Telluride Mineralogy in Ores of the Birgilda Porphyry Copper Deposit (South Urals, Russia)

Telluride–base-metal mineralization within silica alteration of the Birgilda porphyry copper deposit (South Urals, Russia) was studied with optical and electron microscopy with an energy dispersive detector, as well as with X-ray diffraction analysis. The silica alteration is composed of quartz (60–90%) and muscovite 2M1 (up to 30%), as well as a minor amount of illite. Ore minerals are represented by (in order of descending abundance) pyrite, galena, sphalerite, chalcopyrite, tetrahedrite, and minerals of tellurium. The latter ones include: altaite PbTe, tellurobismuthite Bi2Te3, kochkarite PbBi4Te7, volynskite AgBiTe2, coloradoite HgTe, native tellurium, hessite Ag2Te, stützite Ag5 – xTe3, and petzite Ag3AuTe2. Single occurrences of apatite, barite, and minerals similar to monazite and xenotime were also noted. The described assemblages and wall-rock alteration are typical for upper levels of a porphyry system and belong to intermediate argillic alteration. The observed variability of tellurium minerals is determined by fS2 and fTe2 fluctuations at temperature of approx. 200 to 250°C.