Top, Mahoney Canyon, and Sage Flat Deposits

Site Name

Primary: Top, Mahoney Canyon, and Sage Flat Deposits
Secondary: Bald Mountain project

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Commodity

Primary: Gold
Secondary: Silver
Tertiary: Zinc
Tertiary: Tellurium
Tertiary: Mercury
Tertiary: Copper
Tertiary: Bismuth
Tertiary: Arsenic
Tertiary: Antimony

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Location

State: Nevada
County: White Pine
District: Bald Mountain 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: Ely BLM district

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Barrick Gold Corp.
Info Year: 2006

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Deposit Type: sediment-hostedand porphyry-hosted disseminated gold
Operation Type: Surface-Underground
Year First Production: 1985
Year Last Production: 2004
Discovery Year: 1869
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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Physiography

Not available

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Mineral Deposit Model

Model Name: Distal disseminated Ag-Au

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Orebody

Form: pipe-like

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Structure

Type: L
Description: The Top pit contains an array of high-angle faults that appear to radiate circularly from the Bald Mountain Stock, and low-angle, bedding-parallel faults. Both N-trending faults and less prominent W-trending fractures are present.

Type: R
Description: The Bald Mountain district is located in an area of thinned crust along the eastern side of the Late Proterozoic rift that split the North American craton. It is also in the west-central portion of the Late Devonian-Early Mississippian Antler foreland basin, and near the eastern edge of deformation related to the late Paleozoic Humboldt orogeny To the west of the Bald Mountain district, geologic interpretations are dominated by recognition of Paleozoic deformation, whereas to the east, interpretations emphasize Mesozoic contraction and plutonism and Tertiary extension.

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Alterations

Alteration Type: L
Alteration Text: Alteration at the Top Deposit includes decalcification, pervasive silicification, and argillization.The quartz porphyry dike is altered variably from incipient argillic alteration of feldspars to total textural destruction forming a soft white clay-rich rock. Locally, calc-silicate skarn and recrystallized marble have developed along the contact between th intrusive rocks and the calcareous sediments.

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Rocks

Name: Porphyry
Role: Associated
Description: quartz feldspar dikes and sills
Age Type: Associated Rock
Age in Years: 159.000000+-
Age Young: Late Jurassic

Name: Porphyry
Role: Associated
Description: quartz monzonite stock
Age Type: Associated Rock
Age in Years: 159.000000+-
Age Young: Late Jurassic

Name: Quartz Monzonite
Role: Associated
Description: porphyry stock
Age Type: Associated Rock
Age in Years: 159.000000+-
Age Young: Late Jurassic

Name: Argillite
Role: Host
Age Type: Host Rock
Age Young: Middle Ordovician
Age Old: Early Ordovician

Name: Limestone
Role: Host
Age Type: Host Rock
Age Young: Middle Ordovician
Age Old: Early Ordovician

Name: Dolomite
Role: Host
Age Type: Host Rock
Age Young: Middle Ordovician
Age Old: Early Ordovician

Role: Host
Age Type: Host Rock Unit
Age Young: Late Ordovician
Age Old: Middle Ordovician

Name: Porphyry
Role: Host
Description: quartz feldspar
Age Type: Host Rock
Age Young: Jurassic

Name: Quartz Monzonite
Role: Host
Age Type: Host Rock
Age Young: Jurassic

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Clay
Ore: Limonite
Gangue: Pyrite

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Comments

Comment (Location): The Top, Mahoney Canyon, and Sage Flats deposits are clustered about three miles southeast of the Bald Moumtain 1-5 pit area. UTM is to the Top deposit.

Comment (Workings): The mine is developed by both open pit and trackless underground. The Top deposit mine schedule includes 6 stages. An additional Stage 7 was not economic at 2002 gold prices. The total amount of material remaining to be mined in Stage 6 in 2002 was estimated to be 2.2 million tonnes at 2.15 g/t Au and 7 million tonnes of waste. The ultimate pit will be approximately 340 metres deep. Bench heights are 8 metres. Internal high walls vary from 38 to 45 degrees depending on geotechnical conditions. Mining of ore and waste averages 45,000 tonnes per day, seven days a week. The Top pit is being mined by conventional open pit mining methods. The mobile equipment fleet, which was upgraded in 1996 consists of nine Cat 785 Haul Trucks and three LeTourneau L-1100 loaders.

Comment (Commodity): Ore Materials: free gold

Comment (Commodity): Gangue Materials: pyrite, clay, limonite, jasperoid

Comment (Deposit): The Top deposit is the largest known mineral resource in the district. Gold mineralization at Top is hosted in the main quartz monzonite stock, quartz feldspar porphyry, and in limestone, argillite, and dolomites of the Ordovician Antelope Valley Formation along the margin of the Bald Mountain stock. Locally, calc-silicate skarn and recrystallized marble have developed along the contact between th intrusive rocks and the calcareous sediments. NNE-striking shear zones and breccia bodies cut across the south contact between the dike and the prophyry. Higher-grade gold mineralization is controlled by northeast and northwest trending normal faults and is associated with limonitic breccia, gouge, and locally with skarn. The orebody forms a horseshoe to pipe-like shape, which rakes to the northeast along the contact between the quartz feldspar porphyry and the dolomite and along the plunge of the intersection of the major NW and NNE structural zones. Rare visible gold is seen in the eastern portion of the Top deposit.

