Eldorado Gold Property

Site Name

Primary: Eldorado Gold Property
Secondary: WBG deposit (Wall Street-Black Hawk-Gracey)

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Commodity

Primary: Silver
Primary: Gold
Secondary: Copper
Secondary: Zinc
Secondary: Lead

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Location

State: Nevada
County: Clark
District: Colorado District

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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: Nevada Pacific Mining
Info Year: 1997

Owner Name: Nelloro Corp.
Info Year: 1997

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: fault zone
Operation Type: Surface-Underground
Year First Production: 1863
Year Last Production: 1970
Discovery Year: 1857
Years of Production:
Organization:
Significant: Y

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Physiography

Not available

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Mineral Deposit Model

Model Name: Detachment-fault-related polymetallic Cu-Au-Ag-Pb-Zn deposits

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Orebody

Form: subhorizontal lenses

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Structure

Type: R
Description: The northern Eldorado Mountains are characterized by many west-dipping listric normal faults which sole into a west-dipping detachment, all formed about between 15 and 10 Ma due to regional extension. The structural style changes markedly in the southern Eldorado Mountains, where Tertiary volcanic strata dip west and are cut by east-dipping listric faults. The Eldorado Canyon and mining district are located between the two structurally distinct areas and represent an ?accommodation zone?.

Type: L
Description: The deposit is bounded on all sides by post-mineral, high-angle faults.

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Alterations

Alteration Type: L
Alteration Text: Propylitic alteration is widespread throughout the host rocks. Anomalous gold also occurs in zones of local silicification, argillic alteration, and quartz-alunite veining.

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Rocks

Name: Schist
Role: Associated
Description: granodioritic
Age Type: Associated Rock
Age Young: Precambrian

Name: Gneiss
Role: Associated
Description: granodioritic
Age Type: Associated Rock
Age Young: Precambrian

Name: Dacite
Role: Host
Description: tuffs flows and volcaniclastic rocks
Age Type: Host Rock
Age Young: Miocene

Name: Andesite
Role: Host
Description: tuffs flows and volcaniclastic rocks
Age Type: Host Rock
Age Young: Miocene

Name: Mafic Intrusive Rock
Role: Host
Age Type: Host Rock
Age Young: Precambrian

Name: Monzonite
Role: Host
Age Type: Host Rock
Age in Years: 14.500000+-
Dating Method: K-Ar
Age Young: Middle Miocene

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Analytical Data

Not available

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Materials

Ore: Gold
Gangue: Calcite
Gangue: Hematite
Gangue: Clay
Gangue: Quartz

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Comments

Comment (Commodity): Ore Materials: gold

Comment (Commodity): Gangue Materials: quartz, calcite, hematite, manganese oxides, clays

Comment (Workings): The mine area includes old underground workings of the Wall Street Mine area as well as more recent open pits.

Comment (Deposit): Anomalous gold occurs primarily in the Nelson monzonite, a heterogeneous, sill-like stock of Miocene age. Mineralization also occurs in Precambrian mafic crystalline rocks and in a Miocene volcanic sequence of andesitic and dacitic tuffs, flows and volcaniclastic rocks more than 3000 feet thick. The deposit consists of three roughly elliptical, shallow, sub-horizontal pods. Pervasive disseminated gold occurs in flat-lying lenses within host rocks of varying composition and alteration. Mineralization is associated with locally anastomosing shear zones which formed during a period of regional extensional faulting that affected the ElDorado Mountains between 10 and 15 Ma, contemporaneously with the time of mineralization.Propylitic alteration is widespread throughout the host rocks. Gold mineralization is tied to a quartz-calcite-veining event that post-dates the propylitic alteration. Anomalous gold also occurs in zones of local silicification, argillic alteration, and quartz-alunite veining. The WBG mineralized zone trends roughly east-west and is underlain by a seemingly chaoctic distribution of altered volcanic rocks, varied plutonic rocks, and breccia. Structural and lithologic controls on the shape of the WBG deposit are subtle. In the Black Hawk mine area, the Nelson monzonite hosts most mineralization. The host rock is brecciated with strong quartz-calcite veining and pervasive hematite-stained clay alteration. In the Gracey Pit, mineralization is localized along the volcanic/monzonite contact, and to a lesser extent along subhorizontal shears. In the Wall Street Pit area, mineralization is both subhorizontal and along steeply-dipping (50 degrees) faults. The deposit is truncated on all sides by post-mineral, moderate- to steeply dipping faults. Mineralization post-dates the intrusion of the Nelson monzonite, and precedes the bounding faults, bracketing it between 14 and 11 Ma.

Comment (Location): The deposit is located in the central part of the historic ElDorado (Nelson) District in SE Clark County, about 25 miles south of Boulder City. It encompasses the historic Wall Street and Black Hawk mines and extends east to Gracey Wash.

Comment (Development): Gold was first discovered in the area in the 1700s by Spanish explorers who named Eldorado Canyon. Gold was later discovered in 1857 on the Honest Miner claim about 2 miles west of Nelson, after which the district was organized in 1861. Between 1863 and 1907, several mines in the district sporadically produced an unrecorded total amount of gold and silver. Between 1907 and 1954, the mines produced 100,600 ounces of gold and 2,360,000 ounces of silver. A small heap leach operation on the Wall Street claim produced a small amount in the late 1970s, which was the last significant production for the district. Numerous companies have examined the bulk-mineable potential of the district since the 1970s, including Intermountain Exploration, Amselco, Exxon, Weaco, Homestake, Zephyr Resources, and Alta Gold. The combined exploration efforts of these companies resulted in the identification of this laterally-continuous disseminated gold deposit encompassing the historic Wall Street and Black Hawk mines. The deposit was held by Nevada Pacific Mining Company in 1995 and was listed among the properties of Nelloro Corp. in 1997.

Comment (Economic Factors): 1907-1959 early production was estimated at more than 76 kilotonnes of ore containing 3.16 metric tonnes of Au, and 73.4 metric tonnes of Ag, total value estimated at $2 to $5 million. In 1993, the remaining resource at the deposit was estimated at a minimum of 1140 kilotonnes of ore containing 1.7 tonnes of gold (1.26 million short tons grading 0.043 opt). This resource includes tailings at the Nel property.

Comment (Geology): A thick sequence of Tertiary volcanic rocks overlies Precambrian granodioritic gneiss and schist in the Eldorado district. The Nelson Monzonite, a sill-like stock, intrudes both volcanic and Precambrian rocks.

Comment (Identification): This deposit encompasses some historic mines in the district: Wall Street (MRDS No. M031039), Black Hawk, and Gracey.

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References

Reference (Deposit): Longwell and others, 1965

Reference (Deposit): Koschmann and Bergendahl, 1968

Reference (Deposit): Robinson, J.P., 1996, in Coyner, A.R., and Fahey, P.L., eds., Geology and ore deposits of the American Cordillera, 1995; symposium proceedings: Reno, Geological Society of Nevada, v. 1, p. 567-579

Reference (Deposit): Wyman, R.V., 1987, in Johnson, J. L., ed., Bulk Mineable Precious Metal Deposits of the Western United States, Geological Society of Nevada, p. 109-113.

Reference (Deposit): AMH 1997 entry for Nelloro Corp.

Reference (Deposit): Long, K.R., DeYoung, J.H., Jr., and Ludington, S.D., 1998, Significant deposits of gold, silver, copper, lead, and zinc in the United States: U.S. Geological Survey Open-File Report 90-206A, 33 p.; 98-206B. 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.