Geology of the Storm Gold-Silver Deposit, Elko County, Nevada
AuthorTrotman, Richard Bryan
AdvisorThompson, Tommy B
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The Storm deposit is a high-grade gold deposit located near the convergence of the Carlin Trend and Northern Nevada Rift. Mineralization is primarily hosted within brecciated and ferroan-dolomite altered carbonates of the Silurian-Devonian Bootstrap Limestone Formation and to a lesser extent within Jurassic lamprophyre dikes. The deposit is a sedimentary rock-hosted gold deposit that contrasts with other Carlin-type deposits in that it is overprinted by younger low-sulfidation epithermal silver veins. Two successive mineralizing events are recognized and include a replacement style, gold-rich event characterized by decarbonatization, silicification, and sulfidation of carbonatebearing strata with gold-bearing pyrite and native gold; and quartz-sulfide-selenide epithermal vein style silver mineralization with no visible, altered selvages.The genesis of Storm deposit is complex and begins with pre-Mesozoic ferroandolomite alteration of carbonate rocks within the Dee Fault and along the contact between the Silurian-Devonian Bootstrap Limestone and the Devonian Popovich Formation. Emplacement of lamprophyre dikes and sulfidation of iron-bearing rocks during the Jurassic resulted in the creation of abundant pyrite that was the foci for subsequent gold-bearing hydrothermal fluids during the Eocene Carlin event. Gold ishosted by arsenic rich rims on pyrite with lesser amounts of hypogene native gold grains. Silicification temporally and spatially overlaps gold mineralization and is the dominant alteration type. Silver-bearing, quartz-pyrite-selenide veinlets overprint gold-dominant Carlin mineralization and resemble those found in other epithermal vein deposits associatedwith the Miocene Northern Nevada Rift. An apatite fission track date of 20.8 Ma from a dike within the main deposit supports a Miocene age for the silver values. Post-ore collapse brecciation as well as calcite ± barite precipitation during the Pliocene locally modified gold-bearing breccia bodies.