Pediment Gold Property

Site Name

Primary: Pediment Gold Property
Secondary: Cortez Joint Venture
Secondary: Cortez Pediment

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Commodity

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

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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 BLM 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: 1998
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.

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Rocks

Name: Rhyolite
Role: Associated
Description: PLUG
Age Type: Associated Rock
Age in Years: 34.000000+-
Age Young: Late Eocene

Name: Andesite
Role: Associated
Description: FLOWS
Age Type: Associated Rock
Age in Years: 34.000000+-
Age Young: Late Eocene

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
Age Type: Host Rock
Age Young: Early Devonian
Age Old: Wenlock

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

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Pyrite
Ore: Goethite
Ore: Quartz
Ore: Clay
Gangue: Hematite

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Comments

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

Comment (Deposit): The Cortez Pediment deposit has one primary mineralized zone that is about 45 metres below the surface on the southern portion of the deposit and about 170 metres below the surface on the northern end of the deposit. The average thickness of the low-angle tabular zone is about 75 metres. The deposit occupies area approximately 1,000 metres in a northerly direction and about 180 metres in an easterly direction. 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 nearby Cortez Hills deposit. Pervasive oxidation and marble development are key alteration types associated with gold deposit.

Comment (Development): Gold was discovered in 1966 following geochemical studies of the Cortez Window by the U.S.G.S. Subsequent drilling by Placer Dome U.S. (formerly AMEX) led to the outlining of the Cortez gold deposit. In 1968 a joint venture among American Exploration and Mining Co., Bunker Hill Co., Vernon Taylor and Webb Resources announced reserves of 3.4 million tons ore at 0.29 oz/ton gold. Open pit mining began in 1969 with processing in a 1500 t.p.d. mill. Reserves were exhausted and mining ceased in 1976. In 1981-1983, Cortez Gold mines reworked low-grade stockpile ore from the open pit directly above the millsite. This ore was further separated into low and high-grade piles, crushed to -3/4 and then decarbonized and heapleached with cyanide. In 1983 the entire operation employed 104 persons. New mining by Cortez Gold Mine commenced in 1988 and continued until 1993. Total production to that time was about 873,000 ounce of gold from about 6.4 million tons of ore. Estimated additional unmined mineralized material remaining in 1999 totalled about 362,000 ounces. ?1983 ownership was Cortez Gold Mines, Art Walsh, General Manager, Crescent Valley, NV 89821; later a joint venture with Placer Amax, Idaho Mining Co., Vernon F. Taylor, Jr. Cortez is approximately 113km south west of Elko, Nevada. It consists of three distinct units: the Cortez open pit and two Carlin-type disseminated gold deposits - Pipeline and South Pipeline. The operation is owned 60% by Placer Dome Inc and 40% by Rio Tinto. Production began at Cortez in 1969 with the Pipeline deposits, where mining is now centered, being discovered subsequently. In 2000, the Cortez complex produced 1,009,922oz of gold at a cash cost of $60/oz (total cost $136/oz), making the mine the lowest-cost gold producer in North America. Placer Dome is the operator and owner of a 60% joint venture interest in the Cortez Joint Venture("Cortez"). The remaining 40% is held by Kennecott Explorations (Australia) Ltd. All production by Cortez is subject to a 1.5% gross smelter return ("GSR") royalty payable to the grantees of Idaho Resources Corp. 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. Cortez Pediment discovered during the fall of 1998. The Pediment Project, which will allow for the construction and mining of a new ore deposit in 2004, requires a newly developed EIS. Permitting of the Pediment Project is in process with baseline environmental studies, cultural resource evaluations, dewatering and water treatment studies and other environmental permitting activities. Kennecott website 12/03

Comment (Economic Factors): As of year-end 2003, the proven and probable reserve for Cortez Hills is 5.25 million contained ounces (41.3 M tons @ 0.127 opt) @ $325/gold. An additional 1.58 million contained ounces (12.112 M tons @ 0.114) of measured, indicated and inferred resource is calculated. Delineation of this new discovery continues with expansion potential evident to the west and at depth. As reported at December 31, 2003, the Cortez Hills deposit, hosts proven and probable gold mineral reserves of 5.2 million ounces, measured and indicated gold mineral resources of 0.5 million ounces, and inferred gold mineral resources of 1.0 million ounces Cortez currently has 7.5 million ounces of gold reserves in Cortez Hills and another 1.2 million ounces at Pediment (Elko Daily Free Press, 9/04) Pediment deposit currently estimated at 1.2 million ounces consisting of 1.1 million ounces proven (35.4 tonnes at average grade of 0.99 g/t) and 0.1 million ounces probable (3.5 million tonnes at average grade of 0.74 g/t).

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 (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.

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

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, Map 84, Active Mines and Oil Fields.

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

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

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

Reference (Location): Lander County Mineral Impact Assessment, Crescent Valley Area - Update, Along the Department of Energy (DOE), Yucca Mountain Project - Proposed Rail Corridor, October 2004. Two parts. The location map showing Pidement and Cortez Hills properties are in section 2, p. 20.

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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.