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Geologic Overview of the Gold Deposits of the Carlin Trend, Nevada, USA

Steve Garwin

Geoinformatics Exploration, PO Box 1675, West Perth, Western Australia 6872

Centre for Exploration Targeting, 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, 2002). 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 by Marion Fisher and mined on a small scale from 1957 through 1960. Gold was discovered in turquoise workings at Blue Star in 1959 and subsequently produced in 1961. In 1960, Ralph Roberts described the Lynn-Railroad mineral belt in a paper he published on the alignment of mineral districts in North-central Nevada (Roberts, 1960). This paper and discussions with Roberts encouraged John Livermore and Alan Coope, Newmont geologists, to prospect in the vicinity of the original Carlin deposit, which they discovered in November of 1961. At the onset of production in 1965, Carlin 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 consulting work of Ralph Roberts in the mid-1980s for the Pancana Western States joint-venture at Goldstrike gave Brian Meikle and Larry Kornze the impetus to drill test a lower plate carbonate sequence target north of the Goldstrike stock (R.J. Madrid, personal communication, 2005). 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, 2002). 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

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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. CARLIN TREND GEOLOGY Rock Types The composition, porosity and permeability of the local host rocks play a major role in the localization of gold ore in the Carlin trend. The Ordovician to Silurian siliciclastic rocks in the upper plate of the Roberts Mountains thrust are more than 1500 m thick, including repetition of stratigraphic section due to internal low-angle faults and thrusts (Fig. 2; Teal and Jackson, 1997; Jory, 2002). The Ordovician Vinini Formation consists mostly of cherty mudstone and siltstone and minor greenstone and limestone. The Silurian Elder Formation overlies the Vinini Formation in the northernmost part of the Carlin trend and contains micaceous siltstone, limey siltstone and chert (Bettles, 2002). The autothochthonous Ordovician through Devonian rock sequence is exposed in anticlinal hinge zones that approximately coincide with the central axis of the Carlin trend (Fig. 3). The lower plate rocks consist of limestone, dolomite, mudstone, siltstone and quartzite. Lithologic contacts are commonly conformable, however, disconformities occur locally, and intraformational fold-thrusts juxtapose mudstone and siltstone units in the upper part of the autotochthon. The oldest portion of the lower plate sequence exposed in the area consists of Ordovician Pogonip Group limestone and dolomite, which is about 300 m thick (Evans, 1980; Jory, 2002). This unit is overlain by Ordovician Eureka Quartzite (~300 m thick) and Ordovician to Silurian Hanson Creek Formation dolomite (> 200 m thick). The Silurian to Devonian Roberts Mountains Formation is about 400 m thick and includes a 250 m thick lower unit of planar-laminated silty limestone that grades upwards into a wavy- or wispy-laminated silty limestone unit with intercalations of bioclastic debris flows, 1 to 15 mm thick (Teal and Jackson, 1997; Jory, 2002). This upper unit ranges up to 150 m thick and hosts the majority of the gold ore along the Carlin trend (Teal and Jackson, 1997; Bettles, 2002). The overlying Devonian Popovich Formation is up to 400 m thick and consists of silty limestone, micrite and fossiliferous limestone with calcarenite and planar-laminated limey mudstone and silty limestone in the upper part of the unit. The base of the overlying Devonian Rodeo Creek unit, which is up to 250 m thick, is marked by a disconformity north of the Goldstrike intrusion (Bettles, 2002). The variable thickness of this unit is, in part, related to structural repetition caused by fold-thrusts that deform interbedded siliceous mudstone, siltstone and limey siltstone. In addition, the Roberts Mountains thrust has removed the entirety of the Rodeo Creek unit locally. The youngest sedimentary rocks in the Carlin trend consist of poorly consolidated volcaniclastic rocks of the Miocene Carlin Formation that fill local basins with up to 600 m of material (Jory, 2002). Three major episodes of intrusion occurred along the Carlin trend, including late Jurassic alkaline, Eocene calc-alkaline and Miocene rhyolitic events. The late Jurassic, biotite monzodioritic Goldstrike intrusion (158 Ma; Arehart et al., 1993a) is of similar composition to intrusions towards the west, the Little Boulder Basin stock and Vivian sill (Fig. 3). The Goldstrike intrusion forms a northeasterly elongate 4 by 1.5 km stock, sill and dyke complex that lies between the Betze-Post and Genesis deposits. A significant portion of the gold resources in the northern Carlin trend, about 1600 tonnes of gold, occurs adjacent to the Goldstrike intrusion, including the high grade deposits (>25 g/t Au) of Deep Post and Deep Star. Portions of the Deep Post deposit are hosted by the Goldstrike intrusion (Marino, 2002; Streiff and Powell, 2002). Northwesterly trending, quartz monzonite and lamprophyre dykes, also of late Jurassic age, cut the Goldstrike intrusion (Bettles, 2002). Jurassic intrusions are common in the northern Carlin trend, however, are much less abundant in the central part of the belt, where northwesterly trending dykes fill faults in the Mike deposit and near Gold Quarry. Cretaceous intrusions of intermediate composition occur at Welches Canyon, west of the Mike deposit (Teal and Jackson, 1997).

