GEOCHEMISTRY AND TECTONIC SETTING OF THE VOLCANIC ROCKS OF LONGJIANG FORMATION IN SHIWULIQIAO GOLD DEPOSIT, HEILONGJIANG PROVINCE

Study on the lithological association and geochemistry of Longjiang Formation in Shiwuliqiao gold deposit shows that the contents of SiO₂, Al₂O₃ and K₂O in the volcanic rocks are 53.56%-73.43%, 14.90%-18.74% and 1.76%-4.20% respectively, belonging to high-K calc alkaline series. The REE distribution patterns show distinct fractionation of LREEs and HREEs, with weak negative or no Eu anomaly. The trace elements are characterized by enrichment of LILEs (Rb, K, Sr and Ba), and depletion of HFSEs (Nb, Ta and Ti), with the Rb/Sr ratio of 0.04-0.43 and Ti/Y ratio of 144.23-492.19. The samples fall in the volcanic arc, continental arc and post-collision arc setting zones in the tectonic discrimination diagram, indicating the Longjiang Formation was the product of partial melting of lower crust in the transition of plate subduction and collision orogeny.