Mine detail: Borealis Mine

Previously called 'Deep Ore FlatsEast RidgeFreedom FlatsGold ViewGrabenJaimes RidgeNortheast Ridge orebodies'

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Location

Lat / long:

38.38325, -118.75957

Resource(M)

Primary:	Gold
Secondary:	Silver
Tertiary:	Zinc, Copper, Nickel
Ore:	Gold, Cinnabar, Chalcopyrite, Chalcocite, Sphalerite, Covellite, Tetrahedrite, Tennantite, Enargite, Matildite, Nagyagite, Niccolite, Alunite, Feldspar, Barite, Pyrite, Hematite, Montmorillonite, Kaolinite, Marcasite, Arsenopyrite, Pyrrhotite
Gangue:	Quartz
Orebody form:	tabular to irregular
Discovery year:	1930

Production

Operation type:	Surface-Underground
Deposit type:	volcanic-hosted disseminated
Production size:	Medium
Development status:	Producer
Production years:	1981-1990
First production started:	1981
Last production ended:	1990

Geology

Host type:	Andesite,Tuff,Volcanic Breccia (Agglomerate)
Structure:	Major regional structural trends affecting the mine area are the Walker Lane shear zone and the Borealis Trend., NE-trending faults with subordinate N-S and E-W- striking structures.
Alteration processes:	Host rock alteration consists mainly of pervasive silicification, alunitization, kaolinization, oxidation, argillization, and propylitization. The conduit for hydrothermal fluids was a 100-200 ft. wide core zone of silica breccia with abundant iron oxide minerals. The silica breccia zone narrows downward and grades downward into oxidized quartz-sulfide and unoxidized quartz-pyrite alteration. Argillic and propylitic alteration zones develop outward from core. Barren opal and chalcedonic silica overlie deposit.

References

MRDS	M035782
DEP	10310350
Reference	{Deposit:: Reid, R. F., Jr., 1984, The geology of the Borealis deposit: GSA Abstracts with Programs, 97th Ann. Mtg, Reno, NV.}{Deposit:: NBMG Mining District File 200, Items 8, 9, Press Clippings.}{Deposit:: Tooker, E.W., 19?, In USGS Bull 1646.}{Deposit:: Strachan, D.G., 19?, Geologic Discussion of the Borealis Gold Deposit, Mineral Co., Nevada, in USGS Bull 1646.}{Deposit:: Bulk-Mineable Precious Metals Symposium, 1987, Field Trip Guidebook.}{Deposit:: NBMG, 1994, MI-1993}{Deposit:: 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.}{Deposit:: Golden Phoenix Co. website, 2006.}{Deposit:: Gryphon Gold website, 2006.}{Deposit:: Struhsacker, Eric, guidebook editor, 1994, Geological Society of Nevada Special Publication #20, Gold Deposits of the Central Walker Lane, Nevada: mineralization Style and Mine Closure Planning.}{Deposit:: Eng, T., 1991, Geology and Mineralization of the Freedom Flats Gold Deposit, Borealis Mine, Mineral County, in Raines and others, Geology and Ore Deposits of the Great Basin, Symposium Proceedings, Reno, NV: Geological Society of Nevada, v. 2, p. 995-1019.}
Reporter	LaPointe, D.D., Schruben, Paul G.