Mineralogy of the Niederschlema-Alberoda U-Se-polymetallic deposit, Erzgebirge, Germany. II: Hessite, Ag_2Te, and native Te (?), the first tellurium minerals

摘要

Hessite Ag_2Te, and native tellurium (?) constitute two, previously unknown tellurium species within the complex mineral assemblage at Niederschlema-Alberoda, Erzgebirge, Germany. Hessite is always intimately associated with clausthalite and has a composition close to ideal stoichiometry. The mean empirical formula is (Ag_(1.98)Sb_(0.01))_(1.99)(Te_(0.96)Se_(0.05))_(1.01). Paragenetic relations and thermodynamic data suggest that hessite crystallized in equilibrium with clausthalite, berzelianite, and tieman-nite under conditions of almost identical, high fugacitities of Se_2 and Te_2, which very locally were approached in the main selenide stage of Jurassic age. Native tellurium (?) formed as replacement product of hessite. Niederschlema-Alberoda provides the first record of hessite from an uranium deposit worldwide. Hessite and native Te are the first tellurium minerals reported from the Erzgebirge metallogenic province.