Coexisting Bournonite–Seligmannite and Tennantite–Tetrahedrite Solid Solutions of the Darasun Gold Deposit, Eastern Transbaikalia, Russia: Estimation of the Mineral Formation Temperature

Abstract

Mineral assemblages, the peculiarities of intergrowths, chemical composition, and Sb and As distribution in coexisting fahlore and bournonite-seligmannite solid solutions of the Darasun gold deposit are studied. The almost complete solid solution between bournonite and seligmannite with continuous Sb–As isomorphism for Sb/(Sb + As) ratios from 0.21 to 1.00 is identified for the first time for the Darasun deposit using a microprobe. The composition of fahlore coexisting with bournonite widely varies: Sb/(Sb + As) ratio 0.03–0.96 and Fe/(Fe + Zn) ratio 0.36–0.87. The mutual compositional evolution from early Sb to late As coexisting solid solutions is identified. Based on the Sb and As distribution between coexisting fahlore and bournonite-seligmannite, the temperatures of their joint crystallization are estimated, as well as those of the productive stage, where they are associated with native gold and tellurides (90–335°C).