Newly Discovered Devonian Sedex-type Base and Precious Metal Mineralization, Northern Carlin Trend, Nevada
Poul Emsbo, Richard W. Hutchinson, Albert H. Hofstra, Jeffrey A. Volk, Keith H. Bettles, Gary J. Baschuk, Terry M. Collins, Eric A. Lauha, Jeffrey L. Borhauer, 1997. "Newly Discovered Devonian Sedex-type Base and Precious Metal Mineralization, Northern Carlin Trend, Nevada", Carlin-Type Gold Deposits Field Conference, Peter Vikre, Tommy B. Thompson, Keith Bettles, Odin Christensen, Ron Parratt
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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
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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).