Twin Creeks Mine

Site Name

Primary: Twin Creeks Mine
Secondary: Chimney Creek Mine
Secondary: Rabbit Creek Mine
Secondary: Mega pit (the merged pit)
Secondary: DZ Zone
Secondary: Main
Secondary: Chert Zone
Secondary: HGO Zone
Secondary: Jackrabbit Zone
Secondary: LGO Zone
Secondary: Sage
Secondary: Section 8
Secondary: Snowshoe Zone
Secondary: South Layback
Secondary: Section 30
Secondary: South Oxide
Secondary: Upper Sill Zone
Secondary: West Pit
Secondary: SWS Zone

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Commodity

Primary: Gold
Primary: Silver
Tertiary: Arsenic
Tertiary: Lead
Tertiary: Zinc
Tertiary: Mercury
Tertiary: Antimony
Tertiary: Barium-Barite

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Location

State: Nevada
County: Humboldt
District: Potosi 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.
Administrative Organization: Winnemucca BLM Administrative District

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Newmont Gold Co.
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
Operation Type: Surface
Year First Production: 1986
Year Last Production: 2006
Discovery Year: 1985
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

Form: tabular to irregular

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Structure

Type: L
Description: The Conelea overturned anticline dominates the structural picture of the early Rabbit Creek Mine area. The fold axis strikes N20-30W, dips 20-30 degrees southwest, and plunges 5 degrees northwest. The Conelea Anticline is offset by three NE-striking faults; the northernmost of the three (DZ fault) has about 2000 ft. of dextral offset. The DZ fault is interpreted as a Riedel "R" shear associated with an inferred major N-S basement suture with right lateral offset, the "Rabbit Suture". Low angle unconformity developed in the Gough's Canyon Formation. The Chimney Creek deposit occurs along a northeasterly range front lineament that is probably an extension of the Getchell Fault. Host rocks strike NE, dip 21-32 NW.

Type: R
Description: Leviathan allochthon. Antler orogenic belt. major, deep seated, N-S structural zone (suture) 40 km (25 miles) long, known as the Getchell high-angle fault system bounds the eastern flank of the Osgood Mountains. N-S trending belt of gold mineralization that is at least 5.6 km (3.5 miles) long and 300 m (1000 ft) to 450m (1500ft) wide. Roberts Mountain Thrust (below) and the Golconda Thrust (above), intruded by the mid-Cretaceous Osgood Mt. granodiorite and related trachyandesite dikes.

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Alterations

Alteration Type: L
Alteration Text: Decalcification, silicification, dolomitization, argillization, and minor sericitization of sediments. Albitization and propylitization of basalt. Decalcification increased porosity, allowing introduction of mineralizing fluids. Silica was introduced in several stages in the HGO orebody. Dolomitization accompanied one of the silicification stages. Argillization is important in the LGO orebody. Hydrothermal alteration formed sericite, kaolinite, dickite, alunite, natroalunite. A zone of phyllic alteration, 50 m wide around feeder zone, contains ore-grade mineralization. Carbonate dissolution zones; two generations of silicification (jasperoid); propylitic alteration of basalts.

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Rocks

Name: Basalt
Role: Associated
Description: basalt
Age Type: Associated Rock
Age Young: Ordovician

Name: Tuff
Role: Associated
Description: basaltic hydroclastic
Age Type: Associated Rock
Age Young: Ordovician

Name: Limestone
Role: Host
Description: carbonaceous
Age Type: Host Rock
Age Young: Early Permian
Age Old: Middle Pennsylvanian

Name: Mafic Volcanic Rock
Role: Host
Age Type: Host Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Chert
Role: Host
Age Type: Host Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Siltstone
Role: Host
Age Type: Host Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Basalt
Role: Associated
Description: basaltic sills
Age Type: Associated Rock
Age Young: Ordovician

Name: Mixed Clastic/Volcanic Rock
Role: Associated
Description: volcaniclastic
Age Type: Associated Rock
Age Young: Ordovician

Name: Shale
Role: Host
Description: interlayered calcareous
Age Type: Host Rock
Age Young: Ordovician
Age Old: Late Cambrian

Name: Ultramafic Intrusive Rock
Role: Associated
Description: ultramafic (iherzolite) sills
Age Type: Associated Rock
Age Young: Ordovician

Name: Basalt
Role: Associated
Description: lava flows
Age Type: Associated Rock
Age Young: Ordovician

