Abstract The Betze gold deposit in the Goldstrike Mine, north-central Carlin Trend, Eureka County, Nevada, is the largest known, sedimentary rock-hosted, disseminated gold deposit containing 32 million ounces of gold (Leonardson and Rahn, 1996)(Fig.1). The paragenesis of hydrothermal mineralization characterizes the nature of gold mineralization in the deposit. This paper describes stages of gold ore mineralization determined from hand specimen and thin section petrology, XRD analysis and SEM studies; mineral formulae reported are those from Frondel (1962) and may not be exact. The stages result from a poly-phase, mineralizing event that has determined the conditions under which gold was precipitated. Previous studies of paragenesis and associated hydrothermal minerals of Carlin-type deposits were conducted by Arehart et al. (1993a), Bakken and Einaudi (1986), Kuehn and Rose (1992), Peters (1996) and Peters et al. (1997) who determined relative paragenesis of mineralization in a general one or two stage hydrothermal event. Our investigations suggest that three stages of hydrothermal mineral development are associated with gold ore mineralization in the Betzedeposit: Stage I: Early (pre-primary gold deposition); Stage II: Main (primary gold deposition), and Stage III: Late (post-primary gold deposition). Pre-gold stage mineralization events include diagenesis of the sediments and metasomatic processes associated with the intrusion of the dioritic Goldstrike stock. Hydrothermal minerals associated with an individual stage generally are limited to each stage; however, overlap of the major gangue minerals, such as quartz, illite, and sericite (Fig. 2) is common. Some mineralogical overlap between stages is due to cycling of circulating fluid that

Abstract This paper describes outcrop- and hand specimen-scale breccias in the Betze orebody, which is the largest gold deposit on the Carlin trend (Bettles and Lauha, 1991; Leonardson and Rahn, 1996). The Betze orebody lies in the north-central part of the Carlin trend in the Goldstrike Mine (Fig. 1), and it is part of the Betze-Post deposits (Arehart et al. , 1993; Lauha and Bettles, 1993; Smith and Sharon, 1994; Leonardson and Rahn, 1996). The orebody and much of the internal breccia bodies have a general WNW strike, with a sub-horizontal attitude (Peters, 1996; 1997). The open pit Goldstrike Mine exposes the Betze and Post orebodies, the Post anticline (Fig. 2), contacts between the Silurian and Devonian Roberts Mountains Formation, Devonian Popovich limestone and Devonian Rodeo Creek unit, and the northern contact of the Jurassic Goldstrike stock (Volk and Zimmerman (1991). Breccia bodies host much of the Betze ore body. Breccias are common rock types in most Carlin-type deposits (Williams, 1992, 1993), and they are particularly common in ore bodies of the north-central Carlin trend (Clode, 1993; Griffin et al., 1993; Leach, 1993). The host rocks in the Betze orebody are altered and deformed. The complex descriptive geology of the Goldstrike Mine is detailed by Volk et al. (1996), Peters et al.(1996), and Leonardson and Rahn (1996). The WNW-striking Dillon deformation zone (DDZ) hosts the upper central Betze orebody (Fig. 2) and contains several ore types associated with breccia (Peters, 1996, 1997). Rock types that host the orebody include phyllonitic black to

