Geology
Host rockLimestone,Chert,Shale,Sandstone,Porphyry · "Roberts Mountains Fm", "Valmy Fm", "Elder Sandstone"
Associated rockQuartz Monzonite
StructureGold Acres is exposed at the western margin of the Gold Acres window along the NW-trending Roberts Mountains thrust, Cortez-Uinta axis. It lies along the Eureka-Battle Mountain trend of aligned deposits and mineralization., High angle normal faulting of various orientations has broken the mineralized zone into three parts: the main Gold Acres orebody, the Little Squirt orebody, and the Little Gold Acres orebody.
Tectonic settinggeosyncine
AlterationAlteration of the deposit consists of carbonization, silicification, argillization, oxidation, and skarn formation. Carbonization (up to 3% by weight organic carbon) is the dominant alteration type in the deposit and can give a sooty appearance to the rocks. Silicification is strongest at the northern end of the deposit and decreases to the south. Argillization is primarily confined to fractures in lower plate carbonates associated with carbonization. The clays are generally illitic. Supergene oxidation is evident throughout the deposit area as limonitic and hematitic staining along fractures. Skarn development is associated with the emplacement of a Cretaceous granitic stock. Two prograde, skarn zones are developed, both barren of gold. A retrograde skarn alteration mineral assemblage consists of chlorite, tremolite, epidote, calcite, quartz, illite, nontronite, smithsonite(?), pyrite, pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, and galena. Gold is not associated with the retrograde assemblage.
References
Ketner, K. B., 1965, Gold Acres Mine, in Gilluly, J., and Gates, O., Tectonic and Igneous Geology of the Northern Shoshone Range: USGS Professional Paper 465, p. 134-135Koschman, A. H., and Bergendahl, M. H., 1968, Principal Gold-Producing Districts of the United States: USGS Prof. Paper 610, p. 184Roberts, R. J., et al., 1971, Gold-Bearing Deposits in North-Central Nevada and Southwestern Idaho: Econ. Geol. 66 (1): 14-33Stager, H.K. (1977) Geology and Mineral Resources of Lander Co., Nevada; NBMG Bull 88Vanderburg, W. (1939) Reconnaissance of Mining Districts in Lander Co., Nevada; USBM I.C. 7043.Wrucke, C.T. (1974) Geologic Map of the Tenabo Area, Lander Co. Nevada, USGS Map Mf-647.Anctil, R.J. (1967) Gold Acres Project, Report prepared for Union Pacific Land Co.USBM (Winnemucca) MILS No. 54, Ref. No. 3201500052, Mineral Property File 74.500The Nevada Mineral Industry 1990; NBMG Special Publication MI-1990, P.22.Hays, R.C., and Foo, S.T., 1991, Geology and Mineralization of the Gold Acres Deposit Lander County, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W. and Wilkinson, W.H., Eds., Symposium Proceedings, Geology and Ore Deposits of the Great Basin, Geologic Society of Nevada and the U.S. Geological Survey, April 1-5, 1990, p. 677-685.McCormack, John, 1991, Written comments on record, 18 Oct/91.NBMG, MI-83; MI-84; MI-86 thru MI-96; MI-02.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.NBMG Map 91, 1st, 2nd, 3rdAmer. Mines (1989), 1989 thru Amer. Mines (2001), 2000MASMILS 0320150008, 0320150626Crescent Valley Land Status, 1979NBMG Bull. 38.Adella Harding, Elko Daily Free Press Mining Quarterly, Winter 2002-2003.