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Top, Mahoney Canyon, and Sage Flat Deposits

Producer in White Pine county in Nevada, United States with commodities Gold, Silver, Mercury, Copper, Zinc, Bismuth, Arsenic, Antimony, Tellurium
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Public Land Survey System information
  6. Commodities
  7. Materials information
  8. Alteration
  9. Mineral occurrence model information
  10. Host and associated rocks
  11. Nearby scientific data
  12. Geologic structures
  13. Ore body information
  14. Controls for ore emplacement
  15. Economic information about the deposit and operations
  16. Mining district
  17. Land status
  18. Ownership information
  19. Bibliographic references
  20. General comments
  21. Reporter information

Geologic information

Identification information

Deposit ID 10310443
Record type Site
Current site name Top, Mahoney Canyon, and Sage Flat Deposits
Alternate or previous names Bald Mountain project
Related records 10310383, 10310444, 10310446

Comments on the site identification

  • The Top, Mahoney Canyon, and Sage Flat deposits are part of Placer Dome?s Bald Mountain Mine project.

Geographic coordinates

Geographic coordinates: -115.547, 39.92381 (WGS84)
Elevation 2530
Relative position The deposits are located about 60 miles northwest of Ely, Nevada and 60 miles southeast of Elko, Nevada.

Site location context

Political divisions (FIPS codes)

White Pine(county)

Nevada(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Big Bald Mountain(quadrangle 1:24,000 scale)

Newark Lake(quadrangle 1:100,000 scale)

Ely(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Little Smoky-Newark Valleys(hydrologic unit)

Central Nevada Desert Basins(hydrologic accounting unit)

Central Nevada Desert Basins(hydrologic subregion)

Great Basin(hydrologic region)

Federal lands

Bureau of Land Management(Bureau of Land Management NV)

Bureau of Land Management NV BLM(Type of land area)

BLM(Federal land areas administered by BLM)

Geographic areas

Country State County
United States Nevada White Pine

Public Land Survey System information

Meridian Township Range Section Fraction State
Mount Diablo 024N 057E 22, 23 Nevada

Comments on the location information

  • 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.

Commodities

Commodity Importance
Gold Primary
Silver Secondary
Mercury Tertiary
Copper Tertiary
Zinc Critical Tertiary
Bismuth Critical Tertiary
Arsenic Critical Tertiary
Antimony Critical Tertiary
Tellurium Critical Tertiary

Comments on the commodity information

  • Ore Materials: free gold
  • Gangue Materials: pyrite, clay, limonite, jasperoid

Materials information

Materials Type of material
Gold Ore
Clay Ore
Limonite Ore
Pyrite Gangue

Alteration

  • (Local) 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.

Mineral occurrence model information

Model code 75
USGS model code 19c
Deposit model name Distal disseminated Ag-Au
Mark3 model number 18

Host and associated rocks

  • Host or associated Host
    Rock type Plutonic Rock > Granitoid > Quartz Monzonite
    Stratigraphic age (youngest) Jurassic
  • Host or associated Host
    Rock type Plutonic Rock > Porphyry
    Rock type qualifier quartz feldspar
    Stratigraphic age (youngest) Jurassic
  • Host or associated Host
    Rock type
    Rock unit name Eureka Formation
    Stratigraphic age (youngest) Late Ordovician
    Stratigraphic age (oldest) Middle Ordovician
  • Host or associated Host
    Rock type Sedimentary Rock > Carbonate > Dolomite
    Rock unit name Antelope Valley Formation
    Stratigraphic age (youngest) Middle Ordovician
    Stratigraphic age (oldest) Early Ordovician
  • Host or associated Host
    Rock type Sedimentary Rock > Carbonate > Limestone
    Rock unit name Antelope Valley Formation
    Stratigraphic age (youngest) Middle Ordovician
    Stratigraphic age (oldest) Early Ordovician
  • Host or associated Host
    Rock type Sedimentary Rock > Clastic Sedimentary Rock > Argillite
    Rock unit name Antelope Valley Formation
    Stratigraphic age (youngest) Middle Ordovician
    Stratigraphic age (oldest) Early Ordovician
  • Host or associated Associated
    Rock type Plutonic Rock > Granitoid > Quartz Monzonite
    Rock type qualifier porphyry stock
    Rock unit name Bald Mountain Stock
    Stratigraphic age (youngest) Late Jurassic
    Chronological age 159
  • Host or associated Associated
    Rock type Plutonic Rock > Porphyry
    Rock type qualifier quartz monzonite stock
    Rock unit name Bald Mountain Stock
    Stratigraphic age (youngest) Late Jurassic
    Chronological age 159
  • Host or associated Associated
    Rock type Plutonic Rock > Porphyry
    Rock type qualifier quartz feldspar dikes and sills
    Rock unit name Bald Mountain Stock
    Stratigraphic age (youngest) Late Jurassic
    Chronological age 159

Economic information

Geologic structures

Type of structure Local
Structure 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 of structure Regional
Structure 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.

Ore body information

  • General form pipe-like

Controls for ore emplacement

  • At the Top deposit, higher-grade gold mineralization is controlled by northeast and northwest trending normal faults.

Comments on the geologic information

  • 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.

Economic information about the deposit and operations

Operation type Surface-Underground
Development status Producer
Commodity type Metallic
Deposit size Small
Significant Yes
Discovery year 1869
Discoverer G.H. Foreman
Year of first production 1985
Year of last production 2004
Production years 1985-2004

Mining district

District name Bald Mountain District

Land status

Ownership category BLM Administrative Area
Area name Ely BLM district

Ownership information

  • Type Owner-Operator
    Owner Barrick Gold Corp.
    Year 2006

Comments on the workings information

  • 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.

Comments on other 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.

Comments on 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.

Reference information

Bibliographic references

  • Deposit

    NBMG mining district files 323, press clippings

  • Deposit

    GSN 1985 meeting and fall field trip road log

  • Deposit

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

  • Deposit

    NBMG, MI-85 through MI-03;

  • 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.

  • 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.

  • Deposit

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

  • Deposit

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

  • Deposit

    Draft EIS, 1995

  • Deposit

    Final EIS, 1995

  • Deposit

    Environmental Assessment, 1997

  • Deposit

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

  • Deposit

    www.placerdome.com;

  • Deposit

    Nevada Land Status, 1990

  • 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.

General comments

Subject category Comment text
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.

Reporter information

Type Date Name Affiliation Comment
Reporter 01-NOV-2004 LaPointe, D.D. Nevada Bureau of Mines and Geology
Editor 01-SEP-2007 Schruben, Paul G. U.S. Geological Survey Converted from S&A FileMaker format to Oracle. Edit checks on rocks, units, and ages with Geolex search, and other fields.

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

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Authoritative Nevada resources

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