Contrasting fluids in the svetlinsk gold-telluride hydrothermal system, south urals

The large gold-telluride Svetlinsk deposit (~135 t Au) is considered to be a nontraditional one in the Urals and its origin is debated. A specific feature of the deposit is the abundance of various tellurides, such as tellurides of Fe, Ni, Pb, Sb, Bi, Ag, and Au. The new data of microthermometry, Raman spectroscopy, LA-ICP-MS, and crush-leach analysis (gas and ion chromatography, ICP-MS) for fluid inclusions as well as O-isotope data for quartz were obtained for the construction of PTX parameters of ore-formation and fluid sources in the deposit. Mineralisation was formed at a wide range of temperature and pressure (200–400 °C, 1–4 kbar) and from contrasting fluids with multiple sources. At the early stages, the magmatic fluid evolved during its ascent and phase separation and the fluid derived from the host rock decarbonation and dehydration were involved in the hydrothermal system. In addition, mantle-derived fluid might be involved in the ore-forming process during gold-telluride precipitation as well as heated meteoric waters during the late stages. Early fluids were rich in H2S, S0, and CH4, while the Au-Te mineralisation was formed from N2-rich fluid. © 2019 by the authors. Licensee MDPI, Basel, Switzerland

Noble metal speciations in hydrothermal sulphides

A significant part of the primary gold reserves in the world is contained in sulphide ores, many types of which are refractory in gold processing. The deposits of refractory sulphide ores will be the main potential source of gold production in the future. The refractory gold and silver in sulphide ores can be associated with micro-and nano-sized inclusions of Au and Ag minerals as well as isomorphous, adsorbed and other species of noble metals (NM) not thoroughly investigated. For gold and gold-bearing deposits of the Urals, distribution and forms of NM were studied in base metal sulphides by laser ablation-inductively coupled plasma mass spectrometry and by neutron activation analysis. Composition of arsenopyrite and As-pyrite, proper Au and Ag minerals were identified using electron probe microanalysis. The ratio of various forms of invisible gold—which includes nanoparticles and chemically bound gold—in sulphides is discussed. Observations were also performed on about 120 synthetic crystals of NM-doped sphalerite and greenockite. In VMS ores with increasing metamorphism, CAu and CAg in the major sulphides (sphalerite, chalcopyrite, pyrite) generally decrease. A portion of invisible gold also decreases —from ~65–85% to ~35–60% of the total Au. As a result of recrystallisation of ores, the invisible gold is enlarged and passes into the visible state as native gold, Au-Ag tellurides and sulphides. In the gold deposits of the Urals, the portion of invisible gold is usually <30% of the bulk Au. © 2021 by the authors. Licensee MDPI, Basel, Switzerland