gulch and north of Pando are a few outcrops of a porphyry
sheet that was intruded into or just below the Sawatch quartzite.
Near the southeast part of the mapped area other sheets occur at higher
horizons than those mentioned. Very few dikes in the pre-Cambrian rocks
and crosscutting the sediments have been found. The higher sheets can be
traced to the outcrops of porphyry of the Tenmile district. Alluvium and
landslides near the southeast corner of the area mapped conceal the Gilman
sheet and others in the lower part of the Weber beds, but these sheets are
probably connected with the laccolith of Chicago Mountain. The center of
this laccolith is about 5 miles southeast of Pando and 4 miles west of Robinson.
The Tenmile district map published by the United States Geological
Survey shows the laccolith to be at least 2,000 feet thick where it is deeply
eroded by Eagle River.
Excepting the quartz-monzonite porphyry and quartz-diorite porphyry
described in later pages all the porphyry of this district has a dense groundmass
in excess of the volume of phenocrysts. Owing to fineness of grain
in the groundmass and the generally altered character of the entire rock
of most exposures it is difficult or impossible to 'name the rock exactly. The
Gilman sheet and a few others, as well as one or two dikes, probably have
orthoclase greatly in excess of soda-lime feldspar, and hence are rhyolite
porphyry or rhyolite. Some of the sheets seem to carry nearly equal amounts
of orthoclase and soda-lime feldspar. These relationships, together with the
presence of quartz and the character and proportion of groundmass, make
the name quartz-latite porphyry, or dellenite porphyry, appropriate.
The least altered specimens were collected near the southeast corner of
the area mapped, where the rock does not differ greatly from the quartzmonzonite
porphyry described below. The reddish groundmass of these
specimens is dense, and forms more than one-half the rock mass. The phenocrysts
are of biotite, quartz, and white feldspar, in part plagioclase. The
quartz and feldspar phenocrysts have a maximum diameter of three-eighths
of an inch. Under the microscope the groundmass is seen to contain quartz,

IGNEOUS ROCKS
orthoclase, and plagioclase. Secondary limonite, magnetite, and sericite are
present.
Throughout the rest of the district the porphyry is greatly altered, apparently
in large part by warm waters. The biotite has been changed principally
to chlorite and muscovite, while the feldspar of phenocrysts and
groundmass shows much alteration to kaolin and white mica. A thin section
from a drill core that came from the sheet below the Liberty tunnel at a
distance of more than 1,000 feet from the outcrop, shows about the same degree
of alteration as the freshest specimen collected at the outcrop of the
same sheet north of Gilman. Beside the minerals mentioned secondary calcite
and magnetite are often seen. M;ost of the porphyry has a greater proportion
of groundmass than has the variety in the southeastern part of the
district, and the phenocrysts are smaller.
In thin sections of the porphyry are seen apatite, magnetite, plagioclase,
orthoclase, and quartz, beside several secondary minerals. Apatite is very
rare and in minute crystals. Though the magnetite may be partly primary
the most of it has probably been formed by the alteration of biotite. In
many specimens limonite is a common secondary mineral.
The feldspar phenocrysts are nearly all plagioclase, probably andesine.
This feldspar is commonly much altered, and shows calcite, kaolin, and a
finely flaked white mica, probably paragonite. The biotite is the ordinary
brown variety, and rarely appears in fresh condition. Chlorite and muscovite,
with a little magnetite, commonly occur with the biotite or completely
replace it as pseudomorphs. The quartz phenocrysts are generally
rounded and embayed by resorption.
A common type of groundmass is micropoikilitic. Microlites of plagioclase
with roughly rectangular outline are abundant as inclusions in microscopic
grains of orthoclase. In many instances single small grains of quartz
inclose feldspar microlites and add to the micropoikilitic effect. The microlites
show inclined extinction and have a very low birefringence; they are
hence probably andesine. Though individually small, they probably form
one-third of the total feldspar of the groundmass. Adding this to the
phenocrystic plagioclase it is probable that the combined amount of plagioclase
iu phenocrysts and groundmass nearly equals the quantity of orthoclase.
If these estimates are correct the rock of this type is a dellenite
porphyry, or quartz-latite porphyry. A second type of groundmass is microgranitic.
Individual grains are quartz and orthoclase and, in some instances,
plagioclase. Some of the rock with this texture, because of its high
plagioclase content, should be classed with the quartz latites; some, especially
the 'non-porphyritic felsite, carries very little plagioclase, and is
properly called rhyolite. White mica, kaolin, iron oxide, and calcite are
common secondary minerals in the groundmass.
Quartz-Monzonite Porphyry
In the southeast part of the area mapped are several intrusive sheets
of porphyries that carry a larger proportion of phenocrysts than the rocks
described above. About one-half to one-third of the rock is groundmass,
mostly coarse microcrystalline. Locally the groundmass exceeds the volume
of phenocrysts, and the rock becomes dellenite porphyry. Though several
31

32 RED CLIFF MINING DISTRICT
varieties are present they are all characterized by quartz and nearly equal
quantities of alkali feldspar and soda-lime feldspar, and they carry many
crystals of black minerals. These are features of quartz-monzonite porphyry.
These intrusions are continuous with the sheets and the Chicago Mountain
laccolith of the Tenmile district where they were mapped, in 1881-2, by the
United States Geological Survey. The rocks were described by Emmons2
under the name " diorite porphyries" in accordance with the customary
classification of the time. Chemical analyses3, as well as mineral determinations,
indicate quartz monzonite porphyry.
Quartz phenocrysts are abundant; many of them show resorption. In the
"Lincoln porphyry" part of the phenocrystic feldspar is orthoclase, but
most of the feldspar phenocrysts of all varieties are plagioclase, evidently
andesine. Biotite, in small crystals, is common. Accessory minerals noted
in thin section are allanite, apatite and magnetite. The microgranular
groundmass is composed essentially of quartz and orthoclase, with considerable
plagioclase in some specimens. Calcite, chlorite, kaolin, epidote, and
finely flaked white mica are common secondary minerals.
QUARTZ-DlORITE PORPHYRY
One small exposure of quartz-diorite porphyry is found about two and
a half miles southeast of Pando. The intrusion cuts across the bedded rocks
and is either a dike or a stock. The rock differs from the quartz-monzonite
porphyry described in having a higher proportion of plagioclase, there being
about three times as much plagioclase as orthoclase. About three-fourths of
the rock is composed of phenocrysts of quartz, plagioclase, biotite, and hornblende.
The quantity of hornblende is almost negligible., Optical properties
of the plagioclase indicate andesine. The coarse-microgranular groundmass
is composed mostly of quartz and orthoclase. Secondary minerals seen
in thin sections are chlorite, epidote, magnetite, calcite, and kaolin.
2Bmmons, S. F., Tenmile district special folio (No. 48), U. S. Geol. Survey
1898
=See U. S. Geol. Survey Bull. 591, p. 129, B and C, 1915.

CHAPTER IV
PALEOZOIC SEDIMENTARY ROCKS'
By Russell Gibson
The sedimentary rocks of the Red Cliff district include Cambrian, Ordovician
(?), Devonian, Mississippian, and Pennsylvanian strata. The total
thickness of these beds within the area mapped is about 4,600 feet. Except
where streams have cut deep enough to reveal the underlying pre-Cambrian
igneous and metamorphic rocks, most of the surface exposures are of Paleozoic
sediments. Surficial material, such as glacial debris, alluvium, and landslides,
has in places obscured all the older rocks. A scarcity of fossils has
made age determinations on faunal evidence exceedingly difficult. The
correlations are supported partly by lithologic similarity and partly by
stratigraphic position.
CAMBRIAN AND ORDOVICIAN OR DEVONIAN SEDIMENTS
Sawatch Quartzite
description
The sediments herein referred to as the Sawatch quartzite are about
356 feet thick, and consist of the Paleozoic sedimentary rocks older than
the Leadville limestone. The Sawatch lies unconformably on the pre-
Cambrian igneous and metamorphic rocks.
At the base of the Sawatch, a conglomerate about 9 feet in thickness is
made up chiefly of rounded quartz grains whose maximum diameter is onehalf
inch. Most of the material is finer than this, however, and contains
fragments of feldspar. The cementing material is silica and kaolin. The
conglomerate grades upward into a fine-grained, light-colored quartzite of
which most of the superjacent 210 feet is composed. A few beds are less
firmly cemented than typical quartzite; a few thin sandy shale beds are
interlarded; and one brownish sandy limestone bed occurs 76 feet above
the granite, in a section measured in Eagle Bird Gulch near Gilman. The
beds which are not well cemented are commonly ferruginous and darker in
color. Approximately 220 feet above the granite there is a-marked change
in the character of the sediments. For the next 105 feet the rocks are
dominantly thin-bedded impure limestones, sandstones, and shales. The
color varies from gray to brownish-red; some of the beds are mottled
peddish-brown and green. The best defined beds are gray to light-brown or
brownish-red magnesian limestones, most of which are siliceous, and some
are ferruginous as well. At the top of the section there are 30 to 35 feet
of white to gray quartzite, the upper portion of which is calcareous and
conglomeratic with pebbles up to three-eighths of an inch in diameter.
Except for the calcareous cement in the extreme upper part of this 30 feet,
the beds are very similar to the quartzite at the base of the series. The
following section is exposed in Eagle Bird Gulch:
4In this chapter the writer has quoted freely from an unpublished thesis
by E. A. Hall, a portion of which is devoted to the stratigraphy of the Red
Cliff district. This thesis was submitted to the faculty of the Graduate
School of the University of Colorado in partial fulfillment of the requirements
for the degree Master of Science. Professor "\V. C. Toepelman, of the
University of Colorado, identified the fossils named in this chapter.

34 RED CLIFF MINING DISTRICT
Section of Saioatch Quartzite at Eagle Bird G-ulch
(Leadville limestone unconformable upon)
Feet
29. Quartzite, varying from white through gray to brown, coarse
grained, containing near the top pebbles up to three-eighths
inch in diameter. Upper part calcareous 14.5
28. Quartzite, white, hard, fine grained, well bedded 15.7
27. Covered by talus 24.0
26. Shale, mottled reddish brown and green , 6.6
25. Quartzite, dense 0.7
24. Shale, mottled reddish brown and green 0.7
23. Sandstone and sandy shale, green, dark purple, and gray; sandstone,
coarse and not well cemented 8.0
22. Quartzite, dark purple, hard, fine grained, with a few, thin shale
beds; bedding somewhat wavy; weathers brown or dark purple.- 3.4
21. Sandstone, dense, even grained, argillaceous, calcareous, magnesian;
in alternate brown and dark red, thin laminae 0.6
20. Limestone, dolomitic, ferruginous, sandy, dark red, hard, thick
bedded with a few, thin shale beds; bedding somewhat wavy;
weathers brown and dark purple-- 19.0
19. Limestone, gray, crystalline; sandstone, dark red, calcerous,
magnesian; shale, gray, sandy, calcareous, laminated; beds
wavy and uneven in places 5.2
18. Limestone, shale, and sandstone, similar to No. 17 2.5
17. Limestone, crystalline, sandy, gray with brown mottling; shale,
laminated, friable, arenaceous, calcareous; sandstone, thin
bedded, greenish gray; contains SauMa near top 23.4
16. Limestone, gray to light brown, dolomitic, ferruginous, slightly
arenaceous; shale, gray, slightly calcareous, arenaceous, laminated 5.5
15. Sandstone, gray, calcareous, laminated 4.2
14. Quartzite, brownish gray, containing streaks less firmly cemented;
interstratified with purplish arenaceous shale 30.1
13. Quartzite, white, dense - 8.6
12. Sandstone, firmly cemented, medium grained, interstratified
with white fine-grained quartzite; well jointed. Some brecciated
zones recemented with silica 9.2
11. Quartzite, white, fine grained, well jointed in beds 1 to 15 inches
thick , 24.1
10. Quartzite, porous, mineralized 6.3
9. Quartzite, very dense, firmly cemented, in beds one-fourth inch
to 40 inches thick, interstratified with a few beds of porous,
heavily iron-stained quartzite 49.6
8. Sandstone, friable, iron-stained; grades laterally into quartzite 4.1
7. Quartzite, very dense, firmly cemented; contains an 18-inch
bed of brownish arenaceous limestone 16.9
6. Quartzite, loosely cemented, iron-stained; micaceous in places;
less resistant to erosion than adjacent beds 9.5
5. Quartzite, brownish, dense, interstratified with thin beds of 356.0
arenaceous (Unconformable shale; upon micaceous pre-Cambrian bed 3 to igneous 5 inches and thick metamorphic near top rocks.)
22.7
4. Quartzite, medium grained, tightly cemented 17.7
3. Conglomerate, arenaceous, easily eroded; arenaceous shale at
base
2. Quartzite, light gray, coarse grained, firmly cemented, interstrati­
3.2
fied with thin beds of conglomerate 10.7
1.
pebbles
Conglomerate,
up to
gray
one-half
to brown,
inch
fairly well cemented, containing
8.7

SEDIMENTARY ROCKS
Age
Cambrian.—About 252 feet above the pre-Cambrian rocks, fragments
of Saukia pepinensis and a few brachiopods, Oholidae and Westonia ella, were
found. For nearly 50 feet above this point the beds are similar to those
from which these fossils were collected, and careful examination revealed
no unconformity. The quartzite beds in the lower part of this section are
lithologically identical with the Sawatch as described in neighboring areas'1.
The beds in which, and just above which, the fossils were found are very
similar to the upper part of the Sawatch in most of these same areas.
Therefore, in view of the stratigraphic position of this division, the fossil
evidence, and the lithologic character of the beds, the age of the lower
part of the series, that is, the lower 302 feet, is provisionally regarded as
Sawatch or upper Cambrian.
Ordovician or Devonian.—Although it is reasonable to suppose that the
first 302 feiet of this formation in the section measured at Eagle Bird Gulch
is upper Cambrian, it is entirely possible that much of the remaining 54
feet may be either Ordovician or Devonian in age. It is certain that all
or a portion of the top 30 feet, which is quartzite, is younger than the Cambrian,
because a few corals which appear to be Zaphrentis sp. were found
2 feet below the top. Moreover, the 30 feet of quartzite at the top of the
debatable beds is very different from the limestones, sandstones, and shales
wherie the Cambrian fossils are found. Immediately below this top quartzite
member the beds are, in most places, obscured by soil; hence no evidence
of an unconformity—which may be present—was found. Data are insufficient
to correlate these 30 to 35 feet of quartzite with the Ordovician or
Devonian "Parting quartzite" of other districts. It is certain only that
this quartzite is post-Cambrian but not younger than Devonian. The contact
between the post-Cambrian and the Cambrian sediments is probably
at the base of this quartzite member or a few feet below it. On the geologic
map all the sediments below the Leadville limestone are included in the term
"Sawatch quartzite."
DEVONIAN-MISSISSIPPIAN SEDIMENTS
Leadville Limestone
description
The dark-gray, dense, thick-bedded limestone which immediately overlies
the coarse-grained quartzite beds, the upper few feet of which are calcareous,
conglomeratic, and not well cemented, is considered to be the
base of the Leadville limestone. The upper limit of the Leadville is taken
at the bottom of the group of alternate thin-bedded black shales and darkgray,
thin-bedded, dense limestones. The total thickness of the Leadville
"Emmons, S. F., Geology and mining industry of Leadville, Colorado: U.
S. Geol. Survey Mon. 12, 1886, p. 58.
Eldridge, G. H., U. S. Geol. Survey Geol. Atlas, Anthracite and Crested
Butte folio (No. 9), 1894.
Emmons, S. F., U. S. Geol. Survey Geol. Atlas. Tenmile folio (No. 48), 1898.
Spurr, J. E., Geology of the Aspen mining district, Colorado: U. S. Geol.
Survey Mon. 31. 1898, p. 4.
Girty, G. H., Carboniferous formations and faunas of Colorado: U. S.
Geol. Survey Prof. Paper 16, 1903, p. 140.
Worcester, P. G., Geology and ore deposits of the Gold Brick district,
Colorado: Colo. Geol. Survey Bulletin 10, 1916, pp. 51-52.
35

36 red cliff mining district
measured at Eagle Bird Gulch is 199.5 feet; at Rock Creek, 222 feet; and
at a point about one mile south of the mouth of Rule Creek, at least 170
feet.
At Eagle Bird Gulch and at Rock Creek the porphyry is found intruded
at, or very close to, the top of the formation here considered. As mentioned
under the description of the Sawatch, there is an evident disconformity at
the base of the Leadville. The lower 70 to 75 feet of the formation is made
up of even-bedded, dense, fairly hard, dark-gray, crystalline, magnesian limestone
or dolomite, which weathers light gray. Some of the thin beds that
are well jointed weather into small blocks. The weathered surfaces of other
beds exhibit a somewhat knotty or lumpy form. A few narrow chert
layers are present and also a few thin beds of arenaceous shale. Above
this 70 to 75 feet of limestone or dolomite is a remarkably persistent zone of
quartzite and breccia, seemingly marking an unconformity. Five good exposures
of this quartzite were seen between Rock Creek and a point 2
miles south of Red Cliff. The quartzite was found 93 feet above the base
of the Leadville at a point one mile south of the mouth of Rule Creek. The
lower part of the zone is a quartzite bed from 10 to 28 inches thick, composed
of fine to coarse well rounded quartz grains firmly cemented with
both siliceous and calcareous material. The color is gray to brown. The
upper part of the zone is breccia from 5 to 12 feet thick composed of quartz
grains and angular, rounded, and flattened fragments of limestone and
chert bound together by a cement that is calcareous in some places and
siliceous in others. Some of the large fragments of limestone are 5 inches
long, but the average length of the fragments is less than an inch.
The upper part of the Leadville, 110 to 145 feet in thickness, differs
from the lower part in several respects. It is massively bedded; more
coarsely crystalline; contains more vugs; and has an irregularly laminated
structure, commonly parallel to the bedding, which appears on the weathered
face of the rock as closely spaced alternate dark and light lines. In places
there are four or five white lines to an inch; elsewhere they are farther
apart. Not uncommonly the streaks become very irregular, and the limestone
appears spotted rather than banded. The mineral composition of
the light and dark material is identical. The miners term this rock "zebra"
limestone. The vugs are irregular in size, rarely 4 inches long, and are
lined with dolomite and quartz crystals. A few thin chert layers are in
the middle of the upper member of the formation.
The entire Leadville is dolomitic and siliceous; traces of aluminum and
iron are present in most of the beds; and a considerable amount of phosphate
was found in a specimen from a thin bed of limestone 6 to S feet
above the breccia. No outcrop of the Leadville limestone of the characteristic
type has been found east of the river between Silver Creek and the
small exposure of this limestone a mile east of the mouth of Rule Creek.
Through much of this distance (about four miles) the bedrock is covered by
landslides, moraines, and other surficial material. Wherever the bedrock
is exposed in this part of the district the limestone has been replaced
by jasperoid quartz. The character and extent of the replacement are described
in Chapter VI. Below is a section of the Leadville limestone
measured at Eagle Bird Gulch:

sedimentary rocks 37
Section of Leadville at Eagle Bird Gulch
Feet
21.
(Pennsylvanian unconformable upon.)
(Porphyry 80 feet thick)
20. Limestone (similar to bed No. 16 below) 44.4
19. Limestone, gray, medium- to thick-bedded, "zebra" texture; surface
furrowed by weathering 19.0
18. Limestone, well bedded; joints prominent 2.5
17. Limestone, dark gray, cherty . 3.0
16. Limestone, gray to grayish black, crystalline, containing vugs
up to 4 inches in width lined chiefly with quartz, calcite, and
dolomite; bedding indistinct. Limestone grades laterally into
coarsely crystalline, finely banded, "zebra" limestone; surface
furrowed by weathering , 37.5
15. Limestone, dark gray; weathers white to yellow; contains
black chert 2.6
14. Breccia, dark gray, made up of fragments up to 5 inches long
of limestone, chert, and quartzite; light-colored, medium-grained
quartzite; and gray shale 13.5
13. Quartzite, gray, coarse-grained 1.8
12. Limestone, gray, arenaceous; has contorted appearance 1.0
11. Limestone, light- to dark-gray, even-bedded; weathered surface
exhibits alternate light and dark beds , 9.7
10. Limestone, grayish black, dense, even-bedded; contains vertical
veins of calcite and dolomite 7.5
9. Limestone, grayish black, cherty, even-bedded; has contorted
appearance; upper part weathers into blocks 7.3
8. Limestone, brown, arenaceous, argillaceous
7. Limestone, grayish black, dense; has a hard, chert-like appearance;
contains veins of calcite and dolomite, and vugs with
1.3
crystals of calcite and dolomite
6. Limestone, dark gray, containing white to yellowish veins of
4.7
carbonate. Some beds have a knotty appearance; others are
smooth, darker in color, and weather into blocks
5. Alternate beds of dark-gray, dense, arenaceous limestone, and
9.4
arenaceous, thinly laminated, greenish shale 10.0
4. Limestone, dark gray, well bedded; has a knotty, wavy appearance;
weathers in slabs with rounded edges; contains a few
(Unconformable narrow chert layers upon Sawatch.)
3. Shale, gray to light brown, calcareous, arenaceous, unevenly
199.5
13.7
The bedded following fossils were found in the basal part of the Leadville: 0.7
2. Spirifer Limestone, whitneyi, gray, dense, var. animasensis fine-textured; Girty weathers into blocks 6.0
1. Spirifer Limestone, sp., brownish-gray, may be Sp. coniculus dense, Girty unevenly bedded 3.9
Schuchertella sp., resembles Sch. chemungensis Conrad
Crania sp.
Fenestella ?
Pelecypods, two indeterminate species
Fragments of crinoid stems
Zaphrentis ?
Two specimens of Spirifer centr,onatus Winchell were given to the Survey
party by Dr. I. A. Ettlinger, who found them a few feet above the breccia.

•50 RED CLIFF MINING DISTRICT
A few corals, probably Zaphrentis sp., and one brachiopod, which may be
Chonetes illinoisensis Worthen, were found near the top of the Leadville.
Fossil species collected are too few to justify a correlation of these
beds with the Leadville limestone in other regions with any degree of
certainty on faunal evidence alone; but there are other factors which will
support a tentative correlation. The upper part of the formation at Red
Cliff is lithologically similar to the Blue, or ore-bearing, limestone of the
Leadville district, which Emmons6 has determined as Lower Carboniferous
(Mississippian). Girty7 has accepted Emmons' correlation. Emmons8 redescribed
this formation under the title "Blue or Leadville limestone" in
his work on the Tenmile district. Moreover, as is pointed out below, under
the discussion of the Pennsylvanian sediments, the Leadville limestone at
Red Cliff is overlain by beds which are strikingly similar to those which
overlie the Blue limestone of the Leadville district and the Blue or Leadville
limestone of the Tenmile district. In view of the fossil evidence found
in the upper part of the Leadville, the lithologic similarity to other Mississippian
formations in nearby districts, and its stratigraphic position, that
part of the Leadville limestone above the breccia zone or unconformity is
regarded in this report as Mississippian.
The lower part of the Leadville is tentatively placed in the Devonian
for two reasons. An unconformity 70 to 75 feet above the base separates the
lower from the upper part; and the only diagnostic fossils identified with
certainty, found below the unconformity, are Devonian brachiopods, Spirifer
wMtneyi. Girty* mentions that a distinctive Devonian fauna occupies the
lower part of the Leadville limestone of central Colorado and .the lower
part of the Ouray limestone, which is the equivalent of the Leadville. It
is also noteworthy that Girty believes that deposition was not quite continuous
when the Leadville and the Ouray formations were laid down, and
that a slight unconformity may exist between the strata characterized respectively
by the Devonian and Mississippian faunas in the midst of the
Ouray and Leadville formations. There is little doubt that an unconformity
exists at Red Cliff 70 to 75 feet above the base of the Leadville formation.
PENNSYLVANIAN SEDIMENTS
Description
The thin beds of black shale and dark-colored limestone overlying the massive
light-colored upper beds of the Leadville formation are taken as the base
of the Pennsylvanian. In most places in the district the porphyry sill is
found at, or a little above, the contact between the Mississippian and
Pennsylvanian. Most of the following description is based on a section
measured at Rock Creek.
For approximately 175 feet above its base the Pennsylvanian is chiefly
thinly laminated black carbonaceous shale interlarded with four- to twelveinch
beds of dense, dark-gray to black limestone. The shale contains a
"Emmons, S. F„ Geology and mining industry of Leadville, Colorado' TJ.
S. Geol. Survey Mon. 12. 1886, p. 66.
'Girty, G. H., Carboniferous formations and faunas of Colorado- U S
Geol. Survey Prof. Paper 16, 1903, pp. 163, 222.
'Emmons, S. F., U. S. Geol. Survey Atlas, Tenmile folio (No. 48) 1898
"Girty, G. H., Carboniferous formations and faunas of Colorado: U S Geol
Survey Prof. Paper 16, 1903, pp. 162-163. ' ' '

SEDIMENTARY rocks
little disseminated pyrite. A few fossils were found. In this section there
are a very few dark-colored quartzite beds 1 to 2 feet thick, and near the
base a few unimportant thin layers of impure coal. About 175 feet above
the base the character of the sediments changes. The limestone beds become
fewer and disappear; the shales are lighter in color and become
arenaceous and micaceous; gray to greenish micaceous sandstone and
quartzite beds appear, some of which, higher up, become conglomeratic.
At 275 feet the dominant sediments are quartzites and conglomerates. Beginning
between 300 and 400 feet above the bottom of the Pennsylvanian
Figure 8. Pennsylvania* sediments, looking
north from Rex
Shows shale alternating with sandstone and
conglomerate
and extending upward about 450 feet, the sediments are dark or reddishbrown,
in contrast with the light-colored beds below and above. The rocks
are mainly conglomerates and sandstones and are more or less ferruginous;
shales are subordinate. (See Fig. 8) Pebbles in the conglomerate are
chiefly quartz, varying, in size up to 2 inches in diameter. Fragments of
partly altered orthoclase and plagioclase are common. Muscovite, much of
it secondary, is abundant in all of the rocks. The interstices between grains
in both sandstones and conglomerates contain sericite.
The color of the sediments changes again, about 900 feet above the
39

40 RED CLIFF MINING DISTRICT
base, to greenish-gray and gray. For the next 1,600 feet the Pennsylvanian
is composed essentially of shale, conglomerate, sandstone, limestone, and
quartzite, decreasing in abundance in the order named. Cross-bedding is
displayed in places, and many of the beds are lenticular. The shale is micaceous
and arenaceous, and grades into sandstone. Sandstone and con
glomerate of many degrees of coarseness are found. Pebbles up to 3 or 4
inches in diameter are not uncommon; the maximum size of boulders is
15 inches. The pebbles and boulders are for the most part quartz, quartzite,
granite, and gneiss. Feldspar is a common constituent of both sandstone
and conglomerate. Pink feldspar is sufficiently abundant in some
beds to give a pink tinge to the rocks.
Lenticular dolomitic limestones are prominent but irregularly developed
in the upper part of the Pennsylvanian. They are 6 to 50 feet thick; and,
since they are rather resistant to weathering and erosion, they stand out
in cliffs up to 40 feet high and make one of the most conspicuous features
of the topography. The beds are dark to light gray in color, and in places
contain chert. In this upper part most of the sediments not limestones are
coarse conglomerates and sandstones similar to those a little lower down
in the section.
The total thickness of the Pennsylvanian exposed in this district is about
4,000 feet.
Age
The following fossils were collected from the lower 3,500 to 3,700 feet
of the Pennsylvanian. These sediments probably include the Weber shales
and Weber grits of the Tenmile district10:
Orbiculoidea (cf. manhattanensis M. and H )
Lingula carbonaria Shumard
Orbiculoidea convexa Shumard
Derbya crassa ? (M. and H.)
Meekella striaticostata Cox
Productus cora D'Orbigny
Productus punctatus Morton
Productus inflatus McChesney
Marginifera ingrata Girty
Chonetes geinitzianus Waagen
Reticularia. perplexa McChesney
Spirifer cameratus Morton
Spirifer bdonensis ? Swallow
S*piriferina sp. (may be Spiriferina kentuckyensis)
Rhombopora lepidodendroides? Meek
Bryozoa undetermined
Allerisma terminale Hall
Nucula ventricosa Hall
Nucula sp. (cf. N. parva McChesney)
Leda bellistriata ? Stevens
Pleurophorus (cf. P. subcostatus M. and W.)
Myalina cuneiformis Gurley
Aviculopecten rectilaterarius Cox
Aviculopecten occidentalis ? Shumard
Zaphrentis undetermined
Campophyllum ?
Chaetetes milleporaceous ? Milne
Mbnoilopora (cf. prosseri Beede)
Crinoid stems (several types)
"Emmons, S. F., U. S. Geol. Survey Geol. Atlas, Tenmile folio (No. 48), 1898.

