Gold Hill Mine, Round Mountain Mining District, Toquima Range, Nye County, Nevada, USAi

Regional Level Types
Gold Hill Mine	Mine
Round Mountain Mining District	Mining District
Toquima Range	Mountain Range
Nye County	County
Nevada	State
USA	Country

Structure: Northwest-striking faults and joints; a WNW-trending paleotopographic high, may represent the margin of buried caldera located SW of Round Mountain. Ore deposits are localized by a NW-trending lineament.

Alteration: Propylitization and argillization of host rocks are intense. Adularia replacement of K-feldspars and plagioclase is associated with ore. Plagioclase and groundmass are replaced with quartz and sericite. Within propylitically altered rock, biotite is partially or wholly altered to chlorite. Groundmass is altered to chlorite +/- clay +/- carbonate+/- epidote. Plagioclase phenocrysts are altered to sericite (illite) as small points, clots, and veinlets along cleavage planes. Argillically altered rock contains no unaltered biotite or plagioclase, both phases being altered to clay (illite, montmorillonite, kaolinite) and sericite. Groundmass is entirely composed of fine-grained clays and sericite. Quartz-adularia silicification is widespread along the veins. Degree of silicification, sericite + argillic alteration increases with (higher) elevation. Fine-grained secondary quartz has replaced original plagioclase feldspars, occurs as clots in the groundmass, and as hairline veinlets that lace the rock.

Commodity: Ore Materials: free gold, electrum, auriferous pyrite Gangue Materials: clay minerals, quartz, adularia, sericite, hematite, limonite, manganese oxide, pyrite, alunite, jarosite, illite, montmorillonite, kaolinite, fluorite, realgar, scorodite

Deposit: The host rock at Gold Hill includes densely welded rhyolite tuff of the Mount Jefferson Caldera. The Mount Jefferson tuff overlies the Moores Creek tuff which in turn lies over the Round Mountain tuff, the host of the Round Mountain mine. These Tertiary volcanic rocks overlie a volcanic mega-breccia that, in turn, overlies Paleozoic metasediments. The youngest rock in the area is Quaternary-Tertiary pediment gravel. These units are generally composed of cobbles of the younger maroon tuff and are always completely barren of gold mineralization. Alteration in the area ranges from propylitic to argillic to advanced argillic to silicified. The gold mineralization is related to both quartz veining in argillized rock and silicification. The principal feature in the area is the Gold Hill vein and its sub-parallel veins. These all strike N75?W and dip variably, but steeply. In general, the veins dip southerly near the surface but dip back to the north at depth. These veins branch and coalesce and are banded quartz, but can also be composed of crushed quartz and rhyolite. Higher-grade pods generally exist where two periods of veining intersect, the entire zone is up to 500 ft wide and is 3,000 ft long, extending from beyond the range front fault on the west (where it remains open) to near the Toquima shaft on the east. The mineralization extends to the west of the range front fault where one hole hit approximately 80 ft of about 0.11 oz Au/ton.

Deposit type: Hot-spring Au-Ag

Development: The first significant production in the Round Mountain district was principally from the Gold Hill Mine in the 1930s. There was later sporadic production between 1950 and 1964. Total production at Gold Hill was about 28,000 ounces. Grades are estimated to have been about 0.3 ounces of gold per ton. The property was controlled through much of the 1980s by Round Mountain Gold Corporation (RGMC), which was at that time a joint venture of Echo Bay Mining, Homestake, and Case Pomeroy. They conducted extensive exploration including surface mapping, geochemistry, geophysics and a structural evaluation. Their work culminated in drilling, preliminary metallurgical test work and a resource and economic evaluation. According to a 1988 report by Mine Development Associates, a mineral inventory of 3.1 million tons (2.8 million tonnes) grading 0.05 oz Au/ton (1.7 g Au/t) at a 0.025 oz Au/ton (0.85 g Au/t) cutoff was defined. Exploration work during the 1990s included additional geological mapping, surface sampling, geophysics, 100 drill holes by RMGC (both reverse circulation and core), 10 core holes completed by Nevada Star and the preparation of a digital database of all available exploration data. In 1995, Nevada Star staked 55 claims and acquired an option to purchase 53 additional claims in the Round Mountain Mining District, in consideration of $1,010,000 U.S. over 10? years. In a 2000 agreement, RMGC assumed the remaining payment obligations to the vendor and paid $275,000 to Nevada Star by 2005. Thereafter, RMGC will pay annual production royalties to Nevada Star. In 2003, Round Mountain Gold Corp. started the permitting process for a proposed mine at the Gold Hill property and continued drilling to define the gold deposit. The Gold Hill property is undergoing an EIS (Environmental Impact Study) which is expected to be completed in the Fall of 2005. Plant production is scheduled to start in the early spring of 2006. Higher-grade ore from the Gold Hill Project will be trucked to a mill at the existing Round Mountain Gold mine.

Geology: A sequence of water-laid tuff, tuffaceous sandstone, conglomerate, and thinly laminated siltstone overlies the orebody.

Ore(s): There is a ring fracture zone associated with a buried caldera. Gold deposition is controlled by high-angle fractures, particularly the NW-trending sets. Fractures were reactivated by NW-trending strike-slip faulting.

Other Databases

Link to USGS MRDS:	10310493
Link to USGS MRDS:	10197946

Other Regions, Features and Areas containing this locality

References