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Eocene (40-37 Ma; Ressel et al., 2000) medium- to high-K calc-alkaline, porphyritic dacite and rhyolite dykes trend north-northwest to north-northeast through out the northern Carlin trend. These dykes are far less abundant than the Jurassic intrusions. The magma source to the Eocene dykes is not known, however, Ressel et al. (2000) infer that a large, ~500 km2, airborne magnetic anomaly that coincides with the Welches Canyon stock and the Emigrant Pass volcanic field may represent a concealed Eocene pluton and a potential source of heat for auriferous fluid flow in the area. Cross-cutting field relationships and 40Ar/39Ar radiometric dating indicate the emplacement of dacite and rhyolite dykes to be coeval with gold mineralisation in the northern Carlin trend. The perlitic texture in the glassy margins to the rhyolite dykes in Deep Star are inferred by Ressel et al. (2000) to indicate emplacement at depths of less than 2 km from the Eocene paleosurface. Miocene rhyolitic lava flows (~15 Ma) dip up to 15o to the west along the western side of the Tuscarora Spur in the vicinity of Blue Star, indicating minor amounts of post-mineralisation rotation due to Miocene extensional tectonsim. Structural Geology The Carlin trend represents a northwesterly trending first-order crustal basement structure, as indicated by regional radiogenic isotope and geophysical data (Tosdal et al., 2000). A prominent structural high coincides with the Carlin trend and is characterized by a regional anticlinorium developed during the late Paleozoic to early Mesozoic that has been modified by mid-Tertiary extension and horst development. This anticlinorium deforms the Roberts Mountains thrust and related folds formed during the Antler orogeny (Roberts et al., 1958). Second- and third-order faults are steeply dipping and trend northeasterly and north-northwesterly / west-northwesterly, respectively (Fig. 5; Garwin, 2002). The geometric relationships of these faults to the distribution of facies in lower plate rock units, late Jurassic and Eocene intrusions, and Miocene volcanic and volcaniclastic rocks indicate that both fault sets have been active from the Devonian through the Miocene. Hence, inherited structures are reactivated by subsequent geologic events. Steeply dipping fourth-order faults trend northeasterly, northwesterly and north-northwesterly. These fourth-order faults, along with northwesterly to north-northeasterly trending dykes, are commonly localized in step-over zones between third-order faults. High-grade gold (>6 g/t Au) zones within deposits typically coincide with fifth-order low-displacement extensional faults and fracture zones that strike northerly and dip steeply. These faults commonly occur in zones of structural complexity adjacent to the interaction zone between fourth-order faults, and are inferred to have developed nearly perpendicular to the west-northwesterly regional extension-direction in the Eocene (Fig. 5; Seedorff, 1991; Tosdal and Nutt, 1999; Garwin, 2002). The structural controls to ore deposit localization in the Carlin trend, listed in approximate order of decreasing scale (modified from Lewis, 2001), include:

1) Intersections of deep, northeasterly trending fault-fracture zones with the northwesterly structural grain of the trend;

