Geology
Host rockMudstone,Siltstone,Shale,Sandstone,Quartzite · Webb Formation
Associated rockLimestone · "Devils Gate Limestone", "Chainman Formation", "Diamond Peak Formation"
StructureTertiary age faults strike NW and NNE. One set of NW-striking, south-dipping reverse faults controlled ore deposition., The deposit lies within the Mesozoic-age, N- to NW-trending Pinon Range anticline. Tertiary age faults strike NW and NNE. One NW-striking fault set shows reverse displacement and acted as conduits for hydrothermal fluids.
Tectonic settingThe deposit lies within the Pinon Range which occurs within the narrow N-S trending belt which coincides with the position of the Paleozoic continental margin.
AlterationAlteration at South Bullion consists of silicification, decalcification, and argillization. Alteration within the Trout Creek portion of the deposit consists predominantly of silicification and hematization.\nGold mineralization is intimately related, both temporally and spatially, to silicification of the Webb Formation. Silicification of the Webb Formation has resulted in 1) replacement of primary calcareous material by authigenic quartz, forming the major portion of the fine grained jasperoid, 2) development of quartz overgrowths, some of which are multiple overgrowths, 3) the in-filling of fractures and vugs by coarse anhedral and euhedral quartz, and 4) pervasive silica flooding along zones of induced secondary porosity and permeability. Portions of the Webb Formation and Devils Gate Limestone are decalcified in an envelope to the jasperoid. An unsilicified portion of the Webb Formation that directly overlies the jasperoid contains numerous fine calcite veinlets; a similar zone occurs directly below the jasperoid and is characterized by massive vein- and cavity-filling sparry calcite. Weak argillic alteration is suggested by the presence of dispersed hydrothermal clays within the Webb Formation and the Chainman Shale at both the local and district scales. Due to the regional extent of the clays, as contrasted to the limited area of gold mineralization, the gold is thought to not necessarily be temporally associated with this weak argillization event.
References
NBMG MI-88 thru MI-02NBMG Bull. 106Elko Land Status Map 1978Amer. Mines (1996), 1995Thompson, 1999Newmont Ann. Rept. 1988Jackson, P., 1992, Geology and mineralization of the Emigrant Springs Project, Elko County, Nevada, in Buffa, R. and Coyner, A., eds., The Geology and Ore Deposits of the Great Basin-Field Trip Guidebook Compendium, The Geological Society of Nevada, Reno, p. 125-130.Thoreson, R., 1991, Geology and gold deposits of the Rain subdistrict, Elko County, Nevada, in Raines, G.L., et al., eds., Geology and Ore Deposits of the Great Basin, The Geological Society of Nevada, Reno, p. 635-643.Thoreson, R., 1990, Geology and Ore Deposits of the Rain Subdistrict, Elko County, Nevada, Oral Presentation at Great Basin Symposium, The Geological Society of Nevada, Reno/Sparks, April 4.Nevada Dept.of Minerals, 1994Newmont Gold 1993 Sec Form 10k.Jackson, P.R., and Ruetz, J.W., 1991, Geology of the Trout Creek disseminated gold deposit, Elko County, Nevada, in Raines, G.L., et al, eds., Geology and Ore Deposits of the Great Basin, the Geological Society of Nevada, Reno, p. 729-734.Long, 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.2004 Royal Standard Minerals website.Putnam, B. R., and Henriques, E. Q. B., 1991, Geology and Mineralization at the South Bullion Deposit, Pinon Range, Elko County, Nevada: Implications for Western United States Cenozoic Tectonics, in Raines, G. L., et al., Eds., Geology and Ore Deposits of the Great Basin, Geological Society of Nevada, Reno, p. 713-728.Royal Standard Minerals Inc. press releases, 4/21/2003; 11/3/2003; 11/5/2003.