Gold Acres Deposit

Site Name

Primary: Gold Acres Deposit
Secondary: Little Gold Acres
Secondary: Old Kennecott Group
Secondary: Lime Point Claim
Secondary: Lakin Claim
Secondary: Maloney Claim
Secondary: Little Squirt Claim

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Commodity

Primary: Gold
Secondary: Copper
Secondary: Tungsten
Tertiary: Antimony
Tertiary: Arsenic
Tertiary: Mercury
Tertiary: Thallium
Tertiary: Lead
Tertiary: Zinc
Tertiary: Molybdenum

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Location

State: Nevada
County: Lander
District: Bullion District

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Land Status

Land ownership: Private
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.

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Cortez Joint Venture: Kennecott Explorations
Percent: 40.00
Info Year: 2004

Owner Name: Cortez Joint Venture: Placer Dome, Inc.
Percent: 60.00
Info Year: 2004

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Deposit Type: shear zone; breccia fill; sediment-hosted disseminated Au; epithermal
Operation Type: Surface-Underground
Year First Production: 1935
Year Last Production: 1996
Discovery Year: 1920
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: Sediment-hosted Au

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Orebody

Form: tabular; stratabound

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Structure

Type: R
Description: Gold Acres is exposed at the western margin of the Gold Acres window along the NW-trending Roberts Mountains thrust, Cortez-Uinta axis. It lies along the Eureka-Battle Mountain trend of aligned deposits and mineralization.

Type: L
Description: High angle normal faulting of various orientations has broken the mineralized zone into three parts: the main Gold Acres orebody, the Little Squirt orebody, and the Little Gold Acres orebody.

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Alterations

Alteration Type: L
Alteration Text: Alteration of the deposit consists of carbonization, silicification, argillization, oxidation, and skarn formation. Carbonization (up to 3% by weight organic carbon) is the dominant alteration type in the deposit and can give a sooty appearance to the rocks. Silicification is strongest at the northern end of the deposit and decreases to the south. Argillization is primarily confined to fractures in lower plate carbonates associated with carbonization. The clays are generally illitic. Supergene oxidation is evident throughout the deposit area as limonitic and hematitic staining along fractures. Skarn development is associated with the emplacement of a Cretaceous granitic stock. Two prograde, skarn zones are developed, both barren of gold. A retrograde skarn alteration mineral assemblage consists of chlorite, tremolite, epidote, calcite, quartz, illite, nontronite, smithsonite(?), pyrite, pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, and galena. Gold is not associated with the retrograde assemblage.

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Rocks

Name: Quartz Monzonite
Role: Associated
Description: sill
Age Type: Associated Rock
Age in Years: 98.000000+-
Age Young: Late Cretaceous

Name: Porphyry
Role: Host
Description: quartz porphyry dikes
Age Type: Host Rock
Age in Years: 40.000000+-
Age Young: Middle Eocene

Name: Porphyry
Role: Host
Description: quartz porphyry dikes
Age Type: Host Rock
Age in Years: 30.000000+-
Age Young: Early Oligocene

Name: Sandstone
Role: Host
Age Type: Host Rock
Age Young: Silurian

Name: Shale
Role: Host
Age Type: Host Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Chert
Role: Host
Description: siliceous
Age Type: Host Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Limestone
Role: Host
Age Type: Host Rock
Age Young: Early Devonian
Age Old: Wenlock

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Analytical Data

Not available

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Materials

Ore: Molybdenite
Ore: Scheelite
Ore: Pyrite
Ore: Arsenopyrite
Ore: Sphalerite
Ore: Galena
Ore: Pyrrhotite
Ore: Gold

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Comments

Comment (Economic Factors): Gold Acres and Little Gold Acres reserves: 1987: 4.8 million tons of ore grading 0.105 ounces of gold per ton 1988: 5.4 million tons of ore grading 0.093 ounces of gold per ton 1992: reserves-3.1 million tons of ore grading 0.05 ounces of gold and 0.4 ounces of silver per ton Production: Gold Acres: 1942-84: 2.4 million tons of ore grading 0.13 oz ton Au/ton; 2 million tons, 0.041 ounces of gold per ton leached. Little Gold Acres: 800,000 tons of ore grading 0.124 ounces of gold per ton 1988: 42,322 ounces of gold (includes Horse Canyon) 1989: 39,993 ounces of gold , 12,234 ounces of silver (includes Horse Canyon) 1990: 53,945 ounces of gold , 10,150 ounces of silver 1991: 53,500 ounces of gold , 6,600 ounces of silver 1992: 75,000 ounces of gold 1993: 66,850 ounces of gold

Comment (Identification): This record includes all material from earlier record W002496 plus additional material. Older records #M232510 and #M232517 have been deleted.

Comment (Location): Gold Acres is located on the eastern flank of the Northern Shoshone Range. UTM is to the historic Little Gold Acres Mine workings.

Comment (Workings): There are both old underground workings and more recent open pit mines. There were over 3000 feet of underground workings. The historic Little Gold Acres mine is now part of the Gold Acres open pit.