2) Structural culminations or domes comprising anticlinal folds, thrust duplexes, horst blocks, or combinations of the three, where up-dip fluid flow is channelled along outward-dipping bedding surfaces and faults;

3) Major rheological boundaries between units of differing competency, particularly those boundaries at high angles to extension axes, or adjacent to major faults;

4) Fault terminations, dilational bends and step-overs within fault systems active during mineralisation;

5) Lamprophyre dyke swarms, particularly those with faulted margins that may have provided cross-stratal permeability or those that intersect major competent bodies, such as the Goldstrike intrusion; and

6) Eocene dykes within or adjacent to major structures, particularly those associated with structural intersections.

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Many of the gold deposits in the northern Carlin trend coincide with structural intersections formed by steeply dipping fault and fracture zones, which are dyke-filled locally (Teal and Jackson, 1997; Madrid, 2001; Bettles, 2002; Madrid and Garwin, 2002). Through systematic structural mapping near the Carlin mine, Madrid and Garwin (2002) demonstrate that west-northwesterly-, northerly- and northwesterly-striking, syn-mineralisation gold-bearing fault and fracture systems have acted as active conduits for mineralising fluids. Pre-mineralisation north-northeasterly-striking fault and fracture sets and pre-existing fold hinges were also sites of gold deposition where fluids leaked from the active fracture systems into these more passive structures. Post-mineralisation and reactivated structures, such as the northeasterly striking fault zones adjacent to the Carlin deposit, do not significantly offset main-stage gold-bearing structural systems. Hydrothermal Alteration Three major hypogene alteration types are documented in the gold deposits of the Carlin trend: i) decalcification / decarbonatisation and dolomitisation of the carbonate components of host rocks, ii) pervasive replacement silicification (chalcedony and fine-grained quartz) of carbonate rocks, and iii) argillic alteration of siliciclastic components of sedimentary host rocks and intrusions. Weak to moderate propylitic alteration (chlorite-smectite-carbonate) occurs in the Goldstrike intrusion distal to mineralised carbonate units. All these styles of hydrothermal alteration are attributed to the Eocene gold event, in contrast to the quartz-sericite-pyrite alteration and skarn assemblages that formed in sedimentary rocks adjacent to the Goldstrike intrusion during the late Jurassic. Early decalcification and decarbonatisation are characterized by the dissolution of rock-forming carbonate rocks and replacement by hydrothermal dolomite and Fe-Mn carbonate minerals. A zone of increased calcite and dolomite vein abundance precedes the front of decarbonatisation. Dissolution-related volume loss and collapse breccias have enhanced the porosity and permeability of altered carbonate units and led to the concentration of insoluble residues (e.g. organic carbon, clay and iron-sulphide minerals) along bedding planes and fracture networks. This style of dissolution-related brecciation is an essential preparation mechanism for gold mineralisation. Faults, fractures and bedding surfaces acted as conduits for early decarbonatisation and later silicification in carbonate rocks and argillisation in siliciclastic units. The intensity of replacement silicification commonly increases with proximity to steeply dipping faults and fracture zones, inferred to have acted as solution pathways, however, also affect porous debris flow units and calcarenite beds, within and above ore zones. Argillic alteration in siliciclastic rocks is commonly more abundant proximal to ore zones and indicates local zoning characterized by proximal kaolinite and distal illite and inter-layered illite-smectite (Leach, 2000; Garwin, 2002). Late-stage open space- and fracture-fillings consist of quartz, kaolinite, calcite, dolomite, barite, alunite and sulphide- and sulfosalt-minerals. Gold Mineralisation Gold mineralisation occurs as a result of the sulphidation of favourable lithologic units adjacent to fault- and fracture-zones that acted as pathways for hydrothermal fluids during the Eocene (40-37 Ma; Hofstra and Cline, 2000; Ressel et al., 2000). Gold is more abundant in decarbonatised sedimentary rocks that have undergone substantial volume-loss, such as at Carlin (up to 50% volume-loss; Bakken and Einaudi, 1986). However, significant gold (>6 g/t Au) also occurs in silicified carbonate rock in parts of several deposits (e,g. Deep Post and Deep Star; Dunbar, 2001) and within the Goldstrike intrusion, such as at Deep Post (Marino, 2002). Three major styles of deposit are documented, which display structural (fault/fracture)-, dissolution (collapse) breccia-, and stratabound-controls (Fig. 6; Teal and Jackson, 1997; Jory, 2002; Garwin, 2002). The large deposits, such as Betze-Post and Genesis, contain elements of each of these three styles and are termed intermediate in this paper.

