Cove - McCoy Gold Mine

Site Name

Primary: Cove - McCoy Gold Mine
Secondary: Cove
Secondary: McCoy
Secondary: Brown Zone
Secondary: Cove East
Secondary: East Brown Zone
Secondary: Gold Dome Zone
Secondary: Peacock Zone
Secondary: Echo Bay Mine

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Commodity

Primary: Gold
Primary: Silver
Secondary: Copper
Tertiary: Thallium
Tertiary: Lead
Tertiary: Zinc
Tertiary: Tin
Tertiary: Manganese
Tertiary: Arsenic
Tertiary: Mercury
Tertiary: Antimony

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Location

State: Nevada
County: Lander
District: McCoy District

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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: Battle Mountain BLM Administrative District

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Echo Bay Minerals Co.
Info Year: 2004

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Deposit Type: Distal Disseminated/Pluton-related; vein; skarn
Operation Type: Surface
Year First Production: 1925
Year Last Production: 2004
Discovery Year: 1914
Years of Production:
Organization:
Significant: Y
Deposit Size: M

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Physiography

Not available

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Mineral Deposit Model

Model Name: Distal disseminated Ag-Au
Model Name: Skarn Au

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Orebody

Form: replacement; stockwork; tabular to irregular or stratiform

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Structure

Type: L
Description: faults

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Alterations

Alteration Type: L
Alteration Text: Upper ore zone alteration consists of argillization, silicification, amd manganese alteration. Alteration has resulted in the formation of clay and sericite along fractures and within the more permeable beds. Locally, complete replacement of the carbonate to form jasperoid has occurred along bedding and along some structures. Abundant manganese (as manganoan calcite) has been introduced into the rock, giving the clay and jasperoid a sooty brown appearance. Lower ore zone: base metal sulfides and pyrite were introduced into the host rock, filling fractures and partially replacing the host rock.

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Rocks

Name: Conglomerate
Role: Host
Age Type: Host Rock
Age Young: Middle Triassic

Name: Sandstone
Role: Host
Description: calcite-cemented
Age Type: Host Rock
Age Young: Middle Triassic

Name: Limestone
Role: Host
Description: silty
Age Type: Host Rock
Age Young: Middle Triassic

Name: Limestone
Role: Host
Description: microcrystalline
Age Type: Host Rock
Age Young: Middle Triassic

Name: Dolomite
Role: Host
Age Type: Host Rock
Age Young: Middle Triassic

Name: Dolomite
Role: Host
Description: silty to sandy diagenetic
Age Type: Host Rock
Age Young: Middle Triassic

Name: Limestone
Role: Host
Age Type: Host Rock
Age Young: Middle Triassic

Name: Granodiorite
Role: Associated
Description: dikes
Age Type: Associated Rock
Age in Years: 39.500000+-1.500000
Age Young: Middle Eocene

Name: Limestone
Role: Host
Age Type: Host Rock
Age Young: Middle Triassic

Name: Conglomerate
Role: Host
Age Type: Host Rock
Age Young: Middle Triassic

Name: Diorite
Role: Host
Age Type: Host Rock
Age Young: Late Triassic
Age Old: Middle Triassic

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Electrum
Ore: Silver
Ore: Canfieldite
Ore: Tetrahedrite
Ore: Tennantite
Ore: Acanthite
Ore: Galena
Ore: Pyrite
Ore: Chalcopyrite
Ore: Cerargyrite
Ore: Chalcocite
Ore: Cerrusite
Ore: Malachite
Gangue: Sphalerite
Gangue: Cassiterite
Gangue: Stannite
Gangue: Pyrrhotite
Gangue: Arsenopyrite
Gangue: Digenite
Gangue: Covellite
Gangue: Sericite
Gangue: Clay
Gangue: Zeolite
Gangue: Quartz
Gangue: Jasper
Gangue: Calcite
Gangue: Garnet
Gangue: Pyroxene
Gangue: Chlorite
Gangue: Epidote
Gangue: Chatkalite

