Geologic Overview of the Gold Deposits of the
Carlin Trend, Nevada, USA
Carlin Trend, Nevada, USA
Steve Garwin
Geoinformatics Exploration, PO Box 1675, West Perth, Western Australia 6872
Centre for Global Metallogeny, Department of Geology and Geophysics, University of Western Australia,
Crawley, Western Australia 6907
Geoinformatics Exploration, PO Box 1675, West Perth, Western Australia 6872
Centre for Global Metallogeny, Department of Geology and Geophysics, University of Western Australia,
Crawley, Western Australia 6907
Introduction
The Carlin trend contains about 3000 metric tonnes (97 million ounces) of gold in combined past
production and reserves from about 30 sedimentary rock-hosted disseminated gold deposits that form a northwesterly trending belt, ~60 km by 7 km, in north-central Nevada, USA (Fig. 1; Roberts, 1960; Teal and Jackson, 1997; Bettles, 2002).
The majority of the gold deposits are hosted by lower Paleozoic carbonate and siliciclastic rocks in the lower plate of the Roberts Mountains thrust, above which occurs an allochthonous package of lower Paleozoic siliciclastic rocks. The upper plate was transported by easterly-directed thrusting during the Late Devonian to Middle Mississippian Antler orogeny (Roberts et al., 1958). During the late Jurassic, alkaline magmatism led to the emplacement of the Goldstrike monzodioritic intrusion and lamprophyre dyke swarms in the northern Carlin trend, near the present day location of the large Betze-Post mine (~ 1000 t Au; Teal and Jackson, 1997; Bettles, 2002). In the deposits of the Carlin trend, gold occurs as sub-micron particles in arsenian pyrite-bearing ores formed during the Eocene (40-37 Ma; Ressel et al., 2000), which display structural (fault/fracture)-, dissolution (collapse) breccia-, and stratabound-controls (Teal and Jackson, 1997; Jory, in press).
This period of gold mineralisation coincides with the onset of approximately east-west oriented extensional tectonism and related calc-alkaline magmatism in north-central Nevada (Stewart, 1980; Seedorff, 1991). Miocene Basin and Range extension, facilitated by northerly striking normal faults (20 to 14 Ma; Stewart, 1980), has reactivated segments of early formed faults, however, has not significantly disrupt the ore bodies discovered to date. The earliest recorded mining of gold in the Carlin trend occurred in 1907 from placers in Lynn Creek, near the Carlin and Leeville deposits (Fig. 1; Coope, 1991). Gold was discovered in bedrock exposed at Bootstrap in 1946 and mined on a small scale from 1957 through 1960. The discovery of gold in turquoise workings at Blue Star in 1959 and subsequent production in 1961 caught the interest of Newmont geologists, Alan Coope and John Livermore. Coope and Livermore went on to discover the original Carlin deposit in November of 1961, which, at the onset of production in 1965, contained 10 million tonnes at 10 g/t Au (Coope, 1991). Gold was discovered in the vicinity of the Goldstrike stock in 1962 by Harry Ranspot of Atlas Minerals, however, production did not commence in this area until 1978 (Bettles, 2002). Several surface oxide ore deposits with average gold grades that range from ~ 1 to 2 g/t Au were discovered from 1979 through 1984, including Gold Quarry, Post Oxide and Genesis.
The giant Betze open-pit deposit, with a resource of about 900 million tonnes at 7.5 g/t Au, was discovered adjacent to the Post deposit in 1987 by American Barrick (Bettles, 2002). Exploration
strategy changed and began to focus on deeper sulphide ores in 1986, following the discovery of Deep Post, beneath the present Betze-Post open-pit mine. This lead to increased drilling depths to more than 2000 m from surface and the discovery of refractory deposits grading from 12 to 30 g/t Au, including Deep Star, Rodeo-Goldbug and Meikle in 1988 to 1989, and West Leeville in 1994 (Teal and Jackson, 1997; Jory, in press). In 2000 to 2002, high grade gold values, ranging from 8 to 52 g/t Au over drill intervals of 24 to 29 m, were discovered at depths of 700 to 900 m at Ren in the northern Carlin trend by Cameco Gold. The fiftieth millionth ounce of gold (~1600 t Au) was produced from the Carlin trend in April 2002, making this gold belt one of the three most prolific in the world. (SEG-MGEI Gold Deposit Workshop 2009, UGM)
The Carlin trend contains about 3000 metric tonnes (97 million ounces) of gold in combined past
production and reserves from about 30 sedimentary rock-hosted disseminated gold deposits that form a northwesterly trending belt, ~60 km by 7 km, in north-central Nevada, USA (Fig. 1; Roberts, 1960; Teal and Jackson, 1997; Bettles, 2002).