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Analytical Data

Not available

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Materials

Ore: Gold
Gangue: Sericite
Gangue: Chlorite
Gangue: Albite
Gangue: Goethite
Gangue: Barite
Gangue: Fluorite
Gangue: Tourmaline
Gangue: Feldspar
Gangue: Leucoxene
Gangue: Limonite
Gangue: Epidote
Gangue: Augite
Gangue: Pyrite
Gangue: Quartz
Gangue: Amphibole
Gangue: Calcite
Gangue: Kaolinite

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Comments

Comment (Geology): The original Rabbit Creek Gold Deposit was concealed under a thick series of coalescing alluvial fans forming a pediment of the Osgood Mountains. The ore body occurs in Paleozoic sedimentary rocks which are completely covered by quaternary sand, gravel and clay. The Paleozoic rocks deposited in a eugeosynclinal environment were extensively deformed during three pre-Tertiary tectonic events. Thrusting during the Antler and Sonoma orogenies brought Western facies deep water units over or interleaved them with Eastern facies, shallow water units in a complex assemblage. Thrusts are generally N-NE striking. Paleozoic units are tilted and folded, often isoclinally, and steeply dipping. During the basin and range extension mafic and felsic dikes were intruded. High angle faults played a primary role in localizing the flow of hydrothermal systems responsible for the deposition of gold. Host rocks are black, carbonaceous, calcareous shales, siltstones, cherts, interbedded basaltic hydroclastic tuffs, and coeval basalts and volcaniclastics. Concordant sills and lava flow of high-titanium basalts of tholeiitic-to-alkalic composition. The Chimney Creek Deposit is stratigraphically and tectonally complex. The deposit is sandwiched between the mid-Paleozoic Roberts Mountain Thrust and the Permo-Triassic Golconda Thrust. Alteration and mineralization re channeled into the thick bedded lower member of the Etchart Limestone along high angle fault feeder zones in the Gough's Canyon Formation and spread out laterally along bedding to form a conformable sediment-hosted gold-silver deposit above a disconformable structurally controlled volcanic-hosted feeder zone. Mineralization occurs exclusively in the Gough's Canyon Formation and the lower members of the Etchart Limestone. The highest Au-Ag grades are coincident with the most severe carbonate dissolution zones in the etchart formation. Gold grade drops off slightly with increasing distance from the projected feeder pipes. Au-bearing bedded jasperoids form tabular bodies from 30-50m thick extending at least 600 m outward from the center of the chimney creek. Alteration is pervasive and extensive inside and below the orebody. Etchart Formation, 850 m thick, consists of siliciclastic carbonate shallow water sequence ( rich in silicate mineral detritus), pebbly litharenite, siltstone, sandy dolomite and dolomite. Metamorphosed d altered basalts, ranging from greenschists retaining igneous textures to intensely hydrothermally altered rocks. Dacite dikes are related to the Osgood Mountains granodiorite and cut altered rocks and are themselves altered.

Comment (Identification): The Twin Creeks Mine was formed in 1987 from the merging of the pits of the Chimney Creek mine and the Rabbit Creek mine. All pertinent material from earlier records M242950, M042791, W700409, and W700381 for those two mines has been incorporated into this record along with other new material.

Comment (Location): The Twin Creeks Mine is located about 6 miles northeast of the Getchell Mine in the Dry Hills off the northeast flank of the Osgood Mountains.

Comment (Workings): Twin Creeks is developed as a large open pit mine by the Mega-pit with the Sage layback at the north end and the Section 30 layback at the south end, plus the Vista pit to the north. Two mills (Pinon and Sage), heap leach facilities, waste rock dumps, ore stockpiles.

Comment (Economic Factors): From 1987 to 1996, 3,346,538 troy ounces of gold and more than 150,780 troy ounces of silver were produced from 108,531,000 short tons of ore. The remaining resource as of 1996 was 305,449,000 short tons of ore grading 0.06 opt gold. In mid-1996, gold reserves at Twin Creeks stood at 10.5 million ounces. In 2002 the reported proven and probable reserves for Twin Creeks Mine were: 47.6 million tons of ore grading 0.081 ounces of gold per ton plus measured and mineralized material: 55 million tons grading 0.057 ounces of gold per ton, as well as inferred mineralized material of 1.8 million tons grading 0.046 opt Au ounces of gold per ton. Twin Creeks Mine production from 1993 through 2002 was 6,614,829 ounces of gold and 1,794,678 ounces of silver.

