Turquoise Ridge Mine

Site Name

Primary: Turquoise Ridge Mine
Secondary: Powder Hill
Secondary: Bud Hill
Secondary: A Zone
Secondary: Shaft Zone
Secondary: N Beds
Secondary: considered to be a satellite deposit of Getchell Gold Mines

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Commodity

Primary: Gold
Primary: Silver
Secondary: Arsenic
Tertiary: Tin
Tertiary: Lead
Tertiary: Zinc
Tertiary: Bismuth
Tertiary: Copper
Tertiary: Tungsten
Tertiary: Antimony
Tertiary: Mercury
Tertiary: Barium-Barite
Tertiary: Molybdenum
Tertiary: Fluorine-Fluorite
Tertiary: Thallium
Tertiary: Tellurium

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Location

State: Nevada
County: Humboldt
District: Getchell 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: Barrick Gold Corp.
Info Year: 2006

Owner Name: Newmont Gold
Percent: 25.00
Info Year: 2006

Owner Name: Barrick Gold Corp.
Percent: 75.00
Info Year: 2006

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Deposit Type: Sediment-hosted Au; replacement
Operation Type: Surface-Underground
Year First Production: 1938
Year Last Production: 2006
Discovery Year: 1933
Years of Production:
Organization:
Significant: Y

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Physiography

Not available

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Mineral Deposit Model

Model Name: Sediment-hosted Au

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Orebody

Not available

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Structure

Type: L
Description: The Turquoise Ridge deposit occurs on a north-east trending fault system that extends to the Getchell Main Pit where it intersects the main Getchell Fault Zone. To the north-east it heads towards the Chimney Creek orebody. The NNW trending faulting of the Getchell Fault Zone post dates east-west crossing structures, but pre-dates, or is contemporaneous with, north-east and north-west trending structures and joint swarms. These north-east and north-west cross-structures tend not to be displaced, but commonly coalesce with the Getchell Fault Zone, favouring the interpretation that they are largely contemporaneous. They also appear to exert a major control on ore deposition. The older east-west fault and joint sets produce graben structures throughout the mine area, some of which drop the Valmy Formation down to become juxtaposed with the Comus Formation. Gold mineralization is generally found at the intersection of a number of high-angle and low-angle fault sets. The low-angle faults and associated folds are the result of Devonian and Permian-age compressional events and the higher angle faults and fracture sets formed during Tertiary extension. Mineralization is both structurally and stratigraphically controlled.

Type: R
Description: Getchell Fault Zone, Osgood Mountains Pluton

Type: L
Description: The Getchell fault is a zone of overlapping fractures which have an overall strike of N10W. Hotz and Willden (1964) offer evidence for up to 3500 feet of left lateral strike slip displacement and only a relatively small amount of dip slip movement along the Getchell fault. McCollum and McCollum (1991) indicate that the sense of movement on the Getchell fault is right lateral.

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Alterations

Alteration Type: L
Alteration Text: Alteration comments: there is a metamorphic aureole around the Osgood Mountains granodiorite which has produced in the surrounding shaly rocks a mineral assemblage consisting of cordierite-, biotite-, and andalusite-hornfels. Locally limy beds are recrystallized and calc-silicate minerals are developed. Hydrothermal alteration consists chiefly of decarbonatization accompanied by silicification in the limestone beds. Cordierite, andalusite, and biotite of the metamorphic aureole are altered to sericite and/or chlorite. Igneous dikes and portions of the main stock are altered such that plagioclase is altered to sericite and kaolinite and biotite is altered to sericite, chlorite, and pyrite.

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Rocks

Name: Granodiorite
Role: Associated
Age Type: Associated Rock
Age in Years: 90.000000+-
Age Young: Late Cretaceous

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

Name: Limestone
Role: Host
Description: SILTY
Age Type: Host Rock
Age Young: Late Cambrian
Age Old: Middle Cambrian

Name: Shale
Role: Host
Age Type: Host Rock
Age Young: Late Cambrian
Age Old: Middle Cambrian

