Abstract <p>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 Ag_{5 – <i>x</i>}Te₃, 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 <i>f</i>S₂&#xa0;and <i>f</i>Te₂ fluctuations at temperature of approx. 200 to 250°C.</p>