SEDIMENTARY ROCKS
The uppermost beds of the Pennsylvanian system exposed in the Red
Cliff district include a portion of the Maroon of the Tenmile district. From
these sediments the following fossils were collected within the area mapped
for this report:
Productus cora D'Orbigny
Meekella striaticostata Cox
Composita subtilita (Hall)
Reticularia perplexa McChesney
Fusulina cylindrica F. de Waldheim
Phillipsia sp.?
Gastropoda undetermined
The fossils in these two lists are among those which have been found
in the Pennsylvanian in the Tenmile and Leadville districtsu. The belief
that this formation is Pennsylvanian finds support also in the fact that, in
the eastern part of the Red Cliff district, the upper beds are continuous
with the Weber and Maroon beds of the Tenmile district which Emmons
has determined as Upper Carboniferous, or Pennsylvanian. For several
reasons no attempt has been made to divide the Pennsylvanian into Weber
shales, W]eber grits, and Maroon, as Emmons has done in the Tenmile and
Leadville districts. In the Red Cliff district a division of the lower part
of the Pennsylvanian into "shales" and "grits" could not be established
because the change from carbonaceous shale and limestone below to
arenaceous shale, sandstone, and conglomerate above was a gradual one.
Fossils found in the Weber and Maroon appear to belong to the same
fauna, and furnish no basis for a division* between these two formations.
Study of the limestone members of the upper part of the Weber and of
the Maroon has been insufficient to confirm Emmons' conclusion13 that
the limestones furnish the safest means of distinguishing one formation
from the other.
"U. S. Geol. Survey Prof. Paper 16, pp. 242-243.
"U. S. Geol. Survey Geol. Atlas, Tenmile folio (No. 48).
41

4i RED CLIFF MINING DISTRICT
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'

STRUCTURAL GEOLOGY
CHAPTER V
Br R. D. Crawford
Igneous intrusion and metamorphic processes in pre-Cambrian time
have been important factors in modifying the structure of the pre-Cambrian
terrane whose rocks have been described in previous chapters. Vertical
movements have many times effected the submergence and emergence of
the region of which the Red Cliff district is a part, and have left the
district high above sea level; but in this chapter will be considered chiefly
the results of relatively minor movements that have occurred in post-
Paleozoic time.
West of the district are Holy Cross and Notch mountains at the north
end of the Sawatch Range. The rising of these mountains has tilted the
Paleozoic sediments which extend from the mountain slopes to the Mosquito
fault (Fig. 12) where the beds abut against the pre-Cambrian rocks.
In the mapped area the sediments have a northeast dip of 5° to 15°. In
the mines of Battle Mountain the dip is nearly 10°; for the entire district
the average dip is about 1° or 8°.
FAULTING
Faults of great displacement seem to be absent from the Red Cliff
district. Though many of small displacement exist, they are hard to find
in the pre-Cambrian rocks and in the limestone, and can be traced only
short distances. Most of those shown in pre-Cambrian rocks on the accompanying
claim map (PI. II) were disclosed in underground workings. These
range from small displacements, where evidence of movement is scarcely
discernible, to larger faults where the brecciated zone is several feet wide.
In several places between Red Cliff and Gilman there has been movement
along fissures in the igneous rocks. In these larger faults, where displacement
can not be measured because of the character of the wall rock or
the limited evidence available, and where the amount of gouge and brecciation
is considerable, it seems not unreasonable to suppose that an oscillatory
movement has taken place,—that is, the same wall of the fault has
moved in opposite directions at different times. In some instances the
fault is not a single dislocation, but appears as a number of closely spaced
breaks; or a single large fault may fork, and the more mineralized branch
be followed by the drift or tunnel. In several places underground evidence
of two periods of faulting may be seen where the northeast-striking faults
are offset by cross faults of minor importance.
From Gilman to Red Cliff and thence southeastward a mile or more
sharp breaks in the outcropping Sawatch quartzite are numerous. The
most conspicuous cracks, or fissures, strike northeastward in the direction
of dip of the quartzite, and they stand nearly vertical. The quartzite bedding
generally does not show any offsetting at these breaks, and most of
them might easily be mistaken for dip joints. Rarely a bed may be offset
a few inches or, at most, a few feet. Numerous mine workings show many
.of these breaks to be planes of faulting, particularly those that continue

44 RED CLIFF MINING DISTRICT
up into the limestone. Broken and shattered rock, slickensiding, and gouge
are common. In places fault rock forms a zone up to 10 feet wide.
Underground, as at the surface, where there is any stratigraphic displacement
it is very slight.
The conditions observed might have been brought about by a more
or less vertical differential movement along a plane, the fault blocks settling
down into the same relative position that they occupied before the movement;
or there may have been differential movement along these planes
between blocks that slipped in a direction parallel to the bedding planes.
That a differential movement almost at right angles to the bedding did
take place is shown by the nearly vertical grooving on fault walls. This
grooving was observed in the limestone of the Eagle mines and the Foster
Combination mine, in the quartzite of the Ground Hog mine, and in the
quartzite of a cliff south of Eagle River near Gilman. Careful search by
the Survey party has failed to disclose evidence of vertical faulting in
the outcrop of beds overlying the Leadville limestone. Horizontal or nearly
horizontal grooving has been seen in the quartzite of the Ground Hog and
Bleak House mines. It is evident that fault blocks were subjected to
the two kinds of movement mentioned at the beginning of this paragraph.
The name fault implies displacement, and no permanent displacement
on most of the planes can be proved. Yet there is abundant evidence that
at some time there was pronounced differential movement and hence displacement
over extensive surfaces. Those planes or zones along which
movement was effective in slickensiding and crushing the rock will be
hereinafter designated faults, even though they may show no offsetting
of beds. Locally certain faults appear to pass into a fault zone several
feet wide where the movement was distributed over many closely spaced
fractures. This is more easily seen in the outcropping quartzite than in
the mines. In places the movement on each plane was so slight that the
zone would be unimportant did it not pass gradually into a single fault
plane along which movement was concentrated. The dip faults—those that
strike approximately in the direction of dip of the beds—are oftener seen
in the quartzite than in the overlying limestone, owing perhaps to the
greater brittleness of the quartzite. In the deeper mine workings in limestone
a fault apparently may be locally scattered through a minutely
fractured zone that shows practically no indications of movement, or it
may fade out entirely.
Besides the dip faults there are on Battle Mountain faults of high
dip that strike northwestward and others that strike nearly due west.
Most of these are unimportant, but in the mines of the Empire Zinc Company
are two along which there has been much movement. While most
or all of the dip faults were made before the ore was deposited it is possible
that one northwest striking fault is younger than ore.
Bedding faults where one bed has slipped over another along a plane
parallel to the bedding are common in the mines, but are rarely detected
at the surface. These faults commonly show a layer of gouge from a fraction
of an inch to 8 inches thick, mostly less than 2 inches. Locally a
fault may cut across the limestone and continue along a bedding plane only
a few inches above or below the one it left. Generally there has been

STRUCTURAL GEOLOGY 45
very little crushing of the rock along the bedding faults, and the displacement
may be little. In addition to the bedding faults and those of high
dip are others, seen underground, that have intermediate dips and no
uniformity of strike.
Between Red Cliff and the south border of the mapped area are many
faults of small displacement and northeastward strike. These can be seen
in the Cambrian quartzite and jasperoid (p. 56) that has replaced the
faulted Leadville limestone. None can be traced far on the surface. It
is probable that several faults are covered with landslides through part
of their course, owing to deep erosion along the less resistant material
of the fault zones. Many faults that preceded the extensive siliceous
replacement of the limestone (p. 58) have been preserved in the replacing
jasperoid.
About three-fourths of a mile west of the mouth of Silver Creek the
quartzite on the northwest side of a fault has been raised an undetermined
distance and tilted; it now has a northwest dip of about 75°. Owing to
mantle rock and jasperoid which cover the fault the exact strike cannot
be determined, but it is probably about N. 40° E. Considerable limonite
was found southeast of the fault, or in the fault zone, in prospects now
caved. Nearly in line with this fault, on the west bank of Eagle River,
there has been faulting in the gneiss; this is seen in a very small exposure.
East of the river, still in line with the fault, is a landslide 400 or 500 feet
wide (PI. I.) Evidence points to channel cutting along a fault line, and
subsequent slumping. The known fault strikes southwest toward Homestake
Gulch, and many have determined the position of the gulch. Between
the gulches of Homestake Creek and Eagle River the highly resistant
jasperoid prevented rapid erosion along the fault.
Between 1 and 1.5 miles southeast of the fault just described are
several faults in the quartzite. At a few a displacement of several feet is
indicated. One, seen at the railroad and shown on Plate I, dips 50°
southeastward. On the southeast side the quartzite has been dragged up,
and now dips southeast. On the hill toward the southwest and almost in
line with the fault at the railroad the jasperoid has preserved a fault that
dips 76° N. 23° W. The offsetting of the quartzite-jasperoid contact indicates
a downthrow on the north side of the fault. Across the river, toward
the northeast, is one of the largest landslides of the district in an area
probably made weak by faulting.
A small fault shows in the steep slope a short distance northeast of
Pando. Several have been preserved by the jasperoid on both sides of
Elk Creek.
About a mile and an eighth south of Deen Station is a fault in the
Cambrian quartzite and pre-Cambrian rocks. The downthrow is on the
north side and the displacement is about 80 or 90 feet. Owing to talus
along the line of faulting the direction and amount of fault dip has not
been determined. The displacement at this fault is the greatest noted
in the district.
From a structural standpoint faults in the Red Cliff district are
unimportant. Their importance in connection with ore deposition is brought
out in Chapter VI.

MINERAL DEPOSITS"
CHAPTER VI
By R. D. Crawford
In this chapter both ore minerals and minerals of no commercial value
will be treated. The valueless minerals form masses that were deposited by
large-scale geochemical processes that were evidently more or less directly
involved in ore deposition.
GENERAL CHARACTER OF THE ORES
Gold, silver, copper, lead, zinc, and manganese, in commercial quantities,
have been produced in the Red Cliff district. The early production was
chiefly from the oxide zone; it included gold, silver, and lead. In recent
years most of the ore has come from the primary-sulphide zone. The metals
produced from sulphide deposits are zinc and silver in large quantities, besides
considerable gold and copper; comparatively little lead sulphide has
been produced in recent years. Secondary sulphides are unimportant in this
district. Native gold—part of the ore very rich—has been found in pyrite
in the quartzite and in iron oxide derived from pyrite. Many carloads of
manganese oxides have been shipped from Bell's Camp. From Table I,
page 12, it is seen that the average annual value in recent years of ore shipped
from the district ranges from about $17.50 to $30.00 a ton. The figures
below are taken from the record of smelter settlement sheets for many
thousand tons of ore shipped, during the years 1908 to 1918 inclusive, from
several mines operated by Dismant Brothers and others. Where not otherwise
stated the items are for carload lots, or at least lots of several tons
each.
Range in ore constituents
Gold: nothing to 22.8 ounces per ton.
Silver: 2.4 to 306.2 ounces per ton; one lot of 183 pounds from the Ground
Hog mine yielded 303.4 ounces gold and 7,671.2 ounces silver per ton.
Lead: nothing to 56.6 per cent, mostly low.
Iron: nothing to 64 per cent.
CaO: nothing to 28 per cent.
SiO»: 3.2 to 88 per cent.
H20 (moisture): 1 to 46 per cent, mostly below 12 per cent.
The ores with highest lime content came from mines in the Leadville
formation, and those with highest silica content came from mines in the
quartzite. In both cases it is evident that the ore minerals had replaced
only part of the rock, perhaps near the border of the ore body.
Sulphide Enrichment
Secondary-sulphide minerals in the Red Cliff district appear to be nearly
negligible in quantity. Mr. I. A. Ettlinger, who has studied the geology and
ores of the Eagle mines in detail, makes the following statements: "The
only sulphide enrichment observed was the black coating on the pyritic ore.
This coating is found mainly on the ore running high in copper, being a
"'Most of the laboratory tests of ore and gangue minerals collected by
the Survey party were made by Russell Gibson and E. A. Hall Mr Gibson
also wrote the paragraph on fissure veins.

MINERAL DEPOSITS
replacement of the chalcopyrite by covellite or chalcocite. Pyritic ore carrying
this coating runs high in silver." Mr. Hall has found a little sulphide
enrichment in the Ground Hog mine described in Chapter VII. That only
slight secondary-sulphide enrichment has occurred may perhaps be explained
by the rapid flow of ground waters from the veins into the deep canyon
of Eagle River, and the consequent loss of dissolved metals.
MINERALS OF THE ORE DEPOSITS
In this section are noted only the characters shown by the ore and gangue
minerals of this district. Full descriptions of the same minerals are to be
found in many mineralogy text-books. The metallic minerals are listed alphabetically
under the name of the most important contained metal. For
convenience, the formula of each mineral is given, together with the percentage
of the principal-metal content of the pure mineral.
Mr. A. W. Pinger has made for the Empire Zinc Company a thorough
examination of the ores of the Eagle mines. Polished ore specimens were
examined with the aid of a metallurgical microscope, and the microscopic
work was supplemented by numerous assays and analyses by J. D. Hawthorne,
chemist for the same company. The officers of the Empire Zinc
Company generously permitted the writer to read the report on the ores and
quote therefrom. The statements credited to Mr. Pinger in the following
paragraphs are taken from the report mentioned.
Aluminum
Alunite, hydrous potassium-aluminum sulphate, K20.3A1203.4S03.
6H20. Friable white alunite was found associated with zinc carbonate in a
zinc-ore stope in the Eagle No. 2 ore shoot. The one sample taken carries
some zinc, calcium, and magnesium.
Arsenic
Arsenopyrite, iron arsenosulphide, FeAsS—iron 34.3 per cent, arsenic
46.0 per cent, sulphur 19.7 per cent. Mr. Pinger has found minute quantities
of this mineral associated with pyrite from the Eagle mines.
Copper
Bornite, copper-iron sulphide, Cu5FeS4—copper 63.3 per cent. "Bornite
was observed in four specimens. In these it occurs in very minute veinlets
in chalcopyrite, visible only with the aid of the high-power objective. In one
specimen there is a small area apparently intergrown with chalcopyrite. In
this instance it may be contemporaneous with the chalcopyrite; but in the
other observed occurrences it is probably a secondary product" (Pinger).
Chalcanthite, hydrous copper sulphate, CuS04.5H20—copper 25.45 per cent.
Sky-blue chalcanthite fills a few narrow fissures in the quartzite in the
Ground Hog mine. Some specimens collected in this mine show pyrite and
chalcanthite in close association. A blue stain is common on the walls of
other mine workings in the quartzite. This is probably chalcanthite formed
through oxidation of sulphide ore since the mines were opened.
Chalcocite, cuprous sulphide, Cu2S—copper 79.8 per cent. Black, granular
chalcocite was seen in small quantity by Mr. Hall in the Ground Hog mine.
Chalcopyrite, copper-iron sulphide, CuFeS,—copper 34.5 per cent. Speci-
47

48 RED CLIFF MINING DISTRICT
mens of this mineral were collected by the Survey party from the Ground
Hog and Pursey Chester mines. In the latter mine practically pure chalcopyrite
is associated with pyrite, zinc blende, and quartz. The same
mineral is said to have been produced in considerable quantity by the Iron
Mask mine. It probably furnished much or most of the copper that has been
produced by the district in recent years. Of ore from the Eagle mines Mr.
Pinger says: "Chalcopyrite is generally present in the ores in very small
quantities. In many of the specimens studied it was entirely lacking. A few
polished specimens contain nearly three-quarters chalcopyrite. It is rarely
present in the ores in quantities large enough to be readily seen in the hand
specimen. Under the microscope chalcopyrite occurs surrounding, filling in
between, and sometimes corroding grains of pyrite. The chalcopyrite is often
intergrown with sphalerite, and commonly appears to have been corroded
and partially or completely replaced by sphalerite; small residual specks
often occur in the sphalerite and have an arrangement roughly parallel to
the irregular contact between the two minerals."
Covellite, copper sulphide, CuS—copper 66.5 per cent. "Covellite is
present in very small amounts, but rather more widespread than bornite.
When present it occurs as a thin dark-colored film or coating on the surface
of cracks and open spaces in pyritic ore, and is usually restricted to ore
containing chalcopyrite. Under the microscope covellite is observed cutting
and partly replacing chalcopyrite along tiny veinlets. From these relations
covellite is probably to be considered as of secondary origin,—that is, it is
copper sulphide that has been leached out of overlying ores by downward
circulating ground or surface waters, and reprecipitated below the zone of
oxidation by partial replacement of chalcopyrite" (Pinger).
Tetrahedrite, copper sulphantimonite, Cu,Sb2S,—copper 52.1 per cent. Of
tetrahedrite and freibergite Mr. Pinger writes: "These minerals occur in
very small amounts in those ores which have comparatively high silver
values. The freibergite is distinguished from tetrahedrite by the presence
of silver; under the microscope freibergite reacts slightly to dilute nitric acid
and tetrahedrite is negative to this micro-chemical test. The two minerals
are very similar in appearance and in occurrence and associations. In many
instances it was impossible to determine which of the two was under observation.
They are usually associated with chalcopyrite and pyrite, and are occasionally
corroded land partly replaced by sphalerite, and to a less extent
by chalcopyrite."
Gold
Gold commonly occurs in sulphide and oxidized ores found in the
quartzite and pre-Cambrian rocks. In the high-grade ores of the Ground
Hog, Champion, and possibly other mines in the quartzite native-gold nuggets
were frequently found. It is said that nuggets up to 2 ounces in weight
were not rare. The nuggets are reported to have been angular and horn
shaped in the pyrite, and more or less smoothed and rounded in the oxidized
ere.
Iron
Coquimbite, iron sulphate and water, Fe2(S04)3.9H,0—iron 19.87 per
cent. This mineral was found on the walls of a crosscut in the Eagle No. 2
ore body where it evidently had formed by oxidation of the iron sulphide

MINERAL DEPOSITS
after the ore was blocked out. The mineral occurs in aggregates of poorly
formed crystals. A green color predominates; patches are bluish green.
Part of the material reacts only for ferric sulphate and water, though much
of it carries a small amount of copper. Whether copper replaces part of
the iron or occurs in chalcanthite mixed with the coquimbite has not been
determined.
Limonite, hydrous iron oxide, 2Fe2Os.3H20—iron 59.8 per cent. Brown
and yellow limonite is one of the commonest minerals in the oxidized zone,
and is frequently found far from any known ore body. Much of the limonite
is admixed with kaolin and other materials.
Pi/rite, iron disulphide, FeS2—iron 46.6 per cent, sulphur 53.4 per cent.
Pyrite occurs in nearly or quite all the sulphide ore bodies in the district.
Though in places it has no value as ore, it generally carries gold, silver, or
copper. Pyrite is the best silver ore of the deep mines in the limestone.
Much of the gold and silver of the mines in the quartzite occurs in pyrite.
Well formed crystals—cubes or pyritohedrons, or combinations of the two—
are common. They range in size from one-sixteenth inch to an inch or more
in diameter; the largest crystals seen by the writer were found in the
quartzite. Most of the pyrite of large bodies is massive, and shows crystals
only in drusy cavities. Parts of a body may be made up of porous pyrite
where the mineral occupies about three-fourths to seven-eighths of the volume.
Most of the open spaces are narrow and less than half an inch long. The
walls of the spaces are crystallized pyrite.
Pyrrhotite, iron sulphide, about Fe„S12. Of this mineral Mr. Pinger
writes: "Pyrrhotite is present sparingly and has 'been observed only in extremely
minute residual grains in sphalerite and galena. In fact it occurs
in such small quantities that the micro-chemical tests were somewhat
indefinite."
Siderite, iron carbonate, FeC03. Light gray to brownish siderite is one
of the most abundant gangue minerals of the district. Cavities in siderite
masses show well shaped simple rhombohedrons, and the massive mineral
is coarse in texture. Manganese and magnesium replace a large part of
the iron as shown by the nearly complete analyses below. The sulphur
comes from associated pyrite. The two specimens analyzed came from
different parts of the mines.
Analyses of siderite from Eagle Mines
(P. M. Dean, Analyst)
FeO
MnO
MgO
OaO
C02
S
Insoluble
mines and prospects in the oxide Zone.
I
35.73
11.30
10.56
.87 .
40.10
.35
.26
25.07
12.29
16.13
1.75
42.50
.18
.17
Turgite, ferric oxide with water. Red earthy turgite is found in several
49

50 red cliff mining district
Lead
Anglesite, lead sulphate, PbSO,—lead 68.3 per cent. According to S.
F. Emmons" much anglesite in minute crystals, or "sand," was found in
the oxide zone of the mines in the Red Cliff district.
Cerussite, lead carbonate, PbC03—lead 77.5 per cent. This mineral was
common in ores shipped from the district in early days. It is now found
in small quantities on the borders of old stopes. The Survey party collected
only a few samples of lead carbonate, most of which is soft and
carries an admixture of iron oxide. Samples assayed show 9 to 12 ounces
silver and .05 to .07 ounces gold per ton. With the soft earthy carbonate
are small groups of cerussite crystals having adamantine luster.
Galena, lead sulphide, PbS—lead 86.6 per cent. In mines now operating
galena is found only in small quantity. That seen by the field party occurs
in grains and crystals up to half an inch in diameter. The crystals
are combinations of cubes and octahedrons. In the deepest mines in the
limestone the galena carries little or no silver. A sample of galena from
the quartzite in the Ground Hog mine, assayed by Mr. Hall, yielded .72
ounces gold, and 34.30 ounces silver per ton. A second sample from the
same mine assayed .15 ounces gold and 17.92 ounces silver per ton.
Manganese
Oxides of manganese are common in the oxide zone, and a large tonnage
of manganese ore is reported to have been shipped from Bell's Camp
several years ago. Specimens of manganese ore collected are mostly mixtures
of pyrolusite and psilomelane. Some of the material carries iron, and
much of the black material is manganese-bearing limonite. In the mines
and on the dumps were found pseudomorphs of oxides of iron and manganese
after siderite. It is probable that most of the manganese ore has
been formed by the alteration of siderite.
Silver
A large part of the silver produced by the oxidized ore bodies is said
to have been combined with chloride in the mineral cerargyrite, or horn
silver. Samples collected from the Rocky Point and Polar mines contain
a, little cerargyrite that can be detected only by chemical tests. Native
silver and argentite have been reported from the district. Mr. Pinger has
found a small amount of freibergite (silver-bearing tetrahedrite) associated
with pyrite and chalcopyrite. Richard Pearce^ states that hessite
(silver telluride) was found in large quantities in one or two of the
mines at Red Cliff.
Zinc
Goslarite, hydrous zinc sulphate, ZnS04.7H30—zinc 22.73 per cent. White
zinc sulphate is found in old stopes of the Eagle mines near the top of the
sulphide zone. The mineral was formed after air reached the sulphide ore
through mine openings; it is well preserved in dry parts of the mine. This
material lines one of the Iron Mask haulage ways where it protrudes
through the openings between lagging, and hangs like a mass of soft
white hair in fibers a foot long. Qualitative tests show that a little iron
is present with the zinc.
"Colo. Scientific Society Proceedings, vol. 2, 1886, p 101
"A. I. M. E. Trans., vol. 18, 1890, p. 541.

MINERAL DEPOSITS
Smithsonite, zinc carbonate, ZnC03,— zinc 52.2 per cent. Hard, massive,
gray zinc carbonate is found on the borders of a few old stopes. Some
of it carries a little calcium and magnesium. One sample of red carbonate
ore collected contains considerable copper and iron as well as zinc.
Qualitative tests of the gray carbonate show much water, thus indicating
that hydrozincite is present with the smithsonite.
Zinc blende, or sphalerite, zinc sulphide, ZnS—zinc 67 per cent. This
mineral has made practically all the zinc ore that has been produced in
large quantity by the Eagle mines. In these mines the zinc blende is
dark brown to black owing to a considerable percentage of iron and is
the variety known as marmatite. It is partly massive and solid, and partly
friable. Much of the best ore is friable and sandlike. The best bodies of
zinc ore are nearly free from other minerals, but some of the ore shows
an admixture of galena, pyrite, or siderite. Drusy cavities contain numerous
small blende crystals, most of them not more than one-sixteenth inch
in diameter. In the Ground Hog mine blende, too scarce to make zinc ore,
occurs in crystals up to half an inch in diameter. Most of the blende of
this mine is also dark brown. A lighter variety, "rosin zinc," is found in
small amount in a few mines of the district. Zinc blende is found in small
quantity in the deepest mines in the pre-Cambrian rocks.
Exclusively Gangue Minerals
Barite, barium sulphate, Ba90.,. Barite as a gangue mineral in this
district is not common, but in several fracture zones patches of small barite
crystals form a coating on the rock at or near the outcrop. North of Elk
Creek is a narrow vein of coarse, cleavable, massive barite.
Calcite, calcium carbonate, CaCOa. Crystallized calcite is found in cavities
in the oxidized ore where it has evidently been deposited by cold surface
waters.
Dolomite, calcium-magnesium carbonate, CaMg(C03)2. In addition to the
fine-granular and dense dolomite and dolomitic limestone of the Leadville
formation that incloses many of the ore bodies, coarse-granular dolomite
is common near the ore. This coarse dolomite has evidently replaced fault
rock, including gouge. Much of it is medium gray in color, but in several
places it is mottled and shows angular patches of white and very dark
gray. The dark gray dolomite carries minute crystals and grains of pyrite.
After the carbonate and pyrite are dissolved in acids, the small amount
of residue—still dark gray—seems to be composed chiefly of quartz and
carbonaceous material. Nearly complete analyses of the dolomite are given
below.
Analyses of coarse dolomite from Eagle Mines
(P. M. Dean, Analyst)
CaO
MgO
FeO
MnO
C02
S __
Insoluble
30.28
19.72
.78
45.09
.20
2.33
2
30.10
20.18
1.85
.42
46.20
.72
3
29.41
20.48
1.22
.44
46.17
1.30
51

52 RED CLIFF MINING DISTRICT
1. Gray dolomite, Wilkesbarre shaft, intermediate level.
2. White dolomite from mottled white and dark gray mass near ore
body, Eagle No. 2.
3. Dark gray dolomite in contact with white dolomite of sample No. 2.
Gypsum, hydrous calcium sulphate. Gypsum in small quantity can be
detected by chemical tests in the earthy material of the oxide zone in many
mines and prospects. Pieces of transparent crystallized gypsum (selenite)
are found in the Potvin mine, where this mineral is associated with pyrite,
limonite, and oxide of manganese. Small crystals of selenite form a shiny
coating on masses of iron and manganese oxides in the stopes of the old
Black Iron mine, now Eagle No. 2.
Kaolin, hydrous aluminum silicate, Al202.2Si02.2H20. White soft kaolin.
commonly associated with quartz, is found in the veins and on the vein
walls of most of the mine workings in the pre-Cambrian rocks, where
it has been derived from alteration of the feldspars of the wall rock. The
decomposition of the porphyry that lies just above the largest ore shoots
in the limestone has resulted in the formation of much kaolin.
Quartz, silica, Si02. Ordinary vein quartz, both massive and in small
crystals, is found in many mines and prospects; but quartz in these forms
is not an important gangue mineral in the ore shoots within the Leadville
limestone. Quartz of the quartzite walls may be considered a gangue
mineral of some low-grade ores replacing quartzite. To what extent quartz
in the jasperoid form was present near the oxidized ores of the early workings
is unknown. Further reference is made to this in the section on "replacement
ore deposits."
CLASSES OF MINERAL DEPOSITS
All the known ore of the Red Cliff district is younger than the rocks
that inclose it. The two following classes are present: (1) fissure-vein ore
in the pre-Cambrian rocks and Sawatch quartzite; (2) replacement deposits
in the Leadville formation and in the Sawatch quartzite.
Fissure Veins
Most of the fissure veins in the pre-Cambrian rocks strike northeast,
and are vertical or have high dips to the southeast. Movement along the
fissures prior to ore deposition has resulted in gouge and breccia up to
30 inches in width. Wttiere slipping has occurred along closely spaced
breaks the fault zone may be as much as 6 feet wide. The vein minerals are
quartz, pyrite, sphalerite, galena, and probably a little chalcopyrite. The
pyrite, much of which is copper-bearing, commonly carries both gold and
silver. The veins of ore are thin, many being each less than an inch thick;
a foot of solid sulphides is rare. Commonly one thick vein splits into two
or several which, farther on, may coalesce. The associated decomposed
wall rock contains so little disseminated ore that the widening of veins
by replacement of the country rock is not considered important. Although
there have been two periods of fissuring, positive evidence of post-mineral
faulting has not been seen by the writer. In general, pyrite, the most
abundant sulphide, was one of the first minerals deposited; sphalerite and
galena were deposited later.
Fissure veins in the pre-Cambrian rocks pass into the overlying quartzite

MINERAL DEPOSITS
where they inclose workable ore bodies. Other good veins worked in the
quartzite carry little or no ore in the rocks below. Many veins in the
quartzite are narrow, and in places they show distinct crustification. More
commonly there has been replacement of the wall rock, and the veins may
be considered transitional between the replacement bodies described below
and the fissure veins.
Replacement Ore Deposits
In this district nearly all the ore found in limestone and the greater part
of that found in quartzite is of the replacement type. By this it is meant
that the ore was brought in by the same solvent that carried the country
rock away from the place taken by the ore. Both deposition of ore and
removal of rock are believed to have been effected at the same time by
exchange of particle of ore for particle of rock. It is possible that narrow
fissures existed in places in the limestone along the faults, and that such
fissures were afterward filled with ore; but since the replacement extended
far into the wall rock any slight fissure filling is negligible in comparison
with the whole. In the Sawatch quartzite, owing to less easy solubility of
wall rock, fissure veins are relatively much more important than in the
limestone.
The large bodies of sulphide ore blocked' out in the Eagle mines in 1921
afforded excellent opportunity to observe the results of replacement. Evidences
of replacement noted in the Eagle and other mines of the district
are the following: (1) irregular shape of the ore bodies; (2) frequent occurrence
of perfect pyrite crystals in limestone, quartzite, and gouge near
workable ore and, less commonly, in the pre-Cambrian rocks near the veins;
(3) presence of unsupported masses of rock in the ore; (4) preservation by
the ore of original bedding planes, rock fractures, outlines of disturbed limestone
blocks, and structure of fault rocks including faults themselves.
shape of ore bodies
Although the more extensive ore shoots generally follow the northeastward
striking faults (dip faults) and pitch approximately with the dip of
the beds, their outlines are irregular in that bulges and tongues of any
shape may extend many feet on either or both sides of the fault. The
smaller bodies may assume any form, and some have their longer dimensions
nearly parallel to the bedding planes of the rocks.
unsupported rock masses in ore
The sulphide-ore bodies of the Eagle mines inclose occasional small
patches of gouge that have escaped complete replacement. The patches
are likely to carry some pyrite near their borders. Near the top of ore
shoots are seen what might be either shale or gouge along a former bedding
fault. Such a streak 2 inches thick was traced 10 feet nearly horizontally
on the 7th level of the mine. That these patches have not worked into the
ore as a result of faulting after ore deposition is proved by the solid and
unfaulted character of the sulphide that surrounds them. Mr. Hall has
noted blocks of quartzite surrounded by ore in the Ground Hog mine.
CRYSTALS IN COUNTRY ROCK
Pyrite crystals having part or all of their faces developed occur in
limestone and quartzite near the ore bodies and in the wall rock of the
53

54 RED CLIFF MINING DISTRICT
fissure veins in the pre-Cambrian rocks. -The fault rock, including gouge,
locally carries perfect crystals of pyrite. The crystals are commonly less
than one-sixteenth of an inch in diameter. Cubes and pyritohedrons are
the commonest forms. These disseminated crystals in places are rare; in
other places they make up 10 to 20 per cent of the rock volume. Evidently
they have been precipitated from solutions that penetrated the rock beyond
the limits of workable ore.
PRESERVATION OF ROCK STRUCTURES BY ORE
Since most of the limestone is thick bedded or massive, having few or
indistinct bedding planes, it is not to be expected that indications of bedding
planes will be common in the ore that replaces the limestone. A very
fine-grained bed of the quartzite member of the Leadville formation is
laminated and locally shows minute fractures, faults, and folds that were
evidently impressed on it before cementation was completed. All these
structural features are preserved in the pyrite of the Eagle No. 2 ore shoot
in about the position where one would expect to find the quartzite had it
not been replaced. In the No. 1 ore shoot of the Eagle mines, in a stope
below the 14th level, lines of original rock bedding were seen on the
ore face.
More conspicuous examples of preservation of former structures are
seen where the ore has replaced fractured and faulted rock. The phenomenon
is best shown by pyrite or by mixed pyrite and zinc blende.
In pure zinc blende the details of former structure are not so evident. A
good example of replaced shattered limestone was seen near the east side
of the No. 1 ore shoot of the Eagle mines on the 14th level. Here blendepyrite
fragments and blocks from a fraction of an inch to several inches
in diameter made the vertical wall of a drift. This wall, or ore face, was
self-supporting because the component blocks were interlocking and tight
fitting; they had not been subjected to movement or crushing since the
ore was formed. Yet, so loosely were the fractures of the former limestone
cemented, the sulphide blocks could be pried out with a pick. When
this and similar faces of ore are covered with dust they can not be distinguished
from limestone by surface appearance alone. On the 6th level
of Eagle No. 2 pyrite preserved through a zone 7 feet wide all the structural
details, except slickensiding, of a former fault. In this place the
blocks were firmly bonded, probably owing to the presence of gouge before
replacement. This fossil fault is more fully described on page 61.
SIZE OF REPLACEMENT ORE BODIES
The greatest length of most of the replacement ore bodies lies in the
dip of the sedimentary beds and along fault lines, that is, toward the
northeast with a pitch of about 10°. The largest known body has been
developed continuously through a distance of 3,060 feet, all in the dolomitic
limestone. A second body has a known length of nearly 3,000 feet. Others
are known to be more than 1,000 feet long.
Part of the ore shoots are elliptical in cross-section, having the longer
diameter of the ellipse nearly horizontal. One of the largest shoots is 50
to 100 feet thick and 75 to 150 feet wide (PI. Ill, in pocket). A variation
from the above type is the blanket vein, which is parallel to the bedding of

MINERAL DEPOSITS
the inclosing rocks and commonly thrnaer than the shoots with elliptical
cross-section. The largest known blanket-vein deposit in the Leadville
formation is 6 to 50 feet thick and 75 to 150 feet wide. In the underlying
quartzite the blanket veins are said to have been 2.5 to 16 feet thick; in
width these veins were commonly less than 15 feet though locally more than
100 feet. Replacement bodies of very irregular shape have been found,
but almost invariably their longest dimensions were nearly parallel to
the bedding planes of the inclosing rocks. Other replacement bodies have
roughly plane-parallel vertical walls, and have been formed by replacement
of the walls of the fissures through which the ore-bearing solutions came.
SlDERITIC AND DOLOMITIC REPLACEMENT
Siderite, carrying magnesium and manganese, is very common immediately
under and at the sides of the ore bodies; it is less plentiful
above the ore. The siderite layer ranges in thickness from less than an
inch to 25 feet. Analyses of siderite from the Eagle mines are given on
page 49.
Below the siderite, and in places many feet from ore, are large masses
of coarsely crystalline dolomite. Smaller masses are found overlying ore.
This dolomite is commonly bluish gray, but in places many small white
patches are found with dark gray patches. Many of the white patches are
angular, and locally a mass suggests the replacement of former fault breccia
by dolomite, white patches in the place of fragments and gray in place of
matrix. The chemical composition of the white and gray dolomite is almost
identical as shown by analyses Nos. 2 and 3 on page 51. Chemical tests show
a small quantity of carbon after all the carbonate has been removed. This
carbon is probably unreplaced carbon of the original gouge or shale, and to
it the dolomite may owe its dark color.
That the dolomite, like sulphides and siderite, replaces former fault rock
is indicated by the following: (1) the coarsely crystalline dolomite is commonly
found under ore near the large ore shoots which demonstrably follow
faults. (2) On the intermediate level of Eagle No. 1, near the shaft, specimens
of dolomite were collected that had preserved fractures of the former
rock and grooved slickensided fault surfaces lacking only the original polish;
yet the dolomite is solid and shows no indication of breaking since it
crystallized. One specimen from the same place carries a thin streak of
gouge partly replaced by dolomite. (3) On the 6th level, below Eagle No.
2 ore shoot, the back and walls of a newly driven drift were composed of
niottled white and gray coarse dolomite; many of the white patches were
sharply angular. At the breast was a mass of black shale with bedding planes
disturbed and twisted by faulting, a small amount of the shale having been
replaced by pyrite. Some of the fault rock was composed of angular black
shale fragments cemented by coarse dolomite (mostly gray) that had evidently
replaced the original matrix; here the process had stopped before the
difficultly replaceable carbonaceous shale was appreciably affected.
Coarse gray dolomite in many places extends a considerable distance into
dolomitic limestone very similar in chemical composition to the coarse
dolomite. Since the limestone was originally massive no preserved structural
features have been detected outside of a former fault zone. The coarse
55

