Geology
Host rockRhyolite,Andesite,Quartz Latite,Pyroclastic Rock,Mixed Clastic/Volcanic Rock
Associated rockRhyolite,Andesite
StructureTwo approximately orthogonal fault sets running approximately N-S and E-W have influenced hydrothermal mineralization.
Tectonic settingThe eruptive centers and vein deposits at National are situated along the topographic rim of a shallow elliptical basin 14-20 miles in diameter, called the Goosey Lake depression, possibly related to magma withdrawal as at McDermitt caldera.
AlterationAlteration consists predominantly of silicification and intense clay alteration. Alteration outward from the pyritic zone enveloping the Bell vein is kaolinite, followed by illite/montmorillonite, then by quartz-chlorite-quartz-calcite, then fresh rock. The kaolinite zone is more extensive in the hanging wall of the veins. There is little unaltered rock under Buckskin Mountain. Magnetite in the calcite-quartz-chlorite zone goes to pyrite in the illite-montmorillonite zone. Vertical alteration zoning is: top of Buckskin mtn.= silica cap, Hg and silicification; 20- m down (vertically) rhyolite is altered to alunite + quartz; -then to depths of several hundred meters selvages of kaolinitic alteration border the veins to depths of several hundred meters; then at depths below the level of the workings (core-drilled by ASARCO), K-mica alteration reportedly occurs in and around the veins.
References
Willden, R., 1964, Geology and Mineral Deposits of Humboldt Co., Nev; NBMG Bull. 59.Vanderburg, W.O., 1938, Reconnaissance of Mining Districts in Humboldt County, Nevada; U.S. B. M. Inf. Circ. 6995Lindgren, W., 1915, Geology and Mineral Deposits of the National Mining District, Nevada: U.S.G.S. Bull 601.Lawrence, E.F., 1963, Antimony Deposits of Nevada; NBMG Bull. 61.Garside, L. J. And Bonham, M. F., Jr., 18 Aug 83, Field examination and tour led by Peter Vikre of ASARCO Minerals, and sample analyses.Vikre, P. G., 1985, Precious metal vein systems in the National District, Humboldt County, Nevada: Econ. Geol., vol. 80, no. 2, p. 360-393.NBMG Staff, 1985, NBMG OFR 85-3.NBMG Map 88, 1986, Geology of Buckskin Mountain, by P. G. Vikre.Nevada Dept. of Minerals, 1993Miller and Rumpsey, USBM production figuresNBMG MI-86; MI-97NBMG Map 91, 1st, 2nd, 3rdAmer. Mines (1990), 1990National Au Min. Industry News, 1 Aug 1986Carper, 1920,MD133, I12Amer. Mines (2000), 1999Long, 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 disketteRomarco Minerals Inc. press releases, April, May, 2004.