Dames & Moore, 1999 - USDA Forest Service

Section I-I' and shows the six tunnels which accessed the ore body and stopes. The levels of the mine were
numbered based on the approximate elevation below an exposure of the ore body outcrop shown on Figure
4.1-5b; in other words, the exposure of the ore body is the hypothetical "0" level, with the 300-level being
300 feet lower, the 550-level being 550 feet lower, and so on to the 2500-level. The northing and easting
grid system noted on the maps were established utilizing the general strike of the ore body as the northing
line.
The six levels of the mine with portals to the surface, as well as the most laterally extensive lower level
(2325), depicted on Figures 4.1-5c and 4.1-5d, were digitized utilizing the underground mine maps
provided. Figure 4.1-5b shows all seven levels with the associated stopes and mine workings superimposed.
However, Figures 4.1-6 through 4.1 - 13 show the extent of each individual mine level (300, 550, 700, 800,
1000, 1 100, 1500, and 2325, respectively.
The map utilized to generate Figure 4.1-5c displayed the dates of mining for each of the stopes. The upper
workings (300-, 550-, and 700-levels) (Figures 4.1-6 through 4.1-8) were apparently developed during the
early periods of the exploratory efforts. The lower workings (800-, 1000-, and I 100-levels) (Figures 4.1-9
through 4.1- 1 1) were developed during the period from approximately 1920 until 1937, and included several
miles of tunnels. This corresponds to the relatively larger sizes of mine rock piles associated with the lower
workings. All of the portals, except for the 300 level, were timbered.
When Howe Sound purchased the mine, they increased access to the underground mine workings by
installing a primary tunnel at the 1500 level. Referring to Figures 4.1-5b and 4.1-12, the opening to this
tunnel was constructed near and to the west of the uppermost level of the mill building. The tunnel was
initially installed by timber supporting the approximately 60 to 70 feet of glacial soil encountered at the
portal. The remainder of the tunnel was drilled and blasted with limited rock bolt support to intersect the ore
body approximately 2,500 feet to the southwest. A track was placed on the floor of the tunnel to allow the
use of ore cars which transported the non-mineralized rock to the west and east waste rock piles. The tunnel
was driven at an incline of approximately one-half percent to take advantage of gravity when the ore cars
were filled in the mine (McWilliarns, 1958).
Once the ore body was intersected, the tunnel turned and continued to the northwest approximately another
2,500 feet before daylighting out to the west at the 1500-level ventilator portal (Figure 4.1-12). The maps
indicate that the last approximately 300 feet of the tunnel was timbered through glacial soil. This tunnel was
utilized to provide ventilation throughout the mine. Air was piped in through the 1500-level main portal and
then exhausted through the 1500-level ventilator portal; an 8-foot-diameter fan was originally installed in
the opening (Edrnond, 1972). Based on a civil survey completed as part of the RI, the ventilator portal was
found to be approximately 20 feet higher than the 1500-level main portal. This indicates that the one-half
percent grade continues for the entire length of the tunnel from the 1500-level main portal.
The majority of the mine tunnels at the different levels were generally constructed outside the ore body,
within the surrounding rock which, based on the mine maps, had relatively low concentrations of economic
minerals. The rock removed during the construction of the tunnels, after the 1500-level main tunnel was
completed, was generally placed in two piles developed to the west and east of the mill. The tunnels within
rock were constructed without timber support; however, rock bolts were utilized where necessary. The
1500-level was utilized to explore the lateral extent of.the ore body; the maps reviewed indicate that the
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17693-005-019Uuly 19. 1999:4:51 PM:DRAFT FINAL RI REPORT