SKARNS OF THE TARUTINSK SKARN-PORPHYRY COPPER DEPOSIT, SOUTHERN URALS

Abstract

Skarns with magnetite-pyrite-chalcopyrite mineralization develop in the inner-contact portion of a D 3-C 1 small intrusion of quartz diorite porphyry. The bimetasomatic zoning of the skarn bodies comprises the following zones: epidotized diorite porphyry-epidosite-garnet-epidote endoskarn-grandite-marble. The epidote-garnet skarn was produced in the presence of highly oxidized fluid at low temperatures (350-450°C), as also were the altered skarns (300°C and lower), and bears the secondary magnetite-quartz-calcite association and younger sulfide mineralization (T h = 170-283°C for the quartz and carbonate). The latter association formed with the significant participation of meteoric waters (δ 18O from +0.3 to +7.7%‰). In the inner portions of the deposit (closer to the core of the intrusion), the most ubiquitous endoskarn has a pyroxene-garnet composition (T = 500-650°C). Taking into account the dips of the mineralized skarn bodies and acid leaching zones that control them in the granitoids in the central parts of the massif, this zoning marks the pathways of the evolving fluid flow and points to the relatively low temperatures of the thermal field during the autometasomatic recrystallization of the intrusion of the dioritic association. The genetic coherence between the acid leaching processes in the granitoids and the mineralizing processes in the skarns is illustrated by an increase in the concentration of pyrite in granitoids closer to mineralized skarn zones, an increase in the gold content in this pyrite, and similarities between the sulfur isotopic compositions of pyrite from the granitoids and skarns (δ 34S from +1 to +3%‰). The aforementioned features of skarns at porphyry copper deposits make them different from the sulfide-bearing magnetite skarn association of the Urals, which is characterized by the wide occurrence of the weakly oxidized high-temperature garnet-pyroxene skarn facies and is genetically related to K-Na monzonitic granitoids.