Sulfur isotopes in sediment-hosted orogenic gold deposits: Evidence for an early timing and a seawater sulfur source

Abstract

We report sulfur isotopic compositions of sulfi des of various paragenetic stages in the giant Sukhoi Log sediment-hosted orogenic Au deposit in Russia. The overall mean value and the signifi cant variability in early pyrite indicate that the sulfur was from the reduction of seawater sulfate. The later generations of sulfi de have δ 34 S values in successively smaller ranges, coincident with the mode that is around the median value of the whole data set. Together with textural evidence, sulfi de trace element data, and gold occurrence, the data demonstrate that metamorphism has gradually homogenized the early sulfur, accompanied by the segregation of quartz and the release of Au from the lattice of early pyrite and its reprecipitation as inclusions in later pyrite. The S isotopic compositions of sulfi des in Sukhoi Log, and many other major orogenic Au deposits hosted in sedimentary rocks of various ages, show a pattern generally parallel to the seawater sulfate curve through geologic time, indicating that the sulfur in most sediment-hosted orogenic Au deposits was probably also originally from the reduction of seawater sulfate. We conclude that sulfi dation and gold mineralization in many sediment-hosted orogenic gold deposits was early during basin evolution when seawater was the principal active fl uid, rather than later, during or after basin inversion, as proposed in current models.

Orogenic gold: Common or evolving fluid and metal sources through time

“…This was interpreted by Goldfarb et al (1997) and Chang et al (2008) to indicate the sulfur source was required to be disseminated syngenetic/diagenetic pyrite in the terranes being devolatilized at depth. The sulfur was gained by the ore-forming fluids during metamorphic conversion of the pyrite to pyrrhotite, as described by Goldfarb et al (1989) for deposits in the Juneau Gold Belt.…”

A Combined Ingress-Egress Model for the Kianna Unconformity-Related Uranium Deposit, Shea Creek Project, Athabasca Basin, Canada

“…Possible sources of sulfur within the basin are the alumino-phosphate sulfate (APS) minerals, Proterozoic seawater sulfate, which had a sulfur isotopic composition of 16-32‰, (Chang et al, 2008) and/or Proterozoic evaporites that may have existed in the basin, which would have had δ 34 S values from ~10-35‰ (Seal et al, 2000). APS minerals are commonly found in Athabasca Group sandstone (Hoeve and Quirt, 1984;Quirt et al, 1991;Gaboreau et al, 2007), and are closely associated with perched uraninite and sulfides.…”

Involvement of magmatic fluids at the Laloki and Federal Flag massive sulfide Cu–Zn–Au–Ag deposits, Astrolabe mineral district, Papua New Guinea: sulfur isotope evidence

“…The S isotope compositions of many VHMS and SEDEX Zn-Pb-Cu deposits (Goodfellow et al 1993;Huston 1999) and orogenic sediment-hosted deposits (Sangster 1968;Chang et al 2008) positively vary with the seawater sulfate through geologic time, indicating that the S in the deposits was derived by reduction of seawater sulfate. The seawater sulfate reduction can occur during abiotic or biotic processes or via a combination of them.…”

“…The source of S is important to the understanding, the source of the hydrothermal fluids, and the genesis of the deposits. Sulfur can be introduced by metamorphic fluids from wall rock (e.g., Sangster 1992), from the mantle (e.g., Barley and Groves 1990), from magmas (e.g., Sakai et al 1984), from seawater (e.g., Rees et al 1978;Chang et al 2008), and from organic matter (e.g., Gemmell et al 2004;Peters et al 2010).…”