Abstract For the last several decades, gold exploration in Nevada has been strongly focused on sedimentary rock-hosted gold deposits in the Carlin, Cortez, Independence, and Getchell trends in north-central Nevada. Accordingly, less exploration activity has been directed toward the search for similar gold deposits in the eastern Great Basin, south and east of the major trends. Deposits in the central and northern Carlin and Cortez trends are hosted primarily in Upper Devonian middle slope soft-sediment slumps and slides and base-of-slope carbonate debris flows, turbidites, and enclosing in situ fractured lime mudstones. This is in marked contrast to gold deposits in the eastern Great Basin that are hosted primarily in three chronostratigraphic horizons: (1) shallow-water, Cambrian and Ordovician carbonate platform interior, supratidal karsted horizons and shelf lagoon strata, associated with eustatic sea-level lowstands and superjacent, transgressive calcareous shale and siltstone horizons that are deposited as sea level begins to rise, (2) Early Mississippian foreland basin turbidites and debris flows overlying karsted Late Devonian platform strata, and (3) Pennsylvanian and Permian shallow marine basin strata. Stratigraphic architecture in these three horizons was influenced in part by Mesozoic (Elko and Sevier) contractional deformation, including low-angle thrust and attenuation faults, boudinage, and large-scale folds, which in turn affected the orientation and localization of synmineral brittle normal faults. A compilation of past production, reserves, and resources (including historic and inferred) suggests an overall endowment of over 41 Moz of gold (1,275 tonnes) discovered to date in the eastern Great Basin, some in relatively large deposits. Significant clusters of deposits include the Rain-Emigrant-Railroad and Bald Mountain-Alligator Ridge areas on the southern extension of the Carlin trend, the Ruby Hill-Windfall-South Lookout-Pan on the southern extension of the Cortez trend, and the Long Canyon-West Pequop-Kinsley Mountain area near Wells, Nevada. Sedimentary rock-hosted gold deposits extend to the eastern edge of the Great Basin in Utah and Idaho and include the past-producing Black Pine, Barney’s Canyon, Mercur, and Goldstrike mines. The recognition of widespread, favorable host rocks and depositional environments on the Paleozoic platform-interior shelf in the eastern Great Basin opens up vast areas that have been relatively underexplored in the past. A basic premise throughout this paper is that the better we understand the origin of rocks and the depositional and postdepositional processes under which they formed, the more accurately we can make well-founded stratigraphic, sedimentological, structural, geochemical, and diagenetic interpretations. Without this understanding, as well as the rigorous application of multiple working hypotheses to explain our observations, the advance of science and the discovery of gold deposits is problematic.

Abstract The Goldstrike property, located in the Carlin Trend in Nevada, contains a diverse group of Carlin deposits, including some of the largest and highest grade examples known. The largest deposit, Betze-Post, has a gold endowment of approximately 1,250 metric tons (t) Au, and the Meikle deposit, which contains 220 t Au, has a grade of 24.7 g/t Au. Goldstrike is part of the larger Blue Star-Goldstrike subdistrict, which has an areal extent of 58.5 by 2 km and a total gold endowment of 1,970 t. The first discovery of gold at Goldstrike was in 1962. Subsequent exploration culminated in the discovery in 1986 of large high-grade orebodies beneath smaller, lower grade orebodies. Exploration over a 40-yr period has relied on the evolution in understanding of geology and ore controls, supported by the application of geochemical and geophysical exploration techniques. The Goldstrike property is located close to the rifted margin of the North American craton, along an inferred deep crustal structure. Stratigraphy at Goldstrike consists of lower Paleozoic sedimentary rocks, including an autochthonous, miogeoclinal carbonate sequence and an allochthonous eugeoclinal siliciclastic sequence, separated by the early Mississippian Roberts Mountains thrust. Multiple periods of deformation are evident, dominated by contraction in the upper Paleozoic to Mesozoic, followed by extension beginning in the Eocene. This has resulted in a complex structural architecture that is a major control on the location, geometry, and size of the orebodies. Intrusive rocks at Goldstrike include a Late Jurassic calcalkaline suite of diorite, rhyodacite, and lamprophyre and late Eocene calc-alkaline dacite dikes. These dikes, dated at approximately 39 Ma, are coeval with the Carlin gold mineralization and the onset of regional extension. Gold in unoxidized ore is mainly found within arsenian pyrite and is associated with Hg, Sb, and Tl. The ore fluids were low salinity (<10 wt % NaCl equiv), had homogenization temperatures of 200° to 225°C, and are of meteoric origin. Alteration varies considerably between deposits and includes decarbonatization, argillization, and silicification. Dissolution of carbonate has produced collapse breccias, which often host high-grade ore. Supergene alteration has produced oxide ores, at depths up to 200 m. Mineralization at Goldstrike occurs in a variety of settings, reflecting an interplay of both structural and lithological controls. Structural controls include folds, low- and high-angle faults, particularly where faults intersect, and zones of fracturing and brecciation. Fracturing is enhanced in areas of rheological contrast, such as the contact of the Jurassic dioritic Goldstrike intrusion, which is the first-order control of the large Betze-Post deposit. The north-northwest-striking Post fault system is associated with the highest grade orebodies, such as the Meikle deposit and the Deep Post subdeposit. The majority of economic gold mineralization is hosted by the autochthonous rocks, mainly the limy to dolomitic mudstones of the Devonian Popovich Formation and brecciated limestones and dolomites of the Silurian-Devonian Bootstrap limestone. Lesser amounts are hosted in other autochthonous units and intrusive rocks. Characteristics of the host rocks that are believed to enhance their favorability to gold deposition are the presence of reactive carbonate, porosity, permeability, and the presence of iron, which can be sulfidized to form auriferous pyrite.

