Hycroft Gold Mine

Producer in Humboldt county in Nevada, United States with commodities Gold, Silver, Mercury, Sulfur, Antimony

Geologic information

Identification information

Deposit ID 10310408
MRDS ID W700587
Record type Site
Current site name Hycroft Gold Mine
Alternate or previous names Crofoot/Lewis Gold Mine, Standard Slag Mine, Crofoot Gold Project, Crofoot Project, Crofoot Mine, Lewis Mine, Hycroft-Lewis Mine, Brimstone, Gap, Graveyard (Boneyard), North Pit, South Central Pit, South Extension pit, Peninsula

Comments on the site 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.

Geographic coordinates

Point of reference Pit
Geographic coordinates: -118.688, 40.8691 (WGS84)
Elevation 1370
Relative position The mine is located about 86 km (54 miles) west of Winnemucca, near the abandoned historic town of Sulphur.
(click for info)

Geographic areas

Country State County
United States Nevada Humboldt

Public Land Survey System information

Meridian Township Range Section Fraction State
Mount Diablo 035N 029E 36 Nevada
Mount Diablo 035N 029E 25 Nevada

Comments on the location information

  • 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).

Commodities

Commodity Importance
Gold Primary
Silver Primary
Mercury Secondary
Sulfur Tertiary
Antimony Tertiary

Comments on the commodity information

  • Ore Materials: free gold
  • Gangue Materials: pyrite, silica, jarosite, native sulfur, alunite, stibnite, stibiconite, barite

Materials information

Materials Type of material
Gold Ore
Pyrite Gangue
Silica Gangue
Jarosite Gangue
Sulfur Gangue
Alunite Gangue
Stibnite Gangue
Stibiconite Gangue
Barite Gangue

Alteration

  • (Local) 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.

Analytical data

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

Mineral occurrence model information

Model code 150
USGS model code 25c
Deposit model name Epithermal vein, Comstock
Mark3 model number 16

Host and associated rocks

  • Host or associated Host
    Rock type Volcanic Rock (Aphanitic)
    Rock type qualifier flow-banded lavas
    Rock unit name Sulphur Group
    Stratigraphic age (youngest) Tertiary
  • Host or associated Host
    Rock type Volcanic Rock (Aphanitic) > Pyroclastic Rock > Volcanic Breccia (Agglomerate)
    Rock unit name Sulphur Group
    Stratigraphic age (youngest) Tertiary
  • Host or associated Host
    Rock type Sedimentary Rock > Mixed Clastic/Volcanic Rock
    Rock type qualifier volcaniclastic rocks
    Rock unit name Sulphur Group
    Stratigraphic age (youngest) Tertiary
  • Host or associated Host
    Rock type Sedimentary Rock > Clastic Sedimentary Rock > Conglomerate
    Rock type qualifier conglomerate
    Rock unit name Camel Conglomerate
    Stratigraphic age (youngest) Tertiary
  • Host or associated Associated
    Rock type Volcanic Rock (Aphanitic)
    Rock type qualifier Volcanics
    Rock unit name Kamma Mountains Group
    Stratigraphic age (youngest) Tertiary

Nearby scientific data

Pit (1) -118.688, 40.8691

Geologic structures

Type Description Terms
Local The mine area is cut by NNE-trending faults; and by the western, central and eastern fault zones.
Regional The area is affected by N-S-trending Basin and Range structures.

Ore body information

  • General form disseminated, blanket
    Length 4827.9M
  • Strike (FAULTS) NE
    Dip (FAULTS) STEEP

Controls for ore emplacement

  • Mineralization is controlled by structure and host-rock permeability. The NNE-trending central fault zone and related splays are mineralized continuously over a distance of 2.5 miles.

Comments on the geologic information

  • 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.

Economic information

Economic information about the deposit and operations

Operation type Surface
Development status Producer
Commodity type Both metallic and non-metallic
Deposit size Small
Significant Yes
Discovery year 1980
Discoverer Homestake
Mining method Open Pit
Year of first production 1988
Production years 1988-2002
Milling method Heap Leach-Merrill-Crowe

Mining district

District name Sulphur District
District name Black Rock District
District name Kamma Mountains