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Comments

Comment (Development): In January, 1986, Tenneco Minerals Corp. began a McCoy district exploration program, the purpose of which was to evaluate the Triassic rocks which host the McCoy gold skarn deposit. Work consisted of stream sediment sampling, soil sampling, rock sampling, and geologic mapping. By early 1986, 500 stream sediment samples had been collected from the 8 square miles which surround the McCoy mine. Au values for all samples ranged from <1 ppb to 34 ppm; for samples in the vicinity of the Cove deposit, au values ranged up to 72 ppb with anomalous Ag, Hg, As, Sb, Tl. Follow-up outcrop sampling in the cove area identified a zone of over 1000 ft. of strike length with gold values ranging from 0.1 - 1.9 ppm. In September and October, 1986, soil sampling was conducted in the Cove area. 147 soil samples were collected of the B and C soil horizons on a 100 ft. by 200 ft. grid spacing. A geochemical anomaly approx. 2800 ft. long and 100-1000 ft. wide with gold values up to 2600 ppb and As values up to 1000 ppm was identified. The eastern portion of this gold-arsenic anomaly was also anomalous in silver (up to 210 ppm, or 6 opt!). In late 1986, dozer trenching indicated ore -grade mineralization over the strike length of the soil geochemical anomaly. In January, 1987, a 25-hole reverse circulation drilling program of 5000 ft. was started. The first hole intersected 110 ft./0.024 opt gold, 0.92 opt silver and subsequent drill holes encountered equally good ore grade mineralization. Discovery was announced March 31, 1987. Initial development drilling began in March, 1987 with 2 drills operating 1 shift/day. By May, these 2 drills were operating 2 shifts/day. By December, 5 drills were operating 24 hrs./day. By the end of 1988, more than 400,000 ft. of reverse circulation drilling in 475 holes and 38,000 ft. of diamond drilling in 25 holes had been completed. Haul road construction began December, 1987, and limited mining operations began January, 1988, one year after discovery. Full scale mining began March, 1988. Initial mining rate was 75,000 tpd of ore and waste. Mill construction began in 1988, scheduled for mid-1989 completion. In early 1989, additional development angle diamond drill holes were being drilled underneath the Cove open pit. Projected production rate was 225,000 ounces of gold and 2,500,000 ounces of silver annually.

