Geology and geochronology of Naruo large porphyry-breccia Cu deposit in the Duolong district, Tibet

Abstract

Abstract The Duolong district is located in the south Qiangtang terrane of Tibet and is the most significant ore cluster within the Bangongco-Nujiang metallogenic belt. Duolong contains one giant, three large and two medium to small-sized porphyry (±epithermal\u202f±\u202fbreccia) copper deposits and several other mineralized porphyry bodies. All deposits are closely associated with early Cretaceous (123–115\u202fMa) intermediate-felsic intrusions. Naruo is a poorly studied porphyry-breccia copper deposit in the north of the Duolong district. Hydrothermal alteration surrounding the ore-bearing granodiorite at Naruo is characterized by an inner potassic zone and an outer propylitic zone, overlapped locally by minor phyllic and argillic alteration assemblages. A detailed paragenetic study has identified five distinct hydrothermal veins (M, A, B, C, D) within the porphyry system. Hydrothermal B veins are strongly related to copper mineralization. Strong propylitic alteration is also observed throughout the hydrothermal breccias identified at Naruo. Sandstone breccia, diorite-bearing breccia and granodiorite-bearing breccia were identified according to the distribution and composition of clasts. U-Pb zircon dating has determined the ages of the ore-bearing granodiorite (121.6\u202f±\u202f1.3\u202fMa) and a barren intrusion (115.5\u202f±\u202f1.1\u202fMa) within the porphyry system, diorite clasts (122.3\u202f±\u202f0.9\u202fMa) and later diorite matrix (120.5\u202f±\u202f1.0\u202fMa) in the hydrothermal breccia system, suggesting that with the exception of the late barren intrusion, they all belong to the same mineralizing event at Duolong. The geological and geochemical evidence presented in this study suggest that the porphyry and breccia systems may have originated from the same magma source, but are now spatially independent.