G.A. Pal’yanova

Geochemical mobility of Au and Ag during hydrothermal transfer and precipitation: Thermodynamic simulation

The thermodynamic simulation of the geochemical mobility of Au and Ag during their hydrothermal transfer and precipitation was conducted with regard for the formation of continuous nonideal Au-Ag solid solutions (or AuXAg1−X) alloys) and with the analysis of the effects of principal physicochemical parameters (temperature, pH, redox potential, and the concentrations of sulfide sulfur and chloride ions) on the solubility of Au-Ag alloys of various composition. Predominant Au and Ag complexes and the types of solutions were identified, which are characterized by different extractive ability with respect to these metals. A tendency in the variations in the Au/Ag ratio in the solid phase during the evolution of the hydrothermal process was revealed with regard for various conditions under which Ag sulfides can occur. The possible effect of the AuXAg1−X/solution ratio on the composition of the Au-Ag mineralization was demonstrated, and tendencies in the variations in the composition (fineness) of the alloys during their redeposition were identified.

Some sulfides of gold and silver: Composition, mineral mineral assemblage, and conditions of formation

Characteristic mineral assemblage and special features of the composition of Au and Ag sulfides of gold-silver deposits have been established. The forms of the occurrence of Au and Ag in the minerals of the early and last stages have been analyzed. The conditions for the formation of uytenbogaardtite and petrovskaite in supergene and low-temperature hydrothermal processes have been considered. A thermodynamic model explaining their genesis in the oxidation zones is presented.

Synthesis and crystal structure of gold–silver sulfoselenides: morphotropy in the Ag3Au(Se,S)2 series

Gold–silver sulfoselenides of Ag3Au(Se,S)2 series—Ag3AuSe1.5S0.5, Ag3AuSeS, and Ag3AuSe0.5S1.5—have been synthesized by fusing the elements in the required stoichiometric amounts in evacuated quartz ampoules. The single crystal X-ray diffraction data indicate the existence of two solid-solution series: petzite-type cubic Ag3AuSe2—Ag3AuSeS (space group I4132) and trigonal Ag3AuSe0.5S1.5—Ag3AuS2 (space group

First discovery of high-mercury silver in ores of the Rogovik gold–silver deposit (Northeastern Russia)

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The problem of genesis of gold and silver sulfides and selenides in the Kupol deposit (Chukotka, Russia)

). Both crystal structures differ in the distribution of Ag+/Au+ cations in the same distorted body-centered cubic sublattice of chalcogen anions. The morphotropic transformation results from the shrinkage of anion packing accompanied by the shortening of Ag–Ag distances. The structure of uytenbogaardtite mineral, earlier incorrectly interpreted as a tetragonal or cubic cell, is similar to that of the trigonal Ag3AuS2 end-member.

Synthesis and Crystal Structure of the Trigonal Silver(I) Dithioaurate(I), Ag3AuS2

Pyritized bivalve mollusks have been revealed for the first time in upper Norian sedimentary rocks at the large orogenic Sentachan gold–antimony deposit in eastern Yakutia. It has been established that they are related to species of the genus Monotis (M. ex gr. jacutica (Teller) (specimen no. 2077/1, CSGM) and M. pachypleura (Teller) (specimen no. 2077/2, CSGM), which existed during the Monotis densistriata phase of the Norian Age of the Triassic Epoch presumably 211.5–214 Ma ago. The occurrence of two pyrite generations differing in morphology, sulfur impurity, and isotopic compositions corroborates the suggestion that pyritization of fauna was a discrete process. It has been shown that sulfur that formed owing to bacterial sulfate reduction and interaction with organic matter was involved in the pyritization of bivalve mollusks, whereas mixing of magmatic sulfur and sulfur derived from host sedimentary rocks participated in deposition of Au–Sb ore.

Formation of gold and silver sulfides in the system Ag–Au–S

New data on mercurial mineralization are presented, and a detailed characteristic is given for the first discovery of mercurous silver in ores of the Rogovik gold–silver deposit (the Omsukchan trough, Northeastern Russia). It was found that native silver in the examined ores occurs as finely-dispersed inclusions in quartz filling microcracks and interstitions. It also occurs in associations with kustelite, Ag sulfosalts and selenides, selenitic acanthite, and argyrodite. The mercury admixture varies from “not detected” in the central parts of grains to 0.22–1.70 wt % along the edges, or, in independent grains, to the appearance of Ag amalgams containing 10.20–24.61 wt % of Hg. The xenomorph form of grains of 50 μm or less in size prevails. It is assumed that the appearance of mercurial mineralization is caused by the superposition of products of the young Hg-bearing Dogda–Erikit belt upon the more ancient Ag-bearing Omsukchan trough.