Cortez Gold Mine

Producer in Lander county in Nevada, United States with commodities Gold, Silver, Mercury, Arsenic, Antimony

Sections on this page

Identification information
Geographic coordinates
Site location context
Geographic areas
Public Land Survey System information
Commodities
Materials information
Alteration
Mineral occurrence model information
Host and associated rocks
Nearby scientific data
Geologic structures
Ore body information
Controls for ore emplacement
Economic information about the deposit and operations
Mining district
Land status
Ownership information
Reserves and resources
Links to other databases
Bibliographic references
General comments
Reporter information

Geologic information

Identification information

Deposit ID	10310410
MRDS ID	M232243
Record type	Site
Current site name	Cortez Gold Mine
Alternate or previous names	Cortez Joint Venture Gold Mine, Cortez Leach Operation, Cortez Mine, Garrison Mine
Related records	10044681

Comments on the site identification

This record describes the current (2006) Cortez Joint Venture gold mine in Lander county, just west across the county line from the historic Cortez underground silver mine in Eureka County, which is described in a separate record, M232243. This record supersedes records W016364 and M232235 and includes all information from those records. MRDS records # W016364 and M232235 should be deleted from the database and replaced by this record.

Geographic coordinates

Geographic coordinates:	-116.62593, 40.19158 (WGS84)
Elevation	1520
Relative position	The mine area is located about 50 km south of Beowawe. The historic mine workings are in Eureka County just east of the Eureka-Lander County line. Present-day mine operations are in both Lander and Eureka Counties.

Site location context

Political divisions (FIPS codes)

Lander(county)

Nevada(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Cortez Canyon(quadrangle 1:24,000 scale)

Crescent Valley(quadrangle 1:100,000 scale)

Winnemucca(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Middle Humboldt(hydrologic unit)

Humboldt(hydrologic accounting unit)

Black Rock Desert-Humboldt(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	Lander
United States	Nevada	Eureka

Public Land Survey System information

Meridian	Township	Range	Section	Fraction	State
Mount Diablo	026N	047E	5,8,13		Nevada
Mount Diablo	027N	048E	24		Nevada

Comments on the location information

The mine area is located at the edge of Crescent Valley and is part of the Cortez Joint Venture which operates Cortez, Pipeline and South Pipeline mines.

Commodities

Commodity	Importance
Gold	Primary
Silver	Primary
Mercury	Tertiary
Arsenic Critical	Tertiary
Antimony Critical	Tertiary

Comments on the commodity information

Commodity Info: Gold is submicroscopic (micron to submicron-sized particles of native gold), occurring in minute specks of arsenian pyrite.
Ore Materials: native gold, pyrite
Gangue Materials: hematite, goethite; gangue: quartz, carbonate, clays

Materials information

Materials	Type of material
Gold	Ore
Pyrite	Ore
Hematite	Gangue
Goethite	Gangue
Quartz	Gangue
Clay	Gangue

Alteration

(Local) Host rocks have been decalcified, silicified, leached, bleached, argillized, and oxidized. This phase of low grade hydrothermal alteration occurred after intrusion of the porphyry sill, and removed most of the carbon. A decalcification halo extends into the host rock surrounding the mineralized area. Mineralization is associated with silicification.

Mineral occurrence model information

Model code	173
USGS model code	26a.1
Deposit model name	Sediment-hosted Au
Mark3 model number	17