56 RED CLIFF MINING DISTRICT
dolomite is found in large masses in a few places, at the outcrop and in
prospects, far from any known ore deposit. It is probable that this dolomite
replaced rock in and near faults at the same time and in the same manner
that the dolomite was deposited near the sulphides. From the facts noted
above it follows that this dolomite is in itself evidence of faulting in its
vicinity, but an actual fault in the unreplaced underlying quartzite proves
this relationship where the dolomite outcrops about three-fourths of a mile
north of Gilman.
Jasperoid Replacement
Though the largest jasperoid replacements in this district occur far
from any known ore body they are described in this place because of their
evident relation to faults and dolomitic replacements and because of their
probable relation to the sulphide deposits. The name jasperoid was given
to this kind of quartz by Spurr1" who described similar replacements in
the Aspen district.
description of the jasperoid
The jasperoid is composed chiefly of microgranular to cryptocrystalline
quartz, and varies from dark gray to neutral gray to yellowish- and
brownish-gray. Most of the rock feels gritty, and breaks with uneven to
subconchoidal fracture. Another variety resembles flint, and has a good
conchoidal fracture. Both kinds show small cracks and cavities that were
probably formed by shrinkage either in the replacement process or at the
time of crystallization. In the dense variety cavities may have a diameter
up to one inch. In both kinds the openings form only a small fraction of
the rock volume.
The densest jasperoid is in part finely banded or streaky. The streaks
are less nearly parallel than are the bands of agate. The microscope shows
the darkest streaks to be composed of cryptocrystalline or nearly amorphous
quartz with a large proportion of black carbonaceous material. The lighter
streaks are composed chiefly of fine-microgranular quartz with less black
material. Throughout the thin section in the lighter streaks are a few
grains of quartz which, though very small, are many times larger than
most of the grains. The rock carries a few minute flakes of muscovite.
This variety somewhat resembles phases of the Tin tic (Utah) jasperoid
described by Lindgren" who interprets the silicification as "a replacement
of limestone or dolomite by colloidal silica which immediately afterwards
became transformed into chalcedony or in part into granular quartz." A
similar origin for the densest jasperoid of the Red Cliff district is further
suggested by the shape and appearance of cavities that were evidently
formed as a result of shrinkage and settling of the gelatinous mass during
the process of solidification and crystallizaton of the silica.
Most of the coarser variety is macrocrystalline, though locally it resembles
very fine-grained quartzite. In places the small cavities are lined
16Spurr, J. E., Geology of the Aspen mining district, Colorado- TT s Geol
Survey Mon. 31, 1898, pp. 216-221. , ' a' ^
"Lindgren, W., Processes of mineralization and enrichment in the Tintic
mining district: Economic Geology, vol. 10, 1915, pp. 225-240 See also description
by the same author in TJ. S. Geol. Survey Prof Paper 107 1919

mineral deposits
with minute quartz crystals. Some specimens are uniform in texture;
others have angular patches of slightly coarser grain than the matrix.
In a thin section examined limonite, which colors the rock, is more plentiful
in the matrix than in the angular patches. While it is possible that
brecciation occurred before the process of solidification was completed it
seems more likely that the jasperoid has replaced a formerly brecciated rock.
The quartz grains of the coarser variety are irregular and without
crystal outlines. In some specimens the grains are equidimensional; in
others they are elongated or elliptical in outline, having one diameter
two or three times as long as the other. A few thin sections carry occasional
larger grains. Of ten thin sections examined none shows quartz
with crystal outline. In this feature the rock is unlike phases of the
jasperoid at Aspen described by Spurr18 and by Lindgren10.
Most of the jasperoid is remarkably free from residual limestone or
dolomite. Careful search was made for phases that might show only partial
replacement, but the search was unsuccessful at most of the outcrops examined.
However, two thin sections were made of specimens that contain
carbonate. One of these carries anhedral quartz grains among the dolomite
grains in the less siliceous part of the specimen. In the more siliceous
part are a number of fairly large shapeless grains and also roughly
rectangular grains of quartz inclosing a few crystals and anhedrons of
dolomite, while many grains of dolomite occupy the spaces among the quartz
grains. Most of the second thin section is streaky and like the densest
jasperoid described above. The siliceous part ends abruptly in a wavy
line against the unaltered dolomite.
occurrence of jasperoid
Masses of jasperoid many feet in diameter replace Leadville limestone
at the outcrop near Turkey Creek and thence southward at intervals for
about 2 miles. A large body is found about three-fourths of a mile north
of Gilman above the public road. Jasperoid was not detected by members
of the Survey party in the mines at Gilman, but it can be seen on mine and
prospect dumps at the Iron Mask, Little Chief, and several openings between
the Little Chief mine and the Gilman Club House. Blocks up to 18 inches
in diameter were seen in this vicinity, and it is probable that bodies of
considerable size were formed near the ores.
On the hill between Eagle River and Homestake Creek, where comparatively
little limestone remains, there is much jasperoid. Large-scale
siliceous replacement is best illustrated northeast, east, and southeast of
Pando where through a distance of 4 miles no outcrop of Leadville limestone
has been found. Through about half this distance the bedrock is
covered, at intervals, by moraines, talus, and slumped material; but in
the several exposures only jasperoid and a little quartzite occur between
the underlying quartzite and the overlying Pennsylvanian beds. A complete
section of the Leadville formation outcrops half a mile north of Silver Creek,
and is 156 feet thick. A mile southward from the mouth of Rule Creek
the Leadville formation has an apparent thickness of 208 feet; but this may
UU. S. Geol. Survey Mon. 31, pp. 218-219.
MA. I. M. E. Trans., Vol. 30, 1900, pp. 628, 678.
57

58 RED CLIFF MINING DISTRICT
be 37 feet more than the true thickness, owing to a possible repetition of
beds along a strike fault of which there are indications. The formation is
thus at least 170 feet thick at this point. It is therefore highly probable
that limestone having a thickness of about 150 feet has been replaced by
silica through most, if not all, of the four-mile stretch mentioned. Some
of the largest exposures are represented on the geologic map (PI. I).
The jasperoid and underlying quartzite together make a cliff north
of Coal Creek (Fig. 10) where the jasperoid measures 56 feet from top
to bottom, including 9 feet of quartzite. The lower 22 feet of the section
mentioned is softer than most of the jasperoid, but acid tests show only
a trace of carbonate. The appearance of this part of the section suggests
settling and attendant compression. The upper part (34 feet) preserves
the original bedding structure and joint planes of the limestone. The
quartzite member of the Leadville formation, of which 9 feet remains, has
Figure 10. Jasperoid outcrop north of Coal Creek
Here all the limestone and dolomite of the Leadville formation,
having originally a thickness of about 150 feet, has been replaced by
silica. The lower part of the outcrop is Sawatch quartzite. In the cliff
at the top the thickness of the jasperoid (including 9 feet of quartzite
of the original Leadville formation) is 56 feet. Part of the jasperoid
may have been removed by erosion.
also been partly replaced by the jasperoid. This is shown by the irregular
or curved trend of contact between flintlike jasperoid and quartzite and
more certainly by small masses of quartzite suspended in and surrounded
by jasperoid. It should not be inferred that the original 150 feet of limestone
has been replaced by only about 50 feet of jasperoid. Though there
has evidently been shrinkage it is probable that considerable jasperoid has
been removed from the top of the cliff by erosion.
In many jasperoid outcrops the faulted or brecciated structure of the
replaced limestone has been faithfully preserved. South of Elk Creek, where
the jasperoid of the cliff is about 40 feet thick (Fig. 11), six fossil
faults were noted. These are all high-angle faults that strike eastward

MINERAL DEPOSITS
or northeastward. The jasperoid has for the most part replaced broken limestone,
but in places the original bedded structure has been preserved. North of
Elk Creek is a similar cliff where the jasperoid is at least 40 feet thick.
Here the siliceous replacement has preserved details of a strong fault, including
original slickensided surfaces; only the polish is lacking.
In only the largest bodies of jasperoid has the structure of unbroken
limestone been preserved. The evidence points to replacement of limestone
and fault rock by silica from solutions that circulated through the faults.
In part of the district the process extended far enough to replace all the
unbroken limestone of interfault areas.
Figure 11. Jasperoid outcrop south of Elk Creek
Above the prospect dumps is a body of jasperoid, about 40 feet thick,
that has replaced limestone and dolomite of the Leadville formation.
Crystallized Quartz Replacement
•More remotely connected with the faulting and subsequent mineralization
along the faults—if so connected at all—is the limited replacement of
Leadville limestone by quartz crystals. About half a mile north of Silver
Creek a few quartz crystals up to an inch in diameter were found embedded
in the limestone near the top of the formation. Nearer the creek larger
crystals, probably from the same general source, were found on the surface
of the ground near a jasperoid outcrop. The largest crystal measures 2
by 3.3 inches.
STRATIGRAPHIC POSITION OF ORE BODIES
Ore is found at practically every horizon in the Leadville limestone
and underlying quartzite. It thus has a stratigraphic range in these
formations of more than 500 feet; in addition, it extends below the quartzite
to a depth of at least 250 feet in the pre-Cambrian rocks. (See PI. Ill
in pocket and Fig. 14.)
Certain beds of the quartzite, because of higher porosity or higher
lime content, were more easily replaceable than others, and in them the ore
has a much greater horizontal extent than in the more compact pure
59

60
RED cliff mining district
quartzite where the fissure veins were less widened by replacement. Mr.
B. A. Hart states that the lower blanket-vein zone was 160 feet vertically
above the bottom of the quartzite, and that 28 feet of quartzite lay between
this and a higher blanket vein.
The largest ore bodies at Gilman and nearly all the ore mined at Red
Cliff have been found in the upper part of the Leadville limestone just
below the overlying shale. One of the Eagle ore shoots (PI. Ill), extends
from top to bottom of the limestone, and this is said to be the only large
ore body of that mine found below the quartzite miemiber of the Leadville
formation. In addition to the white lenticular crystalline patches of
dolomite of the "zebra lime" (p 36) the uppermost beds of the Leadville
formation are slightly more granular than the lower beds. The lower beds,
in general, seem to be slightly more siliceous than the upper beds. Qualitative
tests of 25 specimens of the Leadville limestone were made by Mr. Hall
who found considerable silica in the lower part of the formation. Mr. I. A.
Ettlinger has found in the upper half of the Leadville formation a dense
bed, 1 to 5 feet thick, that carries silica up to 7 per cent. Most of the ore
in the limestone lies above this bed. However, it is doubtful that the much
greater volume of replacement in the upper part can be accounted for by
texture and chemical composition. It is probable that this zone was most
favored because of the overlying shale which dammed ascending mineralbearing
solutions, thus spreading them laterally and diverting their course
directly up the dip and immediately under the shale. The first three
analyses of the accompanying table are of dolomite collected at the outcrop
of the Leadville formation in Eagle Bird Gulch.
CaO
MgO
FeO
CO,
Insoluble
Analyses of dolomites from. Leadville formation
(P. M. Dean, Analyst)
28.23
19.48
.60
43.21
7.47
29.71
21.95
.55
46.84
.24
29.50
21.37
.63
46.15
.30
30.4
21.9
47.7
1. Dense dolomite, about 30 feet above bottom of Leadville formation
2. Fine-crystalline dolomite, 35 feet below top of Leadville formation
3. Mediumi-grained crystalline dolomite about 30 feet below top of
Leadville formation
4. Theoretical composition of normal dolomite
RELATION OF ORE BODIES TO FAULTS
The large sulphide-ore bodies of the Eagle mines all show a close relation
to the faults, particularly to those faults that strike northeastward.
The same is true of the smaller sulphide bodies of mines in the Sawatch
quartzite and pre-Cambrian rocks. Likewise certain stopes from which
oxidized ores have been mined at Gilman and at Red Cliff are in faulted
zones; and there is little doubt that all the ores of the district have been
more or less connected with pre-existent fractures, fissures, or faults. Owing
to more general fracturing of rock near the present outcrop or to more

mineral deposits 61
favorable conditions for mineral precipitation, or to both, the oxidized ore
near the surface generally extends farther from the principal faults than
do the sulphide-ore bodies at greater depth.
Most of the ore shows clearly that it was formed after the faults that
strike northeastward, and no ore bodies examined by the writer show signs
of having been cut by later faults. However, Messrs. J. M. and R. V. Dismant,
who formerly as lessees mined much ore in the Bleak House and
Rocky Point mines, found indications of faulted ore in those mines. In the
Bleak House mine a blanket vein of zinc blende replacing quartzite was
locally offset about 30 inches by a fault. Since the ore has been removed
there is nothing to show whether the partly replaced quartzite was faulted
before or after the ore deposition. Mr. J. M. Dismant states that a vertical
vein of galena cut across the zinc ore body along the fault plane, that the
galena was somewhat crushed, and that the ore was slickensided. Postmineral
faulting well may have taken place in several mines of the district,
and it is remarkable that so little has come to light. Proof that the
ore lies in and near pre-existent faults is based on observations that follow.
In places the faults can be traced from barren ground directly to solid
ore. Frequently gouge can be seen in contact With the ore, but since the
ore commonly lies immediately under the shale at the top of the Leadville
limestone it is not always easy to distinguish between shale and gouge.
The presence of gouge in unbroken ore many feet below the shale bed proves
conclusively that the ore is in the position of a pre-existent fault. That
the deposition was subsequent to faulting is shown by the relationship between
ore and gouge; the best example of this was seen in the No. 1 ore
shoot of the Eagle mines in the stope below the 14th level where a small
patch of gouge was surrounded by solid and unfaulted ore. A specimen
taken shows the gouge to be partly replaced by pyrite.
On the 6th level of Eagle No. 2, about 80 feet north of the nearly east
west fault and a few feet from ore, a northeasterly striking fault shows
in the drift. Blocks of fault rock are partly replaced by pyrite. A specimen
from a block of quartzite coated with a thin layer of slickensided
gouge shows both quartzite and gouge to be partly replaced by pyrite crystals.
A specimen from a one-inch streak of gouge in the same fault shows
10 or 15 per cent of the gouge replaced by small pyrite crystals. On the
same level in the eastward striking fault, blocks of gouge near the ore
are partly replaced by pyrite crystals.
On the same mine level in the "chimney shoot" a little south of its
center certain features of the pre-mineral faulted rock were clearly evident.
Blocks of fault rock, partly angular and partly having surfaces smoothed
and curved by friction and movement, were accurately preserved in outline.
The only essential feature missing was the polish of once slickensided
surfaces. The fossil fault showed through a zone 7 feet wide many
nearly perpendicular partings, evidently in planes of former slipping3".
Excepting some friable zinc blende the sulphide ore of every face examined
is solid and shows no crushing or slickensiding. The condition
^In the Yak mine at Leadville one of the largest ore shoots has similarly
replaced faulted rock directly in line with a well defined fault in the unreplaced
limestone. This replacement was seen by the writer in the ore of a
pillar.

62 red cliff mining district
of most of the siderite near the ore is similar, though in one place in the
No. 2 ore body of the Eagle mines the siderite presented slickensided
surfaces. Even here the siderite tightly adhered over part of these surfaces,
thus indicating that they may have been smoothed before the siderite
was deposited.
SOURCE OF THE ORES
From the relationships described on preceding pages it is clear that
the horizontal distribution of ore bodies was largely controlled by the
faults through which the mineral-bearing solutions circulated. The position
of the largest ore bodies under the shale and overlying porphyry was in
all probability largely determined by the damming of solutions and consequent
deposition under the barrier of shale and porphyry. The carbonaceous
content of the shale may have aided precipitation. These relationships
indicate that the ore was deposited from ascending solutions.
Whether the solutions rose vertically or from the northeast or from the
southwest is not clear.
The porphyry and ores are probably genetically connected in having
emanated from a common deep-seated magmatic source. From what direction
did the porphyry magma flow? This is an interesting and important
question, though perhaps not vital when considering the immediate
source of the ores. Even if the intrusion of porphyry preceded
the tilting of the beds to their present attitude the comparative scarcity of
dikes toward the southwest makes it improbable that the porphyry magma
came from that direction. The largest porphyry bodies exposed in the region
are in the Tenmile district toward the southeast. Though the Gilman
sheet extends many miles southeast and probably is continuous with
the Chicago Mountain laccolith, it may have reached its present position by
flowing northwest from the laccolithic mass or by flowing west or southwest
from a possible vent much farther north than Chicago Mountain. Careful
search has failed to disclose good evidence for a northeast source for
the porphyry, and the rock probably reached its present position by flow
toward the west or northwest. It is evident that mineral-bearing solutions
could have flowed in the same direction along contacts and through porous
quartzite beds, and thence upward through fault fissures. Such directions
of movement for the bulk of the solutions necessitate also their downward
movement into fissures in the pre-Cambrian rocks where ore and
gangue minerals were deposited. The latter consideration makes it appear
unlikely that the solutions came from the east or southeast.
The primary sulphides of the higher levels in the limestone have a
much higher proportion of zinc and a much lower gold content than have
the primary sulphides in the underlying quartzite and pre-Cambrian rocks.
Though galena is relatively scarce in the present workings in limestone the
large amount of cerussite and anglesite formerly produced from the oxideore
bodies points to much galena in the primary ores of the higher levels.
The zone theory of ore deposition formulated by Spurr21, and found to hold
generally for many districts where the ore has been deposited from ascend-
21Spurr, J. E., A theory of ore-deposition: Economic Geology, vol. 2, 1907,
pp. 7oX—7yi).

MINERAL DEPOSITS 63
ing solutions—probably magmatic—supposes that among others gold and
pyrite, copper-bearing pyrite, and galena-blende ores are successively deposited
with increasing distance from the magmatic source. This order
roughly holds with successively higher zones in the Red Cliff district,
though the data are less complete than one might wish.
No indications of a southwest source for the solutions have been noted.
The great length of the ore shoots, pitching with the dip of the beds and
replacing fault rock, points to (a) upward flow from the northeast or (b)
vertically upward flow through a wide northeast-southwest range or (c)
upward flow through a more restricted range with flaring path above the
vent. In each case it is assumed that the solutions came from considerable
depth through the fault fissures. Geologists of the United States Geological
Survey have shown that the greater part of the porphyry of the Aspen,
Leadville, Alma, and Tenmile districts was intruded prior to the most intense
faulting. There is not complete agreement, however, among geologists
and engineers concerning the amount of faulting that preceded and the
amount that followed ore deposition in the Leadville and Alma districts.
The State Survey party has found no evidence that determines whether .the
porphyry intrusion preceded or followed faulting in the Red Cliff district.
Known porphyry or its continuation at depth has been considered the
probable source of the metals in central Colorado mining districts by
several workers in those districts, but others have supposed that the metals
came from magma at greater depth. In a recent articles the writer22 gives
evidence tending to show that a post-Cretaceous quartz-monzonite batholith
underlies a large part of central Colorado, and that this batholith may have
furnished the solutions from which was deposited ore in several districts.
The eight widely separated exposures of quartz monzonite and closely related
quartz diorite shown on the map (fig 12) are very likely the tops of
masses connected below by a single batholith of which they are part. These
upward extensions of the probable batholith have reached a higher level
in the process of intrusion, and form roughly domelike masses, called
cupolas, on the main batholith which has far greater horizontal extent at a
lower level. There is no reason to doubt that other cupolas on the same
batholith exist, but have not yet been uncovered by erosion.
Phenomena observed in Buckskin Gulch northwest of Alma, and described
in the paper cited, indicate that the quartz monzonite was intruded
after the early porphyries, and hence rose much higher than the roots of
the porphyry dikes and sheets. This condition could, and probably did,
result in bringing large volumes of magmatic solutions to a comparatively
high level where leakage from a slowly solidifying large body was continuous
through a long period. This hypothesis implies that, although
the ores and porphyry originally came from the same reservoir, the reservoir
with irregularly shaped top slowly worked its way upward subsequent
to the rapid porphyry injection, and that the high parts of the batholith
which fed ore minerals to any locality may or may not be far from a former
vent through which porphyry magma flowed to the same locality. The
reader may see in figure 12 that Red Cliff is about 12 miles from the nearest
22Crawford, R. D., A contribution to the igneous geology of central Colorado-
Am. Jour, of Science, vol. 7, 1924, pp. 365-388.

64 RED CLIFF MINING DISTRICT
Figure 12. Map showing positions of post-Faleozoic quartz monzonite
and related auartz diorite

MINERAL DEPOSITS 65
discovered post-Cretaceous quartz monzonite. Though this body may have
a considerable underground extension to the west, structural conditions do
not favor this particular stock as the source of the ores of this district.
It is not improbable that the Red Cliff district is underlain by one or more
cupolas of the quartz-monzonite batholith, that from and through the
cupolas have flowed large volumes of metal-bearing magmatic solutions,
and that these solutions effected ore deposition as well as extensive replacement
by siderite, dolomite, and jasperoid.
FUTURE POSSIBILITIES
How far the ore shoots of Battle Mountain may be expected to continue
to the northeast depends largely on the direction of flow of the
depositing solutions. If the faulting resulted from igneous intrusion directly
below and solutions rose vertically—conditions suggested by the
sequence of metals—'the extent of ore bodies toward the northeast should
be limited by the size of the intrusion. If the solutions came from the
northeast—a source unproved1, but indicated by structure—the ores may be
expected to extend far beyond the present mine workings; a dip of 10°
is too small to lead to an unfavorable change in conditions of temperature
and pressure within a short distance. Whether or not the largest shoots
extend much farther northeast than the present workings there is no apparent
reason why other ore bodies along known faults should not be
discovered at the same depth as those now being mined.
The jasperoid and coarse dolomite previously described point to replacement
in and near earlier faults. In several places faults are found
near the dolomite bodies, and many faults, have been preserved in the
jasperoid. Jasperoid is very common in the Leadville district where it is
not infrequently found near the oxidized ore bodies and, in places, grading
into ore. Emmons28 states that in the Tenmile district jasperoid occurs
on the outer edge of ore shoots, and forms a transition zone between ore
and unaltered limestone. In the Red Cliff district jasperoid was found
near the surface in several mines and prospects on Battle Mountain. Ore
occurs near jasperoid and coarse dolomite in several small mines near the
mouth of Turkey Creek. A pocket of pyrite in jasperoid was opened by a
prospect on Coal Creek. Oxides of iron and manganese are common in the
faulted quartzite near jasperoid bodies stouth of Elk Creek and on both
sides of Eagle River between Pando and Red Cliff. It is evident that both
jasperoid and dolomite were deposited after—though in part perhaps contemporaneously
with—the ore minerals, and it is probable that solutions
that brought in both metallic and non-metallic minerals had a common
source.
Unless the mineral-beiarmg solutions came from the southwest—the
most improbable direction—good prospecting ground should lie east or
northeast of any jasperoid or coarse dolomite body in which or under which
p fault may be traced. Favorable localities, in the writer's opinion, are
about three-fourths of a mile north of Gilman, near Turkey Creek, between
Silver Creek and Coal Creek, and on both sides of Elk Creek. In several
of these places prospectors have noticed the metallic mineralization, and
23U. S. Geol. Survey, Polio 48.

66 RED CLIFF MINING DISTRICT
some sinking and tunneling have been done. Ore bodies have been discovered
at shallow depth on Turkey Creek, but in most or all of the other
places workings have not gone through the jasperoid. To be of greatest
value work should be done at or beyond the northeast border of the
jasperoid, preferably by crosscutting the northeast-striking faults. This
position, in part of the localities named, can be determined only by extensive
prospecting. If the solutions came from the northeast the chances
for finding large bodies of sulphide would seem to be better than if the
solutions came from any other direction. Even then the ratio between
possible metallic sulphides and non-metallic minerals is probably very small,
and there may be faults entirely free from sulphides.
In Chapter V mention was made of faults in the quartzite, traceable
only short distances. Between Coal Creek and Turkey Creek are several
of these faults and fault zones in which erosion has cut to considerable
depth; some of these are covered by soil and grass or timber. Where
erosion has cut to greater depth the faults are covered by landslides.
Whether erosion cut deep into rock weakened only by faulting or by
faulting and subsequent mineralization only prospecting can determine.
Several of these places may be seen east of Eagle River between Turkey
and Coal creeks. None has been seriously prospected, though many shallow
prospects are seen in the quartzite farther west where considerable
iron and manganese are found. To reach the Leadville limestone under or
east of the loose rock covering would entail less expense than to drill
through the large bodies of jasperoid.

DESCRIPTIONS OP MINES
CHAPTER VII
In this chapter no attempt is made to describe fully all the mines of
the district. Many are closed or caved; some are filled or partly filled
with water; and the known ore bodies of others have been nearly or quite
exhausted. A fairly thorough study was made of the geology of the Mabel
mine in the granite, the Ground Hog mine in the Sawatch quartzite, and
the newer workings of the Eagle mines in the Leadville limestone. The
geology of these mines well represents the geology of the productive area,
and the three are described below in considerable detail. Many mines
in the oxide zone are briefly described, but som,e of the largest former
producers are passed with scant notice and without description. Among
these—part in quartzite and part in the limestone—are the Black Iron,
Cleveland, Belden, Iron Mask, Little Chief, Bleak Bouse, and Rocky Point
mines. The old workings are still accessible in many places, and the great
size of some of the former ore bodies is made evident by stopes and drifts
still open. Because the Ground Hog mane is the most easily accessible of
all the larger mines in the quartzite a detailed study of structure and ore
occurrence was made in the Ground Hog, though larger ore bodies may
have been found' in the quartzite in other mines.
In the descriptions that follow the term granite is used for both granite
and related quartz monzonite, and the term limestone is used for the calcareous
rock of the Leadville formation which is in part true dolomite.
MABEL MINE
By Russell Gibson
The Mabel mine was opened by B. A. Hart in 1900, and was still producing
ore in the summer of 1923. It is one of the largest mines in the
district in the granite, and has, according to Mr. Hart, produced $325,000
worth of ore which has averaged 2 to 4 ounces gold and 5 to 15 ounces
silver per ton. In addition to gold and silver, the ore carries 8 to 10 per
cent lead, and copper up to 3 per cent. One shoot is reported to have
produced $40,000 worth of ore that averaged $275 per ton.
The Mabel mine has 3,600 feet of development on five levels which
are connected by an inclined shaft 264 feet deep on the pitch. (See figs.
13 and 14.) The shaft follows the dip of the Mabel vein which increases
from 56° at the collar of the shaft to 66° below the second level. Most
of the ore comes from two fissure veins: the Mable vein which strikes
N. 30° to 40° E., and a cross vein striking N. 55° "to 65° E. In general the
veins dip southeast. Observations on the first level indicate that the Mabel
vein occupies a fissure along which there was faulting prior to ore deposition.
The fault is normal, the hanging wall apparently having moved
down a distance which could not be determined. The cross vein, which
strikes N. 55° to 65° E., is intersected 180 feet northeast of the shaft on
the first level, and at shorter distances in the same direction from the
shaft on each succeeding lower level. Like the Mabel this vein increases

Figure 13. Flan of the Metal mine, reduced from map furnished by J. M. Diamant

"~t3Si3S. &£&£&*&%,
i$n
NOTE:
PULL LINES SHOW STOPES ON CPOSS VEIN
DOTTED UNES SHOW STOPES ON MABEL VEIN
STRIKE OP PLANE OF PROJECTION N6?i'E.
DIP OF PLANE OP PROJECTION SAME AS MABEL SN/tpr,
Ffcrure M. Section through the Mabel vein, reduced from drawing furnished
by J. M. Dismant

70 RED CLIFF MINING DISTRICT
in dip with depth, from 56° on the first level to 76° on the
Wlhere the Mabel vein intersects the cross vein on the first and fourth
levels relationships indicate that the Mabel is the older. Elsewhere the
evidence is more obscure. But in these two places the Mabel vein is offset
by the cross vein, and hence may have been mineralized before the
movement took place along the cross fissure.
The amount and character of the mineralization in the two veins is
similar. The chief minerals are pyrite, copper-bearing pyrite, sphalerite,
galena, and quartz. The order of deposition, so far as could be determined
from remnants of ore, is not regular; but pyrite, the most abundant
mineral, seems to be one of the first minerals deposited and quartz one
of the last. These minerals occur in streaks from less than 1 inch to
10 inches thick, and less commonly in vugs. The wall rock is sparingly
replaced close to the vein.
In most places the fissured zone varies in width from 2 to 6 feet,
and is made up of parallel cracks, not all of which are filled with sulphide.
Commonly one thick vein splits into two veins or fingers into
several, some of which coalesce farther on. The associated decomposed
wall rock and gouge contain more or less disseminated pyrite in good
cubes and pyritohedrons. According to Mir. Hart, richer ore was found
near the intersections of veins. The fissures are tighter and the veins
grow thinner and leaner with depth, especially toward the northeast extremities
of the lower levels. Here the stopes are smaller and the average
length of the stulls does not exceed 2 feet, whereas elsewhere many stopes
are connected through several levels, and are in places 8 feet wide. Where
the drifts intersect the lower Sawatch quartzite contact the veins run up
into the quartzite but thin rapidly at the contact, in places almost disappearing.
The contact, however, and the bedding planes above show good
mineralization; and the quartzite is partly replaced by pyrite.
The mine is equipped with a steam hoist and skip, and electric lights.
An aerial tram connects the head-house with the Mabel-Pursey Chester
mines switch.
GROUND HOG MINE
By E. A. Hall
The workings of the Ground Hog mine extend down the dip of the
quartzite in a general direction of N. 45° E. for a distance of 1,500 feet.
(See fig 15.) The dip of the quartzite is 12° to 15° N. 40° to 45° E., and
as the inclines go into the side of Battle Mountain the deepest workings
are about 800 feet below the surface. The workings extend about 1,400
feet in width in a northwest direction. The mine has been worked from
twelve main inclines and several minor ones. At the present time not all
of the inclines open at the surface. However, they are connected underground.
Once inside the mine it is possible to go through the entire
workings, with the exception of a few drifts filled with water or waste
and a few minor drifts from the surface not joined with the main workings.
The mine was also formerly connected with the surface by several
shafts, all of which have fallen into disuse and have become partly filled
or destroyed. In many places the side drifts become very small, usually

MINES 71
about 2.5 to 3 feet high, with scarcely enough room for a man to crawl
through, though they extend several hundred feet in length. The main inclines
and crosscuts are sufficiently high to allow a man to walk erect,
except in a few places where the quartzite is particularly hard and whero
tracks have taken up some of the space.
At the present time five of the inclines and the Nottingham crosscut
are tracked and others are partly tracked; only two inclines, the Doddridge
and Nottingham, and the main crosscut are used for haulage purposes.
There are two head-houses in repair at the openings of the Nottingham
and Doddridge inclines, and bear their respective names. Mine and
buildings are not wired for electricity, hence gasoline and steam are used
for hoisting. At one time a considerable part of the mine was piped so
that air could be used for drilling, but the air system was out of repair
at the time of our examination.
Production
Although a great part of the production of the Ground Hog mine was
from rich shoots or pockets for which records of approximate production have
leen kept, it is next to impossible to make an estimate of the total production
of the mine. The Forgy "bullion hole," located' in the Nottingham
(right) incline about 225 feet above the main crosscut, produced about
$37,000 worth of ore. The Doddridge winze, in the Nottingham incline 100 feet
below the main crosscut, produced about $50,000 worth of ore. A small stope
on No. 4 South drift produced about $4,000 worth of ore carrying $15.00
in gold and 15 ounces of silver per ton. No. 5 South produced about
$47,000 worth of ore. The Baldwin and Oneal "bullion place," 300 feet down
the Doddridge incline, produced $12,000 worth of oxide ore. The Woods
and Henderson "bullion shoot," 200 feet down the same incline, produced
$10,000 in oxidized ore. The total production in the Doddridge incline area
below the main crosscut is said to have been about $500,000.
The above figures were supplied by Dismant Brothers of Red Cliff, and
represent the production of only a few of the richest shoots or "bullion"
pockets in the mine. However, from these figures ($660,000) it can be
seen that the mine produced much ore.
Faulting
The fissures and faults apparently trend in two general directions.
Those of the first group strike about N. 35° W., and compose the minor
system. Those of the second group strike N. 40° to 45° E., and compose
the major system.
The breaks of the minor group are nearly vertical, and each forms a
single sharp and almost straight fissure. None of the northwest-striking
fissures shows evidence of faulting, but all seem to have originated from a
common cause. These fissures occur very regularly, and often not more
than 10 feet apart. Hence a considerable amount of displacement or adjustment
could have taken place, and yet when distributed among so many
breaks the chances are that there would be no perceptible evidence of
movement in any single fissure. This group of fissures very closely resembles
jointing in igneous rock.

