Manhattan Gold Mine

Site Name

Primary: Manhattan Gold Mine
Secondary: Big Four Mine
Secondary: Reilly Mine
Secondary: Big Pine Mine
Secondary: Little Grey Mine
Secondary: East Pit
Secondary: West Pit

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Commodity

Primary: Silver
Primary: Gold
Tertiary: Antimony
Tertiary: Arsenic
Tertiary: Fluorine-Fluorite

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Location

State: Nevada
County: Nye
District: Manhattan District

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Land Status

Land ownership: National Forest
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: Tonopah USFS Ranger District

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Round Mountain Gold Corporation
Info Year: 2004

Owner Name: Smoky Valley Common Operation
Info Year: 2004

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: lode, replacement
Operation Type: Surface-Underground
Year First Production: 1868
Year Last Production: 1993
Discovery Year: 1868
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: Epithermal vein, Comstock

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Orebody

Form: Tabular to irregular

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Structure

Type: R
Description: A series of thrust sheets that generally dip to the south have affected rocks in the mine area. The Manhattan gold deposit occurs within a NW-trending, NW-plunging faulted antiform.

Type: L
Description: Reilly Fault (ENE), Jumping Jack Fault (NE), Twin Faults (ENE), Big Pine Fault (ENE), and joints associated with the Brugher Fault trend (NE), joints associated with the Little Grey Fault trend (NW), Little Grey Cross Fault (E-W) and joints associated with other unnamed fault trends, all cut through the mine area.

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Alterations

Alteration Type: L
Alteration Text: Host rocks in the mine area are not strongly altered hydrothermally. Quartz/host rock contacts are sharply defined.

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Rocks

Name: Schist
Role: Associated
Age Type: Associated Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Limestone
Role: Host
Age Type: Host Rock
Age Young: Late Cambrian

Name: Phyllite
Role: Host
Description: sandy
Age Type: Host Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Quartzite
Role: Associated
Age Type: Associated Rock
Age Young: Ordovician
Age Old: Late Cambrian

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Analytical Data

Not available

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Materials

Ore: Arsenopyrite
Ore: Fluorite
Ore: Clay
Ore: Pyrite
Ore: Adularia
Ore: Quartz
Ore: Barite
Ore: Stibnite
Ore: Silver
Ore: Gold
Ore: Fluorite
Ore: Realgar
Gangue: Calcite

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Comments

Comment (Development): The central Manhattan Mining District has had a long and productive mining history. The area was first prospected for silver and copper in the 1860s with some small production of ore that was shipped to Belmont. The next phase of exploration began in 1905 when the rich lode and placer gold deposits were discovered and mined more or less continuously until 1947. Suma Corporation acquired the property in 1967 but did little exploration until 1972 when they launched a major mapping, sampling, and drilling program to delineate a bulk-mineable heap-leachable gold orebody in the district. By 1973, more than 200,000 tons of ore grading 0.10 opt gold had been delineated and 6500 tons of it was mined and heap-leached later that year, with poor recovery due to the coarseness of the gold. Continued drilling in 1974 and 1975 defined more ore in the East and West pit areas increasing the proven reserves to more than 400,000 tons grading 0.075 opt gold, of which 60,000 were heap-leached in 1974. In 1977, Summa sold the property to Houston Oil & Minerals Company ( later Tenneco/CanAm/ Echo Bay Minerals). More drilling in 1977-1979 increased reserves to 800,000 tons grading 0.09 opt gold, which was considered sufficient to justify construction of a 750 tpd mill from 1981 to 1983 during which time mining was suspended pending mill feasibility studies. In 1984, Tenneco (Echo Bay) resumed mining from the East and the West Pits, which incorporated several smaller open pits from earlier Summa Corp. mining activity. They operated the two open pits for several years using a combination gravity circuit and flotation-cyanidation circuit in the mill. Heap leach operations were also in use from 1988 through 1990. Mining ceased in 1990, shortly after Round Mountain Gold Corporation acquired the site. Milling operations and tailings deposition stopped later that same year. Heap leaching and gold recovery continued until 1993 when heap closure activities started with biological detoxification of the spent ore. Reclamation of the Manhattan mine site from 1994 through 2001 earned Round Mountain Gold Corporation the BLM?s Hardrock Mineral Environmental award in 2004 for its innovative reclamation designs and new technique for treating water used in the mining process. Both Calais Resources and Royal Standard Minerals are now exploring and developing nearby gold mining properties in the Manhattan District (2005).