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Silver
Ore: Electrum
Gangue: Ilsemannite
Gangue: Stibnite
Gangue: Magnetite
Gangue: Marcasite
Gangue: Arsenopyrite
Gangue: Garnet
Gangue: Chalcocite
Gangue: Covellite
Gangue: Cinnabar
Gangue: Guerinite
Gangue: Epidote
Gangue: Molybdenite
Gangue: Cassiterite
Gangue: Bismuthinite
Gangue: Coloradoite
Gangue: Weilite
Gangue: Pharmacolite
Gangue: Haidingerite
Gangue: Sphalerite
Gangue: Galena
Gangue: Orpiment
Gangue: Pyrite
Gangue: Scheelite
Gangue: Pyrrhotite
Gangue: Hubnerite
Gangue: Calcite
Gangue: Chabazite
Gangue: Sericite
Gangue: Chlorite
Gangue: Barite
Gangue: Gypsum
Gangue: Fluorite
Gangue: Getchellite
Gangue: Galkhaite
Gangue: Laffittite
Gangue: Arsenolite
Gangue: Ferrimolybdite
Gangue: Realgar

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Comments

Comment (Deposit): The gold deposits within the Getchell Trend are Carlin- type, sediment-hosted, replacement deposits containing micron gold. Gold mineralization is found in a number of different rock types generally at the intersection of a number of high-angle and low-angle fault sets. The low-angle faults and associated folds are the result of Devonian and Permian-age compressional events and the higher angle faults and fracture sets formed during Tertiary extension. Mineralization is both structurally and stratigraphically controlled. Gold is associated with arsenic, mercury, and to a lesser extent antimony, and commonly with pervasive decalcification, silicification and carbonaceous alteration. Gold is micron-scale generally intergrown with arsenical pyrite, which in turn, is encrusted in barren, diagenetic pyrite. Late stage realgar and orpiment are commonly associated with high-grade ores. The main deposit is confined to a zone nearly 7000 ft. long at the northern end of the Getchell fault zone. Deep exploration shows that the mineralization persists at least 1 km down-dip on the Getchell fault system and also occurs along the parallel Village fault. Maximum width of ore is 200 ft., with an average width of 40 ft. Within ore zones, gold occurs as native grains that range in size from <1 micron to nearly 1 mm, with smaller grains more abundant than larger grains. Most of the gold is intimately associated with the fine grained quartz-carbon matrix of the altered rock termed "gumbo" by Joralemon (1951). Of the sulfides, pyrite and marcasite are principal hosts to gold. As of 1951, the gold:silver ratio in bullion ranged from 2:1 to 134:1 and averaged 10:1 for the entire bullion production to that date. Joralemon (1951) observed microscopic metallic grains in the Getchell ore that he concluded were native silver, although the particles were so small that conclusive chemical tests were not possible. No other silver minerals have been recognized except for very rare grains of electrum. Geochemical work at the Getchell mine and vicinity has demonstrated that As-W-Hg anomalies occur in rocks and soils over the arsenic-gold deposits and that these anomalies are not broad haloes but are restricted to the mineralized area. The highest metal contents are found in oxidized iron-rich material along fractures and bedding planes in barren bedrock, lesser values in caliche coatings on exposed bedrock, and lowest but still anomalous values in soil.

