Leeville Mine Deposits

Site Name

Primary: Leeville Mine Deposits
Secondary: West Leeville Orebody
Secondary: Four Corners orebody
Secondary: Turf orebody

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Commodity

Primary: Gold
Secondary: Mercury
Secondary: Silver
Tertiary: Zinc
Tertiary: Lead
Tertiary: Copper
Tertiary: Thallium

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Location

State: Nevada
County: Eureka
District: Carlin Trend

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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: Newmont, the Gold Company
Info Year: 2004

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Deposit Type: stratabound replacement
Operation Type: Underground
Year First Production: 2005
Discovery Year: 1994
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 flatlying lenses

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Structure

Type: L
Description: Several major faults and fault zones in the North Lynn subdistrict were developed during multiple tectonic episodes ranging from Mississippian to late Tertiary in age. These main structures include: the Roberts Mountains thrust; Lynn fault; Basin Bounding fault; Four Corners structural corridor; Vivian Gulch fault; Silbar fault, and Turf fault. The northeast-striking, northwest-dipping Lynn Fault is the easternmost structure within the Turf deposit. It is an important mineral control at the historic Big 6 mine workings. Important stuctures at West Leeville are the northwest-striking Rodeo Creek fault and the West Bounding fault.

Type: R
Description: The deposit formed in the lower plate of the Roberts Mountains thrust. The Leeville mine area is located on the Carlin trend, and formed in the lower plate of the Roberts Mountains thrust, in the Lynn window. Some workers believe the windows in the thrust are due to doming of the Paleozoic sediments by intrusions at depth. Leeville lies near the crest of the N-NW- striking Tuscarora Mountains Anticline. The regional scale Leeville fault system (the "Leeville Corridor") consists of numerous high angle fault strands that strike NNW and form an important ore-controlling feature along the eastern edge of mineralization.

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Alterations

Alteration Type: L
Alteration Text: Decalcification and silicification are the dominant alteration types.

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Rocks

Name: Granodiorite
Role: Associated
Age Type: Associated Rock
Age in Years: 153.000000+-
Age Young: Late Jurassic

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

Name: Dolomite
Role: Host
Description: impure silty
Age Type: Host Rock
Age Young: Devonian

Name: Limestone
Role: Host
Description: impure silty
Age Type: Host Rock
Age Young: Devonian

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Analytical Data

Not available

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Materials

Ore: Gold
Gangue: Quartz
Gangue: Dolomite
Gangue: Kaolinite
Gangue: Illite
Gangue: Montmorillonite
Gangue: Alunite
Gangue: Feldspar
Gangue: Pyrite

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Comments

Comment (Development): In 1907, small scale gold placer mining began along Lynn Creek and a series of narrow auriferous quartz veins were discovered approximately 1.5 km north of the Carlin orebodies. These veins were developed as the Big Six Mine, located just east of Leeville, and achieved maximum production of about 500 oz. of gold between 1935 and 1936. The main Carlin orebodies to the south were discovered in 1962, and were mined until 1987. In 1992 and 1993, Newmont identified the Leeville Corridor, an extensive zone of high-grade gold mineralization at depths of 1,500 to 2,000 feet below the surface and extending 1.5 miles northwest from the Carlin deposit. In 1994, exploration drilling targeted the footwall of a north-northeast striking fault zone, the West Bounding fault, along the western margin of the Leeville Corridor and intersected the West Leeville deposit. Most of the West Leeville deposit occurs within the High Desert property, where Newmont was majority interest holder and operator of a joint venture with High Desert Minerals Corporation from 1992 through 1995. After discovery of the West Leeville deposit, Barrick Gold Corporation bought High Desert's 40% interest in the Venture in 1995. During 1995 and 1996, infill drilling and prefeasiblity studies were conducted. In 1999, Newmont acquired Barrick's interest in the West Leeville deposit and High Desert property, as a result of an asset exchange between the two companies. Turf was discovered in 1994 by Newmont Exploration Ltd. during the first drill test of the Four Corners structural corridor. Leeville will be Newmont's first underground mine in Nevada accessed via a shaft. The mine plan outlines ramps and drifts to mine three distinct deposits called West Leeville, Four Corners and Turf, all located approximately 1,400 to 2,100 feet below surface. Development at Leeville commenced in 2002 with the beginning of an almost mile-long drift from the Carlin underground mine, northward to the Leeville deposit. This drift serves as an exploration platform and as secondary access to Leeville.In early 2003, sinking of the ventilation shaft and the adjacent production shaft to an ultimate depth of 1,875 feet began. The project is currently on budget and on schedule for fourth quarter of 2005 gold production. Capital expenditures for the project include a surface de-watering system, offices, shaft hoisting systems, surface backfill plant and underground mining support facilities. Newmont expected to begin producing ore from Leeville toward the end of 2005, and the underground mine will produce 550,000 - 600,000 ounces of gold per year through 2020 with an average mining rate of 3,500 tons per day. Production will come from three deposits, West Leeville, Four Corners, and Turf, and the refractory ore will be trucked to Newmont?s roaster for processing. In March, 2003, the Nevada Division of Environmental Protection issued a Water Pollution Control Permit to Newmont Mining Company authorizing the construction, operation, and closure of the Leeville mining facilities. By early 2006, Newmont Mining?s Leeville underground operation began production and is scheduled to produce approximately 600,000 ounces of gold per year.