72 RED CLIFF MINING DISTRICT
The northeast-striking faults ot the major system are for the most
part about vertical. These are not single fractures, but are grouped in
zones of faulting, each zone being composed of several fractures. Many
of the different faults in a zone come in and leave the zone at a small
angle. In practically all of the strong northeast-striking faults slicken1
siding, grooving, displacement, or other evidence of faulting can be seen.
"V-Ground Hog incline
No. ll\\No. 12
Figure 15. Map showing faults and fissures in the Ground Hog mine;
geology mapped by E. A. Kail
Probably the two most important faults in the mine are the Cleveland
and the Doddridge faults.
Cleveland fault.—This fault strikes N. 45° to 55" E., and is vertical.
It can best be seen about 40 feet east of the Doddridge incline opposite
the main crosscut. The faulted zone is 12 to 15 feet wide, and contains

MINES 73
immense quantities of gouge and breccia. One minor fracture shows a displacement
of 3 feet, and the fault surface is well grooved and slickensided.
The grooves are vertical, showing that the blocks moved up or down with
relation to each other. On the surface small separated faults probably
belonging to the Cleveland zone indicate very little actual displacement,
and give no evidence of great movement. It is possible that the zone represents
considerable movement back and forth. This fault contains red
iron oxide, brown iron oxide, and many quartz crystals.
Doddridge fault.—This fault can best be seen at the Doddridge winze
100 feet below the main crosscut in the Nottingham incline. It strikes
N. 45° E., and is vertical. The zone is about 10 feet wide, and is well
brecciated and filled with gouge. The Doddridge winze has been sunk 160
feet on the fault to the granite, but, owing to water, only two levels below
could be examined. On the two lower levels very highly polished mirrorlike
slickensiding was noticed. The grooves are horizontal, and the movement
must have been at right angles to the direction of movement of the
Cleveland fault. The fault zone is partly filled with sulphide ore and
quartz gangue. In all probability the deposition of most of the ore in the
mine was controlled by the northeast-striking faults.
Bedding faults.—In addition to the faults described many bedding faults
of various sizes were encountered in the mine. They were often cut in two
or displaced by other faults. As a rule these faults are tightly filled with
gouge between walls 2 to 4 inches apart, and were not found to be
mineralized.
Character of Wall Rock
The bed which has been followed by the greater part of the Ground
Hog workings is a medium-grained porous sandstone or quartzite which
dips 10° to 12° northeast. It is not as well silicified as most of the
quartzite formation, and when not entirely replaced by ore the bed is dark
colored as if it had been stained with iron-bearing solutions. This porous,
non-resistant quartzite bed averages about 2 feet in thickness. Below it is
the usual white, pure, compact, fine-grained quartzite. Above the porous
bed is quartzite very little different from the quartzite below the bed, excepting
that it appears to be even more dense and compact, whiter, and
purer than the usual quartzite. In fact the upper quartzite bed is so dense
and hard that it shatters like glass or pure quartz when struck with a
hammer. Stopes Nos. 3 and 4 South have been driven up into the quartzite
a distance of 35 to 40 feet. About 30 feet above the main level the
usual compact, fine-grained quartzite seemingly grades into more shaly members.
Some of these shaly beds are calcareous, and were readily replaced
by ore.
Ore Deposits
The ore deposits of the Ground Hog mine are of two types closely associated
with each other. These are fissure deposits and replacement
deposits.
Fissure deposits.—Nearly every fault, fissure, and fracture in the quartzite
in the Ground Hog mine is partly filled with mineral. However, the

74 RED CLIFF MINING DISTRICT
fissures of the minor system are very narrow, and allow little room for
deposition from solution. Thus the veins striking northwest are of very
little economic importance except where they intersect a vein of the other
system. The major faults striking northeast seem to have controlled the
greater part of the ore-bearing solutions. In addition to being wider than
the fissures striking northwest, they are more closely packed with mineral.
Moreover, the solutions effected a variable amount of replacement of the
quartzite-—usually several inches—• on both sides of the faults of the major
group. The fissure deposits are characterized by a very pronounced
crustification. Crystals of sphalerite were deposited over the pyritohedrons
of pyrite; the last deposition was of quartz or barite. Some of the highestgrade
ore of the mine occurs as fissure deposits in the faults and fractures
striking northeast. Invariably, however, the fissure deposits pinch out
within a few feet above and below the main level.
Replacement deposits.—As was stated in connection with the fissure
deposits, the ore-bearing solutions effected the replacement of several inches
of wall rock on each side of the fissure. In many places the mineral was
found disseminated through the quartzite beyond the zone or limits of
complete replacement. However, the most important replacement deposit
in the mine was the almost complete replacement, especially near one of
the faults or fissures, of the porous, non-resistant two-foot bed of sandy
quartzite. This particular bed must have given to the ore solutions a channel
of easy circulation. It was this easily replaceable bed that made the
mine a commercial possibility: first, because the bed was much easier to
mine than the hard quartzite, thus reducing the cost of mining; second,
because the bed itself contained a large amount of ore, especially where
entirely replaced.
The ore is of two general types: the first is compact and hard; the
second is fragmental and granular. Though the second retains the structure
of the original quartzite it is not as well cemented as the first. Ordinarily
the granular ore has been of lower grade than the other, and though it
is easier to mine it has been looked upon with disfavor by the lessees.
At the time of examination the character of the replacement could be
seen at the Ohmstead ore face about 150 feet from the lower end of the
Doddridge incline. At this face the replaced portion varied from 6 inches
to 2 feet thick. The replacing material (pyrite) carried a small amount
of gold and about 50 ounces of silver per ton.
The mineralized zone in and near the Doddridge fault was probably a
combination of fissure and replacement deposits. This zone has been stoped
out 35 feet overhead. The Doddridge winze, which sinks 160 feet to the
granite, was examined as far as the water would allow. For a distance
of about 80 feet below the main level the rock of the fault zone was replaced
by or filled with solid pyrite varying from 5 to 10 feet in thickness
and extending laterally 40 to 50 feet. This body of ore is too low in grade
to work.
•Character of the ore.—Oxidized ore extends down the dip of the quartzite
for a distance of 500 to 700 feet. This zone included some of the
richest "bullion" pockets, but now no valuable ore bodies are known in the
oxidized zone. The oxides were chiefly those of iron and a small amount

mines 75
of manganese. The manganese oxide seems to have been limited to a few
of the largest northeast-striking faults, such as the Cleveland fault.
The sulphide ores below the oxidized ores continue down the dip of
the quartzite to the deepest faces in the mine. The sulphides are galena,
sphalerite, chalcocite, copper-bearing pyrite, and pyrite. The last is by far
the most important, while the others occur sparingly in the small area near
Nos. 3 and 4 South drifts and stopes. In the sulphide zone pyrite crystals
(pyritohedrons) are very common. The pyritohedrons are well shaped and
uncombined with other forms. Some are 2 inches in diameter. Small cubes
and octahedrons of pyrite were found on the lower levels of the Doddridge
winze area. Most of the pyrite carries silver; some of it runs as high
as 60 ounces per ton. Galena also carries silver, up to 50 ounces to the ton.
The silver probably occurs in the form of argentite, silver sulphide. The
oxidized ore carries very little silver.
Secondary-sulphide enrichment is indicated by the presence of small
quantities of chalcocite, covellite, and probably bornite in the stoped area
of Nos. 2, 3, and 4 South drifts. Here thin coatings of covellite were
found on crystals of pyrite, in addition to granular to massive chalcocite
associated with pyrite.
Native gold has been found in both the oxide and sulphide zones, but
samples collected in 1921 show only small quantities of gold in the sulphide
ore. Much of the gold, particularly in the oxide zone, was in nuggets;
and a large quantity of high-grade gold ore has been produced by this mine.
EAGLE MINES
By R. D. Crawford
In recent years the Empire Zinc Company has developed a group of
claims east, northeast, and southeast of Gilman, and has produced from
these claims a very large tonnage of sulphide ore. The property of this
company includes also the Bleak House, Wilkesbarre, Little Chief, Iron
Mask, Rocky Point, Belden, F. C. Garbutt, Black Iron, and others; some
of these mines have been producers from the early eighties. These mines,
formerly worked by several companies, were bought in 1915 by the Empire
Zinc Company which has worked the group continuously since the purchase.
An average force of about 175 is employed. Under the present ownership
the entire group is called the Eagle Mines.
The newer workings are entered through the Wilkesbarre shaft (Eagle
No. 1) north of Gilman and through the old Black Iron tunnel and incline
(Eagle No. 2) at Bell's Camp. Most of the ore is hauled out through the
Newhouse tunnel Whose portal is near the bottom of the canyon at Belden.
The old mine workings, including adits, inclines, and stopes, are still accessible
in many places. One may get an idea of the size of the developed
area of the Eagle mines from the following statements: The Newhouse
tunnel portal is 9. 21° W. of the Wilkesbarre shaft and distant about
2,300 feet. The Black Iron tunnel portal is S. 17° E. of the Wilkesbarre
shaft and distant about 5,760 feet, or more than a mile. The shortest
underground connection between the last two points is more than 6,000
feet long. Six sulphide-ore bodies have been proved in the newer workings,
and two of them have yielded an unusually large tonnage.

76 RED CLIFF. MINING DISTRICT
The writer traversed all the deeper workings of the Eagle mines for
the purpose of examining and platting faults and other structural features
that might have a bearing on the occurrence of ore. The mineral character
of the ores and many details of ore structure were noted, but no
systematic sampling or thorough study of the ores was made. Many of
the details given here were generously furnished by Mr. A. H. Buck of
the Empire Zinc Company.
Part" of the old workings of the Little Chief, Iron Mask, Belden, and
Black Iron were hastily examined, but nearly all the time spent in the
mines was employed in the stopes and on the lower levels given below with
average or approximate elevations:
Fourth level at 8,830 feet, Eagle No. 2
Fifth level at 8,805 feet, Eagle No. 2
Sixth level at 8,735 feet, Eagle No. 2
Seventh level at 8,770 feet, off Belden incline
Fourteenth level at 8,660 feet, connects Eagle No. 1 and No. 2
Fifteenth level at 8,560 feet, Eagle No. 1
Sixteenth level, including Newhouse tunnel, at 8,505 feet
Geologic Features
Though much ore has been produced from the Sawatch quartzite by the
Bleak House and Rocky Point mines, by far the greatest amount produced
by the group in recent years has conue from the upper part of the Leadville
limestone. The exceptional "chimney shoot" of Eagle No. 2 was
nearly solid sulphide through a vertical range of 200 feet, thus extending
from top to bottom of the Leadville formation. The quartzite member of
this formation underwent about the same degree of replacement by this ore
as did the overlying and underlying limestone.
All the ore examined lies in or near rock broken by faulting. Two
principal kinds of faulting have affected the rock, and their results may
be seen in barren ground between or below the ore bodies. The first type
was differential movement along planes nearly or quite parallel to the
bedding planes of the rocks; in the second type the movement was along
planes that cut across the beds at high angles and are nearly vertical.
The majority of these faults of high dip strike northeastward and are
thus dip faults,—that is, they strike in the direction of dip of the beds. At
least two important faults of high dip strike in other directions: one, on
the 6th level near No. 2 shaft, strikes about N. 80° E.; the other, on the
16th level near the extreme east workings, strikes nearly N. 45° W. The
age of the last mentioned fault has not been determined. It has been
considered possibly younger than the ore, but the writer could see no sign
of post-mineral faulting in the ore face in the stope. The principal northeast-striking
faults are older than the ore. In addition to the bedding
faults and those of high dip are a few unimportant faults and breaks of
intermediate dip and random strike.
In barren ground at several places in the mines are narrow fissures
and veins whose walls show no indication of having slipped. Most of
these fissures are not more than 2 or 3 inches wide. Some are open and
dry; some are partly filled with running water; others are partly or wholly
filled with dolomite or pyrite.

mines 77
Caves a few inches to several feet wide are found at the border of
the ore bodies or are formed in the process of mining. The caves and
pockets contain dolomite sand which runs out in large quantity when the
cave is tapped. Though the sand is composed chiefly of rounded and
angular grains of dolomite some quartz is present. The stratification
sometimes seen and the rounded character of the grains show that much
of the sand has been deposited in water courses. However, a large part
of the so-called sand on the borders of the stopes is disintegrated dolomite
from the Walls. The coarse crystalline dolomite slacks and becomes friable
in the mine workings and probably also on the walls of the caves.
In the Rocky Point mine, not examined in detail by the field party,
gold-bearing pyrite was found in the upper half of the Sawatch quartzite
about 150 feet below the Leadville limestone. In the Leadville limestone,
just below the quartzite member, was a copper-ore shoot 200 feet long and
30 to 50 feet wide. The ore here was chalcopyrite or copper-bearing pyrite.
Above the quartzite member of the limestone and nearer to the quartzite
than to the overlying shale was the No. 1 zinc-ore shoot described below.
All three of these shoots were in the same vertical plane, the last two in
the Iron Mlask claim.
Size and Range of Ore Bodies
All the ore bodies of the Eagle mines have their longest dimensions
in the direction of dip of the inclosing rocks.
No. 1 ore shoot has been developed in the newer workings from the
11th level to the 16th level through a vertical range of 200 feet, and has
been proved by drilling to a depth of 200 feet below the 16th level. The
horizontal range of the shoot in the newer workings, including the ore
proved by drill holes, is 2,000 feet. Through 700 feet of the distance in
the deeper part of the mine the shoot is about 100 feet wide. Cross sections
of the shoot are roughly elliptical, the ellipses having very irregular
peripheries. The long axes of the ellipses are nearly horizontal and range
from 75 to 150 feet in length; the short axes are 50 to 100 feet long.
All the ore here is sulphide. Before the mines were acquired by the
Empire Zinc Company a large part of this shoot had been mined through
the Iron Mask, Little Chief, and other inclines. Most of the earlier mined
ore was oxidized or carbonate ore. The vertical range of oxidized and
sulphide ore in this shoot, as far as it has been proved, is 630 feet. The
pitch length of the proved shoot is 3,060 feet. The ore has been continuous
from the surface outcrop to the greatest known depth of the shoot.
No. 2 ore body differs from No. 1 ore body in that it is a blanket vein
(PI. Ill, in pocket). Excepting that part known as the chimney shoot the
thickness ranges from 6 to 50 feet, and averages about 20 feet. The ore
body is from 75 to 150 feet wide. The "chimney" is part of the No. 2 shoot,
and extends below the blanket roughly in the shape of an inverted cone.
The axes of the elliptical base of the cone (the upper part) are 90 and
220 feet respectively. The height of the "chimney", including the blanket,
is 200 feet. No. 2 shoot, in the newer workings and in the old Black
Iron mine, has a proved pitch length of 2,880 feet. The ore has been continuous
throughout this length from the surface. The oxidized zone ex-

78 RED CLIFF MINING DISTRICT
tended 1,200 feet from the surface down the pitch. About two-thirds of the
way down to the deepest workings is the center of the chimney shoot described
above.
No. 3 ore shoot is evidently the same as the largest one of the Belden
mine worked many years through the Belden incline. Excepting about 200
feet of unexplored ground between the 7th level of the Belden and the new
14th level, the shoot has been developed through a length of 1,400 feet.
The lowest stopes are on the 14th level where the width is nearly 100 feet.
No. 4 shoot has been mined from the surface through a length of more
than 600 feet, and has been proved through an additional 150 feet. Its
average width is about 40 feet. Other ore bodies have been partly
developed, but their extent is imperfectly known.
Character of the Ores
The metals produced in greatest quantity from the sulphide-ore bodies
are zinc and silver. Part of the ore carries a very little gold, part carries
copper, and some lead is produced from galena found in only a few places.
The two most abundant ore minerals are zinc blende and pyrite. The lead
content of the blende varies from less than 1 per cent to 15 per cent. The
blende ordinarily carries no silver, but in places small quantities have
been found carrying silver up to 12 ounces per ton. The lead content in
different ore bodies varies from 18 per cent to less than .5 per cent. Different
ore shoots show different relations between lead and zinc sulphide.
In some shoots the lead is found in larger proportion just below the
oxidized zone, and the lead content decreases with depth; in other shoots
the reverse is true. Throughout the mine the gold content is nearly
negligible.
Practically all the silver produced is found in pyrite. The galena does
not carry silver in paying quantity. Silver values may be very spotted
in pyrite in a single stope; within a small area assays may run from 5 to
150 ounces per ton, with an average of 10 to 15 ounces in carload lots. The
copper content is very low and nearly negligible; small lots have assayed as
high as 8 per cent copper. As a rule high silver accompanies high copper
content, but the silver content does not necessarily rise in the same proportion
as the copper. In a few places high copper is not accompanied by
high silver. In places rich silver-bearing pyrite carries practically no
copper.
Mineral Relationships in Ore Bodies
The relation between minerals is not uniform in all the ore bodies.
In No. 2 ore shoot there is a large core of pyrite surrounded by a shell
of zinc blende from 10 to 20 feet thick. The line of demarkation between
the two is very distinct. In this shoot the line between high-grade zinc ore
and wall rock is as sharp as that between pyrite and zinc ore. A similar
sharp boundary between ore and wall rock is found on the 16th level (16 E.)
The zinc ore of No. 1 shoot is uniformly lower in grade than that of
No. 2 shoot. It carries more lead, and has pyrite and siderite in varying
but small quantities throughout the body. Between levels 15 and 16 there
is a body of pyrite on the south side of the main body of zinc ore. It has
no value as ore, and its extent is unknown.

MINES 79
Siderite is found in varying quantities near the ore bodies; in places
the siderite masses are many feet thick. In the vicinity of lead-free zinc
ore there is very little siderite, but where the lead content increases the
amount of siderite surrounding the ore body also increases. Coarse crysstalline
dolomite is common in and near the fault zones under the ore and
laterally. Though this dolomite locally forms the walls of ore bodies finely
crystalline dolomitic limestone is the commonest wall rock. In places the
contact between ore and wall rock is sharp; in fewer places there is a
gradation from ore to wall rock. Shale, gouge, and broken quartzite and
porphyry overlie the ore, and are sometimes found at the sides and within
the ore.
Mining Methods and Equipment
The mines are supplied with electric power and lighted by electricity.
All the drilling is done by Denver Rock Drill Company machine drills. Thus
far only the square-set method is used, though the managers are planning
to use a modification of the cut-and-fill method on one of the ore bodies.
Ore is moved in the main haulage ways in trains of five-ton cars hauled by
storage-battery locomotives. Tracks are laid at a two-foot gauge with
thirty-pound rails on 6 by 8 inch spruce ties. The maximum, grade is 1 per
cent. On the 14th level there is about 1.5 miles of track for the locomotives,
and on the 16th level about 1.25 miles. The ore is transferred from the 14th
level to the 16th level through three ore pockets each 144 feet deep and
12 feet by 20 feet in cross section. The pockets are in solid rock and have
no timbers in them. The capacity of each pocket is approximately 3,000
tons. From these pockets the ore is hauled on the 16th level to three loading
pockets near the portal of the Newhouse tunnel. Each of the loading
pockets has a capacity of about 500 tons. A short tunnel runs from the
surface to the bottom of these pockets. On this lowest level an electric
lorry car, having a capacity of 12.5 tons, hauls the ore from the loading
pockets, and dumps it directly into the railroad cars on the siding at
Belden.
The zinc ore is shipped to the Company's plant at Canon City, Colorado,
and the silver ore is shipped to the American Smelting and Refining Company's
smelter at Garfield, Utah.
The Empire Zinc Company maintains a club house and modern hospital
at Gilman. A physician and trained nurse are in constant attendance
at the hospital, though their services are not often required. The Company
has a boarding house and a rooming house for single men. Married employees
may rent from the Company attractive dwelling houses each having
four rooms and bath. The Company owns 35 of these houses each with
running water and connected with the sewer system. Home owners in
Gilman are permitted to connect with the Company's sewer system by paying
the cost of connection; there is no charge or tax for maintenance.
EVENING STAR MINE21
The Evening Star tunnel trends southwest 485 feet in the granite. The
tunnel has been driven on a fissured zone where a narrow porphyry dike
'"This and the descriptions that follow were written by Russell Gibson.
Excepting the three previously described, the mines follow in the order of the
list at the margin of the map (PI. I).

80 RED cliff mining district
has intruded the granite. This mine is said to have produced gold, silver,
copper, and lead.
BEN BUTLER MINE
The Ben Butler mine has been worked through two inclines in the
quartzite and a tunnel in the pre-Cambrian rocks below. The mine has
1,100 feet of development on the tunnel level. At least four fissure veins
striking northeast were prospected. One of the largest is at the contact
between granite and quartz diorite. The fissured zones vary in width from
1 to 7 feet, and contain streaks of pyrite which carries gold and silver;
they also contain streaks of vein quartz. There is little replacement of
the wall rock. Most of the ore on this level came from three fissures
which were cut by the main tunnel between 660 and 720 feet from the
portal. Some good ore was produced in a raise to the quartzite 440 feet
from the portal of the tunnel.
The upper and lower inclines have a total of 2,500 feet of workings
in the quartzite. They trend northeast, and follow two similarly mineralized
beds where the ore is the result of replacement of quartzite by pyrite and,
to a less extent, by other sulphides. Near the surface the ore has been
oxidized. In places only a few inches of quartzite has been replaced;
elsewhere there has been partial replacement to a thickness of 6 feet. Most
of the fissures are small and show little movement; in most places they
strike northeast. The mineralization in the fissures is thin and unimportant.
It is estimated that the total production of the mine has been about
$250,000 worth of ore. The mine has not been worked for many years,
but in 1923 Messrs. Henry and Frank Martin were cleaning out the tunnel
for a haulage way for ore mined in the inclines.
TIP TOP TUNNEL
The Tip Top tunnel, which trends northeast for 1,400 feet in the pre-
Cambrian rocks, reaches the quartzite at its face. The tunnel intersects
11 small fissures which are mineralized, some of which have been prospected
by drifts and raises. With one exception these fissures strike northeast,
and seemingly more or less movement has taken place along most
of them. The vein material consists of pyrite, sphalerite, and quartz; the
vein is rarely wide. Pyrite is disseminated through gouge and fault breccia
which may be from one-half inch to 12 inches wide. The same mineral
also replaces the granite wall rock to a slight extent a few inches from
the fissure proper. A flat-lying fissure vein between the granite and
quartzite shows an inch of sulphide, and the quartzite 6 inches from the
contact contains disseminated pyrite.
STAR OF THE WEST INCLINE
The Star of the West is opened by an incline which trends northeast in
the quartzite. The chief ore mineral is pyrite, and it occurs as replacement
bodies in the quartzite. A few tight, scantily mineralized fissures were
seen which are, in most places, approximately vertical and strike northeast.
The mine has not been worked for some time, and the production is not
known to the writer.

PURSEYCHESTER MINE
Mr. B. A. Hart, one of the owners of the Pursey Chester, has kindly
furnished much of the following information concerning the early history,
tenor of the ore, and production of the mine. The mine was opened in
1883 by A. H. Fulford and Judge Ackley. In 1885 J. T. Hart bought the
property. The oxidized ores, which were produced in the beginning and
which ran higher in gold than in silver, averaged $150 per ton. Rarely
ore worth $2,000 per ton was produced. Later the sulphide zone was
reached where silver was more abundant than gold. Returns have always
been made for 4 to 5 per cent copper, but generally not for lead. In 1923
the ore averaged .41 ounces gold and 12 ounces silver per ton. Mr. Hart
states that the total gross value of the ore produced to date is a million
dollars.
The mine is opened by an incline which trends northeast in the quartzite.
The wall rock shows numerous fissures almost all of which strike
northeast; and, although they are fairly tight and only thinly mineralized,
it is observed that drifts follow them and that ore has been produced near
them. Almost all the ore is the result of replacement of two beds or
small groups of beds of quartzite which are separated by barren rock. In
places these beds are partly replaced to a thickness of 4 or 5 feet, though
the average is probably less than 4 feet. The chief mineral is pyrite;
much of it is copper-bearing. Small amounts of chalcopyrite and sphalerite
were seen by the writer. There has been little oxidation in the deeper
workings of the mine, but nearer the portal of the incline remnants of
limonite and altered pyrite may be seen. The stopes are not high, but are
very wide and long; they pitch with the dip of the beds. The great size
of the stopes indicates that thousands of tons of ore have been shipped.
The mine is equipped with an electric hoist and electric lights. The
ore is trammed out through the Mabel whence it is delivered to the Mabel-
Pursey Chester mines switch by an aerial tram.
POTVIN MINE AND F. C. GARBUTT MINE
These mines are opened by inclines which trend northeast, and seemingly
follow a fault zone in the limestone. The workings converge and break
through in several places. Although there is evidence of much disturbance
in both mines, the fault or faults can not be described because many of
the crosscuts and stopes are badly caved. In places the limestone is broken
and brecciated from floor to back. The ore was evidently in pockety replacement
bodies of irregular dimensions and in fissures. Remnants of the
ore indicate that oxidation has been pretty thorough. At the time of the
examination 900 feet of underground workings could be seen in the Garbutt
mine and 1,000 feet in the Potvin.
In 1922 a shaft was sunk to open the Potvin incline, but no ore was
shipped. In the summer of 1923 work had been discontinued.
ALPINE MINE
The Alpine has about 700 feet of development along fissures in the
granite. The fissures strike northeast, dip steeply or are vertical, and
contain as much as a few inches of pyrite. There has been a little re-
81

82 RED CLIFF MINING DISTRICT
placement of the granite wall rock immediately adjacent to the fissures.
The largest stope is about 100 feet long and 25 feet high.
A good blacksmith shop houses an air compressor, and a small mill
has been erected.
PINE MARTIN MINE
The Pine Martin has at least five openings in the quartzite and
thousands of feet of development, but the mine has not been worked for
several years and is partly filred with water.
The ore occurs as irregular replacement bodies in the quartzite. In the
lower workings the chief mineral is pyrite; nearer the surface are large
masses of brown, earthy, limonitic material which, according to Mr. Smith
who was in charge of the property in 1921, carries both gold and silver,
but is low grade and difficult to treat. Some of the pyrite is cupriferous;
manganese oxides are found in some places with the limonite. Two groups
o£ thin, closely spaced, vertical fissures containing scant mineralization,
were seen. One group strikes northeast, the other northwest.
According to the reports of the Director of the Mint the Pine Martin
produced ore to the value of $204,339 in the years 1887-1890 and 1892 (gold
and silver taken at coinage value).
The mine is equipped with electric lights. A mill building is connected
with the main incline by a snow shed.
CHAMPION MINE
The Champion is opened by an incline in the quartzite which trends
N. 51° E. When the mine was examined in 1923 over half of the workings
were under water and could not be seen. The mine has not been operated
since 1916.
Most of the ore was found in beds of quartzite more easily replaced
than beds above and below; fissure filling is of minor importance. The
ore bodies were very irregular in size and shape. Ore was cleaned out
of pockets only 2 inches across in some parts of the mine; elsewhere there
are wide stopes 5 feet high. The chief minerals are pyrite (in part
cupriferous) and iron oxides; small amounts of siderite and manganese
oxides were seen. The fissures in the accessible workings strike northeast
or northwest, and are nearly vertical.
The total production of the Champion is not known to the writer. According
to the Mint reports the mine produced gold and silver having
a coinage value of $100,859 during the years 1887-1892.
The mine is equipped with electric lights, a steam hoist, and an
electrically driven air compressor.
BODY MINE
The Body mine is developed by two tunnels driven on fault fissures
in the granite. Most of the ore has come from one fissure vein which
strikes southwest and dips southeast or is vertical. The upper tunnel is
495 feet long, and the lower, from which little ore was taken, is 460 feet.
Two stopes in the upper tunnel are approximately 35 feet high, and a third
stope is 20 feet high. The fissured zone is rarely 36 inches wide; the
maximum width of mineralization is 18 inches. The ore seen consists chiefly

MINES 83
01 sphalerite, pyrite, and galena, in streaks from a fraction of an inch
to 3 inches thick, frozen to fissure walls; less commonly small amounts
of sulphides are mixed with gouge and decomposed wall rock.
SILURIAN AND OVEE MINES
These two mines connect and are conveniently described togethei, The
Silurian is opened by two tunnels in the limestone, one of Which is short
and caved at the portal. The other, about parallel to the first, trends
N. 27° W. for 45 feet, then N. 10° W. for 285 feet. In addition to these
two tunnels, 370 feet of crosscuts and drifts could be seen in the summer
of 1922. The Ovee tunnel is in the limestone and trends N. 17° W. for
60 feet, thence N. 15° E. 35 feet, thence N. 5° W. 220 feet, at which point
it is caved. An old map shows 300 feet of development beyond this point.
At the time of examination about 275 feet of short crosscuts from the main
tunnel were accessible, most of which ended in caved stopes or raises, or
were filled to the back.
The wall rock is "zebra" limestone. It is dolomitic and somewhat
siliceous. In places it is altered to gray or brown jasperoid. The limestone
is broken and faulted in both mines, but the larger faults are not
well defined and can not be described. There appears to have been much
shearing and brecciation with little net displacement. Most of the small
faults strike northwest, and dip 15° to 24° northeast. A few strike northeast,
and have high dips to the northwest or southeast. Remnants of ore
occur irregularly in patches, vugs, and streaks, replacing the limestone in
or near fault zones; the ore shows fairly thorough oxidation. In places
the mineralization is scanty, and oxides of manganese or iron are mixed
with much calcite, dolomite, quartz, and, rarely, barite.
Small shipments of high-grade ore made between 1916 and 1919 by
George E. Rowland, one of the owners, ran 217 to 361 ounces silver per ton.
In 1923 Frank Tetreault, a lessee, was shipping ore that ran 91 to 141
ounces silver per ton. Gold in the ore is rare and in very small amount.
HENRIETTA MINE
This mine is opened by a tunnel trending N. 5° E. for at least 260
feet in the upper part of the limestone. At the time of examination 460
feet of crosscuts could be seen, but the more remote workings were caved.
The ore was found near fault zones where there is evidence of considerable
shearing, but where the net displacement could not be measured.
The faults strike between north and northeast, and dip from 30° to 90°.
In general the direction of dip is southeast. Remnants of ore in streaks
and patches replacing the limestone show nearly thorough oxidation. No
large stopes were seen in the workings that were still accessible. The wall
rock is dolomitic "zebra" limestone containing a little siderite and vugs
with quartz crystals. In places the limestone is very friable and breaks
down to "dolomite sand."
LITTLE MAY MINE
The Little May is opened by a tunnel which trends N. 7° W. at least
165 feet in the limestone. At this point it is caved; consequently most of
the mine could not be seen.

84 RED CLIFF MINING DISTRICT
The wall rock is "zebra" limestone, spotted and streaked with limonite.
The ore probably occurs in pockets and streaks as it does in other similar
mines in the immediate neighborhood. Oxides of manganese and a little
pyrite in all stages of alteration may be seen with limonite in and near
fault zones.
FOSTER COMBINATION MINE
This mine is opened by a tunnel which trends N. 39° W. for 280 feet
in the limestone. Much of the mine is caved and inaccessible, but about
700 feet of workings could be seen in 1923 when H. T. Wenger, who was
leasing the property, was shipping about $300 worth of ore per month.
The wall rock is a ferriferous dolomitic limestone. In places it is hard
and crystalline, and shows "zebra" texture; elsewhere it is decomposed
and friable, especially near the fault zones. All through the mine are
evidences of disturbed ground, but relationships are, for the most part, concealed
since the ore has been extracted near fault zones, and the old workings
are caved or lagged up. Three northeastward-striking faults were seen.
The dip, which could be measured in only one of these faults, is 70° southeast;
the southeast wall shows vertical grooves. In other places the position
of brecciated areas indicates that stresses were relieved by shearing
along rather flat-lying zones under the porphyry. The ore occurs in patches,
pockets, vugs, and streaks in and near fissures and faults. The streaks,
which may trend in any direction, widen and make pockets of ore. As
they are followed upward, in many places the streaks turn, flatten out
under the porphyry or shale, get wider, and produce more and better ore.
Much of the mineralization is the result of replacement of the wall rock
by sulphides which later altered to oxides; there are also small vugs partlyfilled
with oxides and altered sulphides. The chief minerals are pyrite,
galena, sphalerite, barite, gypsum, and oxides of iron and manganese.
Mr. Wenger stated that his high-grade ore averaged 200 ounces silver
and the low grade 9 to 15 ounces of silver per ton. The ore carries very little
gold. The mine is equipped with electric lights and an electric hoist.
FIRST NATIONAL AND EIGHTY FOUR MINES
As these mines are similar in most respects and are connected, they
are described together. Caved crosscuts or water prevented a complete
examination of either mine.
The First National is opened by a tunnel which trends N. 10° W. in
the limestone. An old map shows two tunnels on the Eighty Four claim,
both trending about N. 20° W., but both are caved at the portals. At the
time the map was made the First National had 575 feet of development
still accessible, and the Eighty Four had 1,080 feet. Very little of the latter
mine could be seen. The wall rock is dolomitic "zebra" limestone that
carries siderite. The ore occurs as pyrite in all stages of alteration, and
limonite in patches and streaks in and near ill-defined fault zones.
Pyrite has replaced the wall rock and filled thin, discontinuous fissures.
The report of the Director of the Mint for 1887 gives the value of the
output of the Eighty Four for that year as $1,991. In 1915 Dismant
Brothers and Company shipped ten lots of ore from the same mine which
netted them $4,825. This ore carried 47 to 73 ounces silver per ton, 0.7

MINES 85
to 9.2 per cent lead, and as much as 12 per cent zinc. One lot contained
a little copper, and two lots ran .02 ounces gold per ton. The reports of
the Director of the Mint give the value of the production from the First
National for the years 1888-1891 as $4,359. Both mines have produced more
ore than mentioned, but the records are not available.
WYOMING VALLEY MINE
The Wyoming is opened by two tunnels which trend southeast in the
limestone. The wall rock is dolomitic limestone with the "zebra" texture
developed in places, and contains vugs of dolomite, siderite, and quartz
crystals. It is rarely replaced by jasperoid, but commonly decomposes to
"dolomite sand." At the time of examination most of the workings were
inaccessible because of water and caving. Much of the following information
was furnished by Messrs J. M. and R. V. Dismant.
There are numerous faults and fissures in the mine, most of which
strike northeast and are vertical or have high dips. Three faults were seen
which strike northwest. The dip of any one fault may vary in amount
and direction; it may dip northwest in the upper workings and southeast
on the lower levels. A few ill-defined, flat-lying, northeastward-dipping
faults were observed in the upper part of the limestone near the base of
the porphyry, Which seem to dip a little more than the beds. It may be that
seme of these are bedding faults. The fault zones vary in width from a
few inches to 4 feet.
The ore, most of which was oxidized, occurred in faulted and fissured
zones and in flat-lying streaks and pockets as a replacement of the limestone.
Remnants of ore showed oxides of iron and rare streaks of pyrite,
galena, and sphalerite. The largest bodies were found above or close to the
fissures in the upper beds near or adjacent to the porphyry. These flat ore
shoots had an average thickness of less than 18 inches and a maximum
of 4 feet. In lateral extent they were very irregular, the largest measuring
approximately 150 feet across its greatest dimension. The mineralization
in the steeply dipping fissures and faults was not wide, and in places occurred
only on one side of the break.
Through the courtesy of Mr. J. M. Dismant, who permitted the writer
to examine the smelter settlement sheets, the following information concerning
the output of the mine from March 11, 1914, to May 18, 1920, is
presented:
Output , 4,307 tons
Lead 11,528 pounds
Silver __ 212,822 ounces
Gold 13.06 ounces
Gross value $128,584.45
Average value per ton , $29.85
LIBERTY MINE
This mine is opened by an incline which trends a little east of north in
the porphyry. As most of the mine was filled with water at the time of
examination Mr. J. M. Dismant kindly furnished the writer with most of
the following.
The incline is driven 250 feet down a 30-degree slope, and for 69 feet

S6 RED CLIFF MINING DISTRICT
more on a 40-degree slope. West of the incline a drift in the limestone below
the porphyry, on a northwest-striking vein, encountered small pockets
of high-grade ore—blende and wire silver. Before much ore was extracted
the flow of water became too great to handle, and the mine was temporarily
abandoned. In the summer of 1923 Mr. Dismant was considering installing
a larger pump and reopening the property.
HORN SILVER MINE
In 1879 the Horn Silver mine was opened by William Greiner and
G. J. Da Lee, and is said to be the first mine operated in the immediate
vicinity of Red Cliff. The ore first produced ran about $3,000 per ton, and
the mine is credited with a considerable production of high-grade silver
ore. The silver is reported to have been chiefly combined in the mineral
cerargyrite, or horn silver, and associated with oxides of iron and manganese.
In 1920 the latest shipment was made from the old workings which are
now caved at the entrance.
The new Horn Silver mine, operated by lessees in 1923, has been
producing silver ore said to average $80 per ton. The mine is worked
through a tunnel and incline in the Leadville limestone. The ore is a replacement
deposit in irregular streaks in broken limestone not far below
the porphyry. Bedding faults, seen in the tunnel walls at a lower position
in the limestone, have streaks of gouge from a fraction of an inch to a
toot thick; oxides of iron and manganese are found in the gouge. The
mine is equipped with a gasoline hoist and fan.

