Geology, geochronology, and geochemistry of the siruyidie’er prospect, Taxkorgan: A possible Miocene porphyry Mo ± Cu deposit in the Central Pamir

Abstract

The Pamir and Tibetan plateaus, which have a similar terrane structure and evolutionary history since the Phanerozoic, are both host abundant Eocene to Miocene intrusions, however, unlike the Tibetan plateau, coeval porphyry deposits appear to be devoid in the Pamir plateau. In this study, we first report a potentially economic Cu-bearing sulfide mineralization at Siruyidie’er prospect in the Central Pamir. The Siruyidie’er prospect is characterized by the development of 14 breccia pipes in the north block and of Cu-bearing sulfide veins in the south block. Field evidence indicates that the brecciation and mineralization are intimately related to the intrusion of granite porphyry. Zircon U-Pb dating of the granite porphyry yields an age of 13.74 ± 0.21 Ma. This age overlaps with the hydrothermal muscovite 40Ar/39Ar data of 13.68 ± 0.17 Ma, which confirms the hydrothermal activity and mineralization at Siruyidie’er prospect are induced by the granite porphyry. The granite porphyries are shoshonitic in composition and have high K2O (6.03–6.46 wt%; K2O/Na2O = 1.70–1.92), Ba (2983–3316 ppm), LREE (317–363 ppm) and Sr (331–378 ppm), and low MgO (0.54–0.63 wt%), Cr (6.73–8.28 ppm) and Y (7.88–9.91 ppm) contents. The rocks are LREE-enriched ((La/Yb)N = 53–66) and display weakly negative Eu (Eu/Eu* = 0.79–0.87), positive LILES (Ba, Rb, and K) and negative HFSEs (Th, U, Nb, Ta, Ti, and Y) anomalies. They have enriched Hf isotopic compositions with ɛHf(t) values ranging from –8.78 to −5.01. The combined major and trace elements and Hf isotopic characteristics of the granite porphyries suggest that the primitive magmas were produced by high extent partial melting of an ancient crust source, possibly a thickened lower crust in the garnet stability field. A comparison of the granite porphyries at Siruyidie’er prospect with Eocene to Miocene ore-forming granitic porphyries of the Tibetan plateau reveals that the granite porphyries have lower water contents and originated from a continental crust rather than a depleted mantle source. Based on geological, compositional, and age data, we propose that the Siruyidie’er prospect has a potential to form porphyry Mo ± Cu deposit. This study provides the first direct evidence for the possible presence of porphyry Mo ± Cu deposit in the Pamir plateau.