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

摘要

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 fsc_2/fs_2, increased with fo_2 being relatively high, resulting in the formation of very rare compounds that have not been previously described in nature. These include Au_2Te_4(Se,S)_3, Se_3Te_2, AuSe and Au(Te,Se,S) phases. The Au_2Te_4(Se,S)_3 compounds have some variations in composition: the complete isomorphic series between Au_2Te_4Se_3 and Au_2Te_4S_3 was observed. The gold and Au-minerals at the main ore stage can be stable within a range of logf_(O2) of-_27.3 and atmospheric oxygen (?); logf(se2) between -1_2.4 and -5.7; logf_(Te2) between -10.5 and -7.8; and logf_(s2) between -1_2.8 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.