Highly differentiated juvenile crust-derived magmas linked with the Xilekuduke porphyry Mo (Cu) deposit in East Junggar, NW China

Abstract

Abstract The East Junggar region links the Kazakhstan-Junggar plate with the Siberian Craton along the western part of the Central Asian Orogenic Belt. Among the major ore deposits in this region, the Xilekuduke molybdenite deposit is a unique example of Mo-dominated porphyry. Molybdenum and copper mineralization here occur as disseminated sulfides or veinlets mainly in granite porphyry and monzogranite, with a prominent alteration from an inner potassic, through sericitic to an outer propylitic zone. Zircon LA-ICP-MS U–Pb ages indicate that the granite porphyry and monzogranite were emplaced at 326.4\u202f±\u202f2\u202fMa and 328.2\u202f±\u202f1.8\u202fMa respectively. Both rocks show enrichment in light rare earth elements (LREE), and Rb, K, Sr, Hf, Zr, but depletion in Nb, Ta, Ti and P, suggesting magma generation in a post-collisional setting. A relatively high oxidation state is inferred from zircon δCe values and oxygen fugacity of parental magma. The ore hosted intrusions also show high Differentiation Index (DI), indicating a highly oxidized parental magma and prolonged differentiation process. The range of zircon eHf (t) values (+11.5 to +17), young zircon Hf model ages, and consistent but slightly low zircon δ18O values (+4.84 to +5.20), together with the range of Mg# (35–53), suggest derivation of the parental magma through partial melting of juvenile crust with minor contribution from mantle components and sediments. We propose that melting of juvenile oceanic components at depth with high degree of differentiation played a significant role in generating the Mo mineralization in Xilekuduke deposit within a post-collisional setting in the East Junggar domain.