Cove mine (McCoy-Cove mine; McCoy mine), McCoy Mining District, Lander County, Nevada, USAi

Regional Level Types
Cove mine (McCoy-Cove mine; McCoy mine)	Mine
McCoy Mining District	Mining District
Lander County	County
Nevada	State
USA	Country

Sec 2 T28N R42E. Gold silver copper lead.

McCoy Au-Ag skarn and Cove Au-Ag deposit. Mining ended in 2001.
Located in the northern Fish Creek Mts.

[Mineral list to be updated with data from Johnston et al. (2008)]

Structure: faults

Alteration: 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.

Tectonics: Post-Sonoma orogeny overlap passive margin sequence.

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

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. 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.

Deposit type: Skarn Au

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. 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.

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

Ore(s): fractures, faults

Other Databases

Link to USGS MRDS:	10310331

Other Regions, Features and Areas containing this locality

References