Abstract:

Granites at the southern margin of Altay, Xinjiang crop out widely in the Keyinbulake copper-zinc deposit, including monzogranite, moyite, biotite granite and tonalite, where ore bodies occur in the exocontact zones between Permian monzogranite and the Upper Silurian-Lower Devonian Kangbutiebao Formation. The monzogranite has two lithofacies of two-mica monzogranite and biotite monzogranite under the microscope. The biotite monzogranites are characterized by enrichment of silica, total alkali, low Na/K value, and metaluminous-prealuminous. Trace elements show characteristics of noticeable positive anomaly of Rb, Th, K, Ce, Nd, Tb and negative anomaly of Ba,Nb,Sr,Ti. The REE patterns show richness of LREE, moderate total REE contents and Eu negative anomaly. The characteristics indicate that the biotite monzogranites are high K-low Ca-metaluminous-peraluminous S-type granites. These rocks have near-zero or negative ε_Nd(t) values and high Sr isotopic compositions, with corresponding to Nd model ages of 1.145 to 1.194 Ga. The granites were probably formed by melting of the middle Proterozoic biotitebearing metamorphic sandstone or orthometamorphite and limited mantle material, with residual of plagioclase in the melting source. Geochemical characteristics showed favorable mineralization potentiality of monzogranite. The deposit was formed in post-collision extension setting,  and metallogenesis is related to the hydrothermal from monzogranite magma.

Key words: biotite monzogranite, geochemistry, Keyinbulake, southern margin of Altay, Xinjiang