Comment (Deposit): The McCoy-Cove mine is listed as one of the USGS world-class ?Giant? porphyry - related gold systems of the world. The Cove Deposit consists of two main ore zones that are stacked. The upper zone is hosted by lower Augusta Mountain Formation, the lower zone by the Panther Canyon Formation. The deposit consists of an oxide orebody and two refractory orebodies. Ore minerals comprise disseminated, crustiform, and vein sulfides, sulfosalts, oxides, and native metals hosted by the middle to early-late Triassic Augusta Mountain Formation, a post-Sonoma orogeny overlap passive margin sequence. Three host units have been exposed by open-pit mining: 1) the early Ladinian (Mid-Triassic) Home Station Member, consisting of massively bedded silty to sandy diagenetic dolostone; 2) the late Ladinian (Mid-Triassic) Panther Canyon Member, consisting of a lower primary dolostone submember and an upper transitional submember, grading from basal microcrystalline limestone through middle silty limestone and calcite-cemented sandstone to upper conglomerate; and 3) the late Ladinian to early Karnian (LateTriassic) Smelser Pass Member, consisting of medium to thickly bedded limestone with lesser carbonate shale interbeds. The host package is overlain by the unmineralized Oligocene Caetano Tuff. The deposit is centered on the N40?W-striking, 19.5? SE-plunging asymmetrical Cove anticline, which is segmented by extensional faulting. The hypogene orebody controls consist of reactive limestone and dolostone strata, reactive and permeable carbonate-cemented clastic strata, semi-permeable intrusive barriers, and structural highs produced through combinations of folding and faulting. In the upper ore zone, gold and silver mineralization are associated with argillization and with penetrative manganese replacement. In the lower ore zone, gold and silver mineralization are associated with disseminated sulfides, sulfide veinlets, and high lead and zinc contents. The strongest ore intervals are stratabound within the 500 ft thick Panther Canyon transitional submember, in a horst block between two N- and NE-striking faults. This structural high apparently localized ascending pregnant hydrothermal solutions. A large sill in the upper clastic part of the transitional unit trapped a significant volume of the mineralizing fluids, producing in its footwall the largest high-grade ore zone in the deposit. The Smelser Pass limestone formed a physiochemical barrier that also focused fluids and Au-Ag deposition in the underlying transitional unit. Other ore zones occur in the carbonate units above and below the transitional unit, also associated with the horst. Although high-grade hypogene Au and Ag ores typically coincide in space associated with favorable stratigraphic and structural settings, lower-grade ores commonly consist of structurally and stratigraphically localized Ag grading into distal Au. Reverse Ag-Au zonations are not uncommon. Reported K-Ar age dates for fresh and altered intrusive rocks at Cove and the adjacent McCoy gold-copper skarn range between 43 and 37 Ma, indicating that hydrothermal alteration and mineralization closely followed and were related to the emplacement of the igneous bodies. Ten hypogene alteration assemblages indicative of an evolving hydrothermal system occur in the Cove intrusive porphyries. In general terms, these assemblages can be grouped into early weak biotitization, middle propylitization and quartz-sericite-pyrite (QSP) alteration, later argillization characterized by smectite-group clays, and latest barren calcite veining. Analogous alteration styles occur in the sedimentary host units, with the exceptions of the biotite and propylitic assemblages that may be expressed by an early decarbonatization event. The main ore stage is associated with the QSP and argillic alteration stages, and consists primarily of base-metal sulfide veins/veinlets with wide halos of disseminated ore minerals.

Comment (Economic Factors): Cove -McCoy is a world-class gold-silver mine, with pre-mining reserves totaling 3.6 million ounces Au and 164.3 million ounces Ag. McCoy-Cove production: 1986: 50,000 ounces of gold 1987-98: 3,046,660 ounces of gold, 85.79 million ounces of silver 1999: 124,500 ounces of gold, 8.43 million ounces of silver 2000: 162,784 ounces of gold, 12,328,297 ounces of silver 2001: 94,633 ounces of gold, 6,451,425 ounces of silver 2002: 33,142 ounces of gold, 1,987,421 ounces of silver 2003: 4,699 ounces of gold, 706 ounces of silver 2004: 8,454 ounces of gold, 64,335 ounces of silver For a total production between 1986 and 2004 of 3,524,872 ounces of gold and 115,052,184 ounces of silver. Reserves/resources proven and probable reserves 1981: 2.5 million tons, 0.08 opt Au, 1 opt Ag (McCoy) 1987: 14 million tons, 0.05 opt Au (McCoy); 4 million ounces of gold, 250 million ounces of silver (Cove) 1989: 2.9 million ounces of gold, 128 million ounces of silver plus a geologic resource of 3.5 million ounces of gold, 1.50 million ounces of silver 1999: proven and probable reserves of 11.8 million tons, 0.043 opt Au, 2.387 opt Ag plus 100,000 tons, 0.350 opt Au, 2.0 opt other mineralization 2000: proven and probable reserves of 4.7 million tons, 0.034 opt Au, 2.309 opt Ag 2001: 430,000 tons, 0.031 opt Au, 2.624 opt Ag Newmont Mining Corp. was still reporting production from its McCoy/Cove Mine in 2004.

Comment (Geology): The post-mineral Caetano Tuff (32-34 Ma) covers +/- 60% of the Cove deposit.

Comment (Identification): All material from earlier records M232459, W700450, M242946, M242947, for the Cove and McCoy mines has been incorporated into the current record. All material from earlier records the McCoy Gold Mine record 10310312 was merged into this record and deleted.

Comment (Location): The mine is located on the NE side of the Fish Creek Mountains. The original Cove Mine was approximately 1.5 miles NE of McCoy Mine, later merged as a single entity.