Comment (Commodity): Ore Materials: native gold and silver, stibnite, microscopic arsenopyrite, realgar, fluorite

Comment (Commodity): Gangue Materials: calcite, drusy quartz, adularia, pyrite, clay, iron oxide minerals; rare fluorite and barite

Comment (Commodity): Commodity Info: Fineness of gold averages about 700.

Comment (Deposit): In the main mined area, gold occurs in drusy quartz-adularia veinlets in brittle, fractured, faulted sandy phyllite of the Gold Hill Formation. Native gold is coarse-grained (.04-10 mm) and occurs on fractures as discrete free crystals and masses. Both the East and West Pit orebodies are characterized by a coarse stockwork of fractures lined by gangue minerals and free gold. Frctures generally range in thickness from 0.16 to 1.3 cm. At the historic Nevada Manhattan/Nevada Consolidated Mine workings, mineralization is localized along the Mud Fault. Ore is controlled by a small north-striking fault in the east part of the mine, and by small fault fissures in the west part of the mine. Gold occurs in solution channels forming rare specks of wire in a muddy matrix of iron and manganese oxides (western part). There is also some replacement along bedding, thinning out away from fissures.

Comment (Geology): The oldest rocks in the Manhattan district are phyllite, schist, quartzite and limestone units of the Cambrian Gold Hill Formation. Of these, a sandy phyllite unit of the Gold Hill Formation has been the most productive gold mineralized unit in the mine area. Locally in the district, the Gold Hill Formation has been overthrust by younger Ordovician sedimentary rocks including the Zanzibar limestone, argillite and quartzite units. The mines in the district are located along the southern margin of the Manhattan caldera, which formed about 25 million years ago. Fluid inclusion data indicates homogenization temperatures of 200-235 degrees C at salinities of 0.3-0.8 wt % NaCl equivalent.

Comment (Identification): This record covers a mineralized area described earlier by MRDS records for the historic Big Four, Reilly, Big Pine,and Little Grey mines as well as other Manhattan District mines which are encompassed by the current mine record, and from which all pertinent material has been incorporated into the current record, but those records should remain in the database for historic reference.

Comment (Location): The mine area is centered about one mile ESE of the townsite of Manhattan, up canyon from the townsite.

Comment (Workings): At the historic Nevada Manhattan/Nevada Consolidated Mine, workings consist of a 500 foot vertical shaft with five levels. The entire district is developed by numerous underground and surface workings, including several open pits. The currently described mine was developed by two open pits: the East Pit (1500 feet by 1000 feet) and the West Pit (1200 feet by 300 feet) developed in the 1980s by Echo Bay Mines Ltd.

Comment (Economic Factors): Lode gold production for the Manhattan District through 1967 was about 193,000 ounces of gold. From 1987 through 1989, the current mine produced more than 62,000 ounces of gold, after which production for 1990-1993 was included with that of Round Mountain Gold Mine to the north. In 1997, proven and probable reserves were reported at 1.7 million tons of ore grading 0.13 opt gold.

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References

Reference (Deposit): Kral, V.E., 1951, Mineral Resources of Nye Co.: Nev. Bur. of Mines and Geol., Bull. 50, p. 125

Reference (Deposit): Ferguson, H.G., 1924, Geol. and ore deposits of the Manhattan District: USGS Bull 723, p. 151-153.

Reference (Deposit): NBMG, MI-1993-MI-2004.

Reference (Deposit): Shawe and others, 1986, Ages of igneous and hydrothermal events in the Round Mountain and Manhattan gold district, Nye County, Nevada, Econ. Geol., vol. 81, p. 388-407.

Reference (Deposit): Maddry and others, 1987, Geology of the Manhattan Gold deposit Nye County, Nevada, in Bulk Mineable Precious Metal Deposits of the Western US, GSN Symposium Proceedings.

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.