Geochemistry and Petrogenesis of Igneous Rocks of the Kutuevsky Au-Cu Porphyry Ore Occurrence (Southern Urals)

The petrological and geochemical features of effusive and intrusive rocks of the Kutuevsky Au-Cu porphyry ore occurrence located in the zone of the Main Ural Fault in the Southern Urals were studied. The composition of the rocks was determined by chemical analysis, mass spectrometry with inductively coupled plasma on an ELAN 9000 quadrupole mass spectrometer, and also partially by atomic emission spectrometry with inductively coupled plasma on an ICPE-9000 spectrometer. It has been established that the Au-Cu-porphyry mineralization of the ore occurrence is associated with an volcano-intrusive complex, combining dolerites, basalts, basaltic andesites, their tuffs, gabbro-diorite and diorite intrusions. All petrochemical rock types have normal alkalinity. Dolerites belong mainly to the tholeiitic series, and basalts, basaltic andesites and intrusive rocks belong to the transitional tholeiitic–calc-alkaline series. The most likely mantle source of magmas for them was spinel peridotites, previously metasomatized by aqueous fluids that arose during the dehydration of slab rocks. At the initial stages of magma formation, a source similar in composition to the depleted mantle dominated, and later a more enriched mantle substrate was subjected to melting. Fractional crystallization played a significant role in the magma generation of effusive and intrusive rocks. The composition of gabbro-diorites and diorites was also influenced by processes of crustal contamination. It is assumed that the igneous rocks of the ore occurrence were formed in the back-arc basin of the frontal island arc of Late Emian age.