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.
In this study, a series of synthetic mercury-bearing sphalerite and zinc-bearing metacinnabar crystals was grown using the salt flux method at 605-650 °C at the hot and cold ends of the ampoule, ...respectively, in a composition range from 2 to 82 mol.% of the HgS component. According to the XAFS (X-ray Absorption Fine Structure) measurements, mercury in the sphalerite-metacinnabar crystals exists in the form of a solid solution. The EXAFS (Extended X-ray Absorption Fine Structure) spectra confirm the increase in the ionic radius of all coordination shells in the crystal structure of the Hg-sphalerite and Zn-metacinnabar on 0.14–0.28 Å, depending on the calculated model compared to the distances in pure sphalerite. However, the crystal structure does not change. The established nominal oxidation state of mercury in the (Zn, Hg)S is 2+.
•Continuous series of solid solutions exists in the ZnS–HgS system at 605–650 °C.•Hg substitutes Zn and generates lattice distortions in the sphalerite structure.•Rising of the Hg–S distance results in increasing the lattice parameter.•The nominal oxidation state of mercury in ZnS–HgS mineral system is 2+.•Extended solid solution series of the sphalerite-type structure exists between ZnS–HgS at 605–650 °C.
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