INDEX
A
Acknowledgments
Page
8
Alexander, H. E. work of 8
Alluvium 19
Alpine mine 81-82
Aluminum 47
Alunite 47
Andrews, E. P., work of 8
Anglesite 50
Arsenic 47
Arsenopyrite
B
Barite 51
4 7
Battle Mountain, jasperoid on 57, 65
Ben Butler mine 80
Bibliography 11
Black Iron mine, gypsum in 52
manganese oxides in 52
Bleak House mine, faulting in 61
Body mine 82-83
Bornite 47
Brush Creek district, production of 10
Buck, A. H., acknowledgments to 9, 76
C
Calcite 51
Cambrian sediments 33-35
Campbell, M. R., cited 17
Cerargyrite- 50
Cerussite +. 50
Chalcanthite 47
Chalcocite D
47'
Dean,
Chalcopyrite
P. M., analyses by .49, 51,
47
60
Denver
Champion
and
mine
Rio Grande Western
82
gold
Railroad,
in
acknowledgment to
48
9
Devonian
Cleveland
sediments
fault
33, 35-38
72
Dismant,
Coal Creek,
J.
jasperoid
M., acknowledgments
near 58, 65
Copper
to
minerals 47-48
9, 85
Coquimbite
cited 61
48
Dismant,
Covellite
R.
,
V„ acknowledgments
48
Crawford,
to
R. D., cited
9,
63
85
work
cited
of
61
9
Doddridge
Cross, W„
fault
cited 20
73
Dolomite 51
analyses of
Dolomite, relation to ore
51, 60
deposits 65-66
Dolomitic replacements 55.56
E
Page
Eagle mines, character of ores in 78
described 75-7!.*
evidences of replacement in 53
faulting in 61
geologic features in 76-77
goslarite in 30
mineral relationships in ore
bodies 78-79
minerals in 47, 48, 49, 52
mining methods and equipment 79
size and range of ore bodies
in 76-77
Eagle River 16
Eagle Valley Enterprise, quoted 9
Eighty Pour mine 84
Eldridge, G. H.. cited 35
Elk Creek, faults near 58, 59
jasperoid near 58, 53
Emmons. S. P , cited__32, 35, 38, 41, 50
Empire Zinc Company, acknowledgments
to 9, 47
mines of 75
Ettlinger, I. A., quoted 46
Evening Star mine
P
Faulting 43-45
79-80
in Eagle mines 61
in Ground Hog mine 71-73
Faults, fossil 58-59, 61
ore bodies in and near 60-62
Felsite 29
Field work, methods of 8
First National mine 84
Fissure veins 52-53
Fossil faults 58-59, 61
Fossils, in Leadville formation 37, 38
in Pennsylvanian sediments 40, 41
in Sawatch quartzite 35
Foster Combination mine 84
Fuller, H. C, work of
Future possibilities of the
8
district
G
Galena 50
65-66
Gangue minerals 51-52
Garbutt mine 81
Garnet-mica schist 22
Gold Granite Geographic Granitic Gilman, Girty, Gneiss Gneissoid Gibson, Glaciation Goslarite Granite views G. of gneiss Russell, jasperoid gneiss quartz-mica H., position cited work at diorite of 8, 20, 46, 35, 9, 16 24 50 28 20 57 21 48 79 21
10 7 38

88
Ground Hog mine, blende in
Page
51
described 70-75
faulting in 71-73
galena in 50
gold in - 48
map of 72
minerals in 47
ore deposits of 73-75
production of 71
Hall, wall E. rock A., of work of 8, 33, 46, 50 73
Hart, B. A., acknowledgments to 9, 81
Hawthorne, J. D., acknowledgment
to 47
Henderson, C. W., acknowledgments
to 9, 11
Henrietta mine 83
Hesslte 50
History of mining 9
Holy Cross City, reference to 10
Holy Cross Mountain 16, 43
Homestake Creek 16
Hornblendite 28
Igneous Horn Silver rocks mine 24-32 86
Iron Hunter, Mask J. mill W., work of 11 8
Iron Hupp, Mask J. E., mine, work chalcopyrite of in 48 8
goslarite in 50
jasperoid in 57
Iron minerals 48-49
Jasperoid, description of 56-57
occurrence of 57-59, 65-66
pyrite in 65
relation to ore deposits 65-66
Jasperoid outcrop, views of 58, 59
K
Kaolin 52
Kleff and Piatt, acknowledgment
to 8
Landslides 18
possibilities of ore under 66
Lead minerals 50
Leadville limestone, age of 37
description of 35-37
re in 59-60
section of 37
Liberty mine 85-86
Liimonite 49
Lindgren, W., cited 57
quoted! 56
Little Chief mine, jasperoid in 57
Little May mine 83-84
M
Mabel mine
Page
67-70
plan of 68
Mabel vein, section through 69
Manganese minerals 50
Marble 22
Marmatite 51
Maroon beds ~ 41
Metamorphic rocks 20-23
Mica gneiss 21
Mica schist 22
Mineral deposits 46-66
classes of N
Mines, descriptions of
52
67-86
Notch Mining, Mountain history . of
Mississippian sediments
43 9
35-38
Mosquito fault 43
Murray, A. N , work of
Ordovician sediments
8
33, 35
Ore bodies, relation to faults 60-62
stratigraphic position of 59-60
Ore deposits 46-55
fissure deposits of Ground hog
mine
fissure deposits of Mabel
73.74
mine 67-70
related to dolomite 65-66
related to jasperoid 65-66
replacement 53-55, 74
Ores, character of 46
minerals of 47
Paleozoic source of sediments
columnar tenor of section of
Ovee dip mine of
33-42 62-65
42 46
43 83
Paul, R. B., acknowledgment to 9
Pearce, R., cited 50
Pennsylvanian sediments 38-42
age of 40
view of outcrop 39
Peridotite 29
Physiography 16-19
Pine Martin mine 82
Pinger, A. W., acknowledgment to 47
quoted 47, 48, 49
Piatt and Kleff, acknowledgment
to 8
Porphyry 29-32
Potvin mine 81
gypsum in 52
Pre-Cambrian rocks 20-23
Preservation of rock structures
by ore 54
Price of metals 15
Production of the district 12-15
Pyroxene Pursey Pyrite Pyrrhotite minerals Chester gneiss in mine 49
21 81 48

Q
Quartz
Page
52, 59
Quartz diorite 26-27
Quartz-diorite gneiss 21
Quartz-diorite porphyry 32
Quartzite 22, 33-35
Quartz monzonite 25-26
Quartz monzonite batholith of
central Colorado
map showing R
63-65
64
Red
source
Cliff,
of
view
Red Cliff
of
ores
Quartz-monzonite
Replacement, dolomitic
porphyry
63-65
8
55-56
31
jasperoid 56-59
sideritic 55-56
Replacement ore deposits 53-55
shape of ore bodies 53
size of ore bodies 54
Ridgwav, Arthur, acknowledgment
to 9
Rocky
Sawatch
Point
quartzite
mine, faulting in
33-35
61
age of 35
ore in 59-60
section of 34
Sawatch Range 16, 43
Schist 22
Sedimentary rocks 33-42
Siderite 49
analyses of 49
Sideritic replacement 55-56
Sillimanite gneiss 21
Silurian mine 83
Silver minerals 50
Slumping 18
Smithsonite 51
Soil I!1
Source of the ores 62-65
Sphalerite 51
Spurr, J. E., cited 35, 56, 57, 62
Star of the West incline 80
89
Page
Structural geology 43
Structure, influence of 16
Sulphide enrichment 46
Syenite 28
Taylor Hill, refernce to 10
Tetrahedrite 48
Thorn, W. B., quoted 9
Thompson, W. O., work of 8
Tip Top tunnel 80
Toepelman, W. C, acknowledgment
to 33
Topography 16
Turgite 49
Turkey Creek, dolomite near 65
jasperoid near 57, 65
Two United Elk States Creek, Geological prospecting Survey, near 10
acknowledgments to 9, 11
Vegetation
W
18
Weber sediments 41
Wenger. H. T., quoted 84
Worcester, P. G., cited 35
Wyoming Valley mine 85
Yoder Falls, view of 18
Zebra limestone 36
Zinc blende 51
Zinc minerals 50-51

PUBLICATIONS OF THE SURVEY.
•FIRST REPORT, 1908: Out of print.
BULLETIN 1910 Geology of Monarch Mining Dist., Chaffee Co.
BULLETIN 1910 Geology of Grayback Mining Dist., Costilla Co.
BULLETIN 1912 Geology and Ore Deposits of Alma Dist., Park Co.
BULLETIN 1912 Geology and Ore Deposits of Monarch and Tomichi Dis­
BULLETIN 5, 1912: tricts, Chaffee and Gunnison Counties.
Part I, Geology, Rabbit Ears Region, Grand, Jackson,
* BULLETIN 6, 1912: and Routt Counties; Part II, Permian or Permo-Carboniferous
of Eastern Foothills of Rocky Mts. in Colorado.
BULLETIN 7, 1914
Common Minerals and Rocks, Their Occurrence and
BULLETIN 8, 1915
Uses.
BULLETIN
BULLETIN 10,
9,
1916
1915
Bibliography Colorado Geology and Mining Literature.
BULLETIN 11, 1921: Clays of Eastern Colorado.
BULLETIN 12, 1917: Bonanza District, Saguache County.
Geology and Ore Deposits of Gold Brick District,
BULLETIN 13, 1917
Gunnison Co.
BULLETIN 14, 1919
Mineral Waters of Colorado.
BULLETIN 15, 1919
Common Rocks and Minerals, Their Occurrence and
BULLETIN 16, 1920
Uses.
BULLETIN 17, 1921
Platoro-Summitville Dist., Rio Grande and Conejos Co.
BULLETIN 18, 1920
Molybdenum Deposits of Colorado.
BULLETIN 19, 1921
Manganese Deposits of Colorado.
BULLETIN 20, 1924:
Radium, Uranium and Vanadium Deposits of South­
BULLETIN 21, 1921 western Colorado.
BULLETIN 22, 1921 Twin Lakes District, Lake and Chaffee Counties.
* BULLETIN 23, 1920 Fluorspar Deposits of Colorado.
BULLETIN 24, 1921 Foothills Formations of North Central Colorado; Cre­
BULLETIN 25, 1921 taceous Formations of Northeastern Colorado.
BULLETIN 26, 1921 Preliminary Notes for Revision of Geologic Map of
BULLETIN 27, 1923 Eastern Colorado.
Geology of the Ward Region, Boulder County.
BULLETIN 28, 1923
Mineral Resources of the Western Slope.
BULLETIN 29, 1924
Some Anticlines of Routt County, Inc. with 24.
BULLETIN 30, 1924
Some Anticlines of Western Colorado.
BULLETIN 31, 1924
Oil Shales of Colorado.
REPORT 2, 1922.
Preliminary Report, Underground Waters, S. E. Colorado.
OIL
TOPOGRAPHIC
MAP OF COLORADO:
MAP OF
A
Part COLORADO, I, Underground 1913: Waters Scale of of La eight Junta miles Area; to Part inch. II,
Unmounted,
seepages, anticlines,
$3.00;
etc.
Underground Mounted, $4.00; W.aters Mounted of Parts with of sticks, Crowley $5.00. and Otero
GEOLOGIC MAP OF COLORADO, Counties; Part 1913: III, Presents Geology by of colors Parts and of Las patterns Animas, the
geological formations Otero of and the Bent state. Counties. Supply almost exhausted. Prices,
$5.00, $6.00, and Oil $7.00. and Water Resources, Parts of Delta and Mesa Co.
COAL MAP OF COLORADO: Physiography A reconnaissance of Colorado. map showing known areas un­
*Out of derlain Print. by coal in Geology the state. and Ore $1.00. Deposits, Redcliff Mining District.
STRATIGRAPHIC SECTIONS, The Como EASTERN Mining Address District. COLORADO: Ready $1.00. for printing.
COLORADO Geology of GEOLOGICAL Line of Proposed SURVEY Moffat Tunnel.
Boulder, reconnaissance Colorado
map showing locations of
$1.00.

COLORADO GEOLOGICAL SURVEY
R. D. GEORGE, DIRECTOR
Topography by E. A. Ha
A. N. Murray, J. E. Hupp,
E. P. Andrews et al.
Surveyed in 1921-23
TOPOGRAPHIC AND GEOLOGIC MAP OF THE RED CLIFF MINING DISTRICT, COLORADO
Scale 31250 or approximately 2 iut-lies tolmilf
z Mile;
y-z 3 Kilcrmetei'S
('ontom* interval 1()0 feet
Datum is rn^an sea, Ivvul
Geology by Russell Gibson,
R. D. Crawford, A. N. Murray
et al.
Surveyed in 1921-23
LEGEND
MINES AND PROSPECTS
1 Evening Star
2 Whipsaw
3 Bleak House
4 Bleak House
5 Eagle No. 2
(Wilkesbarre shaft)
6 Little Chief
7 Gilman tunnel No. 6
8 Eclipse
9 Polar incline
10 Iron Mask
11 Newhouse tunnel
12 Ben Butler tunnel
13 Ben Butler incline
14 Tip Top tunnel
15 Star of the West incline
16 Belden shaft
17 Belden incline
18 Mabel
19 Pursey Chester
20 First Chance
21 Potvin
22 Garbutt
23 Alpine
24 Pine Marten
25 Ground Hog
26 Eagle No. 2
(Black Iron)
27 Champion
28 Warrior's Mark
29 Body
30 Silurian
31 Ovee
32 Henrietta
33 Little May
34 Foster Combination
35
36
Eighty * Four X
First National
37 Wyoming Mine Prospect Valley
38 Mystery
39 Liberty incline
40 Liberty tunnel
41
42
Horn Land Silver corner
Horn Silver known

Colorado Geological Survey
»8IW
\ V - '• \ \
\ .V., ,-W .:. .-'v; • ,• W ,J ... 3 35: • . .&~k;
Bulletin 30, Plate II
LEGEND
•x numbers
»5 >•*
MINING CLAIMS OF THE RED CLIFF DISTRICT, COLORADO
Tl.i- „ a,, wise,moiled and dravwi bvC. I.. Mr.hr. Nearly all the patented claims were copied wilhoutchangc from a claim map made OV
Ilns map wa.s .' • P „ -'V,.,, | • .,„. !.;,„„;„. Zinc Company. A few patented claims were platted from data obtained in the tinted
s Z s teVor'l^rs'ornl'e "n^l.^-r! AeUnpatcnU-d claims tire from a'elaim map made by C .V. T«. and J. M. DiMmm, Jenunes
i.tecology were taken from note* and map* made hy the Survey field party
LIST OF MINING CLAIMS Index N<
RED CLIFF DISTRICT
Index No. Survey No. Name
T. ft S. R. 81 W. Sec. 1
:'
Long Hoy No. !l
I ....UK Hoy No s
4
Ajax Tunnel Sit,
s:
SN
Nil
no
in
'
19.S.56
19960
River Bond Mill
General Pi.T-liiiii!
11
12
13
14
17
|S
2n III
21
2 it
21
20
27
2 s
2'J
30
lit
52
53
34
:«.".
;>o
37
5.S
39
4tl
11
42
4 3
1 1
4:.
40
17
4S
1
.",:
.".-I
,'i-i
56
--
5S
.v.)
1)0
lit
112
03
lit
65
67
tit; us
oti
71)
7 1
72 73
71
75
7i;
77
7s
7fl
SO
S]
S2
S3
si
s5
Mi
T. 6 S. R 80 May W. Sec. No. 6 14
19900 Cericrnl Long Hov Forh No. 7
May I.
Look >ng N.. Hoy !:> No. N, 0
Long Bov No. I
Long Hoy No 14
Long Boy No. 15
T. 6 S. R. 80 W. Sec. S
Lour Hoy No 12
T. 6 S. R. 81 W Sec. 11
!l.~>0(> T. 6 S R. 81 Brooklyn W. Sec. 12 Placer
20043
May No. r.
1 •.Willi
I.ili'ertv Hel
Mav 1 have X.i it I
Lincoln llishuav
May Xo. l.i
Hig •I'linhei'
St.. 1'auiek
6712
R.-ti M
57)2
Pet u
21 IS
Magnolia
24til
Colorado
5S39
Sooner
3S3s
Almv
3S37
Mai-kc
2;iti7
John C Godfrey
Given Tiniliei
Mav l)a\
]w.):i
KaBle No. .7
ItliltCi
Kiiule No. 4
l

Feet
above
sea
level
SlOO-
Colorado Ceologicul Survey
"'".•' J.....""r J, I-J r 1,1 7- T" Lower limit of ootids oxidsation_ of limestone
SKCTION OF KACTE NO. 2 OKI:. BODY
From a more detailed larger-scale drawing made by A. W. Finger for the Umpire 'Zaiic Company
4- j.
I- +
LEGEND
Bulletin 30, Plate III
Zebra Quartzite Blue
Cambrian
Limestone Limestone Quartzite
o'
Scale
too' 200' 300
Shale and
Quartzite
G" i •" ' 7 ^ &,
Ore

O
o>.
o
(V
+-
CD
1_
o
>>
LEGEND
Alluvium
Lake beds
T7
s / / / /// / /;
>// //. ///.
Cretaceous
shale
Dakota
sandstone
Tarryall
formation
^
i
Quariz
Monzonite
porphyry
P^
^
Diorite
porphyry
*-
Dikes and
sills
\
\
Faults
G E O L O G I C M A P O F T H E T A R R Y A L L DISTRICT.
COLORADO STATE GEOLOGICAL SURVEY
R.D.GEORGE, DIRECTOR
scale: miles

GEOLOGY
OF THE
COLORADO GEOLOGICAL SURVEY
BOULDER
R. D. GEORGE, State Geologist
TARRYALL DISTRICT
BULLETIN 31
Park County, Colorado
BY
GARRETT A. MUILENBURG
ASSOCIATE PROFESSOR OF GEOLOGY
Missouri School of Mines and Metallurgy
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy, in the Faculty of Pure Science, Columbia University
ROLLA, MISSOURI
MAY, 1925
i

TABLE OF CONTENTS
Page
INTRODUCTION 1
Field work . 1
Location and area 2
Acknowledgements 2
History 3
Previous work and literature 6
Topography 7
Climate and vegetation 11
GENERAL GEOLOGY 12
Sedimentary rocks _ 12
General stratigraphic summary ..12
Formations present 16
Lower Tarry all formation 17
Upper Tarryall formation 20
Color of the Tarryall series .....23
The Dakota sandstone 25
The Colorado formation 27
Tertiary Lake Beds 29
Quaternary deposits 29
Petrography of the igneous rocks 32
Quartz monzonite porphyry 32
Definition :. 32
Occurrence 32
Description 34
Chemical composition 36
Other types of quartz monzonite porphyry 37
Diorite porphyry 38
Definition 38
Occurrence 39
Description r 39
Chemical composition _ •. _ 41
Silverheels quartz monzonite porphyry 42
Distribution and name 43
Description _ _ _ 43
Chemical composition 44
Comparison of igneous rocks of Central Colorado 44
Age relations of the porphyries 48
STRUCTURAL FEATURES AND GEOLOGIC HISTORY 49
General structure and deformation _ 49
Structural features of the Tarryall district 50
Porphyry intrusions 51
Inclusions in the porphyries 52
Relative ages of the porphyries _ 53
Age of deformation and intrusion 53
Contact metamorphism _ _ _ 54

TABLE OF CONTENTS
Page
ECONOMIC GEOLOGY 56
Character of the ores 56
Mineralogy of the ores and gangue 57
Gold 57
Sulphides 57
Pyrite 57
Chalcopyrite 57
Galena 57
Sphalerite 58
Oxides _ 58
Quartz 58
Hematite 58
Magnetite 58
Limonite 59
Carbonates .: .59
Silicates 59
Garnet - 59
Epidote •. 60
Orthoclase _ 60
Types of deposits - 60
Deposits related to contact action _ 60
Fissure veins 61
Gold placers 62
Genesis _ _ 63
Future development _ _ _ 64

LIST OF ILLUSTRATIONS
Page
Plate 1 Map showing location of Tarryall district 2
2a and b Placer ground on Fortune property 5
3a Mt. Silverheels from Windy Point .'. 7
3b Slide rock on a porphyry hill 7
4a and b Spheroidal weathering in quartz monzonite 8
4c The northeast spur of Mt. Silverheels from Montgomery
Gulch 9
" 5a Looking south from Windy Point. In the background
Little Bald Mountain (on the left) and Mt. Silverheels
10
" 5b Terminal moraine in Little French Gulch 30
" 6a Looking north in the valley of North Tarryall Creek
toward Mt. Baldy, showing the partial filling of the
valley with glacial outwash material 30
" 6b Large phenocryst of plagioclase from quartz monzonite
porphyry, showing strong zonal structure. The
central portion is an aggregate of quartz and feldspar.
Crossed nicols, x 20 33
" 7a Quartz monzonite porphyry. Crossed nicols, x 25.
Shows large phenocryst of quartz partially resorbed, .
and several crystals of plagioclase 33
" 7b Quartz monzonite porphyry. Crossed nicols, x 25.
Shows broken plagioclase crystal and quartz partially
resorbed _ 34
" 8a Diorite porphyry. Ordinary light, x 25. Shows altered
hornblende crystals and large phantom crystal of
plagioclase 38
" 8b Diorite porphyry. Crossed nicols, x 25. Shows one
of the few quartz phenocrysts and abundant plagioclase
39
" 9a and b Silverheels quartz monzonite porphyry. Crossed nicols,
x 25. Shows a type in which quartz is nearly absent
and in which hornblende is abundant in the groundmass
_ 42
" 10 Diagram showing variation in composition of igneous
rocks 45
Geologic Map Inside back cover

Geology of the Tarryall District
Park County, Colorado
INTRODUCTION
Field Work
Field work in the Tarryall Gulch district was begun in
summer of 1923 by the author and a party consisting of Clifford
L. Mohr and Harold A. Hoffmeister. On account of illness, the
author was compelled to leave the field before the end of June
and thereafter the work was in charge of Mr. Mohr. During the
time the party was in the field, a rough preliminary map was
made showing drainage lines, roads and trails, mines and prospects,
and other features that might be of use in mapping the
geology of the region. The map was made by means of the plane
table and telescopic alidade, starting from a base line 3630 feet
long, measured with considerable care and accuracy, in a level
portion of the valley of Tarryall Creek below Marinelli's ranch.
This base line was later tied in to a section corner and also with
the Colorado and Southern Railroad, thus giving a reasonably
accurate horizontal control. In this way, a triangulation net
was first constructed between the principal mountain peaks,
locations and distances being determined by intersections and
scaling, and altitudes by means of the vertical arc. Most of the
prominent points were occupied and all locations and distances
were checked a number of times to insure as much accuracy as
possible. The result was a fairly serviceable base map, which
was later used to map the geology. This ended the field work for
the summer of 1923, but in the summer of 1924 the author again
went into the field, accompanied by Mr. W. E. Richardson, and
carried out the plans that had been made for the preceding
summer.
By permission of Mr. Louis Marinelli, headquarters for the
party on both occasions were established in one of the abandoned
cabins of the Fortune Placers Gold Mining Company, near the
point where Tarryall Creek emerges from the mountains and
flows out upon the plains of South Park. From this point all of
the territory covered by the map could be reached with little
difficulty.

THE TARRYALL DISTRICT
Location and area
The area covered by this report lies in Park County, Colorado,
about five miles northwest of Como, a station on the Leadville
branch of the Colorado and Southern Railroad. It embraces
about 35 square miles, bounded on the south by Mt. Silverheels,
on the west by the Continental Divide as far north as Boreas
Pass or Breckenridge Pass, on the northeast by the irregular
range of hills between Michigan and Tarryall creeks, and on the
east by the plains of South Park. The location with reference
to other mapped areas of the state is shown on the sketch map
(Plate 1). The Colorado and Southern Railroad crosses the
v .'7'' -r^—
Ct'EAlt CREEK
Plate 1. Map showing location of Tarryall district.
district near the eastern edge, and crosses the Continental Divide
at Boreas Pass.
Acknowledgements
The author wishes to acknowledge the courtesy of Professor
R. D. George, State Geologist of Colorado, who has made possible
the investigation and supplied the means for carrying it through,
and very generously put up with the delay occasioned by the
author's illness. To Professor Crawford, of the University of

INTRODUCTION 3
Colorado, the author is indebted for many helpful suggestions
before going into the field, and also for material loaned for study
in connection with the preparation of the manuscript. Further
acknowledgement is due Messrs. Mohr and Hoffmeister for the
way they carried on the preliminary .work during the author's
absence, thereby saving him much valuable time and labor in the
preparation of the base map, and to Mr. W. E. Richardson for
assistance in the field during the summer of 1924. Mr. I. B.
Look of Denver, and Mr. Louis Marinelli of Como also deserve
acknowledgement for information given, and help rendered while
the field work was in progress.
History
Mining began in Tarryall Gulch in 1860, a few miles from
where Como is now located. So far as can be ascertained, this
was the first place where actual mining was carried on in the
entire area known as South Park. These first miners are said to
have been men from Wisconsin, and other middle western states,
who were enroute to Leadville, but having become wearied by
the long journey decided to stop here and rest a while, hence the
origin of the name Tarryall.
Placer mining activities were carried on intermittently for
many years, and Hamilton, a mining town of some size, sprang
up at about the point where Tarryall Creek flows out into South
Park. Dr. A. C. Peale in his report, as geologist of the South
Park Division of the Hayden Survey,1 in 1873, credits Hamilton
with having had a population of about 5000. Various other
reports as to the number of inhabitants are current, but all are
probably greatly exaggerated.
About this time, labor troubles at Leadville are said to have
been responsible for a party of about forty Chinese laborers coming
to Tarryall Gulch. These men were driven from Leadville,
and crossed the divide into the headwaters of Middle Tarryall,.
where they went to work washing gravel.
During the "Seventies" and "Eighties", lode mining was
started in a number of places, and several small stamp mills were
erected, but these ventures all turned out disastrously, and the
undertakings were eventually all abandoned. It is said that several
carloads of ore were shipped to Alma, and some to Denver,
but no authentic evidence can be had supporting this rumor.
lHayden, F. V. United Stat* Geological and Geographical Survey of the Territories,
1873; Report of Dr. A. C. Peale, p. 302.

4 • THE TARRYALL DISTRICT
Placer mining in the gravels along Tarryall Creek, below the
junction of the three branches and also in Montgomery Gulch,
a tributary to Middle Tarryall, continued intermittently until
about 1890, when John Fortune began operating what is now
known as the Fortune Placers. After work had proceeded for a
number of years by hand, a syndicate was formed and hydraulic
mining was undertaken. This continued until 1917, when the
cost of labor and supplies became prohibitive. About this time
also, the ranchers out on the plains of South Park succeeded in
having an injunction served upon the Fortune Placers Gold Mining
Company which resulted in shutting down the largest and
richest placer in Tarryall Gulch. The complaint of the ranchers
was that debris washed downstream by the hydraulic mining
operations filled up the irrigation ditches.
From reports and surface indications of activity, it seems
probable that half of all the gold produced came from the
Fortune Placers. The operations here were the most extensive
in the district, and the equipment included miles of ditches and
steel pipes to lead the water to the hydraulic giants by means of
which the gravel was washed down. (Plate 2).
Other locations operated at this time were the Roberts
Placer and the Peabody Placer, below the Fortune, and the
Liebelt Placer in Montgomery Gulch, up Middle Tarryall Creek.
The Liebelt Placer is said to have ranked next to the Fortune as
a producer. While these operations were going on, many shafts
were sunk and tunnels driven into the mountain sides in the hope
of locating the source from which the placer gold came, but all
apparently ended in failures. Among the larger undertakings
of this kind were those of the Silverheels Mining and Tunneling
Company; the Mineral Ranch Hill Tunnel, now operated by the
Illinois Central Consolidated Mining and Milling Company, and
the Baxter workings at the head of Montgomery Gulch.
At present no active mining is being done anywhere in the
district. A number of men are prospecting and keeping up assessment
work on their properties but no shipments of ore have
been made for many years. Among the areas actively prospected
are Jarvis Gulch, Montgomery Gulch, Little French Gulch and
the head of Indiana Gulch near Boreas Pass. On Mineral Ranch
Hill a property operated by the Illinois Central Consolidated
Mining and Milling Company shows the most development, but
the workings are badly caved and not*accessible. This is the

INTRODUCTION 5
condition of nearly all the old workings, consequently very li
could be learned of the underground condition and of the size and
extent of ore bodies.
-v'.'Mi*"
Plate 2 a
Placer ground on the Fortune property.

6 , THE TARRYALL DISTRICT
Previous Work and Literature
The only previous geologic field work in this district is tha
of the South Park Division of the Hayden Survey in charge of
Dr. A. C. Peale. Dr. Peale made a brief study of that part of
Tarryall Creek which lies within the mountain amphitheatre, and
ascended Mt. Silverheels where he made a partial section of the
rock formations encountered.
The United States Geological Survey has mapped the Breckenridge
district, which, lies just to the north, and the Colorado
Geological Survey has mapped the Alma district to the southwest.
The following publications are the more important ones deak
ing with this section of the state :
Peale, A. C, Report .on the geology of the South Park division
; Seventh Annual Report, U. S. Geol. and Geog. Survey Terr.,
1873, pp. 194-273; 301-302.
Belcher, Gustavus R., Geographical report on the Middle
and South Parks, Colorado, and adjacent country; Ninth Ann.
Rept.; U. S. Geol. and Geog. Survey Terr., 1875, pp. 419-432.
Ransome, F. L., Geology and ore deposits of the Breckenridge
district, Colorado; Prof. Paper U. S. Geol. Survey No. 75,
1911.
Patton, Horace B., Geology and ore deposits of the Alma
district, Park Countv, Colorado; Bull, Colo. Geol. Survey No. 3,
1912.
Crawford, R. D., A contribution to the igneous geology of
central Colorado; Am. Jour. Sci., 5th ser., vol. VII, May, 1924.

INTRODUCTION
Topography
The region is one of great relief, having a vertical range of
about 4,000 feet. According to the U. S. Geol. Survey, Mt. Silverheels,
(Plate 3a) the highest peak, has an elevation of 13,855 feet,
Plate 3a. Mt. Silverheels from Windy Point;
Plate 3b. Slide rock on a porphyry hill.
while the lowest point of the area mapped, about 9,920 feet, is in
Tarryall Creek at the east edge of the map. The entire portion
of the Continental Divide included in the mapped area has an
elevation of over 11,000 feet and many of the high peaks within

8 THE TARRYALL DISTRICT
the area are over 12,000 feet high. The Colorado and Southern
Railroad crosses the Continental Divide at Boreas Pass at an
elevation of 11,480 feet, according to the U. S. Geol. Survey. A
large part of the area lies above timber line, and consequently is
subject to rapid erosion (Plate 3b). Many of the high ridges and
peaks are covered to a depth of many feet with "slide rock",
(Plate 4a and 4b), a name given to slabs and masses of rock de-
Plate 4a Plate 4b
Spheroidal weathering in quartz monzonite porphyry near top of
Little Mountain.
tached as a result of exfoliation. A great thickness of sedime
has been removed by erosion as can be seen in ascending Mt.
Silverheels. Here the sedimentary beds which form a part of the
mountain mass stand at an average angle of about 30 to 35 degrees,
and represent the lower part of a huge fold. Together with
the intruded sills these beds have a total thickness of between
10,000 and 12,000 feet. Assuming that they once formed a continuous'
arch over the Mosquito range, it is evident that a thickness
of strata equal to about two miles has been removed. This
estimate takes into account only those beds below the Dakota
sandstone. How much of the Cretaceous section above the Dakota
was at one time present is not known, nor is it known how
many feet of Tertiary sediments covered the region, but that they

INTRODUCTION 9
were at one time present is shown by remnants here and there.
In spite of this enormous amount of erosion, the topography has
hardly reached the stage of maturity. In many places there still
remain broad rolling uplands, and the valleys are all steep and
narrow, except where normal development has been modified by
glaciation. ' The broad rolling uplands which characterize the
region and which are especially noticeable along the Continental
Divide are perhaps remnants of an older erosion surface or peneplain.
W. T. Lee1 in a recent paper has discussed the peneplains
of the Rocky Mountains and mentions this possibility, and it is
also suggested by Ransome2.
Although the Tarryall district has considerable relief, the
mountains are not particularly rugged. Except for the higher
porphyry peaks which are covered with vast quantities of slide
rock, and the Mt. Silverheels side of Montgomery Gulch (Plate
4c), which is formed by the scarp slope of the great series of sedi-
Plate 4c. The northeast spur of Mt. Silverheels from Montgomery Gulch.
mentary beds forming the mountain mass, the region as a whole
represents a rounded and rolling topography (Plate 5a). Glaciation
has played some part in this development, rounding out the
valley heads and partially filling the middle portions with moraines,
but on the whole it has not been a very important factor.
Much of the rounding is the result of normal erosion, and the ac-
lLee, Willis T. Peneplains of the Front Range and Rocky Mountain National Park,
Colorado; Bull. U. S. Geol. Survey, No. 730-A.
zProf. Paper, U. S. Geol. Survey, No. 75, 1911, p. 15.

