Conditions of formation of Au–Se–Te mineralization in the Gaching ore occurrence (Maletoyvayam ore field), Kamchatka, Russia

Abstract

The Gaching high-sulfidation epithermal deposit in the Maletoyvayam ore field features a wide range of Se-containing minerals and selenides, as well as complex gold oxides, Au tellurides (calaverite, krennerite) and native gold typical for epithermal deposits. Pyrite included in quartzites and quartz-alunite rocks was probably formed during an early stage of the ore-forming process. During the following Au-rich stage, the $f_{{\rm S}{\rm e}_{\rm 2}}$/$f_{{\rm S}_{\rm 2}}$ increased with $f_{{\rm O}_{\rm 2}}$ being relatively high, resulting in the formation of very rare compounds that have not been previously described in nature. These include Au2Te4(Se,S)3, Se3Te2, AuSe and Au(Te,Se,S) phases. The Au2Te4(Se,S)3 compounds have some variations in composition: the complete isomorphic series between Au2Te4Se3 and Au2Te4S3 was observed. The gold and Au-minerals at the main ore stage can be stable within a range of log$f_{{\rm O}_{\rm 2}}$ of −27.3 and atmospheric oxygen (?); log$f_{{\rm S}{\rm e}_{\rm 2}}$ between −12.4 and −5.7; log$f_{{\rm T}{\rm e}_{\rm 2}}$ between −10.5 and −7.8; and log$f_{{\rm S}_{\rm 2}}$ between −12.8 and −6.8 (at 250°C). The increasing oxygen fugacity during the final stage of mineralization resulted in the formation of complex Sb,As,Te,S-bearing Au oxides. Gold-oxide formation occurs due to oxidation of Au-tellurides. The final products of this process are newly-formed secondary mustard gold and Te–Se solid solutions.

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

“…Mixed silver-gold sulfides and selenides, including nanoparticulate ones, have attracted intense interest as minerals and natural sources of precious metals [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and due to high ionic conductivity, tunable optical characteristics, thermoelectric and other properties promising for materials applications [15][16][17][18][19]. Gold chalcogenides, in particular gold selenide, are much less examined, despite aqueous Au chalcogenide-derived complexes play the crucial role as carriers of gold in hydrothermal fluids and brines (e.g., [20][21][22][23][24][25] and references therein), and AuSe, Au(Se,S) and Au(Te,Se,S) phases in intergrowths with native gold have been found in the high-sulfidation epithermal deposits formed from acidic fluids [14]. Solid gold sulfide Au 2 S is metastable [2,5,26,27].…”

Mustard Gold in the Oleninskoe Gold Deposit, Kolmozero–Voronya Greenstone Belt, Kola Peninsula, Russia

“…The mustard gold forms in a process of decomposition of Au-Te and Au-Sb compounds [6,8,10,11] mainly in the zone of oxidation and disintegration of Au-Te and Au-Sb ore, and in residual placers, not actively reworked by alluvial processes [3]. Findings of mustard gold are numerous in the zones of hypergenesis of epithermal low-depth Au-Ag-Te and Au-Ag-Sb deposits in the Mesozoic and Cenozoic volcanic belts [2][3][4][5][6][7][8][9][10][11][12][13][14], which got to the surface and are actively denudated at present.…”

Characteristics of Supergene Gold of Karst Cavities of the Khokhoy Gold Ore Field (Aldan Shield, East Russia)

“…40-43) and goethite ( Figure 6, Table 3, Nos. [14][15]. At a higher magnification, micron gold inclusions are visible in associating minerals ( Figure 5f, Table 3, Nos.…”

“…Aggregates of intimately intergrown unnamed tellurates of Tl and native gold are occasionally observed along cracks in the gold particles ( Figure 5b, Table 3; Nos. [9][10][11][12][13][14][15]. In the interstices between massive gold there are found dendritic gold particles closely interwoven with goethite ( Figure 5c, Table 3, Nos.…”