Bald Mountain Gold Mining District, Nevada: A Jurassic Reduced Intrusion-Related Gold System

Abstract

Nevada also contains significant Tertiary epithermal Au-Ag deposits and Tertiary and Cretaceous porphyry-related base metal-Au deposits (John et al., 2003). Examples of Tertiary porphyry Cu-Au deposits (Fig. 1A) include the Battle Mountain district (Theodore, 2000) and the world-class Bingham deposit near Salt Lake City, Utah (Babcock et al., 1995, and references therein), which is located along a westerly mineral trend that extends into Nevada (Shawe, 1977). Less common and smaller Cretaceous Cu-Mo-Au deposits and related base metal-Au skarn and replacement deposits are present near the towns of Ely (Westra, 1979) and Eureka (Nolan, 1962; Fig. 1B). Distal disseminated Au deposits, with some features resembling Carlin-type Au deposits, are commonly associated with the Cretaceous and Tertiary porphyry systems. Jurassic igneous rocks are typically associated with nil or minor Au concentrations and generally are not targets for exploration. In the eastern Great Basin, minor Au is associated with intrusive rock in the porphyry-related Cu deposit at the small Victoria mine in the Dolly Varden Mountains (Atkinson et al., 1982), replacement Ag, Pb, and Au deposits in the Cortez Range (Stewart and McKee, 1977), and base and precious metal skarn and polymetallic veins associated with the Goldstrike pluton in the northern Carlin trend (Emsbo et al., 2000; Heitt et al., 2003). In the western Great Basin, the Jurassic Yerington porphyry system has low Au (Dilles and Profett, 2000). The Bald Mountain mining district is in east-central Nevada, about 115 km south-southeast of Elko and about 100 km northwest of Ely (Fig. 1B). The district contains 11 orebodies (Fig. 2) that cluster in and around the Bald Mountain pluton and are hosted by Cambrian to Jurassic rocks. In this paper, the deposits in Figure 2 are classified as follows: central and deep (Top, Mahoney, Sage Flat); peripheral and deep (LJ Ridge, LBM, Rat, 1-5 pits); central and shallow (RBM; acronyms are actual mine names). The deposits are enriched in base and precious metals and several trace elements (Table 1), particularly As, Sb, Zn, and Bi. Disseminated Au mineralization occurs along high-angle faults, in certain strata, and in stockworks and veins. In and near the Bald Mountain pluton, quartz stockworks and veins host ore at the Top, Mahoney, and Sage Flat deposits, whereas in the peripheral Rat and LJ Ridge deposits, ore is both discordant and concordant to bedding.

Disseminated gold–sulfide mineralization at the Zhaima deposit, eastern Kazakhstan

“…The syngenetic gold accumu lation in sulfidated cherty and carbonaceous cherty sediments and their elevated background Au content in the West Kalba gold belt have been repeatedly noted by Polyansky et al (1980); Zhautikov and Maulenov (1985); Narseev (1996Narseev ( , 2002; Bol'shoi Altay … (2000); Bakyrchik … (2001); Kovalev et al (2009Kovalev et al ( , 2012; Kuzmina et al (2013b). The occurrence of exhala tion-sedimentary gold mineralization at local strati graphic levels of host and underlying carbonaceous terrigenous-carbonate sequences is also characteristic of Carlin type deposits (Titley, 1991;Ilchik and Bar ton, 1997;Emsbo, 1999;Emsbo et al, 2003;Nutt and Hofstra, 2007;Large et al, 2011). No those Au bear ing rocks are known in the host sequences at the Zhaima deposit.…”

Mineralogical, petrological, stable isotope, and fluid inclusion studies of the Palea Kavala reduced intrusion-related and the transitional Fakos porphyry Cu-Mo to epithermal Au-Te ore systems

“…fO 2 , pH, T, δ 34 S ΣS , and ΣS) of the ore fluid at that particular locality. (Goldfarb et al, 2004;Nutt and Hofstra, 2007). These deviations in δ 34 S from 0 ± 5 per mil may have been caused by devolatilization of, or exsolution of, sulfur from a magma melt within a reduced sedimentary source rock or assimilation of sulfur from sedimentary rocks that are enriched in 34 S (Goldfarb et al, 2004;Nutt and Hofstra, 2007).…”

“…(Goldfarb et al, 2004;Nutt and Hofstra, 2007). These deviations in δ 34 S from 0 ± 5 per mil may have been caused by devolatilization of, or exsolution of, sulfur from a magma melt within a reduced sedimentary source rock or assimilation of sulfur from sedimentary rocks that are enriched in 34 S (Goldfarb et al, 2004;Nutt and Hofstra, 2007). The effects of the progressive interaction of the hydrothermal fluids with a sedimentary source of sulfur is also apparent for the Scheelite Dome and Clear Creek deposits as indicated by δ 34 S values as low as -12 and -13 per mil, respectively (Marsh et al, 2003;Mair et al, 2006 proposed a depth 3 to 3.5 km (assuming lithostatic pressure).…”

“…All data were obtained at Iowa State University except for Kav1, Kav1-1, Kav2, Kav2-7, Kav1/2, and Kav 1/3 which were measured at the Aristotle University of Thessaloniki. The number in parenthesis indicates the number of measurements or calculations for each analysis Melfos et al, 2008); 3 Tetradymite, Chalkero; 4 Bismuthinite, Kavala; 5,6 Cosalite, Chalkero Carbon dioxide abundant in fluid inclusions in hydrothermal veins Carbon dioxide common in fluid inclusions Data for the Palea Kavala deposits from this study, Kyriakopoulos (1987), Dinter et al (1995), Christofides (1996), Kyriakopoulos et al (1996), Neiva et al, (1996, Vavelidis et al (1996), Vavelidis et al (1997), Melfos et al (2008), Vavelidis and Andreou (2008); data for reduced intrusion-related gold systems from McCoy et al (1997), Thompson et al (1999), Lang et al (2000), Thompson and Newberry (2000), Lang and Baker (2001), Baker (2002), and Hart 2007; 1 table modified after Nutt and Hofstra (2007) Mavrokoryfi, and Pefka).…”

“…Reduced intrusion-related gold systems have been identified worldwide, although the best studied examples of this ore type form part of the Tintina Gold Province of Alaska and the Yukon Territory (e.g., Fort Knox, Donlin Creek, Dublin Gulch;McCoy et al, 1997;Thompson et al, 1999;Lang et al, 2000;Lang and Baker, 2001). Other potential examples of reduced intrusion-related gold systems include those in the Bolivian polymetallic belt (e.g., Kori Kollo; Long et al, 1992), central Asia (e.g., Vasilkovskoe; Burshtein, 1996), eastern Australia (e.g., Kidston; Baker and Tullemans, 1990), the Iberian Peninsula (e.g., Salave; Harris, 1980), northern Nevada (Bald Mountain; Nutt and Hofstra, 2007), and northern China (Niuxinshan; Yao et al, 1999). Although reduced intrusion-related gold systems are present in eastern Europe at, for example, Mokrsko and Petrackova hora in the Czech Republic (Morávek et al, 1989;Zacharias et al, 2001), they have not been described in southeastern Europe.…”