Abstract Sedimentary platformal rocks in northern Nevada serve as hosts for the bulk of the gold introduced into Carlin-type gold deposits (Roberts, 1966; Arehart et al, 1993a; Christensen, 1996), and these deposits largely account for this region comprising the most significant gold province in North America. In 1997, approximately 7 MM oz Au will be produced from the province, which amounts to approximately 64 percent of United States and 9 percent of world production (Nevada Mining Association Newsletter, 1996, http://www.nevadamining.org/econ_overview_95.html ). Production since 1965 from the Carlin trend of deposits, a 40-mile-long string of mineralized centers, totals approximately 21 MM oz Au (Christensen, 1996). The most prolific part of the Carlin trend is its northern half which extends from the Gold Quarry Mine on the south to the Dee Mine on the north (Fig. 1). Although sedimentary rocks constitute a fundamental element of the genetic model for Carlin-type deposits (Cox and Singer, 1986), the implications and impacts of Paleozoic sedimentary fabrics and diagenetic processes on the genesis of these deposits have not been investigated as thoroughly as have the types of associated alteration, chemistry of the mineralizing fluids, and structural setting(s) of the deposits. The purpose of this report is to present a facies analysis of those autochthonous Devonian rocks that are the principal hosts for gold in the northern part of the Carlin trend (Fig. 2), and to suggest that some essential attributes derived from the sedimentary environments of these rocks contributed significantly to their becoming the premier gold hosts that

Abstract The Meikle and Betze/Post orebodies are two Carlin-type, sedimentary rock-hosted, disseminated gold deposits, located in north-central Nevada along the Carlin trend (Fig. 1). They display important differences in size, alteration, sihcification, pyritization, and gold grade. The Post/Betze deposit, 14 km northwest of Carlin, Nevada, is fairly representative of Carlin-type deposits. It is a medium- to high-grade, disseminated gold deposit with alteration effected by argillization, decalcification, and local silicification. Published ore reserves are 23.4 million ounces of gold at an average grade of 0.19 oz/ton of gold (Barrick Gold Corp. Annual Report, 1997). The Meikle deposit, is located 2 km northwest along strike of the Betze/Post deposit. It is a high-grade, sediment-hosted gold deposit with extensive silicification, brecciation, and pyritization and contains gold reserves of 6.1 million ounces of gold averaging 0.72 oz/ton of gold (Barrick Gold Corp. Annual Report, 1997). Petrographie and microfhermometric data were gathered from each deposit to determine the mineral paragenesis, pressure, temperature, fluid composition, and depths of formation.

Abstract This report presents evidence for a previously unrecognized type of Au mineralization on the Barrick Goldstrike property that is geochemically, mineralogically, and temporally distinct from classic Carlin-type mineralization (Table 1). This newly recognized mineralization is characterized by a mineral assemblage that includes barite, sphalerite, minor boulangerite, pyrite, galena, minor tetrahedrite, tennantite, chalcopyrite and native gold. Gold occurs as native inclusions in pyrite, chalcopyrite, tetrahedrite, bitumen, dolomite, and barite. In contrast, features recognized in Carlin-type deposits include a mineral asemblage of As-rich pyrite, realgar, orpiment, and arsenopyrite, with a distinct absence of base metal sulfides. Gold occurs as sub-micron inclusions in As-rich pyrite and alteration consists of decalcification, silicification, and argillization. Carlin-type mineralization is younger than a 39 Ma dike (Emsbo et al. , 1996). Recognition of the base metal mineralization resulted from a broad study of the breccia-hosted Carlin-type deposit in the Meikle Mine. Examination of the stratigraphic section adjacent to Meikle revealed that these base metal sulfides and barite are stratiform and occur in unaltered rocks of the Popovich Formation. In Meikle, the base metal-rich assemblage also occurs as discordant veins which were brecciated and cut by Carlin-type mineralization (Lamb, 1995). The association of low but significant gold content with this base metal mineralization outside Meikle prompted a study of its geological and spatial characteristics, its age and significance within the geologic evolution of the Goldstrike property, and the relationship of its gold to its other sulfides. In this abstract we describes textural, stratigraphic/spatial, and geochemical evidence that this base