Comment (Commodity): Ore Materials: gold

Comment (Commodity): Gangue Materials: quartz, dolomite, kaolinite, illite, montmorillonite, alunite, K-feldspar and pyrite

Comment (Deposit): The Leeville mine deposits are 2,300-foot (700 meter) deep consisting of three distinct deposits called West Leeville, Four Corners, and Turf, all located approximately 1,400 to 2,100 feet below the surface. West Leeville is a high-grade, deep, non-hornfelsed, stratabound replacement type deposit of carbonaceous, sulfide refractory, gold ore. High grade (>0.200 opt [6.9 g/t]) gold mineralization in the West Leeville deposit is largely conformable to bedding and occurs in two, 20- to 150-foot (6-45 m) thick, stratabound zones within the upper Roberts Mountains Formation. Mineralization is associated with a broad envelope of strongly decalcified rock and local silica replacement. The thickest and highest-grade part of the West Leeville deposit is located near the intersection of the northwest-striking Rodeo Creek fault and the West Bounding fault. West Leeville ore occurs in gray to black, decalcified and weakly to moderately silicified rocks composed of quartz, dolomite, kaolinite, illite, and pyrite. The Turf deposit is also a deep, highgrade, refractory gold orebody centered about a half mile (0.8 km) north-northwest of the West Leeville deposit.Gold mineralization at Turf is controlled primarily by the Turf fault and by parallel structures in the footwall of the Turf fault. Stratabound, high-grade gold extends up to 300 feet laterally away from the fault along favorable carbonate beds. The micron-sized, disseminated gold is associated with decalcification, silicification, and late-stage sooty fracture-filling veins that postdate the main episode of gold deposition. Gangue minerals, such as montmorillonite, illite, alunite, and K-feldspar, are minor and do not have a direct correlation with gold ore.

Comment (Location): The West Leeville deposit is located about a mile north of the main Carlin Mine, and the Turf, Four Corners are located within a half mile north and west of West Leeville. The historic Big Six Mine lies within a mile to the east of the Leeville Mine deposits the deposit is located beneath the western flank of the mainTuscarora Mountains at the eastern margin of Little Boulder Basin. UTM is to central portion of the West Leeville orebody surface projection.

Comment (Workings): Leeville will be Newmont's first underground mine in Nevada accessed via a shaft. The mine plan outlines ramps and drifts to mine three distinct deposits called West Leeville, Four Corners and Turf, all located approximately 1,400 to 2,100 feet below surface. Leeville is being developed as an underground mine accessible via the Leeville Drift. Shaft-accessible underground mine will use underhand cut and fill and long-hole stoping mining methods Refractory ore will be processed through the Carlin roaster. The average mining rate will be 3,500 tons per day. The proposed Leeville Project will include surface support facilities, access and haul roads, a waste rock facility, stockpiles, power lines, dewatering wells, pipelines, and water treatment facilities. Proposed mining operations and dewatering would last for approximately 18 years, through the year 2020. Surface disturbance is anticipated on approximately 453 acres of public land and 33 acres of private land.