Host and associated rocks

Host or associated

Host

Rock type

Sedimentary Rock > Carbonate > Limestone

Rock unit name

Roberts Mountain limestone

Stratigraphic age (youngest)	Early Devonian
Stratigraphic age (oldest)	Wenlock

Host or associated

Host

Rock type

Sedimentary Rock > Clastic Sedimentary Rock > Siltstone

Rock unit name

Roberts Mountain limestone

Stratigraphic age (youngest)	Early Devonian
Stratigraphic age (oldest)	Wenlock

Host or associated

Host

Rock type

Sedimentary Rock > Clastic Sedimentary Rock > Sandstone

Rock unit name

Roberts Mountain limestone

Stratigraphic age (youngest)	Early Devonian
Stratigraphic age (oldest)	Wenlock

Host or associated Host

Rock type Sedimentary Rock > Carbonate > Limestone

Rock unit name Wenban Limestone

Stratigraphic age (youngest) Devonian

Host or associated

Associated

Rock type

Plutonic Rock > Porphyry

Rock type qualifier

BIOTITE-QUARTZ PORPHYRY DIKES and sills

Rock unit name

Mill Canyon quartz monzonite stock

Stratigraphic age (youngest)	Oligocene

Host or associated

Associated

Rock type

Plutonic Rock > Granitoid > Quartz Monzonite

Rock type qualifier

STOCK

Rock unit name

Mill Canyon quartz monzonite stock

Stratigraphic age (youngest)	Oligocene

Host or associated

Associated

Rock type

Volcanic Rock (Aphanitic) > Intermediate Volcanic Rock > Andesite

Rock type qualifier

FLOWS

Rock unit name

Caetano Tuff

Stratigraphic age (youngest)	Tertiary

Host or associated

Associated

Rock type

Volcanic Rock (Aphanitic) > Felsic Volcanic Rock > Rhyolite

Rock type qualifier

PLUG, dikes, and sills

Rock unit name

Caetano Tuff

Stratigraphic age (youngest)	Tertiary

Nearby scientific data

(1)	-116.62593, 40.19158	ListMap

Economic information

Geologic structures

Type of structure	Local
Structure description	The deposit occurs within the Cortez Window in the Roberts Mountain Thrust.
Type of structure	Regional
Structure description	The deposit lies within the Cortez Window of the Roberts Mountain Thrust (Cortez Range).

Ore body information

General form Irregular; gold is localized where limestone was faulted, brecciated and folded along margin of Tertiary intrusive, gold is micron-to sub-micron-size.

General form	Irregular; gold is localized where limestone was faulted, brecciated and folded along margin of Tertiary intrusive, gold is micron-to sub-micron-size.

Controls for ore emplacement

Gold is localized where limestone was faulted, brecciated and folded along the margin of a Tertiary intrusive.

Comments on the geologic information

The deposit is also associated with the Horse Canyon volcanics (andesite flows, rhyolite plug) and the Roberts Mountain Limestone (silty, argillaceous, carbonaceous, pyrite-bearing limestone).

Economic information about the deposit and operations

Operation type	Surface
Development status	Producer
Commodity type	Metallic
Deposit size	Large
Significant	Yes
Discovery year	1966
Discoverer	U.S.G.S./Placer Dome
Year of first production	1969
Year of last production	1993
Production years	1969-1976, 1981-1983, 1988-1993

Mining district

District name	Cortez District
District name	Bullion District

Land status

Ownership category	Private
Ownership category	BLM Administrative Area
Area name	Battle Mountain BLM Administrative District

Ownership information

Type Owner

Owner Barrick Gold

Interest 60

Year 2006
Type Joint Venture Owner-Op

Owner Cortez Gold Mines, Art Walsh, General Manager

First year 1983
Type Owner

Owner Kennecott Explorations (Australia) Ltd. (Rio Tinto)

Interest 40

Year 2006
Type Joint Venture Partner

Owner Placer Amax

First year 1983
Type Joint Venture Partner

Owner Idaho Mining Co.

First year 1983
Type Joint Venture Partner

Owner Taylor, Jr., Vernon F.

