Geochemistry of the Eocene-ligocene porphyry in the Narigongma region, Qinghai

The Eocene Oligocene ore-bearing porphyry occurs as irregular stocks in the Narigongma region, Qinghai. The porphyry is composed of monzonitic granite porphyry in the subalkaline K-rich calc-alkaline series, and characterized by higher contents of SiO₂, Al₂O₃, K₂O, Na₂O, LREE and Sr, Rb, Ba, Th, Ce, Mo, Cu, Au and Ag, depletion in CaO, TiO₂, HREE, Y, Yb, Cr, Sc, Co and Ni, and well-balanced the element Eu. The geochemical signatures shows that the porphyry may be derived from the continental crust contaminated by the oceanic crust, and initiated from the magmas created by the melting of the lower crust due to the upwelling of the rheosphere triggered by intracontinental subduction.