Comment (Development): Prospectors Edward Knight and Emmet Chase discovered gold in 1933 and located the first claims in 1934. With the financial backing of Noble Getchell and George Wingfield, the Getchell Mine, Inc. was organized in 1936 and was brought into production in 1938. In 1938, the mining rate was about 500 tpd of oxide ore and 150 tpd of sulfide ore. Sulfide ore was roasted at 1500 degrees Fahrenheit for one hour and fifteen minutes preparatory to cyanidization. In 1941, a Cottrell electric precipitating unit was installed to save the arsenic that was liberated by roasting the sulfide ore, and in 1943-45, when government wartime restrictions forced the shutdown of many gold producers, Getchell mine was permitted to continue operations as a producer of "strategic" arsenic. In 1943, arsenious oxide was being produced at the rate of 10-25 tpd from furnace fume. Also in 1942, a 227 tonne scheelite flotation plant was built to recover tungsten from Getchell ore. A slack labor supply, and high supply costs forced the gold operations to cease at the end of World War II. The US Bureau of Mines developed a carbon recovery process on site and the mine reopened in 1948 with expanded mill capacity and more underground development, but closed again in mid-1950 when known oxide reserves were exhausted. Gold production was suspended in 1951. From 1951-56, the mill processed tungsten ores mined from throughout the district. Tungsten production ceased in 1957. in 1960, Goldfield Consolidated Mines Co. purchased the interests in Getchell Mine, Inc. from the estates of Wingfield and Getchell. Gold production resumed in June 1962 and continued to December, 1967, when the mine was closed and the mill dismantled. Cyprus Mines formed a joint venture with Goldfield in 1970, with Cyprus as operator. Cyprus dropped the property at the end of 1971. Conoco leased the property from Goldfield in 1972 and completed exploration including over 300 drill holes. Metallurgically difficult sulfide reserves were identified during this program. Conoco subleased the property from 1975 to 1978 to General Electric Co. who conducted tungsten exploration along the margins of the Osgood Stock. In 1981, Conoco purchased the property from Goldfield Corp., but by 1983 had sold the property to First Mississippi for $5 million. At that time the property consisted of 14,100 acres of fee land and almost 5000 acres of unpatented claims, and reserves at the time of purchase were in excess of 750,000 ounces of gold. Mining feasibility and metallurgical studies were initiated in 1984. Heap leaching of waste rock dumps from previous mining operations commenced at the end of fiscal 1985, producing 91 ounces of gold in that fiscal year. By mid-1985, the Getchell property had increased the area of unpatented claims to 13,900 acres. In May, 1987, the board of First Mississippi Corp. authorized open pit mine development and construction of a new mill utilizing autoclave technology to process 3000 tons of ore per day. The mill was completed and production resumed in 1989 combining a traditional cyanide leach circuit with pressure oxidation. The mill started up on oxide ore in February, 1989. Sulfide ore was run through the first pressure oxidation autoclave in April, 1989 followed by the start up of the other two autoclaves in May and June, 1989. By the end of fiscal year 1989, project capital costs stood at $90.3 million, 14% over the June 1987 feasibility study estimate. In fiscal year 1989, overall gold recovery for combined oxide and sulfide mill ores was 89.8%. Heap leaching of waste rock from previous mining operations was completed in fiscal year 1989. Heap leaching continued beyond this date using oxide reserves from the Summer Camp orebody discovered in 1985.

Comment (Deposit): High-grade gold ore at the north end of the Turquoise Ridge deposit is controlled predominantly by a WNW-trending Upper Cambrian(?) basin margin (Muntean). The basin margin was originally identified by Placer Dome Exploration geologists in 1999. The geometry of the margin and its control on gold mineralization have been refined in the last 12 months during re-logging of close-spaced underground holes and development of a 3D geology model for Turquoise Ridge. The basin margin is defined by a sharp, N60-70?W-trending southern margin to a lower sequence of pillowed basalt and underlying sedimentary breccias. The margin occurs along the northern limb of a monocline that is interpreted to have formed by syn-depositional, reactivation of an underlying north-dipping WNW-trending normal fault. The normal faulting caused local instability and the emplacement of multiple sedimentary debris flow breccias. Soon after the emplacement of the debris flows during this Upper Cambrian(?) extensional event, basalt erupted and flowed up to the WNW-trending topographic barrier. Modeling of gold grade shows that much of ore at the north end of Turquoise Ridge is hosted by the sedimentary debris flow breccias. Modeling of low-grade (~0.01 opt Au) shows NNW-elongated shapes below and within the breccia, suggesting Getchell fault parallel structural fabrics served as conduits for upwelling auriferous hydrothermal fluids. Slope deposits of carbonaceous mudstones and limestones of likely late Cambrian age, this blue unit, are folded into a WNW-trending monocline. The monocline is interpreted to have formed by syn-depositional normal movement along a buried WNW-trending fault. We interpret this buried WNW fault to be linked to underlying basement rift faults that formed during the Proterozoic. The normal faulting caused local instability and the emplacement of sedimentary debris flow breccias - the lavender unit. Later basalt eruptions, this green unit, occurred and basalt flowed up to this WNW topographic barrier. This syn-sedimentary faulting was further supported by logging of close-spaced underground drill hole fans. Similar relationships are seen in the northern Carlin trend.

Comment (Workings): The mine area has been developed by both underground and surface workings at various times during its production history. The current Turquoise Ridge deposit is developed by underground workings. The Turquoise Ridge mine is accessed by two existing shafts. Mining at Turquoise Ridge has been based on using an underhand cut-and-fill mining method.

