Geology
Host rockAndesite · "Coal Valley Formation", "Kate Peak Formation", "Lousetown Formation", "Hartford Hill Tuff"
Associated rockDacite,Porphyry
StructureThe deposit occurs at the intersection of the Gooseberry-Talapoosa Lineament (a major E-W trending structural zone) and the NW-trending Bear Creek structural zone., Important mineralized structures include E-W and NW-striking high angle faults and associated fractures. NE-striking high angle faults are generally post-mineralization.
AlterationAlteration types present are, in order of oldest to youngest: propylitic, phyllic, silicic, argillic, and opaline alterations. The pervasive propylitic assemblage consists of chlorite, zeolites, calcite, smectite clays, sodic rims on plagioclase (partial albitization), minor quartz and epidote, and trace to 2% disseminated pyrite. Magnetite is generally stable. The intensity of propylitic alteration increases with proximity to mineralized veins. Phyllic alteration is dominated by sericite and pyrite (3-5%) with lesser amounts of quartz and adularia. Celadonite and illite are also present. Phyllic alteration is generally pervasive throughout the andesite unit and the andesite breccia subunit. The silicic assemblage consists of multiple stages of banded chalcedony and drusy quartz adularia and contains minor sulfides, sulfosalts, and electrum. Quartz-adularia intergrowths commonly replace calcite cleavage planes. Silicic alteration is manifest by a well developed vein stockwork crosscutting the andesite unit, as a pervasive replacement, and as matrix to irregular zones of hydrothermal breccias. The silicic assemblage overprints both phyllic and propylitic alteration and represents the main stage of precious metal deposition. The argillic assemblage consists of montmorillonite clays, kaolinite, alunite, allophane, halloysite, jarosite, gypsum, and iron oxides. Argillic alteration is best developed in fault zones. It also occurs as a pervasive supergene product of pyrite oxidation, overprinting both phyllic and propylitic assemblages. The opaline assemblage consists of massive, multi-colored opaline-chalcedonic breccia containing iron oxides and occasional cinnabar. Opaline breccia appears to be replacing andesite tuff-breccia. The opaline breccia may represent a higher level equivalent to the silicic assemblage, deposited near the paleosurface.
References
Van Nieuwenhuyse, R., 1991, Geology and Ore Controls of Gold-Silver Mineralization in the Talapoosa Mining District, Lyon County, Nevada, in Raines, G. L., et al., eds., Geology and Ore Deposits of the Great Basin, The Geological Society of Nevada, Reno, p. 979-993.Garside, L. and Silberman, M., 1973, K-Ar Age of Ore Deposition, Talapoosa Mining District, Lyon County, Nevada, Isochron/West, no.7, p. 5-6.Hill, J. M., 1911, Notes on the Economic Geology of the Ramsey, Talapoosa, and White Horse Mining Districts, in Lyon and Washoe Counties, Nevada, USGS Bulletin 470, p. 99-108.Pegasus Gold Inc., 1992, Annual Report for 1991.Moore, J. G., 1969, Geology and Mineral Deposits of Lyon, Douglas, and Ormsby Counties, Nevada: NBMG Bulletin 75.Stoddard, C. and Carpenter, J. A., 1950, Mineral Resources of Storey and Lyon Counties, Nevada: NBMG Bulletin 49.NBMG, 1994, MI-1993Nevada Division of Minerals, 1994Long, 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.California Mining Journal, 6/1/94.NBMG MI-1994Northern Miner, 8/22/94.Denver Mining Record, 2/26/97.NBMG MI-1997Draft Environmental Impact Statement Availability for Talapoosa Mining Inc.'s Talapoosa Mine Project , 1996.Carpenter, Ann, 1992, Geology and Mineralization of the Talapoosa Mining District, Lyon County, Nevada; in Reno Area - Northern Walker Lane Mineralization and Structure; GSN Special Pub. No. 15.NEV. BUREAU OF MINES AND GEOL. BULLETIN 75, 1969, PLATE 2.AMERICAN MINES HANDBOOK, 1996, PP. 166, 167.THE NORTHERN MINER. "MIRAMAR PUTS TALAPOOSA GOLD PROJECT ON HOLD". 2/24/97. P.10.THE MINING RECORD, APRIL 27, 1994, P19.MIRAMAR MINING CORP., NEWS RELEASE 96-03, 02/14/96, "TALAPOOSA PROJECT RESERVES & RESOURCES...".MIRAMAR MINING CORPORATION., NEWS RELEASE 2/14/97. 1P. "MIRAMAR MINING CORPORATION TALAPOOSA PROJECT ON HOLD..."