Geology
Host rockQuartz Monzonite,Porphyry,Dolomite,Limestone,Argillite · "Eureka Formation", "Antelope Valley Formation"
Associated rockQuartz Monzonite,Porphyry · Bald Mountain Stock
StructureThe Top pit contains an array of high-angle faults that appear to radiate circularly from the Bald Mountain Stock, and low-angle, bedding-parallel faults. Both N-trending faults and less prominent W-trending fractures are present., 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.
Tectonic settingThe 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.
AlterationAlteration at the Top Deposit includes decalcification, pervasive silicification, and argillization.The quartz porphyry dike is altered variably from incipient argillic alteration of feldspars to total textural destruction forming a soft white clay-rich rock. Locally, calc-silicate skarn and recrystallized marble have developed along the contact between th intrusive rocks and the calcareous sediments.
References
NBMG mining district files 323, press clippingsGSN 1985 meeting and fall field trip road logAdamson, T. J., 1987, in Bulk Mineable Precious Metal Deposits of the Western U.S., 1987 GSN, field trip guidebook and technical volume.NBMG, MI-85 through MI-03;Nutt, C.J., Hofstra, A.H., Hart, K.S., and Mortensen, J.K., 2000, Structural setting and genesis of gold deposits in the Bald Mountain-Alligator Ridge area, east-central Nevada, in Cluer, J.K., Price, J.G., Struhsacker, E.M., Hardyman, R.F., and Morris, C.L., eds., Geology and Ore Deposits 2000: The Great Basin and Beyond: Geological Society of Nevada Symposium Proceedings, May 15-18, 2000, p. 513-537.Hitchborn and others, 1996, Geology and Gold Deposits of the Bald Mountain Mining District, White Pine County, Nevada, in Geology and Ore Deposits of the American Cordillera Symposium Proceedings, eds. A. Coyner and P. Fahey.The Geological Society of Nevada 1996 Spring Field trip, Geology and Gold Deposits of Eastern Nevada, GSN Special Publication No. 23.BLM, 2004, Bald Mountain Mine Exploration Program Programmatic Environmental Assessment NV040-04-023, Case File # N78825.Draft EIS, 1995Final EIS, 1995Environmental Assessment, 1997Amer. Mines (1996), 1995 through Amer. Mines (2001), 2000;www.placerdome.com;Nevada Land Status, 1990Long, K.R., DeYoung, J.H., Jr., and Ludington, S.D., 1998, Database of significant deposits of gold, silver, copper, lead, and zinc in the United States; Part A, Database description and analysis; part B, Digital database: U.S. Geological Survey Open-File Report 98-206, 33 p., one 3.5 inch diskette.