10 THE TARRY/ALL DISTRICT
Plate 5a. Looking south from near Windy Point. In the background
Little Bald Mountain (on the left) and Mt. Silverheels.
cumulation of residual material along mountain slopes and in val­
leys. A very notable feature, and one which rendered the field
work difficult, is the great abundance of residual debris over the
surface, consisting of slide rock and the decomposed and disinte­
grated products of rock weathering, which effectually hide much
of the bed rock.
The Tarryall district is drained almost entirely by Tarryall
Creek and its tributaries. About a mile above the point where
it flows out on the plains of South Park, this creek forks into
three branches. The north branch heads in the Continental
Divide at Boreas Pass and Warrior's Mark Mt., the south fork
originates in the east spur of Mt. • Silverheels, while the middle
branch again forks, Montgomery Gulch heading on the west side •
of Mt. Silverheels, and Little French ajid Deadwood gulches
originating'in the Continental Divide near Red Mountain. Drain­
age from the eastern part of the area goes into Michigan Creek,
which, joins Tarryall some distance from the mountains, and the
combined streams then cross South Park and join South Platte
River.

Climate and Vegetation
INTRODUCTION 11
In a region of such high altitude the summers are naturally
cool and short and the winters long. During the field season of
1924, thermometer readings were frequently noted and recorded
and these show that the temperature rarely rises above 70° or
75° F. during the day, and often drops below freezing during the
night, even in Jul}- and August. The winter snow is usually
heavy, and snowfalls occur on the mountain tops even in summer.
Many areas of permanent snow are found on the higher peaks in
places where the direct rays of the sun do not strike.
Timber, consisting largely of spruce, pine and fir, with
patches of quaking asp scattered throughout, covers large portions
of the mountain slopes and valleys. Most of the area lies
within the Leadville National Forest Reserve, and as such is
under supervision of forest rangers. Enormous quantities of
timber are destroyed almost annually by heavy windstorms, and
as a result of former forest fires many square miles are covered
thickly with fallen trees. Deadwood Gulch received its name
from the great quantities of such dead timber.
In those valleys in which glacial and landslide debris has
caused a partial obstruction, soil has accumulated to a considerable
thickness, and this supports a dense growth of willow brush
and grass together with great quantities of moss. This vegetation
accumulates from year to year and in places peat-like bogs
have formed to a thickness of from four to six feet. Over much
of the surface of these bogs the growth of willow is so dense that
it defies penetration, and where passage is possible, one sinks up
to his knees, and often deeper, into the water saturated moss.
The lower mountain sides and valleys which are not covered
with timber or willows support a rather abundant growth of
grass, suitable for grazing; and even on some of the higher
slopes above timber line, at 11,500 feet, sufficient vegetation
grows to make possible the grazing of large flocks of sheep.
Every summer from 10,000 to 15,000 or more sheep are brought
up from the ranches in South Park and allowed to graze in the
upper parts of the valleys of Tarryall Creek and its tributaries.

12 THE TARRYALL DISTRICT
SEDIMENTARY ROCKS
General Geology
General Stratigraphic Summary
That portion of central Colorado adjacent to the Tarryall
district has a rather complete section of stratified rocks from the
Cambrian to the Cretaceous. While no formations older than
upper Pennsylvanian occur in the immediate area, they are
known just over the Continental Divide to the west. In order to
give a better understanding of the stratigraphic succession of
this portion of the Rocky Mountain region, it is thought advisable
to include here a tabular summary of the geology of neighboring
areas. This is taken from F. L. Ransome's monograph on the
Breckenridge district, and to it has been added the summary of
the Tarryall section.
As the Tarryall district lies farther east than the areas summarized
in the table, there is exposed here only the upper part
of the succession described in the various reports. Farther east
on the plains of South Park are encountered still younger Tertiary
formations. Naturally, on account of the location, it would
be expected that the sedimentary rocks of the Tarryall district
would conform quite closely with those of the Breckenridge area,
and a study of the accompanying chart will bear this out. Alma
and Leadville are stratigraphicallv too low for the younger rocks
to appear, because they are located about on the axis of deformation.
Tenmile has some of them, while Aspen, on the opposite
side of the uplift, has the complete section.
Correlation of the beds in the Tarryall district with those of
the foothills on the east flank of the Rocky mountains is difficult.
The Dakota sandstone can be easily recognized, and is probably
the equivalent of the Dakota in the foothills region. The underlying
Red-beds, however, present a different problem on account
of the absence of characteristic fossils. Most geologists who
have studied these beds in different parts of Colorado agree in
the assumption that they are at least very nearly the equivalents
of the Red-beds in the Denver Basin1. If this correlation is cor-
lGirty, G. H. The Carboniferous formations and faunas of Colorado; Prof. Paper
U. S. Geol. Survey, No. 16, 1903, p. 190.

SEDIMENTARY ROCKS 13
rect, the Maroon formation of the Tenmile and Aspen areas, and
the Wyoming of the Breckenridge area, are in part equivalent to
the Fountain, Lyons, Lvkins, and Morrison of the foothills of
North Central Colorado, and possibly also to the Gunnison and
McElmo formations of the western slope.
Henderson1 at present regards the Fountain and Lyons as
Pennsylvanian, and the Lykins as Pennsylvanian, Permian, or
Triassic. The Morrison he says is upper Jurassic or lower Cretaceous,
with the evidence favoring the former.
The subdivisions of Henderson and others in the foothills
region can not be carried out in the area under consideration. In
the first place, the exposures are too limited and discontinuous
to be traced for any great distance, and, in addition, the sedimentary
series has been so much cut up and metamorphosed by
igneous intrusions, that correlations with distant formations
even on the basis of lithologic character is out of the question,
and subdivision is equally impossible.
It seems quite likely that the brick red shales and sandstones
which underlie the Dakota belong to the Morrison formation, but
how much more of the series belongs here is difficult to say.
These brick red sandstones and shales grade downward into
darker red and chocolate colored shales and sandstones which are
probably the equivalent of the Wyoming of Ransome2 and Emmons3,
and the Triassic of Spurr*. Below this is a thick series of
alternating beds of shale, sandstone, and arkose, varying in color
from gray through pink to dark red. These are probably the
equivalent of the Maroon.
Just where the line between the Maroon and the Weber
formation should be drawn is problematical. Above the Weber
in Emmons' Hoosier Pass section lies a thick series of sandstones
and shales, lithologically quite similar to the Weber, but differing
greatly in color. The Weber is usually gray, but the beds resting
on it are dark red, although in places various shades of pink
and gray are encountered. This formation is generally known as
the Maroon. It appears to be conformable above the Weber, and
the change from the one to the other is so gradual that no exact
line can be drawn, unless one were to take Ransome's5 suggestion
lHenderson, Junius. The foothills formations of North Central Colorado, Bull. No.
19, Colo. Geol. Survey, 1920.
2Prof. Paper U. S. Geol. Survey No. 75, 1914, pp. 26-42.
3Tenmile district special folio, No. 48, Geol. Atlas U. S., U. S. Geol. Survey, 1898.
4Monograph, U. S. Geol. Survey, Vol. 31, 1898.
50p. cit. p. 29.

14
System
Cretaceous
Jurassic (?)
Triassic (?)
Carboniferous
Series
Upper
Cretaceous
Pennsylvanian
Leadville
Upper Coal
Measures
Weber Grits
Weber Shale
TABULAR SUMMARY
CENTRAL
Alma
Tenmile
Emmons, S.P., Patton, H. B.,
Geology and Geol. & Ore
Emmons, S. F.
mining indus­ Deps. of the
Tenmile Dist.
try of Lead­ Alma district,
special folio
ville, Colo., Park Co., Colo.
No. 48, Geol.
Mon. U.S.G.S., Bull.Colo.Geol.
Atlas U.S.,
Vol. 12, 1886. Survey, No. 3,
U.S.G.S. 1898
1912.
Wyoming fm.
Brick red s s .
with some red
shale and local
coarse c o n g.
1500 ft.
Maroon fm.—
Coarse gray
and red s s.
with a s s o c.
cong. and Is.
1500 ft.
Weber Grits. Weber fm.
Coarse ss. or Coarse gray ss.
grit above, and grit 25 00
shale grading ft., with carb.
to q t z t . and shale at base
calc. shale and and thin beds
ls.below;2500 of dolomitic
feet.
Is. 2 800 feet.

OF FORMATIONS
COLORADO
Aspen
Spurr, J.E., Geology
of the Aspen mining
dist., Colo., Mon. U.
S.G.S. Vol. 31, 1898
Niobrara - Gray lime
-stone; grades up into
Montana formation;
100 ft.
Benton—Black calcareous
shales, 350
ft., Colorado group.
Dakota — Massive
white sandstone
with local variations;
250 feet.
Gunnison fm. Gray
or yellow ss., often
c a 1 c . , overlain by
reddish, grayish, or
varieg. shaly ss., 3 00
ft.
Unconformity
Triassic — Red ss.,
light red below, dark
above; 2 6 00 ft.
Mamon formation—Dark
red ffrits, and thin shaly
1>. Pass gradually into
foregoing; 4,000 ft.
Weber fm. Thin bedded
carbonaceous Is. and calc.
shales; 1,000 ft.
Breckenridge
Ransome, F.L., Geol.
and ore deposits of
the Breckenridge
Dist., Colo., Prof.
Paper, U.S.G.S. No.
75, 1911.
Upper Cretaceous
shale. Dark shales
with a few thin layers
of limestone and
gray quartzite. Contains
Benton, Niobrara,
and possibly
Montana fossils,
3500-5500 feet.
Dakota sandstone — Buff
sandstone passing locally
into white quartzite with
more or less gray shale.
May include some Lower
Cretaceous and some
Morrison formations
Not (L. Cretaceous definitely or recogJurassic)nized. 200-300 Some feet. Morrison
format'on (Jurassic)
may be include
d with the roqks
mapped as Dakota.
Wyoming formation.
Brilliant red ss. and
shales. Probably equivalent
or nearly
so, to the Lykins of
the v Boulder dist.,
Colo., 1000 ft.
Absent
Absent
Tarryall Gulch
15
Upper Cretaceous
shale. Black carbonaceous
shale; thin,
black, fossiliferous
1 s . below. Lower
part carries Benton
fossils, upper part
Niobrara.
Dakota sandstone—Grayish
to buff ss. grading
into grayish white quartzite
locally. Contains a
few thin shale and conglomerate
beds. 250 feet.
Morrison
Xot definitely recognized
probably present,
but included
with the Tarryall
formation.
Upper Tarryall formation.
Bright red sandstone
and variegated shales at
the top, becoming darker
and more chocolate colored
af the base, also gray
ss. Lower with Tarryall pebbly formation. streaks,
6,000. Gray to reddish gritty
ss. and interbedded red
shale. Pebbly and cong.
streaks near the base of
individual beds. 3,000-
5,000 ft.
Not exposed

16 THE TARRYALL DISTRICT
that it be drawn at the first reddish bed. Strata equivalent to
Maroon constitute the whole of the sedimentary series in Red
Mountain and neighboring peaks on the western border of the
area mapped. The beds have been tilted eastward at an average
angle of about 35°. About a mile and a half south of Boreas Pass
they cross the Continental Divide, and can again be seen in Indiana
Gulch. The tops of Red Mountain, and other peaks along
the divide, are composed of a thick porphyry sheet, which was
intruded into the sediments. Throughout this area, such porphyry
intrusions are common, and increase the total thickness of
strata by hundreds of feet. Furthermore, contact metamorphism
by these porphyry sills has greatly changed the appearance and
composition of the sediments, resulting in the formation of much
epidote and some garnet, and giving the rock a greenish gray
color, together with a pronounced banding or "ribbon structure"
due to the difference in susceptibility of the various laminae to
metamorphism. Along with this epidotization, there has been a
general baking and siliciiication, thus making the rock much
harder and more resistent to erosion.
Above the Dakota in the northeast part of the area are small
patches of black carbonaceous shales. Still higher, stratigraphically,
are grayish calcareous beds which in turn grade into dark
colored fissile shales that weather light gray on exposure. Just
east of Boreas Pass these shale beds are intruded by a great porphyry
sill, and northeastward from here, in the hills forming the
divide between Michigan and Tarryall creeks, irregular areas of
shale can be seen included in porphyry sheets. The lower
shale beds, which rest on the Dakota, carry typical Benton fossils,
are black in color, and contain thin beds of black carbonaceous
limestone. The upper shale beds contain Niobrara fossils, especially
Inoceramus deformis.
Formations present
The sedimentary formations represented in the Tarryall district
are as follows:
Quarternary Glacial material
Tertiary (?) Lake beds
r ¥ | Colorado \ Niobrara
Cretaceous -; j Benton
( Dakota
Jurrasic (?) Morrison
Tarrvall ( Upper—Wyoming
Permo-Carbomferous formation^
( Lower—Maroon

SEDIMENTARY ROCKS 17
On account of the great amount of igneous material intruded
into the sediments, and the relatively small area studied, the descriptions
herein given probably apply only to a very limited region
in and around Tarryall Creek. Estimates of thickness are
probably excessive, because of the igneous material, and other
characters ascribed to the various beds are also in part the result
of metamorphism by these intrusions and are therefore more or
less local.
Lower Tarryall Formation
In general the formation is dark red, or chocolate colored,
but on closer examination it appears that the red color is very
largely confined to the thin bedded, argillaceous members, and
that the sandstones are grayish to pinkish, with a red cementing
material. This gives a reddish cast to the whole, which, together
with the darker red of the shale members, gives the entire series
a dull red color.
It is very difficult to define the boundaries but perhaps it is
best to place the base at the bottom of the lowest bed with a distinctly
red color, although this is an arbitrary boundary. In the
Hoosier Pass section, Ransome noted that the Maroon which is
the same as the Lower Tarryall formation, was apparently conformable
on the Weber. This is probably true over much of this
section of the country, and therefore it will be best to accept
current usage and draw the line at the bottom of the lowest red
bed, as there do not seem to be any other reliable characteristics
that can be used. Still more difficulty is experienced at the top,
where there is apparently a conformable gradation into the upper
bed, and where not even a color line can be drawn. That so
thick a series of shallow water (or possibly terrestrial) deposits
could be laid down without apparent disconformity seems improbable.
Yet, on the other hand, no field evidence has been
found in this area to warrant an}- other alternative. Perhaps this
may be explained by the igneous activity which has so broken up
the sedimentary beds and changed their character and appearance
that it is impossible to carry correlations very far, and difficult to
locate stratigraphic breaks. Perhaps also, if detailed mapping
could have been done on an accurate topographic base, some
other relations might have been brought to light, but under existing
conditions it would be unwise to state definitely that the
series is either conformable or disconformable.

18 THE TARRYALL DISTRICT
Lithologically, the Lower Tarryall formation consists of
cross-bedded, fine to coarse sandstones, composed essentially of
grains of quartz and feldspar with flakes of mica, together with
various minor constituents, the whole cemented with silica, calcite,
and iron oxide. The quartz grains are usually clear and
transparent, although pinkish and amethyst particles were observed.
The grains are generally more or less angular, indicating
that they have not been transported far, nor worked over extensively
by waves. The feldspar is principally white but some of a
decidedly pinkish tinge is present. Under the microscope it is
seen to consist of orthoclase, microcline, and small quantities of an
acid plagioclase. The pink feldspar, where present blends with the
gray or colorless quartz, giving to the whole a delicate touch of
pink which in many of the individual beds of the formation is
much augmented by ferric oxide in the cementing material. Close
examination reveals that the red color of the beds is due almost
entirely to this cement and to thin films of ferric oxide over
the grains, which penetrates any minute cracks which may be
present, even the cleavage planes of the feldspars, and permeates
the clay particles. Upon digesting a sample of the typical red
sandstone in hydrochloric acid, the iron can be removed leaving
clear colorless quartz and pinkish feldspars. On the whole, the
color of the sandstone varies from almost pure white to gray,
pink and red with gray predominating.
In the basal portions of some of the beds, the sandstone is
coarse grained and decidedly pebbly, though hardly conglomeratic.
There is quite an admixture of pebbles and cobbles ranging
in size from less than half an inch to small boulders six or eight
inches in diameter. These consist of clear colorless quartz and
pinkish feldspar, and occasionally of granite. The feldspar is
commonly quite fresh and shows good cleavage. In individual
specimens, the quartz and feldspar are intergrown, and resemble
the graphic textures of pegmatites, so common in the pre-Cambrian
rocks.
Interbedded with the sandstone and constituting about half
of the total thickness, are beds of dark red or maroon colored
shales. Many of the shale beds are extremely arenaceous, and
others are micaceous. The presence of the mica flakes which
invariably lie parallel to the bedding causes the shales to split
readily into thin slabs. Ripple marks are common and sun-cracks
were also observed. Occasionally along with the red shale, are
decidedly darker beds verging on black owing to the presence of

SEDIMENTARY ROCKS 19
carbonaceous material. These, however, occupy but a very smal
part of the section, although according to Emmons1 they constitute
a considerable part of the Tenmile section. Another
characteristic feature is the presence of limestone beds of irregular
extent and thickness, interbedded with the sandstones and
shales. These limestones are usually light gray in color and on
exposure weather white, thus giving a striking color contrast,
which can be seen at a great distance. In structure they are
dense and compact, but often show intricate fracturing. Many of
the fractures have been healed with white crystalline calcite.
No fossils were found in any of these beds, hence it is impossible
to attempt any paleontologic correlation.
The characteristics of the formation as thus described apply
only to those portions that have not been metamorphosed by igneous
material intruded into it. Metamorphism is widespread, but
varies much in intensity. At the contact of the smaller intrusion,
little more than a baking or hardening of the shales is noticeable,
and the sandstones have hardly been affected. From this minimum
it increases in intensity to the maximum, where the sedimentary
rock has entirely lost its original character, and now
consists of a banded mass of epidote and garnet, impregnated
with specularite and magnetite. Generally this type of rock has
a decidedly green color, due to epidote which is strongly developed
and masks the brown of the garnet. Where the metamorphism
has been less intense, the so-called "ribbon rock" has been
developed which consists of alternate bands of brownish red,
slate-like material, and epidotized shale. This is by far the more
common rock in the Montgomery Gulch and Little French Gulch
sections, constituting over 50 per cent of the formation.
The number of intruded porphyry sheets or sills in this series
of sediments is large. Only the thicker ones are shown on the
map but in addition to these there are many others. The thickening
of the sedimentary strata by the intrusion of such numbers
of sills is well shown along the steep northwest face of Mt. Silverheels.
Here the sedimentary beds show a decided fan-like
arrangement, the dip increasing in general towards the top of the
mountain. At the base, dips of 20 degrees are common, while
towards the top these have increased to as much as 35 degrees
locally. Along with the increase in dip there has also been a
corresponding variation in the direction of strike due to bowing
of the strata by thick sills.
ITenmile district special folio, No. 48, Geol. Atlas U. S., U. S. Geol. Survey, 1898.

20 THE TARRYALL DISTRICT
The thickness of the Lower Tarryall formation could not be
measured, as it was impossible to determine its boundaries, either
above or below. In addition, igneous intrusions have so increased
the apparent thickness, and caused so much local variation, that
it is difficult to even make estimates. The possibility of repetition
of beds by faulting with resultant increase in thickness must also
be considered. While no direct evidence of important faulting of
this nature was found, it is quite probable that some occurs.
Along Montgomery Gulch, on the Mt. Silverheels mass, a section
was measured which included in the neighborhood of 2,000 feet
of strata. Below this is an unknown thickness of beds to the
Weber, and above it another unknown thickness of beds to the
Upper Tarryall. A conservative estimate would probably be
around 3,000 feet, but even though this is conservative, it should
be taken with due allowance for the various influencing factors
mentioned above. To this there should be added anywhere from
1,000 to 2,000 feet of igneous material, making a total of between
4,000 and 5,000 feet.
Upper Tarryall Formation
It is impossible to define absolutely either the upper or lowe
limits of the formation. At the base, there is an insensible gradation
from the dark red Lower Tarryall into the lighter colored
sandstones and shales here designated as Upper Tarryall. Towards
the top, this color becomes stronger and brighter until
within 150 or 200 feet of the Dakota sandstone it is in places a
brilliant brick red. This greater intensity of red is perhaps in
part due to the decreasing amount of metamorphism, as it has
been noted that the development of epidote .and garnet is everywhere
accompanied by a loss of color. Above these brilliant red
shales, the outcrops are nearly everywhere covered, but in a few
places limestone boulders were encountered and here and there
small patches of greenish gray and dark shale were noted.
It is possible that this apparent break in the series marks
the presence of beds equivalent to the Morrison of the Foothills
area, but no beds such as are described there could be identified
here. From the highest point of outcrop of the bright red sandstone
and shales to the Dakota, the slopes are everywhere covered,
and only in the bed of Tarryall Creek just below the Fortune
placers and on the hillside northeast of the junction of the middle
and north branches of Tarryall Creek, were any of the intervening
beds seen. In the former place a fine grained, grayish blue

SEDIMENTARY ROCKS 21
limestone, weathering yellowish and buff, outcrops for a shor
distance, and is then covered by the stream gravels. In the latter
locality a thin ledge of black limestone outcrops in few places.
From this limited exposure a number of fossils were collected
and submitted to Mr. I. W. Stanton, of the U. S. Geol. Survey,
who identified them as a species of Physa. All the specimens
collected apparently belong to the same genus. Physa is a common
genus of fresh water gastropods, which according to Zittel
ranges from the Upper Jurassic to the present. Stanton1 says,
"In America we have a number of Tertiary and Cretaceous
species, the oldest one known to me being found in the Bear River
formation of southwestern Wyoming in approximately the position
of the Dakota sandstone. I think there is no record of Physa
in the Morrison formation, but it would not be surprising if it
should be found there since the Morrison does contain Lymnaea
and Planorbis, both of which are commonly associated with
Physa at the present time."
The horizon from which the specimens came is below the
basal beds of the Dakota as exposed along Tarryall Creek, and is
therefore probably Morrison.
As already pointed co.it, the whole series is probably the
stratigraphic equivalent of beds in the Boulder district, beginning
with the Fountain and extending up to the Dakota, but any attempt
at further correlation is unsafe.
There is apparently an unconformity at the top of the series.
While no unconformable contacts could be found, the difference
in the direction of strike of the two formations is notable. The
lower beds strike in general a little east of north and the Dakota
strikes slightly west of north, except near the lower end of Tarryall
Gulch, where there is a change in the direction of strike to the
northeast.
Lithologically the Upper Tarryall consists of dark red sandstones
and shales, which in the upper half gradually grade into
the brighter red beds referred to above. Many of the sandstone
beds are coarse and quartzitic, but almost invariably these are
interbedded with finer grained micaceous beds, which in turn
pass into sandy shales with mica flakes along the bedding planes.
Ripple marks and cross bedding may be observed in numerous
exposures, and in the dark red shales, pits resembling rain drop
prints are common.
lPersonal communication.

22 THE TARRYALL DISTRICT
The sandstone members are here and there streaked with
pebbles of white quartz, and pinkish feldspar, rather haphazardly
distributed throughout the quartz sand. Many of them show evidence
of fracturing and subsequent healing of these fractures
with quartz. The pebbles are not abundant enough to call the
rock a conglomerate, but rather tend to make it a pebbly sandstone.
Quartz and feldspar are the most abundant constituents,
but mica is locally abundant.
No limestone, except that in the cases above mentioned, was
noted in this series, but on the surface in several places were
found a number of boulders of a bluish gray to black limestone,
containing veins of secondary calcite. Whether these represent
masses broken off from ledges not now exposed, or whether they
are boulders that have been derived from beds of the Lower
Tarryall which outcrop higher up on the mountain side can not
be definitely stated. The topographic position of the boulders
was such that they might have originated in either way, but lithologically
they are identical with the rock from which the fossils
were obtained. In places outside of the area limestones are
known to occur in this formation, so that it is entirely possible
that the boulders may have come from outcrops not exposed.
Much of the section has been greatly altered by metamorphism
due to the intrusion of large numbers of sills. This has resulted
in the formation of epidote and garnet, accompanied by
loss of the red color, and a general silicification which renders
the rock quartzitic.
The apparent thickness of the sedimentary series has been
enormously increased by the sills. This feature, together with
the lack of definite boundaries, prevents an accurate statement of
the thickness. Moreover, there is the possibility of repetition of
beds by faulting. In view of these difficulties only an approximate
estimate of thickness can be given, and this is provisionally
put at about 6,000 feet, including the igneous material which
probably amounts to about 1,000 feet. Assuming that this thickness
is correct, there are in the neighborhood of 11,000 feet of
sediments and igneous sills between the Weber formation and
the Dakota sandstone. The maximum thickness apparently occurs
in the vicinity of Mt. Silverheels, and from here north to
Boreas Pass there is a gradual thinning of the section. At Hoosier
Pass, Ransome1 has estimated the thickness at about 6,000 feet,
lProf. Paper, U. S. Geol. Survey, No. 75, p. 29, 1911.

SEDIMENTARY ROCKS 23
but in the southern part of the Breckenridge area he gives 1,
as the maximum thickness for the Wyoming, and states that if
the Maroon and Weber are present they are included in the Wyoming,
which a short distance north of Breckenridge also disappears,
allowing the Dakota to rest directly on pre-Cambrian with
no intervening beds.
Color of the Tarryall Series
A detailed examination of the red shales and sandstones of
these beds, in the field, and in the laboratory both megascopically
and microscopically shows that the red color is due to films of
ferric oxide, coating the sand grains. The quartz, feldspar, and
other constituents are not in themselves red. When seen in
thin section, the quartz appears colorless, and the feldspar white
or slightly pinkish. Mixed with them, of course, are a number
of grains which are much more reddish, but on the whole the
red color is not inherent in the individual grains but rather in
the thin films which surround them, and to some extent also
in the cerpenting material which binds them together. In many
instances, ferric oxide itself is the cement and in other cases calcite
and silica, impregnated with ferric oxide, form the binder.
In a few cases it may be noted that white calcite cementing material
surrounds grains which are coated with a film of ferric
oxide. Where the constituent grains of the formation are of such
a nature as to permit penetration of ferrugenous solutions, the
red coloring matter may be seen along lines of weakness, (i. e.
cleavage or fracture), or if the material is porous, the whole mass
may be impregnated.
From these observations, it is apparent that the red color is
not inherent in the original material, and that it was not formed
until after the sediment had come to rest, and is therefore secondary.
If it had been formed as a result of oxidizing conditions
on the original land mass, the thin films would have been removed
by grinding and attrition during subsequent transportation.
Furthermore, it seems likely that the sediments were laid down
in an inland sea or land-locked basin, where the water contained
a large amount of ferric hydroxide, brought in by streams draining
adjoining land areas in which rocks containing iron were
undergoing erosion. The ferric hydroxide in such waters would
be precipitated around the sand grains before consolidation,
partially cementing the sand. During the process of consolidation

24 THE TARRYALL DISTRICT
ferric hydroxide might also be included in calcareous and sil
ceous cementing material. Upon dehydration it becomes red,
especially where the salinity is high, hence the red color of the
sediments. The final consolidation may have occurred at a later
time when the highly ferruginous sea had disappeared and uncolored
calcite was deposited between the iron-coated grains.
That some red beds may be formed by the erosion of pre-existing
red formations is of course possible, but it is not believed that
this takes place on a large scale, since transportion would result
in a loss of the film of ferric oxide. Furthermore, it is not likely
that red beds such as those under discussion would be formed on
land. This would require deposition as large, broad, alluvial fans.
Had this been the case, one would expect to find characteristic
fan structures, such as great variation in thickness within narrow
limits, and a strikingly linear lensing of beds. These structures
are conspicuously absent, and the great extent both laterally and
vertically argues against such origin. It does not seem likely
that formations of such extent as the Tarryall series could have
been deposited as dry deltas with such uniformity.
In conclusion, the presence of red limestone lenses in the
series seems to indicate periods of subaerial erosion. It is hard
to conceive of conditions under which limestones and red beds
could be formed simultaneously. Therefore, it is believed that
the red limestone lenses represent either local unconformities or
surface oxidation and that the red color in the limestone is the
result of the change from ferrous to ferric iron, while exposed at
or near the surface. This process of change was observed going
on in several places. Near the surface the limestone beds were
decidedly red, but with depth the red color gradually gave way
to grays, greens, and blues. Furthermore, a case was noted
where a red limestone showed in a valley wall. A short distance
away in beds that had suffered no dislocation or other disturbance
a shaft was sunk to a horizon below the outcropping red limestone.
At the corresponding level there was a grayish blue limestone,
entirely devoid of red, showing that the high color was
due simply to surface oxidation.
This same line of reasoning does not apply, however, to sandstones
and shales. Numerous oases are on record where no
change is noted in color of such formations. The red beds are
just as red below the surface, even to great depths where surface
oxidation could not possibly have been active, as they are at the

SEDIMENTARY ROCKS. 25
surface, indicating that their color is not due to surface oxi
but to processes in operation at the time of deposition, or shortly
thereafter.
In the neighborhood of igneous intrusions, ferric oxide is
locally reduced by magmatic solutions with a loss of color but
accompanied by the formation of epidote and garnet.
The Dakota Sandstone
This formation outcrops in an almost continuous belt from
the southeast corner of the area, northwest to Boreas Pass. In a
few places, it i's interrupted by faulting, or cut out or covered by
igneous material. It forms the top of Little Bald Mountain in
the southeast corner, where it lies on top of a porphyry intrusion.
Along the north side of the mountain it forms a prominent eastward
dipping hogback, which continues northward with no interruption,
except for the gap cut through it by Tarryall Creek. At
a point about opposite Halfway station, on the Colorado and
Southern Railroad, the formation has apparently been faulted and
partly cut out by a porphyry sill. From here on it passes under
Upper Cretaceous shale and porphyry, and reappears beyond the
Pass in the head of Indiana. Gulch and on the side of Warrior's
Mark Mountain.
The Dakota sandstone is generally easy to recognize and has
been quite definitely and accurately correlated over most of the
Rocky Mountain area. According to Henderson1 it is entirely
possible that the lower sandstone and part of the medial shale
members of the Dakota, as ordinarily mapped, are Comanchean.
The possibility of an inconformity at the base of the Dakota has
.alread)r been mentioned.
Over most of the area where the Dakota is exposed, it is a
hard, fine grained, grayish white, quartzitic sandstone, massively
bedded, which on erosion produces a great assemblage of huge
blocks along the scarp slopes of the exposures.
At Boreas Pass, the best exposure in the area, the Dakota
consists of three distinct members. The upper 50 feet is a massive
fine-grained buff-colored sandstone. Below this, there is
about 100 feet of sandy limestone, usually gray in color, interbedded
with a little dark shale and conglomeratic sandstone.
Below this is 50 feet more of buff sandstone, the lower part of
which is quite strongly conglomeratic.
lColo. Geol. Survey, Bull., No. 19, pp. 83-85, 1920.

