Hycroft Gold Mine

Site Name

Primary: Hycroft Gold Mine
Secondary: Crofoot/Lewis Gold Mine
Secondary: Standard Slag Mine
Secondary: Crofoot Gold Project
Secondary: Crofoot Project
Secondary: Crofoot Mine
Secondary: Lewis Mine
Secondary: Hycroft-Lewis Mine
Secondary: Brimstone
Secondary: Gap
Secondary: Graveyard (Boneyard)
Secondary: North Pit
Secondary: South Central Pit
Secondary: South Extension pit
Secondary: Peninsula

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Commodity

Primary: Gold
Primary: Silver
Secondary: Mercury
Tertiary: Sulfur
Tertiary: Antimony

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Location

State: Nevada
County: Humboldt
District: Kamma Mountains

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Land Status

Land ownership: BLM Administrative Area
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: Winnemucca BLM District

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Holdings

Not available

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Workings

Type: Surface

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Ownership

Owner Name: Standard Slag Co.
Percent: 100.0
Home Office: Canada
Info Year: 1997

Owner Name: Granges Inc
Percent: 50.00
Home Office: Canada
Info Year: 1996
Years: 1987 -

Owner Name: Burl C. Lance, Inc. (Crofoot Claims)
Home Office: Nevada
Info Year: 1982

Owner Name: Granges Inc. (owns Hycroft Corp/Hycroft Inc.)
Company ID: 2670116
Percent: 100.0
Home Office: Nevada
Info Year: 1995
Years: 1987 -

Owner Name: Standard Slag Co.
Years: 1985 -

Owner Name: Gold Belt Mines Inc. (Optionee)
Percent: 40.00

Owner Name: Granges Exploration Ltd and Goldbelt Mines Inc.
Years: 1985 -

Owner Name: Granges Exploration, Ltd (Optionee)
Percent: 60.00

Owner Name: Hycroft Resources and Development Corp (Optionor)
Percent: 40.00

Owner Name: Canyon Resources
Info Year: 2006

Owner Name: Vista Gold
Info Year: 2005

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Production

Year: 1995
Description: Gold Production 101128 T Oz/Yr Gold
Year: 1994
Description: Oz Of Gold 94868 Oz
Year: 1993
Description: Oz Of Gold 86516 Oz
Year: 1991
Description: Au 94340 Oz
Year: 1988
Description: Au 2300000 G

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Deposit

Record Type: Site
Operation Category: Producer
Deposit Type: volcanic-hosted epithermal deposit; hot springs gold-silver
Operation Type: Surface
Mining Method: Open Pit
Milling Method: Heap Leach-Merrill-Crowe
Year First Production: 1988
Discovery Year: 1980
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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Physiography

Not available

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Mineral Deposit Model

Model Name: Epithermal vein, Comstock

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Orebody

Form: disseminated, blanket

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Structure

Type: L
Description: The mine area is cut by NNE-trending faults; and by the western, central and eastern fault zones.

Type: R
Description: The area is affected by N-S-trending Basin and Range structures.

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Alterations

Alteration Type: L
Alteration Text: There are two major types of alteration recognized at Sulphur: solfataric-near surface alteration by hot water, gases, acids; and silica-pyrite-(silica-alunite) characterized by dense siliceous flooding accompanied by fine-grained sulfides, formed at moderate depth. Alteration varies from intense silica-adularia-pyrite to weak propylitic with a widespread cap of late "acid-leach alteration," which appears to have descended along pre-existing structures.

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Rocks

Name: Volcanic Rock (Aphanitic)
Role: Associated
Description: Volcanics
Age Type: Associated Rock
Age Young: Tertiary

Name: Conglomerate
Role: Host
Description: conglomerate
Age Type: Host Rock
Age Young: Tertiary

Name: Mixed Clastic/Volcanic Rock
Role: Host
Description: volcaniclastic rocks
Age Type: Host Rock
Age Young: Tertiary

Name: Volcanic Breccia (Agglomerate)
Role: Host
Age Type: Host Rock
Age Young: Tertiary

Name: Volcanic Rock (Aphanitic)
Role: Host
Description: flow-banded lavas
Age Type: Host Rock
Age Young: Tertiary