Land status

Ownership category BLM Administrative Area
Area name Winnemucca BLM District

Ownership information

  • Type Owner-Operator
    Owner Vista Gold
    Year 2005
  • Type Owner
    Owner Hycroft Resources and Development Corp (Optionor)
    Interest 40
  • Type Owner
    Owner Granges Inc
    Interest 50
    Home office Canada
    Year 1996
    First year 1987
  • Type Owner
    Owner Standard Slag Co.
    First year 1985
  • Type Owner-Operator
    Owner Granges Inc. (owns Hycroft Corp/Hycroft Inc.)
    ID 2670116
    Interest 100
    Home office Nevada
    Year 1995
    First year 1987
  • Type Owner-Operator
    Owner Canyon Resources
    Year 2006
  • Type Operator
    Owner Granges Exploration, Ltd (Optionee)
    Interest 60
  • Type Operator
    Owner Burl C. Lance, Inc. (Crofoot Claims)
    Home office Nevada
    Year 1982
  • Type Operator
    Owner Granges Exploration Ltd and Goldbelt Mines Inc.
    First year 1985
  • Type Operator
    Owner Gold Belt Mines Inc. (Optionee)
    Interest 40
  • Type Owner
    Owner Standard Slag Co.
    Interest 100
    Home office Canada
    Year 1997
    Last year 1987

Production statistics

  • Year 1988
    Description Au 2300000 G
    Importance Item Commodity Group Amount recovered Grade Recovery percentage
    Primary metal recovered Gold Gold 2mt
    Secondary Mercury Mercury 14mt
    Primary Silver Silver 2,600g
  • Year 1991
    Description Au 94340 Oz
    Importance Item Commodity Group Amount recovered Grade Recovery percentage
    Primary metal recovered Gold Gold 3mt
    Primary metal recovered Silver Silver 5mt
  • Year 1993
    Description Oz Of Gold 86516 Oz
    Importance Item Commodity Group Amount recovered Grade Recovery percentage
    Major Gold Gold 2,690,949g
  • Year 1994
    Description Oz Of Gold 94868 Oz
    Importance Item Commodity Group Amount recovered Grade Recovery percentage
    Major Gold Gold 2,950,725g
  • Year 1995
    Description Gold Production 101128 T Oz/Yr Gold
    Importance Item Commodity Group Amount recovered Grade Recovery percentage
    Primary metal recovered Gold Gold 3mt
    Primary Silver Silver 12,995,750g

Reserves and resources

  • Type In-situ
    Estimate year 1985
    Total resources 589,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.988 g/mt Gold Major 1985
  • Type In-situ
    Estimate year 1985
    Total resources 3,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 1.044 g/mt Gold Major 1985
  • Type In-situ
    Estimate year 1986
    Demonstrated 19,051,000mt ore
    Measured 19,051,000mt ore
    Total resources 19,051,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 1.1 g/mt Gold Major 1986
  • Type In-situ
    Estimate year 1987
    Total resources 4,081,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.847 g/mt Gold Major 1987
  • Type In-situ
    Estimate year 1992
    Demonstrated 17,060,000mt ore
    Total resources 17,060,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.754 g/mt Gold Major 1992
  • Type In-situ
    Estimate year 1995
    Demonstrated 60,364,000mt ore
    Total resources 60,364,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.65 g/mt Gold Major 1995
  • Type In-situ
    Estimate year 1996
    Demonstrated 60,327,000mt ore
    Total resources 60,327,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.65 g/mt Gold Major 1996
  • Type In-situ
    Estimate year 1996
    Demonstrated 53,343,000mt ore
    Total resources 53,343,000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold Au 0.65 g/mt Gold Major 1996

Workings at the site

  • Type of workings Surface
    Field Value
    MAS Development Schedule # 1
    Mining Record # 1
    Status of Mining Method ACTUAL
    Mining Method OPEN PIT
    Capacity 13606
    Capacity Units MT ORE/DAY
    Unit Production Cost 2.36
    Units of Production $/MT ORE
    Operating Days per Year 365
    Operating Shifts per Day 3
    Year of Information 1991

Comments on the workings information

  • The property is developed as an open pit mine; with heap leach operation; single bench; and cyanidation facilities.

Comments on other 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.

Comments on 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

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Mineral Resources Data System MRDS M242743 MRDS dep_id 10047440 merged into this record.
U.S. Bureau of Mines Minerals Availability System MAS 320130636 MRDS dep_id 10173611 merged into this record.
U.S. Bureau of Mines Minerals Availability System MAS 320130498 MRDS dep_id 10173913 merged into this record.
USGS Mineral Resources Data System MRDS M242768 MRDS dep_id 10047459 merged into this record.
USGS Mineral Resources Data System MRDS M242949 MRDS dep_id 10047576 merged into this record.
U.S. Bureau of Mines Minerals Availability System MAS 320130476 MRDS dep_id 10125682 merged into this record.
U.S. Bureau of Mines Minerals Availability System MAS 320130635 MRDS dep_id 10125767 merged into this record.

Bibliographic references

  • Deposit

    Tingley, J.V., 6 Sep 85, Field Examination and Sample Analysis.

