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 fi eld 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 quartzalunite rocks was probably formed during an early stage of the ore-forming process.
During the following Au-rich stage, the f(Se2)/f(S2) increased with f(O2) 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 logf(O2), of -27.3 and atmospheric oxygen (?); logf(Se2), between -12.4 and -5.7; logf(Te2) between -10.5 and -7.8; and logf(S2) between -12.8 and -6.8 (at 250 degrees C).
The increasing oxygen fugaciiy during the final stage of mineralization resulted in the formation of complex Sb,As,Te,S-bearing Au oxides. Gold-oxide fonnation occurs due to oxidation of Au-tellurides.
The final products of this process are newly-formed secondary mustard gold and Te-Se solid solutions.