SUBSTITUTION OF Bi FOR Sb AND As IN MINERALS OF THE TETRAHEDRITE SERIES FROM REDZINY, LOWER SILESIA, SOUTHWESTERN POLAND

Various members of the tetrahedrite series, including Bi-rich species, have been found in products of hydrothermal mineralization disseminated in contact zones of the dolomitic marble deposit at Redziny, Western Sudetes, Poland. The occurrence is important owing to the opportunity to observe changes in composition of the minerals occurring in different assemblages formed at varyious temperatures. Bismuth-rich varieties (up to 15.86 wt.%, 1.36 apfu, in tetrahedrite, and up to 18.41 wt.%, 1.51 apfu, in tennantite) commonly form inclusions in, and intergrowths with, other sulfides. A small inclusion with Bi > As and Sb, and with the stoichiometry of "annivite", the Bi analogue of tetrahedrite and tennantite not yet approved by CNMNC IMA, was recognized in association with stannoidite + mawsonite + chalcopyrite + native Bi. Distinct correlations involving Fe, Ag, Cu and Sb at higher temperatures (to about 280 degrees C) and Zn, Cu and As at lower temperatures suggest the predominance of the end-member freibergite, (Ag6Cu4) Fe2Sb4S13-x, at about 340 degrees C, grading to Ag- and Bi-bearing tetrahedrite, (Cu7Ag3)(Fe, Zn)(2)(Sb, Bi)(4)S-13, then to Ag-poor, Bi-bearing tennantite, Cu-10(Zn, Fe)(2)(As, Bi)(4)S-13, and finally to Bi-free, Zn-bearing tennantite, Cu10Zn2As4S13, which predominates at temperatures below 200 degrees C. The sequence of the tetrahedrite series at Redziny indicates that the varieties richest in Bi crystallized at temperatures of 300-230 degrees C together with bismuth sulfides and native Bi, being preceded by numerous sulfosalts of bismuth, especially those enriched in Ag, such as gustavite, pavonite, benjaminite, berryite and giessenite. The substitution of Bi for Sb in tetrahedrite, coupled with an increase in the Fe and Ag contents and depletion in Zn, leads to an increase, and in an extreme case even to a predominance, of Ag-bearing "annivite", (Cu6Ag4) Fe2Bi4S13, at a temperature of about 280 degrees C. This is promoted by high Bi activity and temporal concentration of Cu-6[Cu-4(Fe, Zn)(2)]Bi4S13 in hydrothermal solutions.