  • Deposit

    Unpublished Report, 1983, Homestake Mining Co.

  • Deposit

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

  • Deposit

    A.E.G. Field Trip Guidebook, 1984, Sulphur Mining-District

  • Deposit

    Tooker, E.W., 1986, USGS Bull 1646, P.142-143

  • Deposit

    State Inspector of Mines, 1985, Directory of Nevada Mine Operations Active in Calendar Year 1984.

  • Deposit

    Pay Dirt, April, 1984

  • Deposit

    Bonham, H.F. 1986; NBMG Map 91

  • Deposit

    Bonham, H. F. 1988 in NBMG MI-1987.

  • Deposit

    Mine Search Annual, 1984-85, Vol. V11, P. 111, Metals Economics Group, Boulder Co.

  • Deposit

    Mining Journal, 6/21/85

  • Deposit

    Doebrich, Jeff, USGS Written Communication 1991.

  • Deposit

    NBMG, 1994, MI-1993

  • Deposit

    Nevada Division of Minerals, 1994

  • 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.

  • 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

    D.A. Davis and J. V. Tingley, 1999, Gold and silver resources in Nevada, NBMG Map 120

  • 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.

  • Deposit

    2004 Report by Mine Development Associates, on website.

  • Deposit

    Vista Gold Corp. press release, 9/22/2004.

  • Deposit

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

  • Deposit

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

  • Ownership

    GRANGES INC, 1995 FORM 10-K, PP. 7-8.

  • Reserve-Resource

    THE MINING RECORD, FEBRUARY 22, 1995, PAGE 7, "1994 PRODUCTION AT CROFOOT/LEWIS MINE".

  • Reserve-Resource

    RANDOL, MINING DIRECTORY, 1996/97, U.S. MINES & MINING COMPANIES, P238.

  • Reserve-Resource

    1995/95 NEVADA MINES DIRECTORY, PP. 11, 24.

  • Reserve-Resource

    GRANGES INC. FORM 10-K REPORT, P17.

  • Deposit

    ANNUAL REPORT GRANGES EXPLORATION LTD.,VANCOUVER BC, 1985

  • 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.)

  • 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.

  • Deposit

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

  • Deposit

    GRANGES INC, 1995 ANNUAL REPORT, 52 PP.

  • Deposit

    THE MINING RECORD, VOL., 107, #42, OCT., 16, 1996, P1.

  • Deposit

    THE MINING RECORD, VOL., 107, #47, NOV., 20, 1996, P1.

  • Deposit

    THE MINING RECORD, VOL., 108, #13, MAR. 26, 1997, P1.

  • Deposit

    THE NORTHERN MINER, 1996.

  • Deposit

    SKILLINGS MINING REVIEW, SEPT 27, 1997, V86, #39, P14.

General comments

Subject category Comment text
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.

Reporter information

Type Date Name Affiliation Comment
Reporter 01-APR-86 La Pointe, D.D. (Tingley, J.V.) Nevada Bureau of Mines and Geology
Reporter 01-APR-86 La Pointe, D.D. (Tingley, J.V.) Nevada Bureau of Mines and Geology
Updater 01-AUG-88 Paidakovich, Matthew E. U.S. Geological Survey
Updater 01-OCT-88 La Pointe, D.D. (Tingley, J.V.) Nevada Bureau of Mines and Geology
Reporter 01-OCT-88 La Pointe, D.D. (Tingley, J.V.) Nevada Bureau of Mines and Geology
Updater 01-AUG-89 Beougher, Dee (Spanski, Gregory T.) U.S. Geological Survey
Updater 01-OCT-91 Phinisey, J. D. (Marcus, S.) U.S. Geological Survey
Updater 01-SEP-94 Li, Zhiping (Peters, S.) U.S. Geological Survey
Updater 01-SEP-94 Li, Zhiping (Moyer, Lorre A.) U.S. Geological Survey
Updater 01-SEP-94 Li, Zhiping (Peters, S.) U.S. Geological Survey
Reporter 01-APR-97 Buckingham, David A. U.S. Bureau of Mines
Reporter 01-APR-97 Buckingham, David A. U.S. Bureau of Mines
Reporter 04-AUG-97 Buckingham, David A. U.S. Bureau of Mines
Reporter 17-OCT-97 Buckingham, David A. U.S. Bureau of Mines
Reporter 01-MAY-04 LaPointe, D.D. Nevada Bureau of Mines and Geology
Editor 01-SEP-07 Schruben, Paul G. U.S. Geological Survey Converted from S&A FileMaker format to Oracle. Edit checks on rocks, units, and ages with Geolex search, and other fields.