The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid

Abstract

We studied the mineralization and sulfur isotopic composition of sulfides of gold–palladium ores in olivine clinopyroxenites from the Dzelyatyshor massif made up of a continuous layered series of rocks: olivine-free clinopyroxenite–olivine clinopyroxenite–wehrlite. The primary igneous layering of rocks, manifested as different quantitative ratios of clinopyroxene and olivine in them, controls the local trends of variability in the chemistry of mineral-forming medium and the concentrations of ore components, including noble metals, and sulfur in each separate layer during its cooling. The replacement of primary rock-forming minerals by secondary minerals, when the temperature decreases, is a characteristic trend for pyroxenites: (a) olivine → serpentine, secondary magnetite, and (b) clinopyroxene → amphibole, secondary magnetite → chlorite. The deposition of native gold in parageneses with PGM and sulfides at the Ozernoe occurrence took place during the replacement of earlier rock-forming minerals by chlorite. This process completed mineral formation at the deposit and took place at temperatures 150–250 °С and at the high activity of S, Te, Sb, and As of fluid. The variability of mineral formation conditions during chloritization is reflected in the change of native-sulfide forms of Pd by arsenide-antimonide forms and the sulfur isotopic composition of sulfides. The Pd content in native gold increases in the series—Au-Ag solid solution (<1.5 wt.% Pd)—Au-Cu intermetallides (to 6 wt.% Pd)—Cu-Au-Pd solid solutions (16.2–16.9 wt.% Pd). The sulfur isotopic composition of pyrite, chalcopyrite, and bornite varies from −2.1 to −2.9‰. It is assumed that a deep-seated magmatic basic melt was the source of fluid, ore components, and sulfur.

Cu and Au Mineralization of the Tolparovo Ore Occurrence: Evidence for the Formation of Redbed Copper Occurrences in Neoproterozoic Deposits of the Southern Urals

“…According to these studies, the temperature of the sphalerite-chalcopyrite paragenesis formation ranges between 230 and 350 °C, sometimes reaching up to 400 °C. [62,63]) and (b) compositions of Cu-containing native gold and silver (at %) from deposits/ore occurrences of various types (compiled according to [64][65][66][67][68][69][70]).…”

“…In order to determine the source of gold, data on its chemical composition can be used. The ratio of the main components in gold and the content of certain impurity elements may reflect the conditions of its formation and its typomorphic features [64,66,70,94]. Some phases of Cu-containing gold in the Tolparovo ore occurrence are close to the composition of Cu 3 Au 2 .…”

“…In many cases, XRD studies show that Cu 3 Au 2 compounds are copperenriched cuproauride (cubic CuAu) or tetra-auricuprid (tetragonal CuAu) [64,95]. However, Cu-containing gold of such a chemical composition is often found in igneous deposits and the ore occurrences of gold [64,67,68,70]. It should be noted that native gold from the Tolparovo ore occurrence is chemically similar to that of rhodingites in mafite-ultramafite complexes and to gold, associated with gabbrodolerites (see Figure 8b).…”

“…Figure 8. (a) Au-Ag-Cu diagrams with liquidus isotherms (according to[62,63]) and (b) compositions of Cu-containing native gold and silver (at %) from deposits/ore occurrences of various types (compiled according to[64][65][66][67][68][69][70]). …”

Editorial for the Special Issue “Native Gold as a Specific Indicator Mineral for Gold Deposits”

“…Murzin and coauthors [9] investigated the mineralogy and sulfur isotope geochemistry in sulfides from one Au-PGE deposit, Ozernoe, at the Dzelyatyshor wehrlite-pyroxenite massif, Polar Urals, Russia. They concluded that the variations of sulfur isotopic composition in pyrite, chalcopyrite, and bornite indicated that a deep-seated magmatic basic melt was the source of the ore-forming fluid, ore components, and sulfur during Au-Pd ore formation.…”