The majority of the gold deposits are hosted by lower Paleozoic carbonate and siliciclastic rocks in the lower plate of the Roberts Mountains thrust, above which occurs an allochthonous package of lower Paleozoic siliciclastic rocks. The upper plate was transported by easterly-directed thrusting during the Late Devonian to Middle Mississippian Antler orogeny (Roberts et al., 1958). During the late Jurassic, alkaline magmatism led to the emplacement of the Goldstrike monzodioritic intrusion and lamprophyre dyke swarms in the northern Carlin trend, near the present day location of the large Betze-Post mine (~ 1000 t Au; Teal and Jackson, 1997; Bettles, 2002). In the deposits of the Carlin trend, gold occurs as sub-micron particles in arsenian pyrite-bearing ores formed during the Eocene (40-37 Ma; Ressel et al., 2000), which display structural (fault/fracture)-, dissolution (collapse) breccia-, and stratabound-controls (Teal and Jackson, 1997; Jory, in press).
This period of gold mineralisation coincides with the onset of approximately east-west oriented extensional tectonism and related calc-alkaline magmatism in north-central Nevada (Stewart, 1980; Seedorff, 1991). Miocene Basin and Range extension, facilitated by northerly striking normal faults (20 to 14 Ma; Stewart, 1980), has reactivated segments of early formed faults, however, has not significantly disrupt the ore bodies discovered to date. The earliest recorded mining of gold in the Carlin trend occurred in 1907 from placers in Lynn Creek, near the Carlin and Leeville deposits (Fig. 1; Coope, 1991). Gold was discovered in bedrock exposed at Bootstrap in 1946 and mined on a small scale from 1957 through 1960. The discovery of gold in turquoise workings at Blue Star in 1959 and subsequent production in 1961 caught the interest of Newmont geologists, Alan Coope and John Livermore. Coope and Livermore went on to discover the original Carlin deposit in November of 1961, which, at the onset of production in 1965, contained 10 million tonnes at 10 g/t Au (Coope, 1991). Gold was discovered in the vicinity of the Goldstrike stock in 1962 by Harry Ranspot of Atlas Minerals, however, production did not commence in this area until 1978 (Bettles, 2002). Several surface oxide ore deposits with average gold grades that range from ~ 1 to 2 g/t Au were discovered from 1979 through 1984, including Gold Quarry, Post Oxide and Genesis.
The giant Betze open-pit deposit, with a resource of about 900 million tonnes at 7.5 g/t Au, was discovered adjacent to the Post deposit in 1987 by American Barrick (Bettles, 2002). Exploration
strategy changed and began to focus on deeper sulphide ores in 1986, following the discovery of Deep Post, beneath the present Betze-Post open-pit mine. This lead to increased drilling depths to more than 2000 m from surface and the discovery of refractory deposits grading from 12 to 30 g/t Au, including Deep Star, Rodeo-Goldbug and Meikle in 1988 to 1989, and West Leeville in 1994 (Teal and Jackson, 1997; Jory, in press). In 2000 to 2002, high grade gold values, ranging from 8 to 52 g/t Au over drill intervals of 24 to 29 m, were discovered at depths of 700 to 900 m at Ren in the northern Carlin trend by Cameco Gold. The fiftieth millionth ounce of gold (~1600 t Au) was produced from the Carlin trend in April 2002, making this gold belt one of the three most prolific in the world. (SEG-MGEI Gold Deposit Workshop 2009, UGM)
