Contribution from Mafic Melt to the Zhireken Porphyry Mo-Cu Deposit, Eastern Transbaikalia, Russia: Evidence from Mafic Microgranular Enclaves

Abstract

Mafic microgranular enclaves (MME) were formed in felsic ore-bearing porphyries from the Zhireken por-phyry Mo-Cu deposit, eastern Transbaikalia, Russia. Porphyry rocks were emplaced during the Upper Jurassic. Most of the enclaves are globular, oval-shaped and intermediate in composition (54% SiO2). The MME from the Zhireken deposit often contain the same minerals as the host granite porphyries, though their chemical compositions are different. Accessory magnetite in MME shows higher Cr2O3 and Cu contents while, apatite reveals higher Cl and S concentrations compared to those in host porphyries. Mafic melt may have made substantial contribution for the overall budget of sulphur and ore metals in evolving felsic magma and hydrothermal fluid of the Zhireken deposit. Higher contents of Pd (684 ppb) and Pt (299 ppb) in molybdenites of the Zhireken deposit, as well as high temperatures (1020-910°C) of formation of porphyry rock melt inclusions, indirectly suggest a contribution from mafic melt derived from the mantle.