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Dames & Moore, 1999 - USDA Forest Service

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Other geologic units in the deposit area include:<br />

a An anhydrite (CaSO,) lens which was mapped for 120 feet along strike, immediately<br />

overlying the original hanging wall. The anhydride was described as a light gray, purple<br />

tinged mass, banded with the amphibolite host.<br />

a Occasional bands of marble and limesilicate granulites, with a composition of 5 percent<br />

qua* 30 percent plagioclase, 30 percent diopside, 20 percent grossularite<br />

(Ca3A12Si3012), and 10 percent calcite, with minor wollastonite (CaSi03).<br />

6.1.13 Occurrence of Significant Sulfide Minerals<br />

The primary sulfide minerals in the Holden Mine ore deposit occur in the following forms:<br />

a Pyrite - abundant in mineralized zones, and as disseminations in the argillites. In the ore<br />

zone, it is highly brecciated, with corroded 'kdges. Outside of the ore zone, cubes of<br />

pyrite are "not uncommon."<br />

a Pyrrhotite -Abundant within ore zone, generally massive in form.<br />

a Sphalerite - gradational phases between disseminations and massive replacements in the<br />

footwall of the ore zone: Sphalerite has a high iron content, and approaches mannatite<br />

(Zn-FeS) in composition. It is concentrated in the east-end of the mine.<br />

• Chalcopyrite - Concentrated in the central part of the mineralized zone, varying from<br />

massive to disseminated. Replaces and/or heals fractures in pyrite and pynhotite.<br />

6.1.1.4 Conclusion<br />

The conclusions from the review of mineralogical information are:<br />

The dominant sulfide minerals present at the Holden Mine are iron-based (pyrite,<br />

pyrrhotite). Weathering of these minerals is a primary mechanism of the Holden Mine<br />

Site water chemistry.<br />

a The dominant silicates are aluminum-based (plagioclase and biotite).<br />

Carbonate minerals are rare at the Holden Mine.<br />

a Non-sulfide mineralogy of the tailings is expected to be dominated by minerals contained<br />

in the diabase dykes because the dykes intersect the ore zone, whereas the mine wall<br />

rocks and waste rock are more likely to be dominated by biotite schist.<br />

6.1.2 Mineralogy of Secondary Minerals<br />

Minerals (i.e., crystalline substances) and amorphous solids produced by weathering processes are<br />

visually apparent throughout the Holden Mine Site. These include ubiquitous orange-brown iron-stains<br />

on waste rock and tailings indicating iron oxides and white precipitates observed in the 1500-level main<br />

.portal drainage (Figures 6.1-1 and 6.1-la). The latter is believed to be amorphous aluminum hydroxide.<br />

Green (copper) stain is also present on marble waste rock in the two waste rock piles near the 1500-level<br />

main portal and in the abandoned mill building.<br />

\U)M-SMI\VOLI\COMMOMWR~W)~\hoI~2\n1M).doc 6-4 DAMES & MOORE<br />

1769340541 Wuly 27.<strong>1999</strong>;4:11 -RAFT FINAL RI REPORT a<br />

C,<br />

. .-. J

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