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Analytical Data

Analytical Data: Sample 2683
Analytical Data: Homestake's 1981-82 core drill program yielded 0.015 to 0.11 oz/st Au and 0.1-8.4 oz/t Ag

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Materials

Ore: Gold
Gangue: Pyrite
Gangue: Silica
Gangue: Jarosite
Gangue: Sulfur
Gangue: Alunite
Gangue: Stibnite
Gangue: Stibiconite
Gangue: Barite

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Comments

Comment (Commodity): Ore Materials: free gold

Comment (Commodity): Gangue Materials: pyrite, silica, jarosite, native sulfur, alunite, stibnite, stibiconite, barite

Comment (Deposit): The Hycroft Mine was developed on Tertiary- to recent-age, fault-controlled, low-sulfidation epithermal gold deposits that occur over an area measuring 3 miles in a north-south direction by 1.5 miles in an east-west direction. Mineralization extends to depths of less than 330 feet in the outcropping portion of the Bay deposit on the northwest side of the property and to over 990 feet in the Brimstone deposit in the eastern portion of the Hycroft property. Four major north-northeast-trending, west-dipping, normal fault zones broadly control the epithermal gold mineralization. From west to east, these fault zones are referred to as the Central, Boneyard,Albert, and East faults. Four deposits occurring in the hanging wall of the Central Fault zone are hosted by the Sulfur Group. The deposit is considered to be a fossilized hot springs deposit, preserved by recent normal faulting. Evidence for a hot-springs origin include: deposits of sinter with fossil reeds; deposits of native sulfur; hydrothermal explosion breccias; widespread acid/sulfate alteration; and a close geochemical association between gold, arsenic, antimony, selenium, and mercury.Disseminated gold-silver mineralization occurs in silicified conglomerate and sandstone. Mineralization is described as blanket-like, associated with steep NNE-trending faults. Fault zones seen are 3 inches to 2-3 ft wide; alunite veins occur along the faults; fine-grained pyrite occurs in unoxidized rocks. Oxidized material is tan, brick-red, with coatings of yellow-green minerals, white chalcedony lenses; vuggy with jarosite and coatings of clear silica. Host conglomerate strikes north, dips gently east; model name could also be: hot-springs Au-Ag. Two ore bodies, the Central Fault deposit, active from 1987 until 1997, and the Brimstone deposit, one mile to the east on a parallel structural zone, have been mined at Hycroft.

Comment (Geology): The system is enriched in silver southward and with depth, e.g. Ag:Au 4:1 to 10:1. Base metals increase with depth and As, Sb, and Hg decrease with depth. The system is high in Se.

Comment (Development): Sporadic mining activity has occurred in this area since about 1875, with early activity focused on sulfur, mercury and clay, and later silver and gold. This district was explored for precious metals by various companies in the 1970s through the 1980s. In 1981 Homestake did widely spaced drilling on 600 ft centers, and intersected deep silver values indicating 10-15 million s.t. of low grade mineralization at shallow depth. Homestake continued their exploration in 1982. This deposit was developed by Standard Slag as the Lewis Mine in 1984, employing about 150 workers. In 1985, Granges put down 12 RC holes, 6 of which were fill-in holes in the North zone adjoining the Lewis Mine, which confirmed Homestake's earlier results. Metallurgical results were encouraging enough to justify accelerating the program. In 1985, a 25-hole, 4000-ft RC. drilling program was in progress, 10 holes to be drilled in the central zone and 10-15 in the relatively unknown southern half of the property, which covers 3600 acres total. In October of 1991, the mine was producing at a rate of 45,000 tpd, 6 days a week. The mine was still listed as an active open pit heap leach gold-silver mine as of 2002, employing 7 persons. Mining in the Brimstone deposit was suspended in December 1998, pending better gold prices. Since that time the site has been on care and maintenance and all operating permits and mining claims have been maintained. Gold recovered from recirculating leach pad solutions has helped to defray holding costs. The owners, Vista Gold, completed a new feasibility study in about 2000 indicating resources of approximately 25 million tons of ore at .021 opt Au, or about a half million ounces. In August 2004, Vista Gold Corp. announced an updated resource estimate for its Hycroft Mine prepared by Mine Development Associates of Reno. The resource estimate, based on a database containing 575 drill holes, credits Hycroft with measured and indicated resources of 754,600 oz Au, and inferred resources of 133,600 oz Au. In 2005, the mine was owned by Vista Gold who recently entered into an option agreement to sell the mine to Canyon Resources

