Silver-bearing tetrahedrite-(Cd) from quartz veins of the Tochilnogorsk deposit – the first find in the Urals

Abstract

Introduction: tetrahedrite-(Cd) has the formula Cu₆(Cu₄Cd₂)Sb₄S₁₂S₁ and is a rare mineral, usually forming precipitates of fractions of a mm. To date, the mineral is known in about seventeen deposits and ore occurrences in the world. In Russia, tetrahedrite-(Cd) is found in two places: in the Zmeinogorsk deposit in the Altai Krai and in the Krasnoye ore occurrence in the Bodaibo District of the Irkutsk Region. This paper describes the first find of silver-bearing tetrahedrite-(Cd) from the Tochilnogorsk deposit in the Urals. The Tochilnogorsk deposit of refractory stone is located in the Rezhevsky District of the Sverdlovsk Region, approximately 500 m from the village of Tochilny Klyuch.

Methodology: the chemical composition of tetrahedrite-(Cd) was analyzed in polished washers using a TESCAN MIRA LMS (S6123) scanning electron microscope with an INCA Energy 450 X-Max 80 (Oxford Instruments) EDS attachment at the Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, analyst L. V. Leonova.

Results: tetrahedrite-(Cd) was encountered as inclusions in rock crystal crystals in cavities of a quartz vein, where accumulations of anglesite, cerussite, and crocoite crystals are noted. Tetrahedrite-(Cd) forms isometric grains up to 8 μm in size intergrown with larger galena, no more than 60 μm in size. The chemical composition of the fahlore varies slightly within one grain. The mineral contains a large amount of silver from 7.02 to 8.36 wt.% and in one analysis an admixture of tellurium of 1.15 wt.%.

Conclusion: for the first time in the Urals, in the ancient Tochilnogorskoye deposit located in the Rezhevsky district of the Sverdlovsk region, silver-bearing tetrahedrite-(Cd) was encountered. The mineral forms intergrowths with galena in rock crystal crystals in the cavities of quartz veins in association with crocoite, anglesite and cerussite. Due to the large amount of silver in the mineral, it belongs to the silver-bearing variety of tetrahedrite-(Cd). Fahlore from the Tochilnogorskoye deposit is close in composition to tetrahedrite-(Cd) from the Krasnoye gold occurrence in the Bodaibo district of the Irkutsk region in Russia and from the lead-zinc mineralization of the Tyndrum mine in Scotland. Formation of silver-bearing tetrahedrite-(Cd) occurred in low-temperature hydrothermal conditions.