Том 61, № 2 (2019)

The authors have performed a comparative paleovolcanic and metallogenic analysis of two massive sulfide-bearing regions: the Southern Urals and Rudny Altai, which are located in different parts of the Ural-Mongolian fold belt. Comparison of the geodynamic evolution of these areas, the formation and facies composition of the ore-hosting strata and types of massive sulfide deposits has made it possible to conclude that the regions are similar only in the most general terms. Fundamental differences in the structure and composition of the Earth’s crust in these regions resulted in differences in the profile of island-arc magmatism: basaltoid in the Southern Urals and rhyolitoid in Rudny Altai. This in turn determined the predominant composition of massive sulfide mineralization: copper-zinc in the former region and polymetallic in the latter. They are also characterized by opposite trends in the evolution of volcanism: homodromous in the Southern Urals and antidromous in Rudny Altai, which resulted in different positions of the types of massive sulfide deposits in the strata of ore districts: from bottom to top, copper-massive sulfide deposits are replaced by polymetallic deposits in the Southern Urals, and barite-polymetallic deposits, by massive sulfide-polymetallic and copper-massive sulfide deposits in Rudny Altai. There are also substantial differences in the regularities of lateral ore localization: more starkly manifested control of mineralization by central-type paleovolcanic edifices in the Southern Urals and the frequent position of mineralization in intermediate and remote volcanic facies in Rudny Altai, which is expressed in the predominance of volcanic rock in Ural ore-bearing sequences and a significantly larger fraction of relict rocks (20–80%) in strata hosting mineralization in Rudny Altai.

At the well-preserved Yubileynoe VMS deposit (Southern Urals), sulfide breccias and turbidites host abundant tellurides represented by hessite, coloradoite, altaite, volynskite, stützite, petzite, and calaverite, as well as phases of the intermediate tellurobismuthite → rucklidgeite solid solution. Three telluride generations were highlighted: (1) primary hydrothermal tellurides in fragments of chalcopyrite and sphalerite of chalcopyrite-rich black smoker chimneys; (2) authigenic tellurides in pseudomorphic chalcopyrite and chalcopyrite veins after fragments of colloform and granular pyrite; and (3) authigenic tellurides in pyrite nodules. Authigenic tellurides are widespread in pyrite-chalcopyrite turbidites. Primary hydrothermal and authigenic tellurides are less common in sulfide turbidites and gritstones with fragments of sphalerite-pyrite, pyrite-sphalerite paleosmoker chimneys and clasts of colloform and fine-grained seafloor hydrothermal crusts. Siliceous siltstones intercalated with sulfide turbidites contain pyrite nodules, whose peripheral parts contain inclusions of epigenetic tellurides. It is assumed that Te for authigenic tellurides originated from fragments of colloform pyrite and hydrothermal chalcopyrite of pyrite-chalcopyrite chimneys, which dissolved during the postsedimentation processes. The main Te concentrators in clastic ores include pseudomorphic chalcopyrite, which inherits high Te, Bi, Au, Ag, Co, Ni, and As contents from the substituted colloform pyrite, and varieties of granular pyrite containing microinclusions of tellurobismuthite (Bi, Te), petzite (Au, Ag, Te), altaite (Pb, Te), coloradoite, and hessite (Ag, Te).

This study demonstrates that the bladed texture, which is common in epithermal, low-sulfidation (adularia-sericite) precious metal deposits, can serves as exploration vector towards precious metal mineralization. The paper presents two styles of bladed texture in the Kuklitsa gold deposit (Krumovgrad goldfield, SE Bulgaria) observed at both different altitude and lateral position in respect to regional low-angle detachment fault. The first style has formed as a crackle breccia just above the detachment fault where bladed texture consists of 10–20 vol % pseudorhombic adularia, 90-80 vol % quartz, scarce pyrite, and electrum, which is often observed under optical microscope. The second style is present in steep veins which fill listric faults of sharp tectonic contacts. It is developed at a higher level relative to the detachment fault. Bladed texture there consists of 1–2 vol % pseudorhombic adularia, 99-98 vol % quartz, and scarce both electrum and pyrite. Electrum of the two styles of bladed texture comprises only gold and silver but in different proportions with a higher gold content for the first style: fineness of 765, on average, for the first style vs. fineness of 692 for the second one. In this way, it is found that the adularia abundance correlates positively with the electrum one and negatively with the quartz abundance. The author uses the proportions of adularia, quartz and electrum, the fineness of electrum, and the relative distance to the detachment fault to conclude that the first style of bladed texture has been formed at higher temperature relative to the second style. The author infers that the first style is promising for mineralization of higher grade. Methods used comprise field observations and sampling, optical and electron microscopy, powder X-ray diffraction and electron microprobe analysis.