REE in the Calcite of Au–Cu Porphyry Mineralization at the Kutuevsky Occurrence, South Urals: LA–ICP–MS Data

— The paper presents new data on the trace-element (REE, Y, and Sr) composition of calcite from stockwork Au–Cu porphyry ores and host rocks of the Kutuevsky occurrence, South Urals. Trace elements were analyzed by LA–ICP–MS in calcite and by ICP-MS in intrusive rocks and ophicalcite. We established that REE amounts and patterns of the calcite significantly varied and depend on the ore mineralization location in the metasomatic aureole. The ores in chlorite–sericite–quartz metasomatites in the central part of the gabbro-diorite and diorite intrusion are dominated by calcite, whose REE amounts and patterns are comparable to those of the intrusive rocks. We suggest that REE in the crystallized calcite were borrowed by fluid mainly from the intrusive rocks. Calcite in the ores hosted by biotite–epidote–chlorite–sericite–quartz metasomatites in the eastern inner-contact zone of the intrusive massif contains abnormally low REE amounts. The most likely REE source for this calcite is assumed to be the carbonate cement of the ophicalcites. REE fractionation was largely controlled by fluid temperature. When the calcite crystallized, the mineral-forming temperature exceeded 250°C, and therefore, Eu 2+ dominated in the fluid, and the regime was reducing.