Zircon U-Pb geochronology, Hf isotope, and whole-rock geochemistry of diorite in the Saijiao Cu-Au deposit, Tibet, and its ore-forming significance

The Saijiao Cu-Au deposit is a component part of the Duolong Cu-Au metallogenic concentration area; nevertheless, the study of its metallogenic epoch and genesis remains very insufficient. This paper reports zircon U-Th-Pb isotope and Hf-isotope as well as whole-rock major and trace element data from diorite in Saijiao. Zircon LA-ICP-MS dating of the diorite yields a weighted mean age of 120.5±1.2Ma, which can be regarded as the age of magmatic crystallization. Whole-rock major and trace element data show that the diorite belongs to high (mediate)-K calc-alkaline series characterized by enrichment of light rare earth elements and large ion lithophile elements, indicating that the diorite formed in a continental arc setting. The positive εHf(t) values of zircons are +5.4~+12.1, and second stage Hf mode ages tDM2 are 373~743Ma. The formation of Saijiao Cu-Au deposit was controlled by the Bangong Co-Nujiang River oceanic subduction system, and its rock-forming and ore-forming magma might have resulted from the mixing between the juvenile lower crust-derived melts and mantle-derived mafic melts.