Cortez Hills Gold Property

Site Name

Primary: Cortez Hills Gold Property
Secondary: Cortez Joint Venture

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Commodity

Primary: Silver
Primary: Gold
Tertiary: Antimony
Tertiary: Arsenic
Tertiary: Mercury

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Location

State: Nevada
County: Lander
District: Cortez 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 Administrative District

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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

Owner Name: Cortez Joint Venture: Placer Dome
Percent: 60.00

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: DISSEMINATED; SEDIMENT-HOSTED
Operation Type: Surface
Discovery Year: 2002
Years of Production:
Organization:
Significant: Y
Deposit Size: L

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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: Irregular

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Structure

Type: R
Description: The deposit lies within the Cortez Window of the Roberts Mountain Thrust (Cortez Range).

Type: L
Description: The deposit occurs within the Cortez Window in the Roberts Mountain Thrust.

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Alterations

Alteration Type: L
Alteration Text: Host rocks have been decalcified, silicified, leached, bleached, argillized, and oxidized. This phase of low grade hydrothermal alteration occurred after intrusion of the porphyry sill, and removed most of the carbon. A decalcification halo extends into the host rock surrounding the mineralized area. Mineralization is associated with silicification. Pervasive oxidation and marble development are key alteration types associated with gold deposition

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Rocks

Name: Rhyolite
Role: Associated
Description: PLUG, dikes, and sills
Age Type: Associated Rock
Age in Years: 33.800000+-
Age Young: Early Oligocene

Name: Andesite
Role: Associated
Description: FLOWS
Age Type: Associated Rock
Age in Years: 33.800000+-
Age Young: Early Oligocene

Name: Quartz Monzonite
Role: Associated
Description: STOCK
Age Type: Associated Rock
Age Young: Oligocene

Name: Porphyry
Role: Associated
Description: BIOTITE-QUARTZ PORPHYRY DIKES and sills
Age Type: Associated Rock
Age Young: Oligocene

Name: Limestone
Role: Host
Age Type: Host Rock
Age Young: Devonian

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

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

Name: Limestone
Role: Host
Description: silty, argillaceous, carbonaceous, pyrite-bearing
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: Gold
Ore: Pyrite
Gangue: Hematite
Gangue: Goethite
Gangue: Quartz
Gangue: Clay

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Comments

Comment (Location): The property is located XX and is part of the Cortez Joint Venture which operates Cortez, Pipeline, and South Pipeline mines.

Comment (Workings): The deposit will probably be developed as an open pit mine.

Comment (Deposit): The recent Cortez Hills discovery is the result of focused exploration efforts along an extensive high-angle fault corridor that localizes the distribution of gold in the Cortez area. Projection of this structural corridor under cover, coupled with gravity data, were the key exploration techniques that led to the discovery of Cortez Hills. Gold is localized where limestone was faulted, brecciated and folded along margin of Tertiary intrusive, gold is micron-to sub-micron-size. The upper portion of the Devonian carbonate sequence beneath the Roberts Mountains thrust hosts the Cortez Hills deposit. Pervasive oxidation and marble development are key alteration types associated with gold deposit. The Cortez Hills deposit is hosted in the upper portion of the Devonian carbonate sequence. It has a strike length of more than 300 m and is approximately 200 m wide. The mineralized zone starts approximately 120 m below surface and continues up to 460 m. The deposit remains open with expansion potential evident to the west and at depth.

Comment (Development): Placer Dome is the operator and owner of a 60% joint venture interest in the Cortez Joint Venture (CJV). The remaining 40% is held by Kennecott Explorations (Australia) Ltd. The recent Cortez Hills discovery is the result of focused exploration efforts by CJV staff along an extensive high-angle fault corridor that localizes the distribution of gold in the Cortez area. Projection of this structural corridor under cover, coupled with gravity data, were the key exploration techniques that led to the discovery of Cortez Hills. June 2004, Placer announced that they had drilled a hole in the area between the Cortez Hills and the Pediment deposits that had returned 1.5 ounces per ton over more than 400 feet.

Comment (Economic Factors): As of year-end 2003, the proven and probable reserves for the Cortez Hills deposit are 5.25 million contained ounces of gold (41.3 million tons of ore grading 0.127 ounces per ton.) An additional 1.58 million contained ounces of gold (12.112 million tons of ore grading 0.114 ounces per ton) of measured, indicated and inferred resource is calculated.

Comment (Geology): The deposit is also associated with the Horse Canyon volcanics (andesite flows, rhyolite plug) and the Roberts Mountain Limestone (silty, argillaceous, carbonaceous, pyrite-bearing limestone).

Comment (Commodity): Commodity Info: Gold is submicroscopic (micron to submicron-sized particles of native gold), occurring in minute specks of arsenian pyrite.

Comment (Commodity): Ore Materials: native gold, pyrite

Comment (Commodity): Gangue Materials: hematite, goethite; gangue: quartz, carbonate, clays

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References

Reference (Deposit): .Geological Society of Nevada 1997 Spring Field Trip: Geology and Ore Deposits of Northeastern Nevada, Special Publication No. 25

Reference (Deposit): NBMG, 1983, Map 84, Active Mines and Oil Fields.

Reference (Deposit): Division of Mine Inspection, Dec. 1983, Directory of Nevada Mine Operations Active in Calendar Year 1983.

Reference (Deposit): Wells J.D., Stoiser, L.R., and Elliot, J.E., (1969) Geology and Geochemistry of the Cortez Gold Deposit, Economic Geology v. 64, p. 526

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

Reference (Deposit): Geology and Ore Deposits of the American Cordillera, Field Trip Guidebook Compendium of the April 1995 Geological Society of NevadaSymposium; 501 p

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): Roberts, R.J. et al, (1967) Geology and Mineral Deposits of Eureka Co. Nev., N.B.M. Bull. 64

Reference (Deposit): Robert C. Hays, Jr., 2003, The Cortez Hills Deposit, a recent discovery in an historic mining district, Lander County, Nevada, abstract for Geological Society of Nevada talk given in spring 2004.

Reference (Deposit): NBMG, 1983, Active Mines and Oil Fields, Map 84.

Reference (Deposit): Bentz, J. and Smith, P., 1982, Field Examination Report, July 12, 1982.

Reference (Deposit): Metal Market Consultants, Inc., 1987, Gold Situation Map

Reference (Deposit): Nevada Dept. of Minerals, 1993.95-2

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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.