Pyrite-Pyrrhotite Stability in a Metamorphic Aureole: Implications for Orogenic Gold Genesis

The effects of amphibolite facies metamorphism on the trace element composition of pyrite and pyrrhotite in the Cambrian Nairne Pyrite Member, Kanmantoo Group, South Australia

“…Mass-balance calculations by Hammerli et al (2015) suggest that considerable amounts of Pb and Zn can be released from staurolite-absent metasedimentary rocks during prograde metamorphism in the Kanmantoo Group, with Cu showing no appreciable release. However, unlike Au, which can be released to form metamorphogenic gold deposits during prograde metamorphism (e.g., Pitcairn et al, 2006;Tomkins, 2010), other studies have interpreted their data to suggest that silicates such as biotite and feldspar retain Pb and Zn to mid-crustal conditions and do not carry Cu, Pb, and Zn in solution effectively to form orogenic base metal deposits (e.g., Pitcairn et al, 2006;Yardley and Cleverley, 2015;Zhong et al, 2015;Finch and Tomkins, 2017). Moreover, evidence for metamorphic remobilization of base metal sulfides (chalcopyrite, sphalerite, galena) from Py1 and Po1 in the NPM occurs only at the microscopic to mesoscopic (meter) scale and likely represents solid-state remobilization into tension gashes and fractures (George, 1969a).…”

Mineral composition of Paleoproterozoic metamorphosed massive sulfide ore in the Kola Region (a case study of the Bragino Occurrence, South Pechenga)

“…Широкая пирротинизация колчеданных руд Кольского региона, локализованных в поясе ПИВ, является следствием их глубокой метаморфической переработки. Согласно расчетным и экспериментальным данным (Toulmin, Barton, 1964;Peacock, 1981;Craig, Vokes, 1993;Finch, Tomkins, 2017), чем выше степень метаморфизма, тем более широко проявлена пирротинизация пирита и пирротина. Это характерно не только для руд Кольского региона, но и для Карелии (Рыбаков, 1987).…”

Trace Element Analysis of Pyrite from the Zhengchong Gold Deposit, Northeast Hunan Province, China: Implications for the Ore-Forming Process

“…More reducing conditions occurred in stage III, as demonstrated by the minor redissolution of pyrite and arsenopyrite (Figure 6d,g) [63,64] and the change from a pyrite-arsenopyrite assemblage to a pyrite-pyrrhotite assemblage [65][66][67]; this would have promoted the deposition of gold and especially caused the conversion of pyrite (high sulfur content) to pyrrhotite (low sulfur content) in stage III, which is associated with native gold (Figure 6i) [65][66][67][68][69].…”

“…Co/Ni ratios (<1) with low standard deviations are generally accepted to represent pyrite of sedimentary origin [18,46,47,71]. The Co/Ni ratios of the arsenian pyrite in the Zhengchong gold deposit vary; in general, the average Co/Ni values are 0.15 in PyI, 0.16 in PyII, and 0.38 in PyIII (Figure 15a), thus apparently indicating that the mineralization may have been caused by metamorphic hydrothermal fluids [69]. The higher Co and Ni concentrations (Figure 13d) and higher Co/Ni ratios (Figure 15a) observed from PyII to PyIII may result from a decrease in temperature [15,72].…”