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Gold commonly occurs as submicron particles within 1 to 5 micron wide rims of arsenical pyrite that form around early pyrite or marcasite of diagenic and hydrothermal origin (Arehart et al., 1993b; Emsbo, 1999; Garwin, unpublished data). Main ore-stage pyrite from Meikle and Betze-Post yield mean concentrations of 1800 ppm Au, 180 ppm Ag, 3.4% As, 0.3% Sb and 0.86 ppm Hg (Emsbo, 1999). Individual gold concentrations may reach as high as 1.1 atomic percent in arsenical pyrite analyzed from ore at Carlin (Garwin, unpublished electron microprobe results). Textural relationships indicate that the trace-element rich pyrite and marcasite precipitated after decarbonatisation and volume-loss, probably during, or after, replacement silicification. Ore zone gangue minerals include quartz, kaolinite +/- arsenopyrite and minor illite and illite-smectite (Leach, 2000; Garwin, 2002). Late open space- and fracture-fillings consist of at least two phases: i) early drusy quartz, realgar, orpiment, stibnite, galkhaite [(Cs,Tl)(Hg,Cu,Zn)6(As,Sb)4S12], fluorite, pyrite (brassy) and sphalerite; and ii) late kaolinite, smectite, carbonate, chalcedony, barite and alunite (Hofstra and Cline, 2000; Leach, 2000; Garwin, 2002). A second population of gold occurs as rare, disseminated and fracture-controlled native grains (>99% pure), commonly 100 to 500 microns and locally up to 2 mm in mean diameter, which comprise a minor component of the ore at Rodeo-Gold Bug and Gold Quarry. Emsbo (2002) believes this native gold to be of SEDEX origin, having formed during the deposition of the upper portion of the Devonian Popovich Formation, and estimates this mode of gold occurrence to contribute as much as 60 tonnes of gold in the deposits north of the Goldstrike intrusion (Emsbo, oral. commun., 2002). If this is true, then native gold constitutes about 3% of the total gold resource in this area. SYNTHESIS AND DISCUSSION Genetic Deposit Model and Controls to Mineralisation A conceptual model was developed for large gold deposits in the Carlin trend, such as Betze-Post, Gold Quarry and Genesis, which incorporates geology, alteration and gold mineralisation (Fig. 7). This model benefits from the ideas of Newmont geologists and was originally presented at the SEG Global Exploration 2002 conference field excursion: Carlin-type Deposits of Northern Nevada and their Regional Setting (Garwin, 2002). Many aspects of smaller Carlin trend deposits are also included in this model. Steeply dipping district-scale faults and fracture zones, which are dyke-filled locally, act as major pathways for ascending sulphidising fluids into reactive carbonate host rocks. The gently to moderately dipping Roberts Mountains thrust and lithologic contacts, which separate rocks of contrasting porosity / permeability (e.g. carbonate vs. siliciclastic rocks), control the outflow of mineralising fluids away from these feeder zones. Early decalcification and decarbonatisation are accompanied by hydrothermal dolomite and Fe-Mn carbonate minerals. Subsequent replacement silicification and argillisation follow zones of dissolution-enhanced porosity and permeability. Structurally controlled zones of silicified carbonate rock, termed jasperoid, commonly form in peripheral settings to the ore zones. Collapse breccias form in zones of high fracture abundance and enhanced fluid flow, which are subsequently sulfidised to form the main-stage ore assemblage of quartz-kaolinite-auriferous pyrite and marcasite. This assemblage is typically overprinted by orpiment, realgar and stibnite late in the evolution of the deposit, as sulphidation state increases and temperature decreases. Very late-stage open cavities are filled by carbonate minerals, barite, alunite and clay minerals. The general sequence of hydrothermal alteration and the ore assemblage described above is consistent with sulphidation and related gold deposition from the buffering of an auriferous acidic fluid (pH~4) by carbonate wall rock at a temperature of about 200 to 220oC (Hofstra and Cline, 2000). However, other potential mechanisms exist for gold deposition, including fluid mixing.