First year 1983
Type Operator

Owner Barrick Gold

Type	Owner
Owner	Barrick Gold
Interest	60
Year	2006

Type	Joint Venture Owner-Op
Owner	Cortez Gold Mines, Art Walsh, General Manager
First year	1983

Type	Owner
Owner	Kennecott Explorations (Australia) Ltd. (Rio Tinto)
Interest	40
Year	2006

Type	Joint Venture Partner
Owner	Placer Amax
First year	1983

Type	Joint Venture Partner
Owner	Idaho Mining Co.
First year	1983

Type	Joint Venture Partner
Owner	Taylor, Jr., Vernon F.
First year	1983

Type	Operator
Owner	Barrick Gold

Reserves and resources

Type In-situ

Estimate year 1968

Commodity Subtype Grade units Group Importance Year

Gold Au 8.821 g/mt Gold Major 1968

Comments on the workings information

open pit mine; the original Cortez deposit pit is occupied in part now by Cortez Bass Pond, a pit lake that meets drinking water standards and hosts bass and sunfish. The ADA 52 pit was developed on a satellite to the main Cortez deposit.

Comments on other economic factors

Between 1969 and 1984, the Cortez mine produced 7700 kilotonnes of ore containing 24.6 metric tonnes of gold. 1968-82 production was estimated to be over 1,000,000 ounces of gold.
Production is in part estimated since the Cortez Joint Venture production for Cortez, Gold Acres, and Horse Canyon was not always reported separately.
During 2003, Cortez Joint Venture Gold Mines produced 1,065,402 ounces of gold (61% mill, 31% heap leach and 8% carbonaceous ore sale).
Proven and probable mineral reserves for all the Cortez JV mines as of December 31, 2003 are estimated at 12.7 million ounces of gold with a projected mine life of 11 years. Included in the mineral reserves is the Cortez Hills deposit currently estimated at 5.2 million ounces, consisting of 3.7 million ounces proven (25.1 million tonnes at average grade of 4.59 g/t) and 1.5 million ounces probable (12.3 million tonnes at average grade of 3.91 g/t), as well as the Pediment deposit currently estimated at 1.2 million ounces consisting of 1.1 million ounces proven (35.4 tonnes at average grade of 0.99 g/t) and 0.1 million ounces probable (3.5 million tonnes at average grade of 0.74 g/t). The Pipeline/Cortez Hills/Pediment deposits are expected to produce more than 15.7 million ounces of gold over 17 years (1997-2014).
In their 2005 annual report, Placer Dome Inc. (60%) announced that reserves at the Cortez Complex aggregate 257,940,800 tons grading 0.041 ounces of gold per ton proven+probable.

Comments on development

Gold was discovered in 1966 following geochemical studies of the Cortez Window by the U.S.G.S. Subsequent drilling by Placer Dome U.S. (formerly AMEX) led to the outlining of the Cortez gold deposit. In 1968 a joint venture among American Exploration and Mining Co., Bunker Hill Co., Vernon Taylor and Webb Resources announced reserves of 3.4 million tons ore at 0.29 oz/ton gold. Open pit mining began in 1969 with processing in a 1500 t.p.d. mill. Reserves were exhausted and mining ceased in 1976. In 1981-1983, Cortez Gold mines reworked low-grade stockpile ore from the open pit directly above the millsite. This ore was further separated into low and high-grade piles, crushed to -3/4 and then decarbonized and heapleached with cyanide. In 1983 the entire operation employed 104 persons.
A new phase of mining by Cortez Gold Mine commenced in 1988 and continued until 1993. Total production to that time was about 873,000 ounce of gold from about 6.4 million tons of ore. Estimated additional unmined mineralized material remaining in 1999 totaled about 362,000 ounces.
The original Cortez concentrator was placed on care-and-maintenance in late 1999.
Cortez is now generally described together with the other mine properties of the Cortez Joint Venture, (CJV), Pipeline and South Pipeline, located across Crescent Valley to the west of Cortez. Mining is now centered on the Pipeline deposits. CJV Production will swing back to the Cortez Hills with the impending development of the recently disovered Pediment and Cortez Hills deposits.
In their 2005 annual report, Placer Dome Inc. (60%) announced that reserves at the Cortez Complex aggregate 257,940,800 tons grading 0.041 ounces of gold per ton proven+probable.

Reference information

Links to other databases

Agency	Database name	Acronym	Record ID	Notes
USGS	Mineral Resources Data System	MRDS	M232235	MRDS dep_id 10044673 merged into this record.