Comment (Economic Factors): Reserves of the Crofoot/Lewis mine were reported in 1988 as 25 million tons of ore grading 0.025 opt Au. In 1991, reported reserves were 33 million tonnes of ore at 0.29 oz/t gold with a waste: ore stripping ratio of 1.6. There was an additional 7 million tons of reserves as refractory unoxidized material. In 1999, 23.8 million tons of ore grading 0.0204 opt Au - proven and probable reserves and 2.3 million tons, 0.0177 opt Au indicated reserves. Vista Gold in about 2000 indicated resources of approximately 25 million tons of ore at .021 opt Au, or about a half million ounces. In 2004, Vista Gold reported measured and indicated reserves of 41,865,000 tons grading 0.0196 opt gold for 819,000 contained ounces; and an inferred resource of 14,108,000 tons grading 0.0152 opt gold for 213,000 contained ounces. 2006 proven and probable reserves were reported as 33,320,000 tons of ore grading 0.02 ounces of gold per ton. Reported production for the Crofoot/Lewis Mine: 1988: 75,800 oz Au 1989-98: 868,544 oz Au, and 2,717,170 oz Ag 1999: 40,075 oz Au, 183,190 oz Ag 2000: 13,493 oz Au, 38,418 oz Ag 2001: 3,232 oz Au, 2,000 Ag 2002: 1,771 oz Au, 217 oz Ag totaling slightly over a million ounces of gold and 2.94 million ounces of silver between 1988 and 2002.

Comment (Location): The mine is situated off the NW flank of the Kamma Mountains. The current Crofoot/Lewis Mine is developed on a continous mineralized zone that was originally covered by Standard Slag's Lewis mine, on the north and by the Crofoot property to the south. The claims cover 12,230 acres (4,950 hectares).

Comment (Workings): The property is developed as an open pit mine; with heap leach operation; single bench; and cyanidation facilities.

Comment (Identification): Initially, the Crofoot and Lewis mines reflected different ownership of portions the same continuously mineralized zone. Hycroft Resources acquired the Lewis mine in January 1987 and has since consolidated the two mines into the Crofoot/Lewis mine. This gold mine has been described in many earlier MRDS records: W700587, M242949, W700582, M242768, and M242743. The current record combines all information from the earlier records and supersedes those records. These earlier records should be deleted. In addition, there are several records that describe the sulfur, clay, and mercury deposits associated with the same system (D002144, M232693, and others) which should remain in the database.

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References

Reference (Deposit): Nevada Division of Minerals, 1994

Reference (Deposit): Ebert, Shane W; Groves, David I; Jones, J Kenneth, 1995 Geology, alteration, and ore controls of the Crofoot/Lewis Mine, Sulphur, Nevada; a well-preserved hot-spring gold-silver deposit, in Geology and Ore Deposits of the American Cordillera; symposium proceedings, Geological Society of Nevada.

Reference (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.

Reference (Deposit): D.A. Davis and J. V. Tingley, 1999, Gold and silver resources in Nevada, NBMG Map 120

Reference (Deposit): Wallace, Andy; Friberg, Robert S., 1996, Geology and mineral deposits of the Sulphur mining district, Humboldt County and Pershing County, Nevada; in Gold and silver deposits of western Nevada, Geological Society of Nevada, Special Publication vol.18, pp.67-76.

Reference (Deposit): 2004 Report by Mine Development Associates, on website.

Reference (Deposit): Vista Gold Corp. press release, 9/22/2004.

Reference (Deposit): Crafford, A.E.J. (ed.), 2003, GSN Road Log 2, Interstate 80 Eastbound, Fernley (Exit 48) to Golconda (Exit 194).

