n Alas - Alaska Division of Geological & Geophysical Surveys - State ...

Smaller placer mines ere active on Valdez Creek
itseJf and several of its tributaries. Values in th$
Valdez Creek drainage range from $4.00 to $15.00/m
(at $400.00/troy oz of gold). Gold from the Valdex
Creek area is typically oatmeal size, smaller, and
commonly much flattened with rounded edges. Colors
range from lemon yeUow to a rich golden brown and
reddish brown (iron stained). Gold was panned as far
east as Pass Creek on the extreme east boundary of
the Healy quadrangle.
Several small lode-gold mines are located in the
surrounding Clearwater Mountains. These lodes and,
possibly, other undiscovered lode-gold deposits in the
area are most likely the source for the placer gold in
the Valdez Creek drainage.
An area of the old Bs~lfield milling district,
described by Cap@ (1912), lies at the north edge of the
Healy quadrangle. Mining operations on Totatlanika
and Platt Creeks, near the north-central boundary of
the quadrartgle, and on Portege Creek in the northwest
corner of the quadrangle are small scale and generally
employ 2 to 5 people per opration.
Capps (1912, p. 43) pointed out that the workable
plscers in this northern district have all been found in
areas that drain terrain presently or originally covered
by the upper Tertiary Nenana Gravel, and he postu-
lated that rw * * doubtless a reconcentration of the
gold from these gravels has produced most of the pres-
ent placer deposits, although sorne gold may have been
contained In the Iower Tertiary beds and have been re-
concentrated * * *." This would seem to be a correct
assessment of the gold source in this area, substanti-
ated by the fact that I panned gold from the Lignite
Creek Formation-Nenana Gravel (Tertiary formations)
contact near where the main highway to Fairbanks
crosses Panguingue Creek. Ln the Mount Hayes quad-
rangle, directly east of the Healy quadrangle, gold is
present in conglomerate of early Tertiary(?) age
(Yeend, 1981). It seems increasingly clear that gold
has been recycled through the Tertiary continental
deposits before its incorporation into the Holocene
placers throughout much of interior Alaska.
REFERENCES ClTBD
Capps, S. R., 1912, The Bonnifidd region, ALaska: U.S.
Geological Survey Bulletin 501, 64 p.
Smith, T. E., 1970, Gold resource potential of the
Denali bench gavels, Valdez Creek mining dis-
trict, Alaska, & Geological Survey research
19 7 0: U.S. Geological Survey Professional Paper
700-D, p. D146-D152.
-1981, Geolcgy of the Clearwater Mountains, south-
central Ahka: Alaska Division of Gmlogical
and Geophysicd Surveys Geologic Report 60, 72
P.
Yeend, Warren, 1981, Placer gold deposits, Mount
Hayes quadrangle, Alaska, Albert, N. R. D.,
and Hudson, Travis, eds., The United States Geo-
logical Survey in Alaska: Accomplishments
during 2979: U.S. GeoIogical Survey Circular
853-13, p. B68.
Pmmian plant megafoe& fmm the eongbmerate of
MoantDen,aenfral~~
Only a few occurrences of late Palemoic plant
megafossils ere known in Alaska. Before the discovery
of Permian pplant fossils in the co lomerate of Mount
Dall in the central Alaska Range"$reviously assigned
to the Middle Pennsylvanian by Reed and Nelson, 1977,
19801, no credible Pennsylvarian or Permian plants had
been reported. The sole report of a Pennsylvanian
Calamites arnbwus fragment from the Alaska Penlnm
w a l d , 1871, pl. 4, fig. 9) has never been propedy
corroborated. Sparse but slgnlficant Devonian
plants have been documented (Mamay, 1963; Churkin
and others, 1969), and smdl but stratigraphically informative
collections of Early Mississjppian plants are
made occasionally, especially in the Brmks Range.
The paleotmtany of the Pennsylvanian and Permian of
Alaska, however, has been enigmatic until recently.
This report describes a small collection of plant fossils
that provides a limited but intriguing insight into that
late Paleozoic hiatus.
These fossils were colleoted in 1976 by B. L.
Reed, B. L. Detterman and S. W. Nelson while investigating
the geology of the Talkeetna quadrangle in the
central Alaska Range (area 12, fig. 44). The fossiliferous
shale and siltstone are exposed south of the Denall
fault, about 5.2 krn N. 26' E. from Mount Dall (at lat
63°25r52u N., long 152 11'40" W., in the SE1/4NW1/4
sec. 23, T. 29 N., R. 16 W., Talkeetnn C-5 quadrangle)
at about 1,525-m elevation. They occur within a thick
(min 1,500 m) sequence of chiefly terrestrial conglomerate,
sandstone, ~Lltstone, and shale. The unit consists
largely of massive lenticular beds of conglomerate and
sandstone, with numerous cut-and-fill channels; the
top is not exposed. This unit bas been informally
called the conglomerate of Mount Dall by Reed and
Nelson (1977). The lower part is believed to be gradational
downward into a depositionally and structurally
complex terrane of mostly marine flyschoid sedimentary
rocks containing fossil marine invertebrates of
Devonian, Mississippian, and Pennsylvanian age ( ~eed
and Nelson, 1977). Before the 1976 investigntions in
the Talkeetna quadrangle, the sedimentary rocks south
of the Denali fault in the Mount Dall area were regarded
8s part of a sequence of upper Mesozoic graywacke
and qillite, and any unit of conglomerate was
assurn& to be Late Creteceous or Tertiary. The fossil
plants discussed here, however, establish a late Paleozoic
age and a continental origin for at least parts of
the conglomerate of Mount Dall. The conglomerate
and flyschoid sediment are part of the Mystic tectonostratigraphic
terrane (Jones and others, 1981).
The fossils, which were found in the upper half of
the conglomerate, are most abundant in a hard finegrained
dark-gray irregularly bedded matrix. About 20
small to mediumsize slabs Iapprox 4-30 crn in maximum
dimension) containing discernible plant parts constitute
the collectjon. Some of these slabs contain
only n single leaf fragment; others hove sufficiently
abundant interbedded plant parts to suggest the original
presence of a fairly luxuriant growth of vegetation
near the site of deposition. All the specimens are
fragmentary; the largest Is 28 cm long by 2 cm wide.