Comment (Commodity): Ore Materials: gold

Comment (Commodity): Gangue Materials: albite, chlorite, kaolinite, sericite, calcite, amphibole, quartz, pyrite, augite, epidote, limonite, leucoxene, K-feldspar, tourmaline, fluorite, barite, organic carbon, goethite

Comment (Deposit): The original gently dipping mineralized zone containing significant gold values was found in an area about 1600 by 800 feet covered by 60m to 165 m of alluvium. It consisted of a gold-bearing tabular jasperoid body 30-50 m thick extending at least 600 m outward from the center of Chimney Creek. Seven other nearby gold mineralized zones were soon recognized. These zones were first developed as the separate Rabbit Creek and Chimney Creek open pit mines, later merged into a single ?Mega-pit?. In the Section 30 South Mega pit area, mill-grade oxide mineralization was found in both limbs of a large fold, with mineralization extending more than 1,500 feet south of the limit of the Mega pit as currently planned. All three target areas were drilled extensively in 1996 and1997, and Santa Fe Pacific Gold intersected "high-grade" in some of their drilling below the Twin Creeks pit. The Galena vein underground target is relatively high-grade (0.25-0.40 opt) mineralization within a northeast-southwest trending fault zone in the greenstones immediately beneath the Vista deposit north of the Mega pit. The target extended along strike for over 1,000 feet and about 500 feet down the structure, averaging about 10-15 feet wide, open along strike and at depth. The Zone 40 target is a fold-controlled zone of high-grade (about 0.5 opt) refractory mineralization at the bottom of the Mega pit. The Sage ore body is a northern extension of the existing Twin Creeks Mega pit, and occurs in the overturned fold axis of a NW-trending anticline at depths of 600 to 1200 feet. The carbonaceous and sulfide ore will be processed through the Sage autoclave. Most gold values are found in calcareous shales in the Ordovician sequence and in limestones in the Etchart Formation, although not all layers contain the same amount of gold. Strongest gold mineralization is not adjacent to faults but the form and distribution of mineralization suggests that gold-bearing solutions gained access to favorable layers along faults. In the Ordovician sequence, gold values are highest in shales that have undergone maximum dissolution of carbonate minerals. Petrographic study shows that some gold is associated with adularia, but deposit-scale comparisons do not show a consistent relation between K/Al ratios and gold values. The distribution of antimony is similar to that of gold, whereas mercury is more concentrated than gold, and arsenic is more widely dispersed than gold. The relation between gold, iron, and sulfide sulfur values shows that mineralization is concentrated in rocks that have gained sulfur, but not iron, to form gold-bearing arsenian pyrite. Thus, these rocks have undergone sulfidation rather than pyritization. The iron that underwent sulfidation came largely from preore, diagenetic(?) ferroan dolomite and was released into solution by decarbonation, a common form of alteration associated with Carlin-type deposits. It appears tha wall-rock iron content and decarbonation processes which liberate this iron are the most important factors controlling formation of this Carlin-type gold deposit.

Comment (Development): The Chimney Creek deposit was discovered in 1985 by Gold Fields Mining Corp., after which Santa Fe Pacific geologists reviewed the railroad grant sections in the adjacent Rabbit Creek area. They identified and drilled a strong N-S photolineament between the Chimney Creek to Rabbit Creek deposits and the third round of drilling in January 1987 dicovered the Rabbit Creek orebody. Prestripping commenced March 1989, mill and heap leach construction began in August 1989, and initial production began August 1990 utilizing oxide ores with an output of 200,000 ounces of gold per year. In 1993, Santa Fe Pacific Gold Company's Chimney Creek Mine and Rabbit Creek Mine merged into one "mega pit" which since that time has been called the Twin Creeks Mine. In 1997, Newmont Gold Company acquired the property as part of its takeover of Santa Fe Pacific. Since the merger of the two mines, Twin Creeks' production has averaged about a half million ounces of gold per year. Production decreased temporarily due to an incident in late 1994 in which about 3 million tons of overburden slid into the Twin Creeks pit covering ore that was scheduled to be mined in 1995. In mid-1996, gold reserves at Twin Creeks stood at 10.5 million ounces. Santa Fe Pacific increased its exploration budget to drill test extensions south of the main pit, as well as sulfide mineralization around the Vista Pit and two underground targets. In early 1997, the mine began a sulfide expansion project which included construction of two 4,000 tpd autoclave circuits, which was expected to increase Twin Creeks' annual production by about 100,000 ounces of gold. SFPG also invested $30 million in its shovel and haulage fleet, including the addition of a new electric shovel with a 56-cubic yard bucket, the largest of its kind in the industry. In 1996, deep exploration targets (to 3,000-feet) were drilled below the Vista and Mega pits. Santa Fe?s efforts to expand gold resources at the Twin Creeks mine during 1996 focused on three areas: the Galena vein, Zone 40, and Section 30 South Mega pit. Newmont acquired Santa Fe Pacific Gold Corporation in 1997, adding Twin Creeks, Lone Tree and several satellite deposits near Winnemucca to its portfolio. The Sage layback was broadly drilled by Santa Fe Pacific Gold in the mid-1990s. Infill drilling and a new model by Newmont in late 2002 were successful in adding high-grade ounces and reducing layback costs by $50 per ounce. Sage was added to Twin Creeks? reserves in 2003. The Sage ore body is a northern extension of the existing Twin Creeks Mega pit, and occurs in the overturned fold axis of a NW-trending anticline at depths of 600 to 1200 feet. The carbonaceous and sulfide ore will be processed through the Sage autoclave

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References

Reference (Deposit): Rabbit Creek Mine, Santa Fe Pacific Ld Corp. brochure.

