Age, geochemical features and Cu-Au mineralization significance of the magnesian dioritic dykes in Baogutu area of west Junggar

Abstract：The magnesian dioritic dykes widely distributed in west Junggar of Xinjiang recorded the Late Paleozoic tectonic evolutionary history of the area. The LA-ICP-MS zircon U-Pb and amphibole Ar-Ar dating of dioritic dykes yielded a 206Pb/238U age of 316.3±3.8 Ma and a plateau age of 313.1±3.5 Ma, respectively, suggesting that they were generated in Late Carboniferous. The magnesian dioritic dikes (56.8%-62.9%) are characterized by high MgO (2.39%-4.04%; Mg#= 54-62), Cr (30×10-6-80 ×10-6), and Ni (20×10-6-62×10-6) content. These samples show negligible to negative Eu values, high Sr/Y (36-44) ratios, strong depletion of HREE (e.g., Yb = 1.32×10-6-1.54×10-6 and Y=13.1×10-6-15.5×10-6), and enrichment of large-ion-lithophile elements (LILE) (K, Sr, Ba) with negative Nb-Ta-Ti anomalies. These features are compatible with slab-derived adakites interacted with mantle materials and related to ridge subduction. The interaction between high oxygen fugacity slab melt and mantle peridotite caused the decomposition of metal sulfides and the Cu and Au mineralization. Baogutu area of west Junggar thus has good metallogenic prospect.