Rat Deposit, Bald Mountain Mining District, White Pine County, Nevada, USAi

Regional Level Types
Rat Deposit	Prospect
Bald Mountain Mining District	Mining District
White Pine County	County
Nevada	State
USA	Country

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. NW-striking normal faults that dip steeply west and east, with lesser N-striking faults.

Alteration: The porphyry dikes were sericitized, argillized and silicified.

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: free gold Gangue Materials: pyrite, clay, limonite, jasperoid, quartz

Deposit: The deposit is hosted in the lowermost part of the Dunderberg Shale. Ore was structurally controlled and adjacent to and locally within NW-striking dikes of quartz-feldspar porphyry. Interbedded limestone and siltstone are altered to marble and hornfels adjacent to the dikes. Silicification and decalcification are concentrated in the lower Dunderberg above its contact with the underlying Hamburg, and in faults and fractures in the Dunderberg. The Hamburg is silicified along bedding and fracture networks in the Rat deposit. Pervasive sericitization and weak argillization (mainly supergene) affected the dike, and spotty silicification is along the margins of the dike and in the adjacent Dunderberg. Fine-grained disseminated gold is associated with silica, clay, carbonaceous material, iron oxides, and secondary iron-arsenic minerals. Ore zones are characterized by quartz veining, stockwork formation, and silicified breccia. The ore zone is overlain b a blanket of barren remobilized carbon.

Deposit type: Distal disseminated Ag-Au

Development: Placer Dome began exploration in the Bald Mountain mine area in 1977 and the Rat deposit was discovered by 1978. In 1993, mining started in the Rat pit. In 2006, Barrick Gold Corp. acquired the Rat property through its acquisition of Placer Dome U. S., Inc.

Geology: The Rat deposit has a low to non-existent base metal signature with higher Hg, As, and Sb values. The Rat deposit is characterized by Au, As, and Sb; the deposits are Au rich, with high Au/Ag ratios, values of As to about 2,000 ppm and Sb as much as 1,300 ppm, and low base metals.

Ore(s): The ore is both structurally and stratigraphically controlled. Ore is controlled by NW-striking normal faults that dip steeply west and east, with oreshoots forming at intersections of NW- and N-striking faults. One rich orebody up to 15 meters thick was localized by favorable lithology in interbedded sandy siltstone and limestone in the lower Dunderburg.

Other Databases

Link to USGS MRDS:	10310446