Bibliographic references

Deposit

Roberts, R.J. et al, (1967) Geology and Mineral Deposits of Eureka Co. Nev., N.B.M. Bull. 64
Deposit

Wells J.D., Stoiser, L.R., and Elliot, J.E., (1969) Geology and Geochemistry of the Cortez Gold Deposit, Economic Geology v. 64, p. 526
Deposit

Stager, H.K., (1977) Geology and Mineral Deposits of Lander Co., N.B. of M. Bull. 88
Deposit

Division of Mine Inspection, Dec. 1983, Directory of Nevada Mine Operations Active in Calendar Year 1983.
Deposit

NBMG, 1983, Map 84, Active Mines and Oil Fields.
Deposit

NBMG, 1983, Active Mines and Oil Fields, Map 84.
Deposit

Bentz, J. and Smith, P., 1982, Field Examination Report, July 12, 1982.
Deposit

Metal Market Consultants, Inc., 1987, Gold Situation Map
Deposit

Nevada Dept. of Minerals, 1993.95-2
Deposit

.Geological Society of Nevada 1997 Spring Field Trip: Geology and Ore Deposits of Northeastern Nevada, Special Publication No. 25
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.
Deposit

Geology and Ore Deposits of the American Cordillera, Field Trip Guidebook Compendium of the April 1995 Geological Society of NevadaSymposium; 501 p.
Deposit

Gulf Resources 1971-1974, Placer Development 1975-1984 Annual Reports.

General comments

Subject category	Comment text
Deposit	Gold mineralization at Cortez is dominantly fault-controlled by low-angle thrust-related features (Duplex Zone) and high-angle faults. Mineralization was further modified by post-mineral faulting. Ore is hosted mainly bySilurian Roberts Mountains Formation and to a lesser extent by the Wenban Limestone. Crosscutting Tertiary dikes have been dated at 34.5 Ma and are barren of mineralization. Gold is localized where limestone was faulted, brecciated and folded along margin of Tertiary intrusive, gold is micron-to sub-micron-size. Anomalous amounts of Hg, As, Sb, and W are associated with ore in veinlets, and as individual grains in hematite-goethite pseudomorphs after pyrite.

Subject category

Comment text

Deposit

Gold mineralization at Cortez is dominantly fault-controlled by low-angle thrust-related features (Duplex Zone) and high-angle faults. Mineralization was further modified by post-mineral faulting. Ore is hosted mainly bySilurian Roberts Mountains Formation and to a lesser extent by the Wenban Limestone. Crosscutting Tertiary dikes have been dated at 34.5 Ma and are barren of mineralization. Gold is localized where limestone was faulted, brecciated and folded along margin of Tertiary intrusive, gold is micron-to sub-micron-size. Anomalous amounts of Hg, As, Sb, and W are associated with ore in veinlets, and as individual grains in hematite-goethite pseudomorphs after pyrite.

Reporter information

Type	Date	Name	Affiliation	Comment
Reporter	01-JAN-1976	Weeks, Robert	Nevada Bureau of Mines and Geology
Updater	01-OCT-1980	Kirkham, Richard A.	Nevada Bureau of Mines and Geology
Updater	01-JUL-1981	Zigler, Jan L.	U.S. Geological Survey
Updater	01-NOV-1984	La Pointe, D.D. (Tingley, J.V.)	Nevada Bureau of Mines and Geology
Updater	01-SEP-1991	Moyer, Lorre A. (Marcus, S.M.)	U.S. Geological Survey
Updater	01-SEP-1994	Li, Zhiping (Moyer, Lorre A.)	U.S. Geological Survey
Reporter	01-JAN-2000	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.

External references

Wikipedia: Cortez Gold Mine
Wikidata: Q5173246 (Cortez Gold Mine)

Maps centered on this site

Authoritative Nevada resources

These are landing pages for further research — the state agencies don't currently expose per-mine deep links.