Luerma, a newly discovered late Triassic porphyry copper-gold ore-spot in the western Gangdise metallogenic belt, Tibet

Previously, almost all the porphyry copper-gold deposits in the Gangdise metallogenic belt are located at the eastern section of the Gangdise metallogenic belt, and their mineralization ages are younger than the late Triassic epoch. This paper discusses Luerma, the newly discovered late Triassic porphyry copper-gold ore-spot in the western Gangdise metallogenic belt. Zircon U-Pb dating and molybdenite Re-Os dating indicate that Luerma copper-gold occurrence is with a 212 Ma mineralization age, implying it is related to the subduction process of the Indian ocean plate northward to the Gangdise plate in the late Triassic epoch. The Luerma copper-gold ore-spot developed typical porphyry hydrothermal alteration zones, which can be divided into a potassium-silicification zone, asericitization zone, a clayization zone, and a propylitization-propylitization zone from ore-bearing quartz monzonite porphyry to wall rocks, respectively. By so far, three ore bodies are determined in Luerma copper-gold occurrence:one porphyry copper orebody occured in quartz monzonite porphyry, one hydrothermal vein gold-copper orebody and one hydrothermal vein-typed copper orebody occured in structural fracture zones respectively. Moreover, three main types of hydrothermal veins have been identified based on their mineral assemblages,cutting relationship and alteration features: the potassium-silicification vein (A-typed vein), the medium-term quartz-polymetallic sulfides vein (B-typed vein), and the epidote-carbonatation (D-typed vein), respectively. The discovery of Luerma ore-spot suggests that the western part of the Gangdise metallogenic belt is potential for porphyritic copper-gold deposits.