Comment (Commodity): Ore Materials: Cove mine - electrum, native silver, canfieldite, tetrahedrite, tennantite, acanthite. McCoy mine - native gold, cerargyrite, malachite, galena, cerussite, pyrite, chalcopyrite, chalcocite.

Comment (Commodity): Gangue Materials: Cove mine - clay, sericite, calcite, iron oxides, manganese oxides, pyrite, sphalerite, galena, cassiterite, marcasite, chalcopyrite, stannite, pyrrhotite, arsenopyrite, digenite, covellite, chalcocite, chatkalite. McCoy mine - quartz, opalite, jasper, iron oxides, calcite, garnet, pyroxene, calcite, epidote, zeolite, chlorite, pyrite.

Comment (Development): McCoy mine only: the discovery of gold-bearing ore was made in 1914 by J.H. McCoy who located nine claims. McCoy Consolidated Mines (1929). Summa Corp drilled over 200 holes in what is now the McCoy deposit, in 1969; Houston Oil bought out Summa's holdings in 1977 and drilled another 120 holes in the deposit and in 1981 announced sub-economic reserves. Property was leased to Consoidated Goldfields PLC who in 1984 decided that the property was still subeconomic and turned it back to Tenneco (successor of Himco). Tenneco reappraised the property and decided to put it into production as an open-pit, heap leach operation in 1985. Development began in Sept. 1985 with first gold poured April, 1986. Tenneco explored adjacent ground and more than doubled the mineable reserve to 615, 000 ounces of gold. Echo Bay acquired Tenneco's precious metals properties in Nov. 1986, and Newmont subsequently acquired Echo Bay's properties.

Comment (Deposit): McCoy mine only: Gold occurs with quartz, opalite, jasper, iron oxides, and calcite in highly altered diorite or shear zones in the diorite. Lode consists of quartz and clay stringers 15-30 feet wide, with up to 80% quartz.

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References

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

Reference (Deposit): Emmons, D.L, 1989, The Cove Gold-Silver Discovery, Lander County, Nevada, Oral Presentation At 118th Annual Meeting of AIME, Las Vegas, March 2.

Reference (Deposit): Emmons, D.L., and Coyle, R.D., 1988, Echo Bay Details Exploration Activities at its Cove Deposit in Nevada; Mining Engineering,, August, 1988, p. 791-794.

Reference (Deposit): NBMG Mining District File 157, item 12, unpublished report by Echo Bay Mines, and numerous press Clippings.

Reference (Deposit): Engineering and Mining Journal, June, 1988, p. 43.

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

Reference (Deposit): Marcus K. Johnston, 1999, Structural and stratigraphic controls on hypogene alteration and precious metals distributions at the Cove gold-silver mine, Nevada; GSN Newsletter, May, 1999.

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): Felix E. Mutschler, Steve Ludington, and Arthur A. Bookstrom, 1999, Giant Porphyry-Related Metal Camps of the World-A Database; USGS Open-File Report 99-556.

Reference (Deposit): Burgess J.A. (1914) Report on Camp McCoy, Lander Co. Nev., N.B.M. District file 157, item 1

Reference (Deposit): Smith, P. and Bentz, J., Nov, 1981, NBMG Field Examination Report.

Reference (Deposit): Stager, H.K. (1977) Geology and Mineral Resources of Lander Co., N.B.M. Bull 88

Reference (Deposit): Lane, M.F., 1987, Geology and Mineralization of The McCoy Skarn, Lander Co., Nevada; Unpub. paper presented at 93rd NW Mining Assoc. Convention, 1987.

Reference (Deposit): Unpub. report by Echo Bay Mines, on file at NBMG, mining district file 157.

Reference (Deposit): Kuyper, B.A., 1986, Geology of the McCoy Gold Deposit, GSN Precious Metals Symposium Paper.

Reference (Deposit): Shrader, F.C., 1934, USGS IC. #10.

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

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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.