Coexisting bournonite-seligmanite and tennantite-tetrahedrite solid solutions in Darasun gold deposit (Eastern Transbaikalia, Russia): Estimation of the mineral formation temperature

Abstract

Mineral associations, intergrowth features, chemical composition and Sb and As distribution in coexisting fahlore and bournonite-seligmanite solid solutions in the Darasun gold deposit were studied. For the first time the almost complete solid solution was found between bournonite and seligmanite with a continuous isomorphism between Sb and As in the range of Sb/(Sb + As) ratios from 0.21 to 1.00 in the Darasun deposit by EMPA. The composition of the fahlore coexisting with bournonite varies widely: Sb/(Sb + As) ratios 0.03-0.96 and Fe/(Fe + Zn) ratios 0.36-0.87. The coupled compositional evolution from early antimony to late arsenic in coexisting solid solutions has been established. Based on the investigation of the Sb and As distribution between coexisting fahlore and bournonite-seligmanite, the temperatures of their joint deposition and, as a result, of the productive stage, in which they are closely associated with native gold and tellurides (90–335 °С), are estimated.