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The major controls to mineralisation for the deposits of the Carlin trend are summarized below:

1) Fluid focussing by a structural culmination created by an anticline, thrust duplex or horst; 2) Steeply dipping faults, fracture zones and intrusions create conduits for hydrothermal

fluids; 3) Gently to moderately dipping lithologic contacts and thrusts create traps for fluid and, in

the case of the thrusts, can thicken prospective stratigraphic section; 4) Receptive and reactive host rocks encourage fluid infiltration and dissolution; 5) Contrasting rheology and porosity and permeability of host rocks create competency

contrast and localize fluid flow; and 6) Decalcification, dissolution, brecciation and silicification contribute to volume-loss and

provide preparation for sulphidation and gold deposition. Carlin Trend - Looking Forward The Carlin trend holds the potential for the discovery of an additional 1000 tonnes of gold (30 million ounces) to the 3000 tonnes already found. The future of the trend lies in the efficient targeting of high-grade underground sulphide ore bodies, such as Deep Post and Deep Star. Such deposits can be found through rendering the upper plate to the Roberts Mountains thrust transparent by better understanding the stratigraphy of the allochthon and delineating zones of structural complexity that point towards targets in the lower plate carbonate rocks. In addition, geological and geochemical vectors to ore need to be enhanced by applying methods that utilise fracture mapping, alteration zoning and 3D models. Non-traditional host rocks, such as intrusions, the upper plate siliciclastic sequence and the autotochthon, below the Roberts Mountains Formation, should be tested rigorously. Innovative drilling techniques will be required to explore for deep deposits from underground platforms. Lastly, further improvements of the bio-oxidation process would enhance gold recovery from low- to moderate-grade refractory ores. ACKNOWLEDGMENTS The present understanding of the geology and gold mineralisation of the Carlin trend is a function of the work of Newmont and Barrick mine and exploration geologists, USGS personnel, academicians and many consultants. Several of the concepts presented in this paper were formulated by Newmont geologists working with consultants from 1999 to 2001. The role of company geoscientists, Alan Flint, John Jory, John Norby and Robert Jackson, Steve Moore and consultants, Jean Cline, David Groves, Jeff Hedenquist, Terry Leach, Peter Lewis and Raul Madrid, are gratefully acknowledged. A previous version of this manuscript was published in February 2002, as part of a short-course series prepared by the Centre for Global Exploration, the predecessor to the Centre for Exploration Targeting, at the University of Western Australia. REFERENCES Arehart, G.B., Foland, K.A., Naesar, C.W. & Kesler, S.E., 1993a, 40Ar/39Ar, K/Ar, and fission track

geochronology of sediment-hosted disseminated gold deposits at Post-Betze, Carlin trend, northeastern Nevada: Economic Geology, v.88, p. 622-646.

Arehart, G.B., Chryssoulis, S.L. & Kesler, S.E., 1993b, Gold and arsenic in iron sulfides from sediment-hosted disseminated gold deposits: Implications for depositional processes: Economic Geology, v. 88, p. 175-185.

Bakken, B.M. & Einaudi, M.T., 1986, Spatial and temporal relations between wall rock alteration and gold mineralization, main pit, Carlin gold mine, Nevada, USA: in Macdonald, A.J., ed., Gold 86: Willowdale, On, Canada, Konsult International, p.388-403.

Bettles, K., 2002, Exploration and geology, 1962-2002, at the Goldstrike property, Carlin trend, Nevada: Society of Economic Geologists, Special Publication 9, p. 65-93.

Coope, J.A., 1991, Carlin Trend exploration history: Discovery of the Carlin deposit: Nevada Bureau of Mines and Geology Special Publication 13, 16 p.

