Hollister deposit (Ivanhoe/USX; Butte; Velvet; Clementine), Ivanhoe Mining District, Elko County, Nevada, USAi

Regional Level Types
Hollister deposit (Ivanhoe/USX; Butte; Velvet; Clementine)	Deposit
Ivanhoe Mining District	Mining District
Elko County	County
Nevada	State
USA	Country

Structure: The deposit occurs along the northern projection of the Carlin Trend, just south of the Midas Trough.

Alteration: The deposit is affected by silicification, argillization, and propylitization. The ore is generally argillized beneath a barren near surface silica cap. The ore is also locally silicified. Tuffaceous rocks are altered to quartz, chalcedony, kaolinite, adularia, and alunite. The andesite is altered to montmorillonite, nontronite, and chlorite, and is crosscut by fractures which contain silica, pyrite, and adularia.

Commodity: Ore Materials: native gold grains. quartz, chalcedony, kaolinite, adularia, alunite, montmorillonite, nontronite, chlorite, calcite, sulfosalts, very fine-grained pyrite Gangue Materials: quartz, chalcedony, kaolinite, adularia, alunite, montmorillonite, nontronite, chlorite, calcite, sulfosalts, very fine-grained pyrite

Deposit: In the sulfide zone, gold is associated with pyrite, marcasite, and trace amounts of chalcopyrite, cinnabar, stibnite, realgar, tetrahedrite-tennantite, and sphalerite. Arsenopyrite, covellite, galena, millerite, and pyrrhotite have also been tentatively identified. In the oxidized zone, gold is associated with goethite and limonite. Gold occurs as discrete native gold particles attached to or included in pyrite and marcasite or their oxidized equivalents. Gold is not encapsulated by silica.

Deposit type: Hot-spring Au-Ag

Development: The opalite at the mine site has been used for toolmaking by native Americans for some 8000 years. Prospecting of the surface mercury showings began at the turn of the century. Between 50 and 150 flasks of mercury were produced from 1915 to 1917. The district was idle from 1918 to 1929. From 1929 to 1943, 1032 flasks were produced from the Butte #1, Butte #2, and Clementine mines. Other mines in the district produced a total of less than 1000 flasks. Auric Metals drilled 100 shallow rotary holes around the Velvet Mine for mercury in 1969-70. APCO Oil drilled a porphyry molybdenum target during the 1970's. Noranda drilled a core hole in 1980 on a uranium target. Homestake explored for a McLaughlin-type gold deposit in 1979-80. Placer Amex drilled several rotary holes in 1982 for Au, Ag, and Hg. In 1984, Kennecott drilled 13 rotary holes for gold in the area. From 1980-86, United States Steel Corp. Completed detailed geologic mapping, rock chip and soil geochemical grids, and geophysical surveys over the Hollister deposit area. Anomalous surface rock chip assays at the extreme southwestern end of the deposit led to drill intercepts of ore grade gold in 1982. USSC completed 123,031 ft. of drilling (195 rotary and 33 core holes), then sought a JV partner or buyer for the property in 1986. Touchstone acquired the property in 1987 and a JV with Galactic was formed later that year. By the end of 1987, Touchstone had completed 240 holes for 127,950 ft. of drilling. A feasibility study was initiated in 1987. Continued drilling identified four mineralized zones that correspond closely with historic mercury mines. Mining commenced in 1990 and continued through 1995. In 2005, Great Basin Gold Ltd.(50%) announced that the access decline at the Ivanhoe Project has now intersected the Gweniver Vein system at a depth of roughly 2,720 feet from the portal.

Geology: The south boundary of known ore is controlled by an arcuate east-trending, near-vertical fault. Siliceous lake bed sinter occurs only north of this fault (probably a caldera margin fault). Alteration is best developed on N-S trending faults. Hg, As, Sb, and Tl all form geochemical haloes that extend above the gold deposit.

Ore(s): The gold is closely related to mercury-bearing sinter and associated silicification that resulted from hot spring activity. The ore is semi-concordant and favors the disconformity between the Valmy Formation and the overlying tuffs and andesite in the lower portion of the volcanic sequence, and fractures in quartzite and argillite of the Valmy Formation. Local gold concentrations are controlled by the intersections of prominent northeast, northwest, and minor east-west striking structures.

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Link to USGS MRDS:	10310531

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References