Origin of phenocrysts in mineralized porphyries of porphyry copper deposits

The genetic mechanism of phenocrysts in mineralized porphyries of the Yulong porphyry copper deposit, Tibet, China, has been studied in the context of fluid inclusions in quartz and K-feldspar phenocrysts, phenocryst textures and mineral crystal textures. Phenocrysts in mineralized porphyries are not the product of direct crystallization of magmas derived from the mantle or lower crust but are very likely to originate mainly from metasomatism, recrystallization and secondary enlargement of copper-bearing rocks in the upper crust by deep-seated, alkali-rich, siliceous hydrothermal fluids.