26 THE TARRYALL DISTRICT
On the east side of the pass, this section cannot be recognized,
partly because the Dakota outcrops are covered by porphyry
and surface wash, so that only occasional exposures can be seen.
However, over ajl this area blocks of typical Dakota sandstone
and basal conglomerate are scattered about on the surface. This
condition is seen nearly everywhere from Boreas Pass down the
valley of North Tarryall Creek to its confluence with Middle
Tarryall. From about this point on, the Dakota outcrops in
a well-defined ridge, which becomes more pronounced all the
way down to a point below the Fortune placers, where Tarryall
Creek has cut a deep notch across the dipping beds.
There is a decided change in the character of the Dakota
from Boreas Pass along the valley of North Tarryall Creek towards
South Park. At the exposure where the section was measured
it is predominently a sandstone. East of the Pass it changes
to a hard gray or buff quartzite, and this quartzitic character is
more or less evident all the way down the valley. On the top of
Little Bald Mountain, both quartzite and sandstone phases occur.
In many places the quartzite has been brecciated and recemented
with secondary quartz, mingled with carbonaceous material which
at times is so abundant that it gives the rock a black color.
The upper beds of the Boreas Pass section can be traced
satisfactorily over most of the outcrops within the Tarryall district,
but the lower beds are not well exposed at any place. Most
of the outcrops occur in the scarp face of ridges, and the lower
beds are covered with detrital blocks of quartzite and porphyry.
Apparently, however, the succession is unlike the Boreas Pass
section. No evidence was found of the sandy limestones which
are there encountered, although the dark shale is probably present,
as are the conglomeratic beds. Interbedded with the quartzite,
near the top of the formation, in many places, particularly
on the mountain side southwest of Boreas Pass, and on the divide
between South Tarryall Creek and Jarvis Gulch, are dark
shales which contain coaly material. Throughout the upper part,
the sandstones contain carbonaceous streaks with plant remains,
most of which, however, are incapable of identification.
All along the northwest slope of Little Bald Mountain from
the head of South Tarryall Creek to the top, the surface is strewn
with large boulders of Dakota sandstone and quartzite. About
half way to the top occurs a crushed zone where the rock is much
more finely broken up and highly ferruginous and quartzitic. The

SEDIMENTARY ROCKS 27
fresh quartzite here is fine grained and grayish blue in
on weathering becomes yellowish, brownish and finally reddish.
Most of the blocks on the surface show beautiful slickensiding,
and a very high degree of polish. Apparently a fault zone extends
along the west side of the mountain and the boulders and
blocks have been dislodged from the escarpment by erosion. As
one approaches the mountain top, the blocks become larger and
more numerous, until finally on top there is nothing but a tumbled
mass of huge blocks some measuring as much as 20x30x50
feet in size. No outcrops in place were observed, all being apparently
hidden by this detritus. Where the sandstone is slightly
calcareous solution along joints and bedding planes, and on the
exposed surfaces, is pronounced. The surfaces of blocks often
present a miniature karst topography due to pitting and channeling
by the solvent action of water.
Many of the blocks show coatings of iron oxide, and the
outer portion, to a depth of as much as two inches, is impregnated
and stained with the same material, producing an effect of case
hardening or desert varnish.
The thickness, where it could be determined, ranges from
175 to 200 feet and seems to be fairly constant.
The Colorado
Both members of the Colorado formation are thought to be
represented. Fossils found in a black bituminous shale, and in
associated beds of black fetid limestone above outcrops of recognized
Dakota, were identified as typical Benton forms1. Among
those found were:
PELECYPODA
CEPHALOPODA
Ostrea lugubris, Conrad
Inoceramus labiatus, Schlotheim
Inoceramus dimidius,' White
Inoceramus fragilis, Hall & Meek
Trigonarca depressa, White
Scaphites warreni, Meek & Hall
Prionocyclus wyomingensis, Meek
lProfessor J. Bridge of the Missouri School of Mines identified fossils for the author.

28 THE TARRYALL DISTRICT
Stratigraphically higher in the series were found fragmentar
specimens of Inoceramus deformis^Meek, with attached specimens
of Ostrea congesta—Conrad, both typical Niobrara forms.
The exact position of these with respect to the Benton fossils or
with respect to the Dakota sandstone could not be determined,
since igneous intrusions have disturbed the strata considerably,
and the fossils were obtained from localities several miles apart,
with the intervening strata cut out by the igneous material.
From these fossils it seems probable that part of the dark shale
included in the porphyry on Little Mountain and nearby places is
Niobrara as well as Benton, but it is not possible to recognize
any division because of the limited extent of the outcrops, and
the disturbance to which the beds have been subjected.
The distribution of the Colorado shale is very irregular. The
largest area is near Boreas Pass. Here it consists of beds of
fine-grained gray sandstone, and a few thin limestones interbedded
with a great thickness of dark shales. Just east of Boreas
Pass there is intruded into these beds a thick porphyry sill which
constitutes the greater part of Mt. Baldy, Little Mountain, and
the other peaks which form the divide between Tarryall and
Michigan Creeks. This sill, with a number of offshoots from it,
has so disturbed the shale that no estimate of thickness could be
made.
Along the edge of South Park, in a number of places, outcrops
of black shale occur, usually more or less isolated and
largely covered by porphyry debris. On the ridge extending from
Little Bald Mountain towards Como, several outcrops are found,
and in a number of prospect holes, dark shale and black, fetid,
fossiliferous limestone can be seen. From these occurrences
some of the fossils mentioned were obtained. Another small
area occurs just at the end of the ridge between Jarvis Gulch and
Middle Tarryall Creek. This is probably the remnant of a down
faulted block, as there is evidence of considerable disturbance.
Other small patches occur here and there, included in the porphyry
which occupies the northeast part of the area, but it was
found impracticable to show them on the map. On the whole,
metamorphism of the Colorado shales has been much less intense
than that of the red beds. Along Selkirk Creek and on the
neighboring mountain sides were noted several instances of baking
and silicification, with the development of a hornstone-like
material at the immediate contact, but epidotization and garnetization
so common in the lower formations is not visible.

SEDIMENTARY ROCKS 29
In conclusion, the Colorado formation of the Tarryall district
is so disturbed and cut up by igneous activity that it does not
present its true characteristics, and attempts to divide it into
Benton and Niobrara, consistent with such division elsewhere, is
impossible. Furthermore, no accurate estimates of thickness can
be made because of igneous intrusion.
Tertiary Lake Beds
In a few places deposits were encountered that ma}' represent
Lake Beds. The best exposures are on the flanks of Little
Mountain at Boreas Pass and along the railroad track near
Marinelli's ranch.
These deposits vary from coarse conglomerates to fine sandstones,
shales and marls. The boulders of the conglomerates are
sometimes a foot or more in diameter, and consist of porphyry,
red sandstone, and metamorphosed phases of the red beds. In
color they range from dark red to greenish gray, depending upon
the color of the rocks from which they were derived. Great variation
in size of the constituents occurs within very narrow ranges,
and single beds often exhibit lateral gradation from one extreme
to the other within a few feet. Stratification is fairly well developed,
and the explanation that they were laid down in bodies of
water as delta deposits seems plausible, although they may represent
terrestial deposits. The character of much of the material,
and the gradation from coarse to fine permit either conclusion
but the presence of marls points to a lacustrine origin. While
the areal distribution of these beds is very limited, their position
and relation to the other formations is rather significant, inasmuch
as they lie with angular unconformity on the older beds
and have themselves been tilted as much as 20 or 25 degrees
from the horizontal. The importance of this fact will be treated
more fully in connection with the geologic history of the region.
Quarternary Deposits
Quarternary deposits are of no great importance in the
Tarryall district, but there is distinct evidence that glaciers once
occupied the heads of North and Middle Tarryall creeks and their
tributaries (Plates 5b and 6a).

30 THE TARRYALL DISTRICT
tWMm
'
Plate 5b. Terminal moraine in Little French Gulch.
Plate 6a. Looking north in the valley of North Tarryall creek
toward Mt. Baldy, showing the partial filling of the valley
with glacial outwash material.

SEDIMENTARY ROCKS 31
Glacial debris, mixed with stream gravels, extends all the
way down both stream valleys and is particularly abundant at
the Fortune placers and opposite Mineral Ranch Hill in Mont­
gomery Gulch, a tributary of Middle Tarryall Creek.
The glacial deposits consist of boulders of all sizes mingled
with sand, gravel, and clay in all proportions. At the junction of
Middle and North Tarryall creeks these deposits are better de­
veloped than anywhere else along the creeks. Flere can be seen
an unassorted, unstratified mass of boulders and sand, attaining
a thickness of about 40 feet. Many of the boulders show stria­
tions and grooves characteristic of glacial material, and in addi­
tion, the great majority are subangular, or planed off on one or
two sides only. Along the lower end of the ridge forming the
divide between the two creeks, occurs a terminal-medial moraine
formed at the point where the glaciers came together, depositing
irregular ridges of boulders and gravel. Below this ridge the
material has been modified considerably by post glacial stream
action, and consists in part of glacial moraine, and in part of out-
wash material which shows a rough stratification.
No attempt has been made to map the glacial deposits sep­
arately, since they are of limited extent, and are mingled in part
with stream deposits. Towards the heads of the valleys the
covering of drift is very thin, and does not hide the bedrock. In
their lower portions, the deposits are thicker, but even here bed­
rock comes to the surface in many places.
The glacial material is in general subangular, and varies in
size from coarse gravel to boulders 3 and 4 feet in diameter. Most
of the pebbles and boulders have been derived from the porphyry
intrusions and on account of superior hardness, have resisted ero­
sion better than the sedimentary rocks. Mingled with the por­
phyry boulders, are many representing the metamorphosed phases
of the sediments. Silicified sandstones and shales with epidote
and garnet are abundant, and easily recognized by the greenish
color. Micaceous sandstones of the red beds are present; and
also occasional masses of shale. Among the more unusual types,

32 THE TARRYALL DISTRICT
are cobbles and small boulders of magnetite, which undoubted
came from the veins and contact zones associated with the porphyry
intrusions. There is enough clay to serve as a binder for
the coarser material so that wherever excavations have been
made the walls stand for a time with perpendicular faces.
The glacial deposits are naturally confined to the valleys,
very largely to the middle portions, thinning rapidly towards the
heads where they are absent or covered by more recent hillside
wash. Down the stream they grade into glacio-fluvial gravels,
in which most of the placer gold has been found, mingled with
quantities of black sand.
No attempt has been made to distinguish between the socalled
terrace gravels, and the low level gravels. Both types are
found, but they are not distinctly separated because the terrace
gravels are in large part obscured by more recent hillside wash.
Petrography of the Igneous Rocks
Quartz monzonite porphyry (Plates 6b and 7a and b)
Definition. Porphries are igneous rocks which contain phenocrysts
of one or several minerals, in a finer grained or only
partly crystallized groundmass. When approximately half or
more of such a rock is composed of phenocrysts, the term porphyry
is applied, prefixed by the name of the mineralogically
equivalent holocrystalline rock. Therefore this rock having the
composition of quartz monzonite1 is designated a quartz monzonite
porphyry.
Occurrence. The greater part of the Tarryall district lying
northeast of the Colorado and Southern railroad is made up of a
great sill of quartz monzonite porphyry, intruded into the Cretaceous
shales. The same type of rock is found on Little Bald
Mountain and in many other places in smaller sills, and a slightly
different facies forms the hill within the loop of the railroad just
after crossing Tarryall Creek at the mouth of the gulch.
lThe name quartz monzonite is used in this report to include those rocks whose feldspars
cunclcit of orthoclase and plaarioclase in proportion of a third to a half orthoclase
and the remainder plagioclase. The plagioclase, however, must be of the soda-lime series.
If the feldspar is almost exclusively of the alkali variety, even though it may be in large
part albite, the rock is put in with the granites.

IGNEOUS ROCKS
Plate 6b. Large phenocryst of plagioclase from quartz monzonite porphyry,
showing strong zonal structure. The central portion is an aggregate
of quartz and feldspar. Crossed nicols, x 20.
Plate 7a. Quartz monzonite porphyry. Crossed nicols,
x 25. Shows large phenocryst of quartz partially
resorbed, and several crystals of plagioclase.

34 THE TARRYALL DISTRICT
Plate 7b. Quartz monzonite porphyry. Crossed nicols, x 25.
Shows broken plagioclase crystal and quartz partially resorbed.
Description. This rock is quite uniformly gray in color, but
variations from light gray to dark gray may be seen. Megascopically,
the texture is finely granular with a few larger crystals of
feldspar, but on the whole it does not appear to be porphyritic.
Orthoclase, plagioclase, biotite, quartz, and hornblende can be
readily recognized. Both orthoclase and plagioclase are prominent,
and the latter can easily be detected by the twinning. Biotite
leaves are common, and sometimes distinct prismatic crystals are
seen, distinguished from hornblende by the basal cleavage. Hornblende
is sparingly found in small acicular crystals. Quartz is
abundant among the phenocrysts in rounded grains, characterized
by the usual vitreous lustre which is in notable contrast with
the duller, more stony lustre of the feldspars.
Under the microscope the rock appears to be distinctly porphyritic.
The minerals observed in hand specimens constitute
the phenocrysts which are contained in a finely granular groundmass
of quartz and orthoclase, with small amounts of biotite,
plagioclase, and hornblende. It is also quite evident from thin
sections that all the minerals recognized in hand specimens belong
to the same period of crystallization, and that there is a
sharp distinction between .phenocrysts and groundmass.

IGNEOUS ROCKS 35
In thin sections of this rock, orthoclase, plagioclase (oligoclase-andesine),
quartz, biotite, hornblende, magnetite, apatite,
zircon, titanite and pyrite, are present in nearly all cases, and in
one or two, allanite was noted. In the altered varieties, in addition
to the above, calcite and a little chlorite and sericite may be
seen.
Of the feldspars, plagioclase is more abundant than orthoclase.
The crystals are subhedral to anhedral, and show twinning
according to the Carlsbad and Albite laws. Zonal structure
is common with a difference in extinction angles for adjacent
zones up to 5 degrees (Plate 6b). Judging from the index of refraction
and the extinction angle, it belongs to the oligoclaseandesine
series. Biotite and quartz are poikilitically inclosed in
many crystals, and occasionally titanite is so found. Frequently
crystals are broken, or fractured, and slightly bent, and others
show an outer rim of decidedly more acid feldspar than the interior.
The orthoclase crystals are as a rule not quite as large as
those of plagioclase. The former are cloudy and turbid, in contrast
to the clear fresh appearance of the latter. Most of the
orthoclase is untwinned, though occasionally a Carlsbad twin is
seen. Crystal outlines are subhedral to anhedral.
The quartz phenocrysts show much resorption and magmatic
corrosion. Grains with large embayments are a striking feature
under the microscope. Most of the phenocrysts show no bounding
planes, but occasionally perfect hexagonal and bipyramidal
sections are seen. Poikilitically enclosed crystals of plagioclase
and biotite are common, while around some, rims of sericite have
formed.
Hornblende and biotite generally occur in small phenocrysts
and present only the usual features. A small amount of chlorite
has formed around them, as a result of alteration. The hornblende
is usually green, and shows marked pleochroism while the
biotite is characterized by strong absorption.
Of the accessory constituents, magnetite, and perhaps ilmenite,
are most abundant. Apatite, titanite, and zircon are present
in small quantities, and show their usual habits. Not all of these
are present in every section, but they are sparingly distributed
throughout the rock mass. Allanite, a rather rare mineral, containing
several of the rare elements, was noted in a few slides.

36 THE TARRYALL DISTRICT
The groundmass of the rock is variable in appearance. In
some cases it is merely an aggregate of quartz and orthoclase,
and again it may contain also biotite and hornblende. On the
whole it is microgranitic.
Chemical Composition. The following analyses represent
the chemical composition of this rock. The specimens analyzed
came from different localities, but the similarity is marked.
SiOa
AL03
Fe203
FeO
MgO
CaO
Na,0
K26
H20+
H20—
TiO,
C02
MnO
Others
1
65.38
17.54
. 2.14
* 1.72
1.51
2.90
3.82
2.98
0.89
0.20
0.50
2
64.44
16.97
2.79
1.31
1.70
2.88
3.77
3.04
1.32
0.28
0.40
1.75
3
66.71
15.04
0.92
1.74
1.53
2.92
3.37
5.04
0.43
0.34
1.29
0.46
0.24
4
68.14
15.29
0.35
1.66
0.26
3.03
3.59
4.07
0.39
0.40
0.36
0.12
1.99
5
66.67
16.72
2.54
0.72
1.47
3.03
3.67
3.10
1.05
0.13*
0.30
6
68.34
16.96
0.44
1.62
1.94
3.12
3.25
2.49
1.12
0.05
0.40
0.26
Total 99.58 100.65 100.03 99.65 99.40 99.99
1. Quartz monzonite porphyry, near Halfway, Colo.
H. W. Mundt and A. L. Cairns, analysts.
2. Quartz monzonite porhyry, north of Halfway, Colo.
PI. W. Mundt and A. L. Cairns, analysts.
3. Quartz monzonite porphyry, Clover Mountain, Colo. •
~R. M. Butters, analyst. Crawford, R. D., Bull, Colo.
Geol. Survey No. 4, 1913, p. 158.
4. Quartz monzonite porphyry, Browns Gulch, Breckenridge
district, Colo. R. C. Wells, analyst. Ransome,
F. L. Prof. Paper U.S. Geol. Survey, No. 75,1911, p. 45.
5. Quartz monzonite porphyry, Little French Creek, Tarryall
district, Colo. H. W. Mundt and A. L. Cairns,
analysts.
6. Quartz monzonite porphyry, Mineral Ranch Hill, Tarryall
district, Colo. H. W. Mundt and A. L. Cairns,
analysts. :•• .

IGNEOUS ROCKS 37
Analyses numbers 3 and 4 represent rocks which are very
similar to the quartz monzonite porhyry here described, except
that large phenocrysts of orthoclase are an important constituent
in them. The rocks represented by the first two analyses do not
have these phenocrysts. A small mass of porhyry almost identical.with
the Etna quartz monzonite porhyry of Crawford1 and the
silicic type of quartz monzonite porphyry of Ransome2 occurs
near the eastern edge of the area and is shown on the map northeast
of Marinelli's ranch. Unfortunately this mass is entirely detached
from other porphyry intrusions, consequently relationships
could not be determined.
Other Types of Quartz Monzonite Porphyry
Besides the type above described, which is most characteristic
of the quartz monzonite porphyry, and occurs in large
masses in the areas mentioned, there are other types which represent
local variations. All of them, however, are more or less
related and transitional phases between the several types can be
found.
With few exceptions, these rocks all have porphyritic habits.
In some the groundmass can scarcely be detected megascopically,
but under the microscope it is very apparent. In others, the
groundmass and phenocrysts can be easily distinguished in hand
specimens. The phenocrysts of quartz and feldspar range in size
up to a quarter of an inch in diameter, but the majority are smaller.
Biotite and hornblende phenocrysts are invariably much
smaller. The feldspars and quartz are in general anhedral to subhedral
in outline, but the latter also occurs in euhedral crystals
and exhibits bipyramidal terminations. In some varieties, large
irregularly rounded grains of quartz are visible, and where the
rock has been much weathered it is sometimes difficult to tell
from a megascopic examination that it is not clastic.
When fresh the color of most of these rocks is light gray to
dark gray, and the luster is bright and vitreous, but as weathering
progresses the feldspars become dull and biotite and hornblende
change to chlorite. Quartz alone remains unchanged, the
bright vitreous luster contrasting sharply with the duller luster
of the rest of the rock.
lOp. Cit. pp. 155-159.
20p. Cit. pp. 44-50.

38 THE TARRYALL DISTRICT
Under the microscope, varying amounts of plagioclase and
orthoclase may be seen in the different varieties. In some, the
chief feldspar is orthoclase with but little plagioclase, and from
this type there are all gradations to those in which the two feldspars
are present in about equal quantities. Quartz varies greatly
in amount and distribution, being abundant among the phenocrysts
in some varieties, and confined almost wholly to the
groundmass in others. In nearly every case it shows considerable
magmatic corrosion. Biotite and hornblende are nearly always
present, but the former more abundantly than the latter. Among
the accessory minerals, apatite, zircon, titanite, magnetite, pyrite,
and allanite are usually found. The last named mineral is not as
abundant as some of the others, but was observed frequently. It
is probably present in small amounts in all the porphyries of the
district.
Diorite Porphyry (Plate 8)
Plate 8a. Diorite porphyry. Ordinary light, x 25. Shows altered
hornblende crystals and large phantom crystal of plagioclase.
Definition. A diorite is a granitoid rock consisting essential
ly of plagioclase and hornblende with more or less biotite and
augite, together with various other accessory constituents. Small
quantities of orthoclase are frequently associated with the plagioclase.

IGNEOUS ROCKS 39
Plate 8b. Diorite porphyry. Crossed nicols, x 25. Shows part of
large hornblende crystal and numerous small ones in the groundmass.
A diorite porhyry is a rock with the above mineral composition
but with a porhyritic texture.
Occurence. This rock is found in a sill of considerable size
near Boreas Pass. It outcrops in the valley of North Tarryall
Creek east of the Pass and forms a considerable part of Little
Mountain northeast of the railroad. Other small sills were observed
in the vicinity of Warrior's Mark and Red Mountain and
a few were encountered on Buck Mountain but none of these
were considered of sufficient size to be indicated on the map,
without undue exaggeration. It seems probable that this rock is
the equivalent of the monzonite porhyry described by Ransome1
in the Breckenridge district and which he regards as equivalent
to the diorite at the Wellington Mine.
Description. The rock is dark gray when fresh, but weathering
produces a brown iron stain over the surface. Below this
surface veneer of brown the weathered rock is greenish gray. In
hand specimens the naked eye can detect plagioclase, hornblende
and biotite. Biotite is rather uniformly distributed in small flakes
and easily detected by its glistening lustre. Hornblende, while
lRansome. F. L., Geology and ore deposits of the Breckenridge district, Colo., Prof.
Paper, U. S. Geol. Survey, No. 75, 1911, pp. 50-57.

40 THE TARRYALL DISTRICT
not particularly abundant, is conspicuous on account of its oc
currence in long slendeptohenocrysts. Frequently two such crystals
cross or penetrate each other in the form of an "X". Oc­
casionally clusters of crystals with well developed cleavage occur
sparsely distributed throughout the rock. Plagioclase constitutes
a part of both phenocrysts and groundmass. The grains are irregular
or rounded and without sharp boundaries. An unusual
feature of this rock is the presence of garnet in irregular grains
and masses. It is not abundant but small amounts may be seen
in nearly every specimen. On the whole the rock is not conspic­
uously phenocrystic to the naked eye.
Under the microscope, all the minerals identified megascopically,
can be seen among the phenocryts and in the groundmass.
The rock is distinctly porphyritic, but the groundmass is holocrystalline.
Plagioclase is the most abundant constituent. The crystals
are subhedral to anhedral but show considerable alteration to
carbonate, kaolin, and epidote, even in the freshest specimens.
Twinning according to the Albite law is common and cases
where such twinning is superimposed on Carlsbad twins may also
be seen. Some crystals which show only Carlsbad twinning
are present and together with many untwinned ones are probably
orthoclase since potash is known to be present in considerable
quantity.
Hornblende is abundant as phenocrysts and in the ground-
mass. Alteration to chlorite and epidote is very common and
associated iron oxide suggests that this also is a result of alteration
of hornblende.
Biotite is present throughout in irregular flakes, much of it
showingi alteration to chlorite and magnetite. Very few crystals
show the original boundaries but have a frayed appearance resulting
from alteration.
In the thin section very little.garnet appears, but where observed
it shows strong anomalous double refraction. It is pos­
sible that it does not represent an original constituent but has
resulted from partial assimilation of country rock by the magma.

IGNEOUS ROCKS 41
Sporadic quartz grains were noted among the accessory constituents
and apatite is present in the form of needles inclosed in
other minerals and as rods and grains in the groundmass. The
iron oxide is probably ilmenite or possibly a titaniferous magnetite
since the chemical analysis shows 1.4 percent of titania
and no titanite was seen in the thin section.
Chemical Composition. The chemical composition of the
rock shows that it lies within the range of the andesite-diorite
series. Compared with the quartz monzonite poryhyry it shows
a considerable increase in the bases and a decrease in the silica.
Potash and soda show only a slight decrease. The following
table shows the similarity between this rock and a diorite por­
phyry from the Breckenridge district.
Chemical analyses of diorite porphyries
Si02
A120,
Fe2Os
FeO
MgO
CaO
Na20
K20
H20+ .
H20—
Ti02
co2
MnO
Others
53.60
17.01
4.06
4.81
3.54
5.73
3.42
2.08
2.58
0.11
1.40
0.84
0.87
55.44
14.95
4.37
5.18
3.58
6.12
4.44
2.83
0.84
0.12
1.22
0.35
0.22
0.78
57.35
16.29
3.15
4.36
2.41
5.66
4.50
3.39
0.70
0.15
1.07
0.46
0.12
0.94
Total 100.05 100.44 100,55
1. Diorite porphyry, Boreas Pass, Colorado. H. W. Mundt
and A. L. Cairns, analysts,
2 and 3. Diorite porphyry, Wellington mine dump Breck­
enridge district, Colo. W. T. Schaller, analyst, Ran­
some, F. L., Prof. Paper, U. S. Geol. Survey, No. 75,
1911, p. 55.

42 THE TARRYALL DISTRICT
Plate 9a. Silverheels quartz monzonite porphyry. Crossed nicols, x 25.
Shows one of the few quartz phenocrysts and abundant plagioclase.
Plate 9b. Silverheels quartz monzonite porphyry. Crossed nicols, x 25.
Shows a type in which quartz is nearly absent and in which
hornblende is abundant in the groundmass.

IGNEOUS ROCKS 43
Sliverheels quartz monzonite porphyry (Plate 9)
Distribution and name. This type of quartz monzonite porphyry,
which forms a large part of Mt. Silverheels and neighboring
peaks at the head of Little French Creek, is sufficiently different
from the preceding type to warrant separate description.
Although in the field it was found impossible to distinguish between
the two consistently, some difference could be recognized.
It contains more hornblende and less quartz than the first type
and in addition contains numerous inclusions resembling a hornblende
schist. The more basic character of this rock is also
revealed in the chemical analysis which shows less silica and
alkalies and a corresponding increase in iron, magnesia and lime.
Description. Fresh specimens of this rock are gray but on
weathering readily become greenish due to the development of
chlorite and epidote. Most of the feldspar shows little cleavage
but occasionally cleavages occur on which albite twinning striations
can be detected with the aid of a good lens. Hornblende
is abundant in most specimens and small inclusions of a hornblende
rock resembling amphibolite are almost everywhere present.
Quartz is as a rule not recognizable in hand specimens and
biotite occurs but sparingly.
Under the microscope, the rock is seen to be porphyritic
with phenocrysts of plagioclase and hornblende and occasionally
quartz and biotite embedded in a fine grained groundmass of
orthoclase, quartz and hornblende. The quartz phenocrysts are
much rounded and strongly resorbed and frequently contain
poikilitic plagioclase. Magnetite is present both as an original
constituent and as a secondary alteration product. Other alteration
products are epidote and chlorite, both abundantly present,
the former derived from plagioclase, and the latter from hornblende
and biotite.
All specimens examined show considerable alteration, even
those which in hand specimens look fresh. In some cases the
changes have advanced so far as to obscure the primary minerals
with a host of secondary products.
The plagioclase, as determined by the index of refraction and
by extinction angles, belongs to the andesine-labradorite series.
Twinning after the Albite and Carlsbad laws is common, but

44 THE TARRYALL DISTRICT
much of it is obscured by epidote and other secondary products
The form of the plagioclase varies from anhedral to subhedral
with a few nearly euhedral forms enclosed in grains of quartz.
A large part of the groundmass consists of a fine grained
aggregate of quartz and a feldspar, presumably orthoclase, while
small irregular grains of hornblende make up most of the remainder.
The hornblende is usually brownish or yellowish green, and
shows pleochroism to various shades of green. It shows considerable
alteration especially to chlorite and is often surrounded by
dark rims containing magnetite. This alteration is particularly
noticeable in the phenocrysts.
The chemical composition of a representative specimen of
this type from the top of the divide at the head of Little French
Creek is as follows :
(H. W. Mundt and A. L. Cairns, analysts.)
sio2
Al2Os
Fe203
FeO
MgO
CaO
62.51
17.49
2.52
2.80
2.27
5.08
Na20
K,0
I-LO+
H20—
Ti02
MnO
3.31
1.80
0.66
0.08
0.70
0.36
99.58
Comparison of Igneous Rocks of Central Colorado
The igneous rocks of the Tarryall district are part of the
same petrographic province that the rocks of neighboring areas
belong to. Thus, for instance, in the Breckenridge district Ransome1
has distinguished three principal types, a quartz monzonite
porphyry, a monzonite porphyry, and a quartz monzonite porphyry
of intermediate type. He has also pointed out the fact
that they are all closely related and correspond to certain parts of
a continuous series, and has further shown that they are in turn
related to similar rocks of the Tenmile and Leadville areas.
lProf. Paper U. S. Geol. Survey, No. 75, 1911, pp. 43-62.

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Scale: SiOc~i;AleO,°i Diagram Showing. Variation In Composition' Or Igneous Rocks

IGNEOUS ROCKS 45
In the Leadville district, Cross1 described six main varieties
which, however, were classified on a purely local basis depending
in part upon the type of alteration which they exhibit, but investigation
shows that at least one of them, the Lincoln porphyry,
extends beyond the area and is encountered elsewhere. Patton2
in the Alma district and Howell3 in the Twin Lakes area have
described rocks which as far as mineralogic composition is concerned
might very well be closely related to those here dealt with.
Cross4 has shown the similarity between the Lincoln, Elk Mountain
and Quail porphyries of the Tenmile area, and in a recent
paper Crawford5 has pointed out the relationships between a
large number of rather widely separated occurrences of a monzonite
porphyry over a considerable area in Central Colorado and
has suggested that they are related to the Princeton quartz monzonite
batholith.
With this in mind, the writer has brought together a number
of analyses of rocks from neighboring areas, and attempted to
show graphically the relationships and similarities between them
and the rocks of the Tarryall district6. The accompanying charts
were constructed by plotting the percentages of silica as ordinates
and the percentages of the other oxides as abscissas, for each of
the analyses (Plate 10).
SiO.,
AL03
Fe203
FeO
MgO
CaO
Na20
K20
H,0+
H20—
Ti02
co2
MnO
Analyses of Rocks from Tarryall District
(H. W. Mundt and A. L. Cairns, analysts.)
1
65.38
17.54
2.14
1.72
1.51
2.90
3.82
2.98
0.89
0.20
0.50
2
64.44
16.97
2.79
1.31
1.70
2.88
3.77
3.04
1.32
0.28
0.40
1.75
3
53.60
17.01
4.06
4.81
3.54
5.73
3.42
2.08
2.58
0.11
1.40
0.84
0.87
4
66.67
16.72
2.54
0.72
1.47
3.03
3.67
3.10
1.05
0.13
0.30
5
68.34
16.96
0.44
1.62
1.94
3.12
3.25
2.49
1.12
0.05
0.40
0.26
6
62.51
17.49
2.52
2.80
2.27
5.08
3.31
1.80
0.66
0.08
0.70
0.36
Totals 99.58 100.65 100.05 99.40 99.99 99.58
iMonograph, U. S. Geol. Survey, Vol. 12, 1886, pp. 323-333.
2Bull. Colo. Geol. Survey, No. 3, 1912, pp. 62-94.
3Bull. Colo. Geol. Survey, No. 17, 1919, pp. 42-72.
4Fourteenth Ann. Report, U. S. Geol. Survey, Pt. 2, 1894, pp. 165-241.
sCravvford, R. D., A contribution to the igneous geology of central Colorado, Am.
Jour. Sci., 5th series, Vol. VII, 1924, pp. 365-388.
eRansome, F. L., Geology and Ore Deposits of the Breckenridge district, Colorado,
Prof. Paper U. S. Geol. Survey No. 175, 1911, pp. 60-62; and Crawford, R. D., Geology
and Ore Deposits of the Monarch and Tomichi districts, Colorado, Bull. Colo. Geol.
Survey, To. 4, 1913, pp. 185-194.

46 THE TARRYALL DISTRICT
1. Quartz monzonite porphyry, near Halfway, Tarryall district,
Colorado.
2. Quartz monzonite porphyry, north of Flalfway, Tarryall
district, Colorado.
3. Diorite porphyry, Boreas Pass, Tarryall district, Colorado.
4. Diorite porphyry near Boreas Pass, Tarryall district,
Colorado.
5. Quartz monzonite porphyry, Little French Creek, Tarryall
district, Colorado.
6. Quartz monzonite porphyry, Mineral Ranch Hill, Tarryall
district, Colorado.
The analyses of rocks from the Tarryall district were made
for this report. The other rock analyses plotted in the following
diagrams were taken from pages 186 to 189 of bulletin No. 4 of
the Colorado Geological Survey, by R. D. Crawford.
For convenience of reference the names and localities are
here reproduced.
1. Quartz diorite. Shoshonose. Lost Mountain.
2. Andesite. Shoshonose. Jennings Gulch.
3. Quartz diorite (monzonitic) Shoshonose. Monarch.
4. Pomeroy quartz monzonite. Amiatose. Pride of the
West tunnel, Pomeroy Mountain.
5. Quartz latite porphyry. Toscanose. Mohammed tunnel,
Middle Fork.
6. Etna quartz monzonite porphyry. Toscanose. Clover
Mountain.
7. Princeton quartz monzonite. Toscanose. Taylor Mountain.
8. Quartz monzonite gneiss. Toscanose. Jennings Gulch.
9. Granite. Liparose. Browns Gulch.
10. Porphvrite. Yellowstonose. Storm Ridge.
11. Diorite. Tonalose. Brush Creek.
12. Porphyritic diorite. Yellowstonose. Mount Marcellina.
13. Hornblende-mica porphvrite. Adamellose. Cliff Creek.
14. Quartz porphyrite. Amiatose. Mount Carbon.
15. Quartz porphyrite. Lassenose. Crested Butte.
16. Rhyolite. Toscanose. Round Mountain.