Reference (Deposit): The Nevada Mineral Industry, 1990, NBMG Spec. Pub. MI-1990.

Reference (Deposit): Willden, Ronald 1964, Geology and Mineral Deposits of Humboldt County, Nv: Nbmg Bull. 59p.

Reference (Deposit): NBMG, 1994, MI-1993

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.

Reference (Deposit): David P. Stenger, Stephen E. Kesler, Dean R. Peltonen, and Charles J. Tapper, 1998, Deposition of gold in Carlin-type deposits; the role of sulfidation and decarbonation at Twin Creeks, Nevada, Economic Geology; April 1998; v. 93; no. 2; p. 201-215.

Reference (Deposit): Bloomstein and others, 1991; Bonham, 1986, 1989, 1991; F. Breit, oral communication, 2000; Davis and Tingley, 1999; Gardiner, 1989, 1990

Reference (Deposit): Gardiner and Giancola, 1991

Reference (Deposit): Giancola, 1995, 1996, 1997, 1998, 1999, 2000

Reference (Deposit): Harding, 2004m

Reference (Deposit): Mason and others, 1996;

Reference (Deposit): Nevada Mining Association Bulletin, Oct-Nov., 1985.

Reference (Deposit): The Mining Record, Nov. 13, 1985, P.3

Reference (Deposit): Nevada Bureau of Mines and Geology, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004; Newmont Mining Corp., 2003; Osterberg and Guilbert, 1991; Santa Fe Pacific Gold Corp., 1995a, 1995c; Schack, 2003; Tingley, 1998; United States Bureau of Land Management, 1979g, 1996e, 1996h; United States Bureau of Mines, 1995; United States Geological Survey, 1980d, 1980e.

Reference (Deposit): Mining Engineering, 1/1/97

Reference (Deposit): Northern Miner, 2/6/95,

Reference (Deposit): Northern Miner, 6/3/96

Reference (Deposit): California Mining Journal, 3/1/95

Reference (Deposit): California Mining Journal, 3/1/96

Reference (Deposit): Pay Dirt, 2/1/96

Reference (Deposit): Pay Dirt, 3/1/96

Reference (Deposit): Pay Dirt, 11/1/96

Reference (Deposit): Reno Gazette Journal, Nov. 11, 1985.

Reference (Deposit): The Northen Miner Newspaper, Nov. 11, 1985.

Reference (Deposit): Mine Search Annual, 1984-85, Metals Economics Group, Boulder, Co, Vol vii, p. 93-94.

Reference (Deposit): Geol. Soc. Nevada, 1987, Precious Metals Symposium, lectures, abstracts.

Reference (Deposit): E. I., Massengill, G.L. et. al., 1991, Discovery, geology and mineralization of the Rabbit Creek gold deposit, Humboldt Co., NV. Geology and Ore Deposits of the Great Basin, GSN Symposium Proceedings Reno, Nevada, p. 821-843.

Reference (Deposit): Oral Communication from Jim Delong, 16 Jul. 1986, geologist formerly with Gold Fields.

Reference (Deposit): Madden-Mcguire, Dawn J., Smith, Steven M., et al., 1991, Nature and origin of alluvium above the Rabbit Creek gold deposit, Getchell Gold Belt, Humboldt Co., Nv. Geology and Ore Deposits of the Great Basin, GSN Symposium Proceedings Reno, Nevada,p. 895-911.

Reference (Deposit): Grauch,V.J.S., and Bankey, Viki, Preliminary results of aeromagnetic studies of the Getchell disseminated gold deposit trend, Osgood Mountains North Central Nevada. Geology and Ore Deposits of the Great Basin, GSN Symposium Proceedings Reno, Nevada, p. 781-791.

Reference (Deposit): California Mining Journal, April 1990

Reference (Deposit): The Humboldt Sun, Winnemucca, NV, July 27, 1990, p. 32 and 34.

Reference (Deposit): Santa Fe Pacific Gold 1996 SEC Form 10K

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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.