Dames & Moore, 1999 - USDA Forest Service

strength was determined by Hart Crowser to range from 34 degrees for the medium dense sand, to as much
as 38 degrees for the silt.
Approximately 85 percent of the tailings was reported to consist of insoluble silicate minerals. The
relatively soluble Fraction appears to consist largely of sulfide minerals, with only minor amounts of marble
(calcium carbonate) (Thorsen, 1970). The sulfides were also reported to consist of pyrite (FeS), sphalerite
(ZnS), and chalcopyrite (CuFeS2) (PNL, 1992). As discussed in Section 6, the mineralogy of the tailings
piles was confirmed by evaluating the chemistry of the seeps and groundwater sampled and analyzed as part
of the RI.
Waste Rock
Waste rock is present in two large piles at the Site, one pile is located to the east of the mill building, the
other directly west of the building. The piles cover a few acres and based on the results of the seismic
refraction survey (Appendix A) range in thickness of up to about 70 feet. Smaller piles are associated with
the 1100, 800-, 700-, 550-, and 300- level portals in the Honeymoon Heights area. The volumes of two
waste rock piles near the mill building are estimated to be 250,000 cubic yards. The combined volume of
the Honeymoon Heights waste rock piles are estimated to be less than either of the west or east waste rock
piles. The waste rock consists of angular rock, ranging in grain size from mostly cobbles to some silt and
gravel. The rock is oxidized with some minor economic mineralization observed.
The detailed composition of the waste rock material is unknown, although visual inspection during the RI
indicates that they consist of some mineralized ore-type material containing pyrite, sphalerite and
chalcopyrite mixed with host alumino-silicate rods and some marble. A detailed discussion of the
mineralogy of the host rocks and ore deposits is provided in Section 6.1.
Alluvium/Reworked Till - ..
A laterally extensive gravel unit, herein named the alluviumlreworked till unit, is indicated by boring logs
throughout the Site south of Railroad Creek. The unit is logged in borings which penetrate the base of the
tailings piles, except for borings TP3-4 and PZ4A (Appendices B and E) at the southwest comer of tailings
pile 3; at this location, the unit presumably underlies the colluviuh logged at the base of those borings.
The alluviumlreworked till unit is described in various boring logs as a relatively loose to moderately dense
silty gravel, a gravelly silty sand, and a gravel. The unit grades into or interfingers with the alluvium of
Railroad Creek. The precise location of the contact is not known. Thickness of the alluvial reworked till
ranges from approximately 5 to 15 feet based on boring logs.
Glacial Till
Dense glacial till underlies the Site on both sides of Railroad Creek. Based on evaluation of geophysical
data (~~pendix A) the till appears to range in thicknessqfrom about 5 feet (adjacent to Railroad Creek, along
seismic line F-F') to about 95 feet (south of tailings piles 1 and 2 in Copper Creek drainage, at the southern
end of seismic line G-G'). The only Site boring that penetrates the dense till at the Site is boring TPI-4A.
While the boring log is incomplete, it does indicate that the dense till becomes dry with depth. Till at the
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17693405-019Uuly 19, 19W4:51 PM;DRAFT FMAL RI REPORT