IGNEOUS ROCKS 47
17. Rhyolite. Alsbachose. East Mountain.
18. Diorite porphyry, Andose. Wellington mine, Breckenridge
district.
19. Hornblende-mica porphyrite. Andose. Buckskin Gulch,
Leadville district.
20. Diorite porphyry. Andose. Wellington mine, Breckenridge
district.
21. Diorite porphyry, McNulty type. Lassenose. Tenmile
district.
22. Quartz-hornblende-mica porphyrite. Yellowstonose.
Gold hill, Tenmile district.
23. Quartz monzonite porphyry. Amiatose near Yellowstonose.
Mount Guyot, Breckenridge district.
24. Biotite porhyrite. Tonalose. North Mosquito Amphitheater,
Leadville district.
25. Granite porphyry. Toscanose. Jefferson tunnel, Tenmile
district.
26. Lincoln porphyry. Lassenose. Mount Lincoln, Leadville
district.
27. Diorite porphyry. Yellowstonose. Copper Mountain,
Tenmile district.
28. Quartz porphyrite. Toscanose. Sugarloaf, Tenmile district.
29. Quartz monzonite porphyry. Amiatose near Toscanose.
Brewery Hill, Breckenridge district.
30. Gray porphyry. Yellowstonose. Johnson Gulch, Leadville
district.
31. Quartz monzonite porphyry. Toscanose. Browns Gulch,
Breckenridge district.
32. Quartz porphyrite. Lassenose. Chicago Mountain, Tenmile
district.
33. Granite porphyry. Toscanose. McNulty Gulch, Tenmile
district.
34. White porphyry not fresh). Riesenose. California Gulch,
Leadville district.
35. Mount Zion porphyry. Toscanose. Prospect Mountain,
Leadville district.
36. Nevadite. Liparose. Chalk Mountain, Leadville district.

48 THE TARRYALL DISTRICT
A study of these variation diagrams shows quite clearly that
most of the rocks are quite closely related and that very probably
they all belong to the same general period of volcanism. It is to
be expected that minor variations should occur, but the general
similarity is quite apparent. Such variations as do occur are no
greater than those often encountered in rocks within the same
intrusive mass.
The diagrams further show that the difference between rocks
of the six districts are no greater than those between rocks of
the same region, and from a chemical standpoint it is manifest
that all belong to the same petographic province. Mineralogically
the same resemblance is noted. This is especially to be seen
in the presence of the same accessory minerals, such as apatite,
zircon, allanite and titanite, and in the percentages of the different
feldspars.
In detail, the diagrams show that the amounts of the several
constituents vary irregularly. Apparently, there is no uniform
change in any direction. For example, as one constituent in a
rock increases, another one decreases, but in the next rock perhaps
an entirely different constituent shows a decrease. It is to
be noted, however, that alumina and the alkalies remain quite
constant throughout the series.
Crawford1 has discussed the occurrence and distribution of
the Princeton quartz monzonite, and has pointed out rather conclusively
that many of the apparently isolated stocks are in reality
only high points of the same plutonic intrusion which he refers
to as the Princeton batholith. In view of the close chemical
similarity of the porphyries to the Princeton quartz monzonite,
the present writer believes that the Princeton batholith is the
plutonic mass from which the sills came and that it underlies
most, if not all, of the area under consideration.
Age Relationships of the Porphyries
The age relation of the several kinds of porphyry is a difficult
one to settle. While in a few places there is. an apparent gradation
from one to another, in man}- other places they occur as
separate, distinct sills. Moreover, most of the porphyries occur
as sills in the sedimentary rocks, and do not cut one another;
hence it is impossible to tell which is the older. A number of
dikes of small size occur which cut the sills and therefore are
younger.
lOp. cit.

GEOLOGIC HISTORY 49
Structural Features and Geologic History
General Structure and Deformation
The most common conception of the structure of the Rocky
Mountains in central Colorado is that of two approximately parallel
axes of uplift, the one to the east marked by the present
Colorado or Front range, and the other to the west by a series
of ranges often referred to as the Park ranges, and between
these a series of depressions now known as parks. This uplift
took place before the Paleozoic since the oldest sedimentary
rocks of the region, the Cambrian, lie unconformably upon the
Archean. These two land masses remained areas of erosion for
a long time, and contributed very largely to the thick sedimentary
series now resting upon their flanks, a series which extends from
Cambrian to Cretaceous, and which shows no great angular unconformities,
therefore indicating that during all this time the
region was apparently free from major dynamic movements.
Following the deposition of the Cretaceous beds, and marking
the close of the Mesozoic era, there was another period of
uplift, during which the Rocky Mountain region was uplifted to
about its present position, after which erosion continued and
beds of later age were laid down locally with angular unconformity
on the Mesozoic strata.
Such post-Mesozoic beds are found in the Tarryall district,
but it was impossible to determine their exact age. That they
are post-Cretaceous is evident because of their structural relations
to beds known to be of that age but whether they are Tertiary or
Quaternary can not be told. Their significance lies in the fact
that they have been tilted to an angle of about 20 to 25 degrees
from the horizontal. It might be argued here that this inclination
is original dip and represents the angle at which the sediments
were laid down. If it is initial dip the conditions of deposition
must certainly have been very unusual. Initial dips of 8
degrees and more are known to occur in torrential deposits and
the writer measured dips on accumulations of hydraulic mining
debris deposited in water which were even a little larger, but it
is doubtful whether initial dips of 20 degrees or more exist in
stratified or even partially stratified deposits. Furthermore, the
fact that these beds grade into, and are interbedded with marls,
is incompatible with the assumption that they are torrential de-

50 THE TARRYALL DISTRICT
posits. In consequence we are led to the conclusion that they
have been tilted from their original position during a period of
deformation subsequent to the revolution marking the close of
the Cretaceous.
The exact date of this deformation cannot be determined in
this area. In other parts of the Rocky Mountain region similar
tilting of post-Cretaceous beds has been noted and there is some
indication that it may have occurred during Miocene time but
there is also evidence in other areas of tilting and faulting after
the first glacial period. In conclusion it may therefore be said
that although the age of the tilting movement cannot be settled
there is evidence of at least one period of disturbance following
the Cretaceous revolution.
Structural Features of the Tarryall District
In the area under consideration we are concerned chiefly
with the western uplift mentioned above, and the depression between
it and the eastern uplift. The ancient western land mass
is now represented by the Sawatch range, and the depression is
known as South Park. The present topographic boundary on
the west side of the park, the Mosquito Range, is not part of the
original uplift but was formed at the close of the Cretaceous.
During most of Paleozoic and Mesozoic time, the present
site of South Park was an area of deposition and extended a considerable
distance farther west than its present boundary. The
Archean land-mass to the west furnished much of the material
for the thick sedimentary beds of this portion of central Colorado
which range in age from Cambrian to upper Cretaceous. They
were laid down in a gradually advancing sea as is shown by the
numerous overlaps of younger formations on the pre-Cambrian
and on the whole show but little interruption of deposition. The
lithologic character of the beds indicates deposition in shallow
water, near shore. Although typical conglomerates are not abundant,
pebbly streaks in the coarse sandstones are widely distributed
and together with ripple marks and crossbedding bear witness
of such deposition.
The general structure is that of a huge monocline, the initial
eastward dip of the sediments having been greatly increased by
the post-Cretaceous uplift which resulted in the formation of the
Mosquito range. In detail, however, the structure is far from a
simple monocline, as faulting and igneous intrusion have greatly

GEOLOGIC HISTORY 51
complicated it. On the west in the Leadville and Alma districts
the basal beds of the Cambrian rest on the pre-Cambrian but to
the north there is progressive overlap until just north of Breckenridge
the Dakota sandstone rests on the pre-Cambrian. The
eastern boundary of this tectonic block is somewhat obscure.
Opposite the Tarryall district it is covered by the sediments in
South Park and farther north, opposite the Breckenridge area,
faulting has brought Cretaceous beds into juxtaposition with pre-
Cambrian. Apparently the whole block has been rotated around
a north and south axis to the extent of 20 to 25 degrees since the
deposition of the Dakota.
Sedimentary beds on the west side of the Mosquito range
probably represent strata at one time continuous over the range
but subsequently cut off by faulting and erosion. Still further
west these beds are cut by the Mosquito fault described by
Emmons1. According to Ransome2, the Breckenridge area presents
similar conditions. He says,—"the sediments of the Breckenridge
area once extended across the line of the present Tenmile
range and were continuous with those of the Tenmile district.
Whether prior to their erosion, the beds swept uninterruptedly
up over what it now the crest of the range until they reached the
Mosquito fault, or whether they were stepped down by intervening
faults, has not been determined."
Porphyry Intrusions
The sedimentary rocks have been very intricately intruded
and greatly disturbed by igneous material in the form of irregular
sills. In a rough way these have followed the bedding but in
many places the intruded mass was so great that the original
attitude of the beds has been obliterated and new structures imposed
upon them by the igneous material. Beds originally in
contact have been separated and forced into entirely different relation
with each other. As a rule, the overlying bed has suffered
a considerable change in the angle of dip and locally also in the
direction of strike. The structure on the whole appears laccolithic,
except that instead of being horizontal as in the ordinary conception
of a laccolith, it is inclined at an angle of about 30 degrees.
During the process of intrusion many of the adjacent beds
were broken up and fragments of these may still be seen scattered
lTenmile district special folio (No. 48), Geol. atlas U. S., U. S. Geol. Survey; Geology
and Mining industry of Leadville, Colo., U. S. Geol. Survey, 1898, Vol. 12, 1886.
2Ransome, F. L., Geology and Ore deposits of the Breckenridge district, Colo. Prof.
Paper U. S. Geol. Survey, No. 75, 1911, p. 63.

52 THE TARRYALL DISTRICT
in the porphyry as inclusions. In other places faulting accompanied
the intrusive processes. Such was the case on Little Bald
Mountain where the Dakota is found on top of the mountain at
an elevation of over 11,500 feet while a short distance north in
the general line of strike on the side of the mountain, it lies at an
elevation of about 10,000 feet. The two outcrops are separated
by a mass of porphyry which was intruded just below the Dakota
and lifted up a large block of it producing a structure resembling
a bysmalith. On the north, west and south sides of the mountain,
the presence of large numbers of slickensided blocks suggests
faulting which probably occurred at the time of intrusion. The
fault along the west side of the mountain apparently continues
northeastwardly towards Halfway, although it cannot be traced
continuously, and beyond this point it is covered by porphyry.
Evidence of other faulting was seen in a number of instances
but it was found impossible to work out the relations without a
more detailed base map.
Inclusions in the Porphyry
A conspicuous feature of nearly all exposures of porphyry is
the large number of inclusions or segregations, consisting principally
of hornblende. These may represent actual fragments of
older rock which the magma picked up on its way towards the
surface, or they may represent differentiation products from the
magma. Petrographically the evidence favors the first view.
Most of the fragments examined are apparently metamorphic
rocks of the hornblende schist or amphibolite class. Hornblende
with biotite, quartz and feldspar are the chief constituents and
these show the same parallelism of arrangement characteristic of
schists. The writer is of the opinion that many of these inclusions
are fragments of pre-Cambrian metamorphic rock brought
up from below by the magma. A comparison of these inclusions
with specimens of pre-Cambrian amphibolites showed a striking
resemblance between the two. Mineralogically and texturally
they are so nearly alike that they can hardly be told apart. Additional
evidence that they are fragments of the pre-Cambrian
metamorphic series is shown by two specimens which the writer
found embedded in porphyry. These specimens are water-worn
pebbles, the one a hornblende schist % by 2% by 2% inches in
size and the other a highly contorted and intricately crumpled
feldspar, biotite gneiss, 2 by 3 by 4 inches in size. Both specimens
are such as can be seen in great numbers along any

GEOLOGIC HISTORY 53
stream in an area of metamorphic rocks. Their position in
the porphyry removes all doubt as to the manner of transportation.
They must have been picked up by the magma on its
way to the surface. Whether they were picked up from the original
pre-Cambrian terrane or whether they came from a conglomerate
bed somewhere in the sedimentary series cannot be determined.
The evidence is in favor of the latter view since pebbles
of pre-Cambrian granites are abundant in the conglomerates and
there is no reason why pebbles of gneiss and schist could not
occur in the same way. Also, since they show no contact effect,
one is lead to the conclusion that they were not transported far
by the magma. In sharp contrast with the absence of contact
effect upon these pebbles, is the effect produced on numerous
other inclusions. One can see all steps in a gradation from the
unaltered types to those whose former presence can now be inferred
only from a local, abnormal abundance of hornblende or
biotite. Between these two extremes many excellent illustrations
of partial assimilation may be observed. In nearly all cases the
original rock seems to have been one rich in hornblende and biotite
and therefore it is assumed that they came originally from
the pre-Cambrian.
Relative Ages of the Porphyries
The several types of porphyries are very intimately associated
and apparently grade into each other. No definite line of
contact was noted anywhere and it is impossible to determine
the relative ages except possibly in the case of the Little Bald
Mountain sheet. If this porphyry intrusion was the cause of
faulting as it appears to be, it is earlier than the intrusions northeast
of Halfway, which appear to cover the fault. However, on
account of large quantities of talus it was impossible to determine
whether the fault was actually covered or whether it merely died
out. There are, however, a number of dikes of minor importance
which cut both sediments and porphyries and are therefore later.
Age of Deformation and Intrusion
As above mentioned the initial deformation of this part of
central Colorado took place in pre-Cambrian time and throughout
most of Paleozoic and Mesozoic time there were land masses on
both sides of the area under consideration and the site now occupied
by the Mosquito Range was submerged and receiving

54 THE TARRYALL DISTRICT
sediments from neighboring land areas. Following the depositio
of the Cretaceous formations a great diastrophic movement took
place which folded and faulted and raised this area high above
the sea. Presumably the porphyries were intruded during this
period of deformation but whether during the early or late stages
cannot be determined definitely on account of insufficient evidence.
Such evidence as is available indicates that at least some
of the igneous activity occurred in the early stages. Cases were
noted where the porphyry partook of both folding and faulting,
but on the other hand the majority of cases show no conclusive
evidence that they participated in either folding or faulting.
Contact Metamorphism
The effect of igneous intrusion upon surrounding rocks depends
upon a number of factors among which are the size and
character of the intrusive, and the character of the country rock
which it invades. Other things being equal, subjacent igneous
masses produce considerably more metamorphism than the injections.
In the Tarryall district, since most of the intrusions
belong to the injection type, there has been little of the typical
contact effect. It is true, however, that conspicuous changes of
varying degrees of intensity may be seen over most of the area.
The rock alongside the larger sills shows all stages of change
from incipient metamorphism to a complete baking and indurating.
The development of new minerals is confined largely to
epidote, garnet, specularite, magnetite and actinolite. Accompanying
the metamorphism there has been a change of color in the
red beds, which are now a dull green, mottled with brown owing
to the formation of epidote and garnet. In some places the ferric
oxide which gives the red color to the formation has been recrystallized
into specularite. Actinolite is often formed in tufts
along the bedding planes and in cavities along with epidote.
In most instances these changes are not the result of direct
contact with the igneous rock but are more or less uniformly
distributed throughout a great thickness of sandstone and shale
in such a way as to produce a decided banding. It is thought that
the altered bands represent portions of the original rock more
susceptible to change by hot solutions and vapors coming from
a body of magma at greater depth or that they mark those layers
which were more porous and therefore afforded better opportunity
for solutions to circulate. In other words, the visible

GEOLOGIC HISTORY 55
effects represent only the fading out stages of much more intensive
changes nearer to the body of magma where the solutions
were necessarily more potent.
Great thicknesses of strata have been changed from original
argillaceous sandstones and shales to a rock resembling quartzite
and hornfels. Concurrently epidote and garnet were formed,
producing a hard, dense, brownish-green banded rock, which is
very resistent to erosion. In most cases there are no distinct,
recognizable crystals of either garnet or epidote but the whole
mass is impregnated with very finely disseminated grains of these
minerals. Such garnetized and epidotized sedimentary rock is a
conspicuous feature of much of the Tarryall formation. As a
rule all gradations may be seen from gray-green, hard, siliceous
shale to solid masses of garnet-epidote rock. On Mineral Ranch
Hill this is accompanied by micaceous specularite, in both the
shale and sandstone layers.
Metamorphism of considerable local intensity was observed
near the heads of Little French Creek and Montgomery Gulch.
Here a heavy garnet zone has been formed containing besides
garnet, much magnetite and calcite. This garnet zone occurs
along the contact of a calcareous shale with a thick sill of quartz
monzonite porphyry. A partial analysis of the garnet shows that
it is of the andradite variety. Since all the iron was determined
as ferric iron, the result is a little too high. Undoubtedly some
is present in ferrous form and this would reduce the total amount
as shown in the analysis. No alkali or manganese determinations
were made.
Partial Analysis of Garnet from Little French Creek
(A. L. Cairns, analyst)
Si02
A1203
Fe203 )
FeO )
CaO
MgO
H20+
H20—
34.61
5.14
29.56
31.72
0.63
0.13
0.09
101.88

56 THE TARRYALL DISTRICT
In texture it varies from granular massive to fine crystallin
The largest crystals observed'here were less than three-fourths
of an inch in diameter, but these were exceptional and rare. Most
of the deposit is fine grained and massive. Under the microscope
anomalous double refraction is common.
The magnetite associated with the garnet is also massive.
Occasionally octahedral crystals having a maximum size of
about a quarter of an inch occur in calcite. In the upper part of
Montgomery Gulch a massive magnetite zone about two feet
wide has been prospected in a number of places but all were
abandoned and only such material as was on the dump could be
studied. Assays show that it contains traces of gold and silver.
On the whole, metamorphism such as is found at actual contacts
is absent but a large part of the area shows evidence of a
thorough soaking or saturation with solutions and vapors given
off by a large body of magma at greater depth. If the Princeton
batholith underlies this area, as is thought to be the case, it is
probably the source from which the solutions came along with
the numerous sills.
Economic Geology
The history of mining in the Tarryall district has already
been reviewed. As previously stated, most of the old workings
have been abandoned for many years, and as nearly all are inaccessible
because of caving, very little could be learned from them.
In consequence, discussion of economic features must be confined
to surface indications, supplemented here and there by'such information
as may be gathered from the old dumps.
Character of the Ores
Most of the ore observed around the old workings consists
of magnetite and pyrite, carrying small amounts of gold and
silver. Garnet and epidote are present in much of it, and occasionally
a little chalcopyrite is found. On Mineral Ranch Hill, in
addition to the minerals mentioned, a ferriferous variety of sphalerite,
resembling marmatite, is present in considerable quantity.
Native gold in quartz is said to occur in veins, but none was observed.
That it does occur, however, is witnessed by the placers
alone the creek. No record of tonnage or value of ores shipped
from the district is available anywhere, hence it is not possible to
give any exact figures as to production. Rumors are current that

ECONOMIC GEOLOGY 57
the ore shipped ranged from 15 to 30 dollars per ton. On the
other hand, it is also said that some ore was shipped which did
not bring sufficient returns to pay the freight.
Mineralogy of the Ore and Gangue
Gold. While no specimens containing native gold were
noted, it is quite evident that it occurs in the district, since a considerable
quantity has been taken from the placers. Most of the
placer gold was in form of fine flakes, more or less angular and
in general showing but little effect of transportation. Reports as
to the findings of large nuggets are numerous, but none seem to
be very authentic. According to the best information available,
very few nuggets of any size were found. A careful microscopic
study of the magnetite-pyrite ores from veins has not revealed
gold, although fire assays prove that it is there.
Sulphides
Pyrite. This mineral is widely distributed in small quantities
in some of the porphyries. It was noted in the quartz monzonite
porphyry in the vicinity of Halfway, and farther north and
northeast in the porphyries that cap the divide between Tarryall
and Michigan creeks, and also in some of the sills on Mount
Silverheels. It forms an important part of the veins that have
been opened up in numerous prospect holes, and is associated in
considerable quantity with the contact magnetite deposits. Much
of it is massive, but here and there well formed cubes and pentagonal
dodecahedrons may be seen.
Chalcopyrite. This sulphide of iron and copper was not noted
in any appreciable quantity, but in the ores on Mineral Ranch
Hill small irregular grains ma}' be seen mixed with pyrite and
sphalerite. Possibly some of the pyrite is copper bearing, as the
peacock colored tarnish so common on chalcopyrite is seen on
much of the pyrite. Copper has been reported, but only as a
negligible constituent, in some of the ores of the district, especially
on Mineral Ranch Hill.
Galena. Lead sulphide is present in small quantities and
carries a little silver. Not enough galena is present to constitute
an ore, although its silver content adds to the value. In every
instance noted, it was fine grained and associated with pyrite and
quartz. The principal localities where it was seen were in the
workings of the Silverheels Tunnel Company, and in an abandoned
tunnel on the southeast side of Mineral Ranch Hill.

58 THE TARRYALL DISTRICT
Sphalerite. This mineral is perhaps the most abundant sulphide
noted, especially in the ore from the Illinois Central Consolidated
Tunnel on Mineral Ranch Hill. It is found principally
as coarsely crystalline aggregates, associated with pyrite, magnetite,
and quartz, and as fine grained disseminations in vein matter.
Most of it is a black ferriferous variety, with a reddish brown
streak, to which the name marmatite is applied. It is said to
carry small values in gold and silver, but most of the determinations
show that the precious metals are associated chiefly with
pyrite and magnetite.
Oxides
Quartz. This is a very common constituent of nearly all the
rocks in the district, but in addition to its occurrence as a rock
forming mineral, it is also present as a gangue mineral in some
veins. It forms an important part of the gangue in a number of
veins on the west side of Montgomery Gulch, and is found associated
with orthoclase in the Silverheels tunnel, but in most of
the other prospects it is conspicuously absent.
As a rock forming mineral, it is abundant. In some of the
porphyries, it forms bipyramidal phenocrysts up to three fourths
of an inch in length, and in addition shows prism faces ranging
in width from the merest line up to an eighth of an inch.
Hematite. Specular hematite is abundant in some of the
metamorphosed sedimentary beds. Especially interesting are the
occurrences on the west side of Mineral Ranch Hill, where flat
rhombohedral crystals of hematite from a quarter of an inch to
three quarters of an inch in diameter are found along the bedding
planes of metamorphosed shales. Micaceous varieties are also
common in some of the sandstones, and are associated with
epidote, garnet and calcite.
Magnetite. Magnetite occurs abundantly in veins and metamorphosed
sediments, intimately associated with garnet, epidote,
calcite, and pyrite. It is the principal constituent of most of the
ores, and can be found in considerable quantities on the dumps,
at many of the tunnels and prospect holes. At some of the old
mill sites many tons of ore, chiefly magnetite, can still be seen.
According to reports most of the values in gold and silver were
found in magnetite.

ECONOMIC GEOLOGY 59
As a general rule it occurs massive with but little tendency
towards crystalline structure, but in the workings at the head of
Little French Gulch and in the neighborhood of the Baxter Mine
at the head of Montgomery Gulch, distinct octahedrons a quarter
of an inch in diameter are found associated with calcite and
garnet.
Boulders and nuggets of magnetite are found abundantly
in the gravel along the creek. These undoubtedly came from
veins outcropping higher up on the mountain sides and were
brought down to their present position by the streams and by
the glaciers. Black sand, which is largely magnetite, is also very
abundant and may be seen along the streams, even out on the
plains of South Park.
Limonite. This mineral, which is one of the common products
of oxidation of any mineral containing iron is everywhere
present in the oxidized zone and needs no special mention.
Carbonates
Carbonates, except calcite, are rare. Small amounts of azurite
and malachite were seen as stains on ore minerals, and small
amounts of oxidized siderite were noted. Calcite is of widespread
occurrences, having been formed during metaphorism of the sediments.
Intimately associated with it are garnet and epidote.
Usually it is massive, but always shows its usual cleavage. In
some of the epidotized rocks, it is green, due to included epidote,
and except for its cleavage might easily be mistaken for that
mineral.
Silicates
Only a few of the silicates need special mention here, as they
have already been described in the section on petrography.
Garnet. Garnet formed during metamorphism of the sediments,
is so abundant that it deserves special mention. It is
present in small quantities near all of the igneous intrusions, but
a particularly heavy garnet zone has been developed near the
head of Little French Gulch. From here it extends northward
and southward parallel to the strike of the beds, and can be seen
in a number of places along the mountain sides. It has been
considerably prospected, but, judging from the character of the
workings, proved valueless. In the material thrown out on the

60 THE TARRYALL DISTRICT
dumps, magnetite, epidote, and a little quartz were intimately
associated with the garnet. Most of it.is massive or granular,
but occasionally crystalline masses and well-formed individual
crystal's were found. Under the microscope, between crossed
nicols, it frequently shows anomalous double refraction in zones
parallel to the' trapezohedral faces. A chemical analysis shows
that it is probably the variety andradite. (See analysis on page 55).
Epidote. Epidote is perhaps the most widely distributed
silicate, exclusive of those which occur as primary minerals in the
igneous rocks. It has been abundantly developed by metamorphism
in the red sandstones and shales, and as a result of its widespread
dissemination, it has given a decidedly greenish color to
the rocks. Wherever the development of garnet and epidote has
been noted, it has been accompanied by a loss of the red color of
the sediments.
Orthoclase. This feldspar was found in large masses with
graphic intergrowths of quartz, on the dump of the Silverheels
tunnel but as the workings had caved, nothing could be learned
of its occurrence. In appearance it resembles that found in pegmatite
dikes.
Types of Deposits
Since the old workings are at present inaccessible, very litt
could be learned as to the real character of the ores or the
types of deposits represented. Such material as was found on
the dumps at various prospects indicates two principal types,
(1) deposits related to contact action showing replacements of
country rock along bedding planes; and (2) fissure fillings with
a quartz gangue. Both types of deposits are found in the area
around the headwater of Middle Tarryall Creek, which has been
the center of nearly all the active prospecting in the district. In
addition to these types, mention must also be made of the placers
along the streams.
Deposits Related to Contact Action
Under this heading will be included those deposits which
though not formed directly at the contact of igneous intrusions
with surrounding rock are nevertheless thought to have been
formed as the result of solutions and vapors given off by the
magma.

ECONOMIC GEOLOGY 61
This type of deposit was noted on Mineral Ranch Hill where
the Illinois Central Consolidated Mining and Milling Company
has driven a tunnel nearly 1500 feet long to explore it. The ore
body said to have been cut by the tunnel is at present inaccessible
because of caving but material thrown out on the dump showed
replacement of calcareous shales and sandstones and thin limestones
as well as porphyry by pyrite and sphalerite. Garnet,
epidote, magnetite and specularite are associated with the ore in
var).ing quantities. The ores carry a little gold and silver and
traces of copper. The sphalerite is dark brown to black and is
probably the ferriferous variety known as marmatite. It varies
in texture from fine crystalline to massive and is rather intimately
associated with pyrite. Evidence that the ore bearing solutions
entered along bedding planes and other lines of weakness is seen
in the much greater percentage of ore minerals near such lines
of weakness than elsewhere. There is no sharp line of contact
between the ores and the wall rock but a gradual decrease in the
amount of ore may be seen away from the channel of access.
Many other small deposits that belong to this type were
observed but most of them carried no sphalerite. The most
common constituent is magnetite which carries small quantities
of gold. Shipments of this ore are said to have run from 20 to
30 dollars in gold per ton with a little silver. Reports of richer
ore in some of the workings are current but could not be verified.
Many attempts were made in the past to mill and concentrate
the ore. The results of the various projects can be judged from
the many abandoned mills and stamps which give silent testimony
in the form of ruins. At one time a smelter was built in
Montgomery Gulch in an attempt to recover the valuable metal
from the ores and concentrates at the mine to avoid heavy freight
charges, but it too resulted in failure.
Fissure Veins
Along with the deposits just described are some which are
termed fissure veins because as a rule they represent a different
type of deposit. They carry none of the minerals of contact
origin noted in the preceding type but on the other hand they
consist mainly of quartz and pyrite. All of those observed were
narrow and probably represent fissure fillings as there was no
evidence of replacement of wall rock. Apparently the}- are later
than the contact-replacement type described, since they cut across

62 THE TARRYALL DISTRICT
these. No actual cases could be studied but the information
obtained from specimens on the dump showed that there was no
replacement effect at the crossing. In all the cases observed
there was a sharp clean break, which had subsequently been filled
with quartz.
These quartz veins are said to carry small amounts of free
gold and they are looked upon as the sources from which the
placer gold was derived. As a result they have been persistently
followed but as yet the hopes of the prospectors have not been
rewarded with success. Either the richer parts of the veins have
been entirely removed by erosion or else the real source of the
gold has not yet been found.
Gold Placers
The most productive placer workings were the Fortune,
Roberts and Peabody claims in the lower part of Tarryall Gulch
and the Mineral Ranch Hill and Liebelt placers on Little French
Creek. The material of these placers consists very largely of
stream worn sand and gravel together with glacial debris. The
sedimentary series with interbedded sills forms the bed rock on
which the gravel rests. As these beds dip down-stream they form
natural riffles behind which the gold particles collect.
Very little could be learned as to the amount of gold recovered
from these gravels or as to yield per yard. All work has
ceased and only the abandoned sluices and pipe lines bear witness
to the activities of former days.
The earliest means of exploitation was with shovel and pan,
and later the rocker was added, to lessen the labor and increase
the output. Drifting in the gravel just above the bedrock floor
was resorted to in all the important placers and later, the Fortune
Placers Gold Mining Company introduced hydraulic washing.
For a number of years they operated with varying success but in
1917 the cost became too great and work was abandoned. Meanwhile
the ranchers of South Park had an injunction served on
the company restraining them from further work, because the
silt and sand washed downstream clogged their irrigation ditches.
Prospecting for placer ground has very largely been carried
on by means of pits but no systematic attempts have ever been
made. A large part of the valley above the Fortune Placers offers
an excellent opportunity for prospecting and may prove to be

ECONOMIC GEOLOGY 63
rich enough to permit exploitation. Similarly a large area at th
mouth of Tarryall Gulch, where the Creek flows out on the plains
of South Park will bear further prospecting. This is so situated
that it can be handled with a dredge, provided the gravel contains
sufficient gold to warrant such an installation.
Genesis
Such ores as occur in this district are very largely associated
with rocks in which epidote, garnet, magnetite and specularite
have been formed. These minerals are very commonly of contact
metamorphic origin, even though they may not always occur
directly at the contact. As has already been pointed out, in spite
of the fact that no very intense changes are found in rocks at the
contact with the porhyry sills, there has nevertheless been a
great amount of change brought about in the sedimentary rocks,
by solutions or gases of magmatic origin which permeated and
penetrated a great thickness of strata. This change is manifested
by the formation of garnet, epidote, magnetite, specularite and
other minerals. Since the same set of minerals are found associated
with the sulphides it is entirely reasonable to assume that
all came from the same source. Moreover, they are very intimately
associated in a way that suggests contemporaneous deposition
or possibly overlapping periods of deposition. Silicates
and oxides were deposited first, followed by sulphides and these
in turn followed by more sulphides.
It does not appear likely that the metamorphic changes in
the country rock of the Tarryall district can all be attributed to
the quartz monzonite porphyry sills but rather that some of the
changes resulted from the escaping materials from a large batholith
which is thought to underlie the area. If this is true it also
probably is true that the ore bearing solutions came from the
same batholith at the same time. In fact it is impossible to draw
a line between the formation of metamorphic minerals and ores.
The conclusion that these ores were deposited from solutions
rising from a deep lying batholith is therefore strengthened, and
although they are not contact metamorphic deposits, stricth'
speaking, they partake of some contact action.
The ore in the veins probably came from the same source at
a slightly later period, perhaps during the final stages of solidification
of the batholith. The fissures are not thought to be related
to major faulting as no great displacement is apparent.

64 THE TARRYALL DISTRICT
The time of mineralization can not be determined from the
limited area studied. Undoubtedly it occurred after the intrusions
of quartz monzonite porphyry had taken place but whether it
occurred before or after the folding and uplift cannot be determined
definitely. There is no evidence to show conclusively
whether the porphyry sills participated in the folding or whether
they were intruded afterwards.
Future development
If the origin of the ore deposits has been correctly interpreted
and if a great batholith underlies the area and furnished
the solutions which deposited the ores, there is no great probability
of encountering deposits of valuable ore at lower depth. In
accordance with the recognized zonal distribution of the metals
around intrusive rock bodies, sulphides of copper and zinc are
among the first to be deposited and occupy positions nearest to
the intrusive. Above and beyond these would come lead and
silver ores and still farther out from the intrusive one would
expect silver and gold ores. If this distribution holds true it can
be seen that the deposits above described belong to the first zone
and therefore it does not appear likely that very large or valuable
deposits will be found at depth even though the limestones which
are heavily mineralized at Leadville and Alma, dip eastward and
are found under the younger strata in the Tarryall district.
The future of the Tarryall district probably lies in more
systematic prospecting of the gold placers. There is still a considerable
amount of placer ground which might be handled by
improved methods and up-to-date equipment.

VITA.
GARRETT A. MUILENBURG
Orange City, Iowa, Sept. 17, 1889.
Northwestern Classical Academy, Orange City, Iowa.
State University of Towa, 1908-191:3 (B.A. 1912, M.S. 1913)-
University of Missouri, 1913-1914.
Columbia University, 1923-1924.
Missouri School of Mines and Metallurgy (E. M. 1925).
Scabbard and Blade, 1913.
Sigma Gamma Epsilon, 1921.
Sigma Xi, Columbia University, 1924.
Phi Kappa Phi, Missouri School of Mines, 1925.
Tau Beta Pi, Missouri School of Mines, 1925.
Instructor in Geology, Colorado School of Mines, 1914-1916.
Instructor in Geology, Missouri School of Mines, 1916-1917.
Assistant Professor of Geology, Missouri School of Mines, 1917
1921.
Associate Professor of Geology, Missouri School of Mines, 1921-
PUBLICATIONS
*.
Precious stones in the drift; Iowa Academy of Science, Proceedings
for 1914.
Manganese resources of Colorado, Bull. Colo. Geol. Survey, No.
15, 1919.
Field methods in petroleum geology (McGraw-Hill Book Co.,
New York), 1921 (joint author).