Abstract:

Jiama copper polymetallic deposit is a superlarge porphyryskarn one in the middle-eastern Gangdese metallogenic belt. It has the highest level of prospecting, a variety of ore-forming elements and ore body types, and brings huge economic benefit for Tibetan. Based on the “quaternity” prospecting model and nearly 350 drillholes in more than four years, not only has the skarn mineralization prospecting been achieved, but also the porphyry copper-molybdenum ore bodies have been proved from the 0 line to 40 line. In depth, porphyry molybdenum (copper) ore bodies are located in the monzonite granite porphyry and quartz diorite porphyrite. Porphyry ore bodies are generally below 4 600 m，with the strike NW-SE, dipping in NE direction, nearly vertical, and with vertical extension  over 350 m. The porphyry ore is characterized by veinlet-disseminated structure, ore minerals mainly include chalcopyrite and molybdenite, with rare bornite, and the gangue mineral is mainly quartz. It is preliminary ascertained that the orebearing rock of the copper mineralization is mainly quartz diorite porphyry, with potassic alteration typically formed by the phenocrysts and matrix of hornblende replaced by the fine-grained hydrothermal biotite. The ore-bearing rock of molybdenum mineralization is acidic monzogranite porphyry, with the major alteration of silicification, secondary epidotization, argillization and potassic alteration. The huge skarn ore body, over 200 m wide, usually occurs around the contacts between the carbonate and porphyry. There develops endoskarn on the side of the porphyry. The deep porphyry ore body in Jiama deposit not only confirms the view that the deposit belongs to the porphyry-skarn deposit, but also perfects the metallogenic model and exploration model of Jiama deposit.

Key words: porphyry-skarn deposit, porphyry ore body, metallogenic prediction, ore deposits, Jiama copper polymetallic deposit, Tibet