ZIRCON U-Pb CHRONOLOGY, GEOCHEMISTRY AND PETROGENESIS OF ORE-BEARING GRANODIORITE IN TSAV SILVER POLYMETALLIC DEPOSIT, MONGOLIA

The research on magmatic rocks related to mineralization was weak in Tsav-Jiawula Ag polymetallic ore concentration area on the China-Mongolia border. Taking the ore-bearing granodiorite and its dioritic enclaves in Tsav Ag polymetallic deposit as object, the paper studies the petrology, zircon U-Pb chronology, geochemistry and in-situ Lu-Hf isotopes. The zircon ²⁰⁶Pb/²³⁸U weighted average ages of 195.7±1.3 Ma and 196.5±2.4 Ma for granodiorite and diorite enclaves respectively are consistent within the error range, indicating that both were products of the Early Jurassic magmatism. The host granodiorite belongs to I-type granite of quasi aluminous-weakly peraluminous and high K calc alkaline-calc alkaline series. The diorite enclaves are of consanguineous magma mixing origin. The host granodiorite has broad ε_Hf(t) values (4.4-10.7) with the two-stage Hf model ages ranging from 550 to 960 Ma, reflecting the primary magma of host granodiorites originated from the partial melting of new crustal accretion from depleted mantle in Neoproterozoic with mantle-derived materials mixed. Combined with the regional tectonic evolution data, it is considered that the Tsav Ag polymetallic deposit was formed in the active continental margin setting caused by the subduction of Mongolia-Okhotsk oceanic plate.