Comment (Commodity): Ore Materials: native gold, native silver, electrum

Comment (Commodity): Gangue Materials: realgar, orpiment, pyrite, scheelite, pyrrhotite, arsenopyrite, marcasite, magnetite, stibnite, ilsemmanite, cinnabar, hubnerite, calcite, chabazite, sericite, chlorite, barite, gypsum, fluorite, getchellite, galkhaite, laffittite, arsenolite, guerinite, haidingerite, pharmacolite, weilite, coloradoite, bismuthinite, cassiterite, molybdenite, ferrimolbdite, galena, sphalerite, covellite, chalcocite, garnet, epidote

Comment (Development): Production of oxide open pit ore commenced at the nearby Turquoise Ridge mine in 1991 and in the same year, an underground orebody adjacent to the pit area. This ore was to be mined when the pit level was deep enough to provide lateral access. In 1995, FirstMiss Gold changed its name to Getchell Gold. Underground production commenced at Turquoise Ridge Mine in May 1998. On May 27, 1999 Placer Dome completed a merger with Getchell Gold Corporation, resulting in Placer Dome owning 100% of the Getchell gold property. Gold production has been suspended since July 1999 and the property is on care and maintenance. Production from approximately 58% of the property is subject to a 2% net smelter return royalty payable to Franco Nevada Mining Corporation Ltd. Placer Dome wrote off the carrying value of the property in 2001. On October 25, 2001, Newmont Mining Corporation and Getchell Gold Corporation signed a letter of intent under which Newmont would buy ore from the Getchell mine for processing at Newmont's adjacent Twin Creeks mine. In 2003 Placer Dome reopened its Turquoise Ridge Mine at Getchell in Humboldt County entering into a joint venture with Newmont Mining to process Turquoise Ridge ore at Newmont facilities. When Barrick acquired Placer Dome propeties in early 2006, the PD portion of the mine came under Barrick?s ownership. In 2006, the Turquoise Ridge underground gold mine was 75% owned by Barrick Gold Corp.,and 25% owned by Newmont Gold, with Barrick as the operator. It employed more than 420 persons. Mining was to be incresed to 1250 tons per day by the end of 2006 using underhand drift-and-fill methods. Mine life was projected to be 20 years. Because of its refractory nature, ore was being processed at Newmont?s Twin Creeks Sage Mill facility

Comment (Economic Factors): As of the end of 2004, Placer Dome?s share of the proven reserves at Turquoise Ridge was reported at 3.08 million tonnes, grading 20.9 grams per tonne, for 2.065 million contained ounces of gold. The deposit also contains additional probable reserves 1.586 million tonnes of ore grading 21.3 grams per tonne for 1.085 million contained ounces. This amounts to a total proven and probable mineral resources of 4.666 million tones of ore grading 21.0 grammes per tonne, for 3.15 million contained ounces, with an expected recovery of 90.8 %. Turquoise Ridge's production forecast for 2005 calls for an increase in Placer Dome's share of production to 150,000 ounces and its cash and total costs per ounce forecast is $310 and $350, respectively. Production will continue to increase in 2005 as mining moves from the topcuts to the more productive undercuts. In their 2005 annual report, Newmont Mining Corp.(25%) announced that reserves at the Turquoise Ridge Mine aggregate 1,900,000 tons grading 0.560 opt Au proven+probable. (was 1,700,000 tons grading 0.610 opt Au proven+probable). In 2006 the Turquoise Ridge underground gold mine had a reported 4 million ounces of reserves in ore grading more than 0.5 ounces oer ton.

Comment (Geology): Geology comments: Bagby and Cline (1991) offer preliminary results from research which indicate that confining pressures on the Getchell ore system varied from approximately 370-430 bars either during, or at some time subsequent to mineralization. These fluid pressures are greater than those which are normally accepted as epithermal.

Comment (Location): The Turquoise Ridge Mine is located approximately 1 km to the east of the Getchell Main Pit; UTM is to center of Main Pit, which has encompassed earlier South and Central pits.

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References

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.

Reference (Deposit): Barrick Gold Corporation, Nevada Mine Tour, September 2006. online presentation on website.

Reference (Deposit): John Muntean,2005, Turquoise Ridge Deposit: Basin Margin Control on Gold Grade, abstract, Winnemucca GSN meeting, Aug.17, 2005.

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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.