Structure: The Bald Mountain district is located in an area of thinned crust along the eastern side of the Late Proterozoic rift that split the North American craton. It is also in the west-central portion of the Late Devonian-Early Mississippian Antler foreland basin, and near the eastern edge of deformation related to the late Paleozoic Humboldt orogeny To the west of the Bald Mountain district, geologic interpretations are dominated by recognition of Paleozoic deformation, whereas to the east, interpretations emphasize Mesozoic contraction and plutonism and Tertiary extension.

Alteration: Alteration consists predominantly of silicification, argillization, and potassic alteration.

Tectonics: The Bald Mountain district is located in an area of thinned crust along the eastern side of the Late Proterozoic rift that split the North American craton. It is also in the west-central portion of the Late Devonian-Early Mississippian Antler foreland basin, and near the eastern edge of deformation related to the late Paleozoic Humboldt orogeny.

Commodity: Ore Materials: gold Gangue Materials: quartz, pyrite, arsenopyrite, sericite, and small amounts of sphalerite, chalcopyrite, tetrahedrite and galena.

Deposit: The LJ Ridge deposit is located about a mile east of the Pits 1-5 deposits and about two miles northwest of the Top deposit area. Ore at LJ Ridge is hosted mainly by a north-south-trending structure 6 to 15 meters wide and to a lesser degree by favorable stratigraphic horizons in the Dunderberg Shale.

Deposit type: Distal disseminated Ag-Au

Development: Placer Dome began exploration on the Bald Mountain property in 1977. IN 1996, it was reported that the LJ Ridge deposit was the most recently discovered of the Bald Mountain district orebodies, after the No. 1-5, RBM, Rat, Top, Mahoney Canyon and Sage Flat deposits. Mining the LJ Ridge deposit was completed in 2000. In 2006, Barrick Gold Corp. acquired the LJ Ridge property through its acquisition of Placer Dome U. S., Inc.

Geology: Alteration comments: silicification, argillization, potassic alteration. The main alteration feature at Bald Mountain is the large halo of silicification and strong argillization. Potassic alteration is recognized at depth. Geology comments: Host rocks are calcareous shales and dark gray limestones which weather to iron-oxide stained red-brown-maroon and tan colors. Granitic intrusive with quartz phenocrysts and oxidized pyrite was noted in cut face of drill roads. Sulfur isotope studies indicate that ore fluids that formed the LJ Ridge deposit ere derived from the central part of the Bald Mountain stockigneous system.

Ore(s): Mineralization is structurally controlled. The dominant structural trend is N45W, but there are NE-, N-S, and E-W-trending structures as well. The E-W structures show the youngest period of movement, some of which is post-ore

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Standard Detailed Gallery Strunz Chemical Elements

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

ⓘ 'Tetrahedrite Subgroup'

8 valid minerals.

Rock Types Recorded

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