Goldbanks Gold Deposit, Goldbanks Mining District, Pershing County, Nevada, USAi

Regional Level Types
Goldbanks Gold Deposit	Mine
Goldbanks Mining District	Mining District
Pershing County	County
Nevada	State
USA	Country

Structure: An extensive network of NNW-, NE-, and strong NW to almost E-W-trending faults dissect the property in the vicinity of the Main Zone. Late Paleozoic rocks in the area are part of the allochthonous block of the Golconda thrust plate emplaced during the Sonoma Orogeny.

Alteration: Widespread, pervasive silicification affects all rock units stratigraphically below the mudstone. Breccia units are most strongly silicified as is the lithic sandstone in some areas. Very fine-grained adularia accompanies silicification. Argillic alteration overprints the silica with illite as the main alteration clay mineral. Zones of intense iron oxidation (goethite and limonite) follow fractures and veins to depths as much as 365 meters below the surface. In the Main gold zone, a gray pervasive silicification resembling jasperoid is associated with gold mineralization, although open-space drusy quartz is also common. A thick layer of opaline sinter overlies the gold mineralized units and capping mudstone. The opalite hosted the mercury deposits in the area.

Tectonics: Tertiary strata were deposited into a rapidly subsiding basin which encompasses most of the Goldbanks area. Basin development coincided with the onset of Basin and Range faulting approximately 17 m.y. ago.

Commodity: Ore Materials: gold Gangue Materials: quartz, pyrite, arsenopyrite, marcasite, goethite, hematite, cinnabar

Deposit: Mineralization does not crop out, and is covered by a cap of basaltic flows and weakly consolidated Tertiary sediments. Kinross has delineated two mineralized deposits: the Main Zone, and the KW area. Main ore host rocks are Tertiary basin sediments deposited about 17 million years ago. The best hosts for gold mineralization are permeable lithic sandstone and the polylithic breccia at the base of the basin sequence. Fractured areas in Paleozoic Havallah sequence and leucogranite intrusive rocks also host minor amounts of gold mineralization. The epithermal mineralization is interpreted to have been formed by gold and silica-rich solutions ascending along steep fault structures until they encountered permeable clastic sediments along which the solutions migrated outwards to form a siliceous blanket-shaped deposit in the Main Zone measuring 2 km by 1 km and approximately 90 m thick. Mineralization in the KW area is largely structurally controlledwith higher grade mineralization localized in a pipe-like breccia body at the intersection of N- and NNE-trending faults. The higher-grade material in the KW zone does not have a significant envelope of lower grade mineralization around it, as is the case in the Main Zone. Gold mineralization in the KW area occurs primarily within polylithic breccia, the Havallah sequence rocks and brecciated Koipato rhyolite.

Deposit type: Hot-spring Au-Ag

Development: The Goldbanks district was first explored for gold, which was discovered in 1907. Around 1912, mercury in cinnabar was discovered a few miles west of the gold deposits, in the area of the current gold property. During World War I, the Goldbanks Quicksilver mine yielded over 34,473 kg of mercury. After a 20-year lull, the area again produced 10,342 kg mercury in 1937 and produced an additional 45,573 kg of mercury, between 1941 and 1969. The cinnabar area was most productive in the 1960s when Star City Mines, Ltd. operated silica pits in the area. In 1986, G. L. Grauberger located 300 lode mining claims in the Goldbanks district and through 1988 drilled 21 reverse circulation holes on approximate 305 meter centers,which outlined a gold mineralized zone approximately 1,830 m by 914 m. In November 1990, the property was assigned to Restoration Minerals, a new company controlled by Grauberger, and drilling continued on the property. In May 1995, Kinross Gold USA, Inc. executed a joint venture agreement to further explore and develop the Goldbanks property under the corporate name of Kinross Goldbanks Mining Company and in 1998, Kinross acquired a 100 percent interest. Work carried out to date includes core drilling, reverse- circulation drilling and metallurgical testing. This work has delineated two distinct gold deposits along a north-south trending axis 6.4 kilometers in length: the Main Zone, with 92 percent of the gold resource, centered under Squaw Butte and the KW area, 3.2 kilometers to the north. The Goldbanks deposit has had 1176 holes drilled to outline a geologic resource of 166 million tonnes with a grade of 0.48 g/t gold and 1.40 g/t silver. In 1999, plans to open the Kinross Goldbanks Mine were put on an indefinite hold. The company planned to complete the EIS for the mine, but all other permit applications were put on hold.

Geology: The Tertiary rocks have been subdivided, based on dominant lithologies, into six rock units at Goldbanks, although interbedding, intertonguing and facies changes are apparent within individual units. The basal unit (main ore host) is a lithic sandstone (litharenite) and is followed successively upwards by polylithic breccia (main ore host), lacustrine mudstone, opaline sinter, weakly-cemented sediments and basalt flows. The Tertiary strata were deposited into a rapidly subsiding basin, which covers most of the Goldbanks area. Basin margins are buried under basalt or Quaternary alluvium in the south and west portions of the property, but have been mapped in areas to the north and east. The basin development probably coincided with the onset of Basin and Range faulting approximately 16 Ma, and most mappable structures within the basin are consistent with Basin and Range trends.

Ore(s): Epithermal mineralization is interpreted to have been formed by gold and silica-rich solutions ascending along steep fault structures until they encountered permeable clastic sediments along which the solutions migrated outwards to form a siliceous blanket-shaped deposit in the Main Zone measuring 2 km by 1 km and approximately 90 m thick. The predominant permeable host rock lithologies are a basal lithic sandstone (well-sorted litharenite) and an overlying polylithic breccia (mostly conglomeratic with abundant hydrothermal and tectonic brecciation). Overlying these two lithologies is a thick unit of lacustrine mudstones which appears to have acted as an impermeable cap for localizing silica and gold mineralization in the more permeable units below it. The structural axis and hydrothermal conduit for the Main Zone mineralization does not appear to have a surface expression; but drilling has outlined a major north-south zone about which the gold mineralization has spread laterally. Because the major gold resource has no surface expression, and Quaternary alluvium and basalts blanket much of the area, the presence and amount of any fault displacement of the ore zones is speculative. Mineralization

References

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Link to USGS MRDS:	10310549

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