Geochemistry of ore-bearing porphyries in the Kalaxianger copper belt on the southeastern margin of the Altay Mountains, Xinjiang

Abstract：The Kalaxianger porphyry copper deposit (belt) is located in a Late Paleozoic island arc on the southern margin of the Altay Mountains. The ore-bearing porphyries are mainly represented by mid-late Hercynian intermediate-acid porphyries and the country rocks are the Middle Devonian Beitashan Formation. Petrological and geochemical studies of the ore-bearing porphyries indicate that there are at least two types of porphyry in the study area, mainly including quartz monzonite and granodiorite. Some quartz monzonite has the distinct features of adakite：SiO2>56％，Al2O3>15％，MgO<3％，Sc<10％, positive Eu and Sr anomalies and initial 87Sr/86Sr<0.704. However, some porphyries, which have higher HREE contents (Y>18×10-6 and Yb>1.9×10-6), are deviated from the compositional range of adakite. The cause for higher HREE contents might be due to the existence of relict hornblende in the source region during subduction and melting of oceanic crust. Analysis of the chemical characteristics of rocks and geological conditions of the Kalaxianger copper belt shows that the study area probably has good porphyry copper metallogenic prospects.