Dunbar, W., 2001, A structural model mineralization at Deep Star, Carlin trend, Nevada, in Shaddrick, D.R., Zbinden, E.A., Mathewson, D.C., and Prenn, C., eds., Regional tectonics and structural control of ore: The major gold trends of northern Nevada: Reno, Nevada, Geological Society of Nevada, Special Publication no. 33, 19 p.

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Emsbo, P., 1999, Origin of Meikle high grade gold deposit from the superposition of Late Devonian SEDEX and mid-Tertiary Carlin-type gold mineralisation: unpublished Ph.D. thesis, Golden, Colorado, Colorado School of Mines, 394 p.

Emsbo, P., 2002, Geology, geochemistry and genesis of sedex Au ores on the Carlin trend, Nevada: Abstracts with Programs, Annual Meeting and Exposition, Denver 2002, Geological Society of America, abstract 63-4, p. 140.

Evans, J.G., 1908, Geology of the Rodeo Creek and Welches Canyon quadrangles, Eureka County, Nevada: US Geological Survey Bulletin 1473, 81 p.

Garwin, S.L., 2002, Geologic overview of the Carlin trend, Nevada: oral presentation in: Thorman, C., compiler, Carlin-type gold deposits of northern Nevada and their regional setting field trip, Global Exploration 2002: Integrated methods for discovery, Society of Economic Geologists, Littleton, CO, USA, 10 p.

Hofstra, A.H. & Cline, J.S., 2000, Characteristics and models for Carlin-type gold deposits: Reviews in Economic Geology, v. 13, p. 163-220.

Jory, J., 2002, Stratigraphy and host-rock controls of gold deposits of the northern Carlin trend: in, Thompson, T.B., Teal, L. & Meeuwing, R.O., eds., Deep deposits along the Carlin trend: Nevada Bureau of Mines and Geology Bulletin 111.

Leach, T.M., 2001, Comments on the geology geochemistry workshop, February, 2001, Elko, Nevada: unpublished report for Newmont Mining Corporation, 15 p.

Lewis, P.D., 2001, Structural analysis of gold deposits of the Carlin trend, Elko and Eureka Counties, Nevada; Part I: Project Objectives, methodology and results: unpublished report to Newmont Mining Corporation, 36 p.

Madrid, R.J., 2001, Preliminary structural systematics of the Carlin mine area including the Carlin, Leeville, Turf, and Four Corners systems: unpublished consulting report to Newmont Mining Corporation, November 2001, 49 p.

Madrid, R.J., & Garwin, S.L., 2002, Structural methods for targeting gold deposits, northern Carlin Trend, Nevada: in, Vearncombe, S. ed.., and Reddy, S., Stone, B., Swager, C., Tabaert, F., and Thomson, J., co-eds., Applied Structural Geology for Mineral Exploration and Mining: Australian Institute of Geoscientists, International Symposium, Abstract Volume, Bull. 36, p. 118-121.

Marino, F. A., 2002, Structural and mineralogical features of the Deep Post mine, Carlin Trend, Nevada: in, Vearncombe, S. ed., and Reddy, S., Stone, B., Swager, C., Tabaert, F., and Thomson, J., co-eds., Applied Structural Geology for Mineral Exploration and Mining: Australian Institute of Geoscientists, International Symposium, Abstract Volume, Bull. 36, p. 122-124.

Ressel, M.W., Noble, D.C., Henry, C.D. & Trudel, W.S., 2000, Dyke-hosted ores of the Beast deposit and the importance of Eocene magmatism in gold mineralisation of the Carlin trend, Nevada: Economic Geology, v. 95, p. 1417-1444.

Roberts, R.J., Hotz, P.E., Gilluly, J. & Ferguson, H.G., 1958, Paleozoic rocks of north-central Nevada: American Association Petroleum Geologists Bulletin, v. 42, no. 12, p. 2813-2857.

Roberts, R.J., 1960, Alignment of mining districts in north-central Nevada: U.S. Geological Survey Prof. Paper 400-B, p. B-17-B-19

Seedorff, E., 1991, Magmatism, extension and ore deposits of Eocene to Holocene age in the Great Basin Mutual effects and preliminary genetic relationships: Geology and Ore Deposits of the Great Basin Symposium, Geological Society of Nevada, Reno, Nevada, Proceedings, p. 133-178.

