Dames & Moore, 1999 - USDA Forest Service

from approximately 25 to 80 feet. The bedrock surface was noted to be variable in depth, with a trough-like
feature noted to the north of Railroad Creek.
Holden Village
Based on data collected during the installation of groundwater monitoring wells in Holden Village by others
(USBM, 1995), the village area appears to be underlain by a combination of colluvium and glacial till soils.
The soils are moderately dense and consist of a mixture of silt, sand, and gravel.
Winston Home Sites
Seven test pits (DMTPW-I through DMTPW-7) were completed immediately downslope of the western
portion of the Winston home sites area as part of the underground storage tank assessment (Figures 4.1-5a
and 4.2-6b, and Appendix C). The test pits were completed to depths ranging from 3-112 to 8 feet bgs. The
excavations disclosed the soil underlying the area to consist of a mixture of relatively loose to medium
dense silt, sand, gravel, and cobbles. The subangular nature.of the soil indicated the origin to be colluvium
originating upslope and to the north of the area.
Honemoon Heights
In the area of the Honeymoon Heights, to the southwest of the mill area, the glacial till soil appears to
terminate slightly south and upslope of the 1100-level portal. Bedrock is generally exposed near or at the
ground surface above this level; a reconnaissance of the area during the RI disclosed a relatively thin layer
of soil, consisting of weathered bedrock, covering portions of the area immediately above the 1100-level.
4.2.3.2 Geology Exposed in Mine
Referring to Figures 4.2-14 and 4.2-15, which are based on the review of available underground mine maps,
the bedrock exposed in the underground mine is composed primarily of interlying sequences of
metamorphic rocks with igneous intrusives. The igneous rocks are primarily biotite-hornblende quartz
diorites and the metamorphic rocks generally consist of hornblende, schist, gneiss, amphibolite, marble, and
quartzite.
The ore body was observed to occur within an extensive pyritized shear zone in the metamorphosed
sedimentary rocks. The shear zone is one of several in the area and was found to be approximately 2,500
feet long with the width of economic mineralization up to 80 feet. The shear zone and ore body are oriented
in a nearly east-west direction, and were found to be nearly vertical. The strike of the economic
mineralization is exposed at the ground surface which allowed J.H. Holden to find it in 1887. The ore body
is situated within a rock formation named the Buckskin schists, which consists of a thick series of quartz-
amphibole schist containing two horizons of intermittent marble beds and calcareous schists (Youngberg
and Wilson, 1952). Minerals observed in the ore zone are shown on Table 4.2-la (Youngberg and Wilson,
1952). As discussed in Section 6, the mineralogy of the underground mine was confirmed by evaluating the
chemistry of the mine discharge (1 500-level main portal drainage) which was sampled and analyzed as part
of the RI.
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