Comment (Economic Factors): At the end of 2002, Newmont reported Leeville?s reserves were 2.7 million ounces with an expected seven-year mine life. Mineralized material not in reserves at that time was reported at 2.6 million tons grading 0.5 ounces of gold per ton. Initial production from the Leeville Mine is expected in the fourth quarter of 2005 at the rate of 550,000 to 600,000 ounces per year at total cash costs of between $195 and $205 per ounce. The Turf deposit as described in 2002 is a gold resource of approximately 1.22 million ounces (38 t) with an average undiluted gold grade of 0.42 ounces of gold per ton (14.4 grams of gold per tonne) and a sulfide content of 3-4%. At that time, Turf was not yet included in Newmont?s mine plan. End of 2002 reserves: for Leeville were 2.7 million ounces (12/31/02)plus mineralized material not in reserves: 2.6 million tons grading 0.5 ounces of gold per ton.

Comment (Geology): At West Leeville, the entire section of Popovich limestone is silicified over the core of the deposit. The silicified Popovich limestone at West Leeville is generally barren of gold and anomalous in base metals, which suggests early, pre-gold deposition of base metals and quartz. Early silicification is also suggested by the relationships of strong silicification to high-grade gold mineralization.

Comment (Identification): Leeville will be Newmont's first underground mine in Nevada accessed via a shaft. The mine consists of three distinct deposits called West Leeville, Four Corners, and Turf.

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References

Reference (Deposit): Roberts, R.J., et al., 1971, Gold-Bearing Deposits in North-Central Nevada and Idaho: Economic Geology, v. 6, 14 p.

Reference (Deposit): Radtke, A.S., 1985, Geology of the Carlin Ore Deposit, Nevada, USGS Professional Paper 1267.

Reference (Deposit): Bakken, B., 1990, Gold Mineralization, Wall-Rock Alteration, and the Geochemical Evolution of the Hydrothermal System in the Main Orebody, Carlin Mine, Nevada, Unpublished Ph.D. Dissertation, Stanford University.

Reference (Deposit): Newmont Gold Company, Annual Report for 1990.

Reference (Deposit): Ryneer, R., 1992, Economic History of the Carlin Trend, in Buffa, R. and Coyner, A., Eds., Geology and Ore Deposits of the Great Basin-Field Trip Guidebook Compendium, The Geological Society of Nevada, Reno, p. 838-843.

Reference (Deposit): Lewis, P., 1992, Carlin Mine Geology, in Buffa, R. and Coyner, A., eds., Geology and Ore Deposits of the Great Basin-Field Trip Guidebook Compendium, The Geological Society of Nevada, Reno, p. 854-858.

Reference (Deposit): Kuehn, C.A., 1989, Studies of Disseminated Gold Deposits near Carlin, Nevada: Evidence for Deep Geologic Settings of Ore Formation, Unpublished Ph. D. Dissertation, Pennsylvania State University, 350 p.

Reference (Deposit): Roberts, R. J., 1960, Alinement of Mining Districts in North-Central Nevada: USGS Prof. Paper 400-B, Art. 9, p. B17-B19.

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

Reference (Deposit): Nevada Division of Minerals, 1994

Reference (Deposit): USBM, 1975, Mineral Industry Surveys: USBM Mercury Quarterly

Reference (Deposit): Noble, L.L., Radtke, A.S., 1978, Geology of the Carlin Disseminated Replacement Gold Deposit, Nevada, Nevada Bureau of Mines and Geology Report 32, p. 40-44.

Reference (Deposit): Roberts, R.J., et al., 1967, Geology and Mineral Resources of Eureka County, Nevada: Nevada Bureau of Mines and Geology Bulletin 64.

Reference (Deposit): Radtke A.S. and Dickinson, F.W., 1976, Structural Controls and Genesis of Carlin Type Deposits: Open-File Report 76-I-39.

Reference (Deposit): US Bureau of Mines (Winnemucca) MILS No. 299, Ref. No. 3201100027, Mineral Property File 30.016.

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): Newmont Gold website, 2004.

Reference (Deposit): Mac Jackson, Margie Lane, and Brad Leach, 2003, Geology of the West Leeville Deposit, in NBMG Bull. 111.

Reference (Deposit): Jerry W. Mohling, 2002, Geology and Gold Mineralization of the Turf Deposit; in NBMG Bull. 111.

Reference (Deposit): Adella Harding, Elko Daily Free Press, 8/6/02, 10/21/02.

Reference (Deposit): BLM, 2002, Draft Environmental Impact Statement (EIS) for Newmont Gold Company?s Leeville Project.

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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.