Electron microprobe analysis (EMPA), X-ray powder diffraction (XRD), and Raman spectroscopy (RS) were applied to characterize the synthetic gold chalcogenides of the Au-Te-Se-S system and natural analogs from the Gaching deposit (Central Kamchatka, Russia). The EPMA results showed that the synthetic chalcogenides have different Te/Se/S and Au/X (X = Te + Se + S) ratios: AuX 2 , Au 3 X 10 , and AuX. They are similar in composition to natural compoundscalaverite (AuTe 2 ), maletoyvayamite (Au 3 Te 6 Se 4 ), and unnamed minerals AuTe 0.7 Se 0.3 and AuSe 0.7 S 0.3 . It was established that chalcogenides AuX, Au 3 X 10 , and AuX 2 have a specific Raman spectra with characteristic peaks. The position of the peaks and the character of the spectra of the synthetic phases and their natural analogs from the Gaching deposit coincide within the limits of accuracy. Different ratios of chalcogenes Te/Se/S in compounds influence the Raman peak positions. The positions of the peaks for natural compounds AuX differ depending on the predominance of Te (AuTe 0.7 Se 0.3 ) or Se (AuSe 0.7 S 0.3 ). AuSe synthetic phases consist of a mixture of αand β-polymorphs. Raman spectroscopy can be used for the identification of natural gold chalcogenides worldwide, which are difficult to diagnose by other methods due to the microscopic grain sizes and close intergrowths with other ore minerals. The similarity of the Raman spectra upon changing the concentrations of Se and S suggests identical structures and possible isomorphism in the composition range of AuTe 0.

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.

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The unique minerals of the Au-Pd-Hg system in gold grains from heavy concentrates of the Itchayvayam placers and watercourses draining and ore samples of the Barany outcrop at the Itchayvayam mafic–ultramafic complex (Kamchatka, Russia) were investigated. Gold grains from watercourses draining and heavy concentrates of the Itchayvayam placers contain substitution structures formed by Pd,Hg-rich low-fineness gold (Au0.59–0.52Pd0.24–0.25Hg0.17–0.23, 580‰–660‰) and Pd,Hg-poor high-fineness gold (Au0.94–0.90Pd0.02–0.04Hg0.03, 910‰–960‰). Potarite (PdHg) without and with impurities (Au < 7.9, Cu < 3.5, Ag < 1.2 wt.%), Ag-poor high-fineness gold (Au0.91Ag0.09, 950‰), Ag,Pd,Hg-bearing middle-fineness gold (Au0.75Ag0.08Pd0.09Hg0.08—Au0.88Ag0.09Pd0.02Hg0.01, 820‰–930‰), and Pd,Hg-rich low-fineness gold with minor contents Ag and Cd (Au0.51–0.55Pd0.25–0.22Hg0.21–0.16Ag0.03–0.06Cd0.01, fineness 580‰–630‰) were observed as individual microinclusions in the ore samples of the Barany outcrop. XRD and EBSD study results show that the Pd,Hg-rich low-fineness gold is isotypic to gold and has the same structure type, but different cell dimensions. According to data obtained for the Itchayvayam and some deposits and ore occurrences with Pd,Hg-bearing gold, the stable ternary phases and solid solutions of the following compositions in the Au-Pd-Hg system have been identified: Pd,Hg-poor gold (Au0.94–0.90Pd0.02–0.04Hg0.03), Pd,Hg-rich gold (Au0.59–0.52Pd0.24–0.25Hg0.17–0.23), Au-potarite (PdHg0.62Au0.38—Pd1.04Hg0.96—Au0.80Pd0.68Hg0.52), and Au,Hg-bearing palladium (Pd0.7Au0.3Hg0.1). The genesis of Pd,Hg-rich gold is insufficiently studied. We supposed that the meteoric waters or low-temperature hydrotherms rich in Pd and Hg could lead to the replacement Pd,Hg-poor gold by Pd,Hg-rich gold. High concentrations of Pd in Pd,Hg-bearing gold indicate a genetic relationship with mafic–ultramafic rocks.

—We have studied the mineral composition of ores from the Pepenveem epithermal Au–Ag deposit, which is a promising new object of the Chukchi Peninsula. It has been found that the ore formation process was developed in the following sequence: Pyrite, arsenopyrite, and marcasite were deposited at the early stage, next were Pb, Zn, and Cu sulfides; at the late stage, native gold, pyrargyrite, stephanite, proustite, minerals of the pearceite–polybasite series, acanthite, and other Ag minerals were deposited. The results of fluid inclusion studies indicate that the Au–Ag mineralization formed from low-temperature (236–137 °C) low-concentration chloride hydrotherms (0.18–1.57 wt.% NaCl eq.). The results of calculation of thermodynamic equilibria have shown that in the temperature range from 200 to 100 °C, there were a decrease in the fugacity of sulfur (lg fS2 from –10 to –21) and oxygen (lg fO2 from &lt;–36 to &lt;–48) and a change from near-neutral to acidic solutions. Compared to other Au–Ag deposits on the Chukchi Peninsula (Corrida and Valunistoe), which are characterized by wide distribution of Se- and Te-bearing Au–Ag chalcogenides (naumannite, cervelleite, and hessite), ore formation with gold–silver–sulfosalt mineralization at the Pepenveem deposit took place at lower temperatures and lower selenium, tellurium, and oxygen fugacity. The data obtained permit us to refer the Pepenveem deposit to the group of epithermal low-sulfidation (LS) deposits.