Reference (Deposit): DUNCAN, D. AND B. WIGGLESWORTH. CROFOOT'S PROJECT JOINS NEVADA'S FORMIDABLE LIST OF GOLD PRODUCERS. MIN. AND ENG. J., JUNE 1988, PP. 40-41. (NOTE: DUNCAN IS THE DIRECTOR AND PROJECT MANAGER AND WIGGLESWORTH THE SENIOR STAFF ENGINEER, BOTH OF HYCROFT RESOURCES AND DEVELOPMENT CO., RENO, NV.)

Reference (Deposit): NEVADA DEPARTMENT OF TAXATION, MINING DIVISION. HYCROFT RESOURCE AND DEVELOPMENT NET PROCEEDS TAX RECORDS. CARSON CITY, NV, FEB. 1991.

Reference (Reserve-Resource): 1995/95 NEVADA MINES DIRECTORY, PP. 11, 24.

Reference (Reserve-Resource): GRANGES INC. FORM 10-K REPORT, P17.

Reference (Reserve-Resource): RANDOL, MINING DIRECTORY, 1996/97, U.S. MINES & MINING COMPANIES, P238.

Reference (Deposit): ANNUAL REPORT GRANGES EXPLORATION LTD.,VANCOUVER BC, 1985

Reference (Ownership): GRANGES INC, 1995 FORM 10-K, PP. 7-8.

Reference (Reserve-Resource): THE MINING RECORD, FEBRUARY 22, 1995, PAGE 7, "1994 PRODUCTION AT CROFOOT/LEWIS MINE".

Reference (Deposit): Doebrich, Jeff, USGS Written Communication 1991.

Reference (Deposit): NBMG, 1994, MI-1993

Reference (Deposit): State Inspector of Mines, 1985, Directory of Nevada Mine Operations Active in Calendar Year 1984.

Reference (Deposit): Pay Dirt, April, 1984

Reference (Deposit): Bonham, H.F. 1986; NBMG Map 91

Reference (Deposit): GRANGES INC, 1995 ANNUAL REPORT, 52 PP.

Reference (Deposit): THE MINING RECORD, VOL., 107, #42, OCT., 16, 1996, P1.

Reference (Deposit): THE MINING RECORD, VOL., 107, #47, NOV., 20, 1996, P1.

Reference (Deposit): MILLER, M.S. 1993, EMIGRANT TRAIL STUDY AREA, US BUREAU OF MINES, OPEN FILE RPT, MLA 7-93, P89.

Reference (Deposit): THE MINING RECORD, VOL., 108, #13, MAR. 26, 1997, P1.

Reference (Deposit): Bonham, H. F. 1988 in NBMG MI-1987.

Reference (Deposit): Mine Search Annual, 1984-85, Vol. V11, P. 111, Metals Economics Group, Boulder Co.

Reference (Deposit): BELING, D. C., J. HARRINGTON, AND B. WIGGLESWORTH, TREATING LOW GRADE SOLUTIONS AT THE CROFOOT MINE. CH. 22 IN GOLD '90, ED. BY D. M. HAUSEN. SOC. MIN. ENG. AIME, 1991, PP. 231-234.

Reference (Deposit): THE NORTHERN MINER, 1996.

Reference (Deposit): SKILLINGS MINING REVIEW, SEPT 27, 1997, V86, #39, P14.

Reference (Deposit): Mining Journal, 6/21/85

Reference (Deposit): Tingley, J.V., 6 Sep 85, Field Examination and Sample Analysis.

Reference (Deposit): Unpublished Report, 1983, Homestake Mining Co.

Reference (Deposit): NBMG Mining District File 143, Item 11-Unpub. Report for Cordex, 1980, by Andy Wallace. also NBMG File 143 Press Clippings

Reference (Deposit): A.E.G. Field Trip Guidebook, 1984, Sulphur Mining-District

Reference (Deposit): Tooker, E.W., 1986, USGS Bull 1646, P.142-143

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Nevada Gold

Nevada has a total of 368 distinct gold districts. Of the of those, just 36 are major producers with production and/or reserves of over 1,000,000 ounces, 49 have production and/or reserves of over 100,000 ounces, with the rest having less than 100,000 ounces. Read more: Gold Districts of Nevada.