Литосфера (Feb 2018)
Petrology of Yaluninogorsk granitoid massive (Alapaevsk-Sukhoi Log porphyry copper zone, Middle Urals)
Abstract
Yaluninogorsk quartz diorite-trondhjemite massif is situated in Alapaevsk-Sukhoy Log zone of Eastern-Ural High potentially productive for Cu (±Mo) porphyry type of mineralization. The massif is a magma chamber 3 × 2 km under central type volcano. The rocks of massif frame are transformed into propylites, sometimes intensively sulfidized. In this regard the massif is considered as an ore-forming. Petrological study of Yaluninogorsk massif shows, that is formed by holocrystalline rocks of meso-abyssal facies, varying from quartz-gabbro-diorites to tonalities, accompanied by veined trondhjemites. Early mineral phases of quartz diorites consist of augite, basite plagioclase An70-50, titanomagnetite. Late phases are represented by acid plagioclase An30-25, quartz, titanomagnetite, biotite, magnesiohornblende, which substitutes pyroxene. Crystallization process of quartz diorites and trondhjemites occurred under isobaric conditions with 1.5-2.0 kbar and a slow cooling. Crystallization temperature exceeded 900°C for the early phases, and 800-720°С for the late phases. The initial melts can be characterized as having low water content. Their oxidation rate was ΔNNO = 0.5-0.8. Residual melts with trondhjemite composition contained about 3.5-4.0 wt % H2O under Pgen = PH2O. Deep erosion of the volcano together with low water content of the initial melts are likely to be negative factors for the discovery of industrial porphyry-type ore deposits associated with Yaluninogorsk massif. The study of post-magmatic transformations of rocks from the massif and its environs revealed the presence of no industrial significance skarns with magnetite-chalcopyrite-pyrite mineralization, accompanied by nickel sulfides and nickel sulfoarsenides; veined carbonate-quartz-chlorite metasomatites with chalcopyrite mineralization, containing selenium-bearing sulfosalts and Ag, Cu, Bi tellurides.
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