Comment (Development): Gold mining from the North Ore zone (Gold Acres) began in 1935, first by underground methods then by open pit after 1942. From 1942-1961, Gold Acres produced $10 million in gold and silver and was one of the largest gold producers in Nevada in the 1950s. Placer Dome U.S., Inc. began exploring the district in 1959 and consolidated the land position at Gold Acres in 1969 by and conducted a drilling program. By 1973, mineable reserves for what became the South Pit (Little Gold Acres) were estimated at 1.6 million tons grading 0.106 opt gold. Cortez Gold Mines mined Little Gold Acres from 1973-1976. Heap leaching and milling of the Gold Acres dumps and stockpiles followed until 1983. Development drilling continued from 1984-1986. In 1987, mining activity was reactivated at the North Pit where a refractory mineable reserve of 2.2 million tons/0.118 opt gold was exploited. In 2002, Cortez Gold Mines announced plans to reopen the old Gold Acres Mine to recover carbonaceous ore that was left unmined in the bottom of the old open pit. The ore was to be mined by a contractor and transported to Barrick?s Goldstrike The property is owned by Cortez Joint Venture: Placer Dome, Inc. (60%); Kennecott Explorations (40%) (2004).

Comment (Deposit): The deposit is in the west edge of a window in the upper plate of the Roberts Mountains Thrust, and is localized in brecciated chert and limestone in the lower plate (siliceous, volcanic and carbonate rock assembles). The ore is localized in the Roberts Mountains thrust fault breccia zone, in a shear adjacent to a sill. The shear zone is between limestone and sill; sandstone and chert overlie sill. Blocks of tactite within the shear zone are mineralized, the zone is mineralized with native gold, molybdenite, and scheelite. The intrusive contains minor pyrrhotite. The breccia zone contains disseminated iron-oxides and gold as submicroscopic particles. The intrusives exposed in the pit have been dated as 98 my old. The surrounding country rocks have been pyrometasomatized to various degrees, with the introduction of some scheelite. Tactites zones best developed in the lower plate rocks. Epithermal gold mineralization may be overprinted on Cretaceous tactite Cu-Zn mineralization. The orebody strikes N40W, dipping nearly flat to the southwest. The ore limits are determined by assay values. Gold is hosted primarily in the Silurian Roberts Mountains Formation.

Comment (Commodity): Ore Materials: native gold, molybdenite, and scheelite, pyrite, arsenopyrite, sphalerite, galena, pyrrhotite

Comment (Age): Age of mineralization is younger than 98.8, +/-2.0 Ma. Gold deposition postdates Cretaceous skarn development.

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References

Reference (Deposit): Ketner, K. B., 1965, Gold Acres Mine, in Gilluly, J., and Gates, O., Tectonic and Igneous Geology of the Northern Shoshone Range: USGS Professional Paper 465, p. 134-135

Reference (Deposit): Koschman, A. H., and Bergendahl, M. H., 1968, Principal Gold-Producing Districts of the United States: USGS Prof. Paper 610, p. 184

Reference (Deposit): Roberts, R. J., et al., 1971, Gold-Bearing Deposits in North-Central Nevada and Southwestern Idaho: Econ. Geol. 66 (1): 14-33

Reference (Deposit): Amer. Mines (1989), 1989 thru Amer. Mines (2001), 2000

Reference (Deposit): MASMILS 0320150008, 0320150626

Reference (Deposit): Crescent Valley Land Status, 1979

Reference (Deposit): NBMG Bull. 38.

Reference (Deposit): Adella Harding, Elko Daily Free Press Mining Quarterly, Winter 2002-2003.

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): NBMG Map 91, 1st, 2nd, 3rd

Reference (Deposit): Wrucke, C.T. (1974) Geologic Map of the Tenabo Area, Lander Co. Nevada, USGS Map Mf-647.

Reference (Deposit): Anctil, R.J. (1967) Gold Acres Project, Report prepared for Union Pacific Land Co.

Reference (Deposit): USBM (Winnemucca) MILS No. 54, Ref. No. 3201500052, Mineral Property File 74.500

Reference (Deposit): The Nevada Mineral Industry 1990; NBMG Special Publication MI-1990, P.22.

Reference (Deposit): Hays, R.C., and Foo, S.T., 1991, Geology and Mineralization of the Gold Acres Deposit Lander County, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W. and Wilkinson, W.H., Eds., Symposium Proceedings, Geology and Ore Deposits of the Great Basin, Geologic Society of Nevada and the U.S. Geological Survey, April 1-5, 1990, p. 677-685.

Reference (Deposit): McCormack, John, 1991, Written comments on record, 18 Oct/91.

Reference (Deposit): NBMG, MI-83; MI-84; MI-86 thru MI-96; MI-02.

Reference (Deposit): Stager, H.K. (1977) Geology and Mineral Resources of Lander Co., Nevada; NBMG Bull 88

Reference (Deposit): Vanderburg, W. (1939) Reconnaissance of Mining Districts in Lander Co., Nevada; USBM I.C. 7043.

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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.