Stewart, J.H., 1980, Geology of Nevada: Nevada Bureau of Mines and Geology Special Publication 4, 136p. Streiff, R., and Powell, J., 2002, Deep Post 2001 year-end summary report: unpublished Newmont internal

report, January 2001. 5p Teal, L. & Jackson, M., 1997, Geologic Overview of the Carlin trend gold deposits and descriptions of

recent deep discoveries: Society of Economic Geologists Newsletter, no. 31. Tosdal, R.M. & Nutt, C.J., 1999, Late Eocene and Oligocene tectonic setting of Carlin-type Au deposits,

Carlin trend, Nevada, USA: in, Stanley et al., eds., Mineral deposits: Processes to processing: Roterdam, Balkema, p. 905-908.

Tosdal, R.M., Wooden, J.L. & Kistler, R.W., 2000, Geometry of the neoproterozoic break-up, and implications for location of Nevadan mineral belts: in Cluer, J.K., Price, J.G., Struhsacker, E.M., Hardyman, R.F. & Morris, C.L., eds., Geology and Ore Deposits 2000: The Great Basin and Beyond: Geological Society of Nevada Symposium Proceedings, May 15-18, 2000, p. 451-466.

Figure Captions Figure 1. Simplified geology map of the Carlin trend, Nevada, which shows the location of major gold deposits

(after Teal and Jackson, 1997). The locations of the town of Carlin, Welches Canyon (WC) and Emigrant Pass (EP) are indicated.

Figure 2. Idealized stratigraphic column for the lithologic units in the Carlin trend, which shows the correlation

between sedimentary host rocks and gold deposits (after Teal and Jackson, 1997). Recent work at Gold Quarry in the central Carlin trend indicates that the Rodeo Creek unit hosts significant gold ore, more than the figure illustrates.

Figure 3. Simplified geology map of the northern and central Carlin trend, which shows the relationships

between the rock sequences in the upper- and lower-plate of the Roberts Mountains thrust, intrusions, major faults and folds, and gold deposits. Note that the vast majority of the intrusions labelled as Jurassic-Cretaceous are actually late Jurassic in age. The cross-section line for figure 4 is indicated.

Figure 4. Schematic cross-section for the northern Carlin trend, adjusted to a horizontal datum for the Popovich

Formation Rodeo Creek unit contact, which shows the relationship between gold distribution (>1 g/t Au), rock units, the Goldstrike intrusion and the stocks thermal aureole. This aureole is characterized by calc-silicate skarn, marble and hornfels. Location of section is indicated in figures 3 and 5.

Figure 5. Structural interpretation of the northern and central Carlin trend, which shows major fault zones,

competent bodies, structural culminations or domes, and gold deposits. The direction of the regional Eocene extension-direction (s 3) is from Seedorff (1991). The northwesterly trending axis of the Carlin trend coincides with a major structural high, as indicated by the ~3500 foot (1100 m) contour of the top of the Roberts Mountains autotochthon, as estimated from the interpretation of wavelet edge-enhanced gravity data collected by Newmont Mining Corporation. The cross-section line for figure 4 is indicated.

Figure 6. Schematic illustration of the different styles of ore deposits that occur in the Carlin trend, which

indicates the varying types of controls to gold mineralisation, including the relationship of ore to host rock, structure and dissolution-related collapse breccias (modified from a drawing made by John Norby in 2001).

Figure 7. Conceptual model for large gold deposits (e.g. Gold Quarry) in the Carlin trend, which indicates the

relationships between host rock, structure, hydrothermal alteration and gold mineralization (modified from a drawing made by John Norby in 2001). Steeply dipping faults and fracture systems create zones of upflow, whereas, gently dipping lithologic contacts and the Roberts Mountains thrust control the outflow of mineralising fluids. Gold zones correspond to 1 g/t (0.03 opt Au) and 10 g/t (0.3 opt Au). RMA denotes the Roberts Mountains allochthon.

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