Comment (Geology): The Top and RBM deposits both have high Cu, Zn, and Ag contents associated with gold mineralization as well as anomalous values in Bi, Hg, As, Sb, and tellurides. Granitic intrusive with quartz phenocrysts and oxidized pyrite was noted in cut face of drill roads.

Comment (Identification): The Top, Mahoney Canyon, and Sage Flat deposits are part of Placer Dome?s Bald Mountain Mine project.

Comment (Economic Factors): 617,266 ounces of gold were produced from all Placer Dome?s Bald Mountain deposits from 1999 through 2003, from more than 20 million tonnes of ore. From 1985 to 1988, the initial stages of the Top Deposit were mined producing 5 million tons of ore grading 0.047 ounces per ton for a total 250,000 ounces. The deposit was idle until 1996, when mining Stage Four of the deposit was begun. The deposit is currently in Satge 7 of production (2004). Reserves of the Top Deposit alone in 1996 were about 14 million tons of orre grading 0.060 ouncesper ton, for about 840,000 contained ounces.

Comment (Development): The Bald Mountain mining district was established on August 20, 1869, when G.H. Foreman staked the Nevada claim group on silver chloride-bearing outcrops near the present site of the Top Deposit. During the 1870s and 1880s minor Cu, Ag, Sb, and Au were produced from area claims. Minor placering was followed by a period of inactivity, after which mining activity recommenced in the 1890s. The Copper Basin mine, adjacent to the east side of the Top deposit, was reactivated with minor Cu and Au production. The modern era of exploration in the district began with porphyry copper exploration by Bear Creek (Kennecott) Mining Company between 1956 and 1965. Ed Hager, with Cordero and in partnership with Steve Damele, explored the area during the late 1960s and 1970s and was instrumental in getting Placer Amex, predecessor company of Placer Dome, involved in Bald Mountain. The Top deposit was discovered in 1981. In May of 1983, Placer Amex began their first heap leach production of Au from the 5-pit deposit. In 1984, Placer announced mineable reserves of 2.8 MT grading 0.090 opt Au contained in six separate deposits and full-scale production at Bald Mountain Mine was achieved in late 1985 when mining commenced from the Top deposit, the largest economic gold occurrence discovered in the district mining district to date. Placer developed the Top deposit in 6 stages and is currently (2004) developing the Stage 7 layback of the Top Pit area, the total amount of material remaining to be mined in Stage 6 is estimated to be 2.2 million tonnes at 2.15 g/t Au and 7 million tonnes of waste. The ultimate pit will be approximately 340 metres deep. Bench heights are 8 metres. Internal high walls vary from 38 to 45 degrees depending on geotechnical conditions. Mining of ore and waste averages 45,000 tonnes per day, seven days a week. The Top pit is being mined by conventional open pit mining methods. The mobile equipment fleet, which was upgraded in 1996 consists of nine Cat 785 Haul Trucks and three LeTourneau L-1100 loaders. Drilling equipment consists of two DML and one DM45 Ingersoll Rand drill rigs. In 2002 Placer Dome reported plans to extend mining into Sage Flats, a deposit almost adjacent to the Top Pit, for which a proposed small open pit was already permitted. In 2006, Barrick Gold Corp. acquired the Top, Mahoney Canyon, and Sage Flat deposits through its acquisition of Placer Dome U. S., Inc.

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References

Reference (Deposit): NBMG mining district files 323, press clippings

Reference (Deposit): GSN 1985 meeting and fall field trip road log

Reference (Deposit): Adamson, T. J., 1987, in Bulk Mineable Precious Metal Deposits of the Western U.S., 1987 GSN, field trip guidebook and technical volume.

Reference (Deposit): NBMG, MI-85 through MI-03;

Reference (Deposit): Nutt, C.J., Hofstra, A.H., Hart, K.S., and Mortensen, J.K., 2000, Structural setting and genesis of gold deposits in the Bald Mountain-Alligator Ridge area, east-central Nevada, in Cluer, J.K., Price, J.G., Struhsacker, E.M., Hardyman, R.F., and Morris, C.L., eds., Geology and Ore Deposits 2000: The Great Basin and Beyond: Geological Society of Nevada Symposium Proceedings, May 15-18, 2000, p. 513-537.

Reference (Deposit): Hitchborn and others, 1996, Geology and Gold Deposits of the Bald Mountain Mining District, White Pine County, Nevada, in Geology and Ore Deposits of the American Cordillera Symposium Proceedings, eds. A. Coyner and P. Fahey.

Reference (Deposit): The Geological Society of Nevada 1996 Spring Field trip, Geology and Gold Deposits of Eastern Nevada, GSN Special Publication No. 23.

Reference (Deposit): BLM, 2004, Bald Mountain Mine Exploration Program Programmatic Environmental Assessment NV040-04-023, Case File # N78825.

Reference (Deposit): Draft EIS, 1995

Reference (Deposit): Final EIS, 1995

Reference (Deposit): Environmental Assessment, 1997

Reference (Deposit): Amer. Mines (1996), 1995 through Amer. Mines (2001), 2000;

Reference (Deposit): www.placerdome.com;

Reference (Deposit): Nevada Land Status, 1990

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.

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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.