RBM deposit, Bald Mountain mine, Bald Mountain Mining District, White Pine County, Nevada, USAi

Regional Level Types
RBM deposit	Deposit
Bald Mountain mine	Mine
Bald Mountain Mining District	Mining District
White Pine County	County
Nevada	State
USA	Country

Structure: NW-striking normal faults that dip steeply west and east, with lesser N-striking faults. 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: The porphyry dikes were sericitized, argillized and silicified. Intense argillic alteration almost totally obliterated the texture of the protolith host rock, and grades outward to phyllic 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: free gold Gangue Materials: pyrite, clay, limonite, jasperoid, quartz, marcasite, arsenopyrite, galena, sphalerite, chalcopyrite, possible tellurium-bearing sulfides

Deposit: The RBM deposit is located along a NW-trending structural zone and consists of two main minerlized zones: the RBM main vein , which strikes N45W, and the RBM west vein, which strikes N75W. Dips are vertical to 60E. The West vein is oxidized near surface with a massive sulfide ore zone at depth consisting of pyrite, marcasite, arsenopyrite, galena, sphalerite, chalcopyrite, and possible tellurium-bearing sulfides. Sedimentary rocks at the deposit are fine-grained limestone, impure sandstone, quartzite, and siltstone of the Antelope Valley Formation and Eureka Quartzite. The sediments were intruded by quartz feldspar porphyry which has been altered. The quartz feldspar porphyry is present in the western portion of the deposit and hosts most of the gold mineralization. Faulted contacts betwen the sedimentary rocks and the dikes acte as conduits for mineralizing fluids. The RBM deposit was originally in the upper part of the Bald Mountain system above the Top deposit, and was subsequently downdropped along the Ruby listric fault to its present position. More than 1 km of gold-bearing rock between the RBM deposit and present day exposures of the originally underlying Top deposit was removed by erosion.

Deposit type: Distal disseminated Ag-Au

Development: Placer Dome began exploration in the Bald Mountain mine area in 1977 and the RBM deposit was among the earliest discoveries in the first year of exploration. The RBM deposit was placed into production late in 1988. In 2006, Barrick Gold Corp. acquired the RBM property through its acquisition of Placer Dome U. S., Inc.

Geology: The Top and RBM deposits both have high Cu, Zn, and Ag contents associated with gold mineralization as well as anomalous values in Bi, Hg, As, Sb, and tellurides.

Ore(s): 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 sltsone and limestone in the lower Dunderberg.

Other Databases

Link to USGS MRDS:	10310444

Other Regions, Features and Areas containing this locality