Abstract Including past production, reserves and resources, the Carlin Trend forms the largest and most prolific accumulation of gold deposits in North America. More than 40 separate deposits have been delineated since disseminated gold mineralization in carbonate rocks was discovered in 1961. From this discovery, a classification for this style of gold mineralization has come to be referred to as “Carlin-type” deposits. To date, more than 25 million ounces of gold have been mined on the Carlin Trend from 26 separate operating, or past producing mines (Table 1 ). Open pit mining on the Carlin Trend began in 1965 at the Carlin Mine, and underground mining began in 1993 on the same deposit. The scope of this paper is to first present a regional overview of the Carlin Trend, followed by summary descriptions of some of the more recent discoveries of deep, predominantly refractory gold deposits. As part of a concluding discussion, a spectrum of Carlin Trend deposits are categorized on a quaternary diagram to illustrate the I relative influence of structural and stratigraphic controls on each deposit. The Carlin Trend is a 60 kilometer long north-northwest trending alignment of gold deposits located in northeastern Nevada, within the larger Great Basin physiographic province of the western United States (Figs. 1, 2). Gold deposits are hosted in a variable stratigraphic package of Ordovician through lower, Mississippian rocks. Within specific deposits, gold mineralization hosted in Cretaceous and Tertiary dike swarms and the Jurassic-Cretaceous Goldstrike granodiorite stock constitutes up to 15% of the mineralized material. Regional Tectonic Development Regional stratigraphic and isotopic data indicate that northeastern Nevada was situated along a stable paleo-continental margin during much of the Cambrian through Early Mississippian (Stewart,1980). During this period, a westward-thickening, prism-shaped package of sediments were deposited from the outer margins of the paleo-continental shelf into an oceanic basin. Within this depositional environment, sedimentary facies graded from western eugeoclina1, to eastern miogeoclinal sequences. During Late Devonian through Middle Mississippian time, eastward-directed compressional tectonism associated with the Antler orogeny resulted in regional scale folding and imbricate thrusting of the western eugeoclinal assemblage of predominantly siliciclastic rocks, over the eastern autochthonous assemblage of silty carbonate rocks (Roberts et al., 1958). The resultant accretionary mass formed the emergent Antler highlands which shed an eastward directed overlap assemblage of clastic rocks during Middle Mississippian to Early Pennsylvanian (Smith and Kettner,1975). Late Paleozoic tectonism during Early to Middle Pennsylvanian time (Humboldt orogeny) was followed by deposition of shelf carbonate sequences during the Late Pennsylvanian and Permian (Smith and Kettner,1975; Kettner, 1977).

Abstract The Blue Star/Genesis Mine is located in northern Eureka County, Nevada, near the north end of the Carlin Trend. Prospecting activity in this area dates back to the 1870’s. In 1929, turquoise was originally mined at the Blue Star Mine. Exploration and development for gold began in the 1960’s, but production was limited. Open pit gold mining at the Blue Star deposit began in 1974, and at the Genesis deposit in 1986. In 1989, after a short hiatus at the Blue Star Mine, production resumed, resulting in the formation of a single Blue Star/Genesis pit. As of December 31, 1992, reserves are calculated to be 74,493,000 tons at 0.032 oz of gold per short ton, containing 2,358,000 ounces. The rocks in the area are comprised of Paleozoic allochthonous and autochthonous siliceous and carbonate assemblage rocks, overlain by Tertiary tuffs and intruded by the Goldstrike intrusive. Mineralization primarily occurs within Devonian carbonate and siliceous rocks that have had complex structural events imposed upon them. Gold occurs as micron-size particles and within very fine grained pyrite. Alteration within the deposit is associated with contact metamorphism/metasomatism, hydrothermal, and supergene alteration events. Arsenic and antimony haloes are associated with gold mineralization; mercury does not have a direct correlation.