Abstract:

The exploration of porphyry copper deposits in western Tianshan, Xinjiang, had attracted much attentions. The Almalyk copper deposit in western Tianshan, Uzbekistan, is one of the largest porphyry copper deposits in Asia, but has not well been dated. The Almalyk copper ore field is located in the southern part of CaledonianHercynian central Tianshan fold belt, and includes four copper deposits: Kalmakyr, Dalneye, Sarcheku and Kyzata. Copper mineralization occurred within the porphyries. The primary ores are characterized mainly by stockwork and disseminated structures, and  the  major metallic minerals are in assemblage of pyrite, chalcopyrite, molybdenite, hematite, magnetite, nature gold and bornite.  The present paper obtains the  weighted model age of 320.4±2.3 Ma and an isochron age of 317.6±2.5 Ma based on the ReOs isotopic method  by using the molybdenites from the Sarcheku coppermolybdenum ores.  On the basis of  the sequence of magmatic formation in this area, it is suggested that the  tectonomagmatic hydrothermal process in Almalyk ore field started at the early Carboniferous, developed during the late Carboniferous, and finished at the early Permian, and the porphyry copper mineralization mainly occurred during the late Carboniferous. The worldclass large and supper large porphyry copper mineralization including the Almalyk copper deposit in western Tianshan  is  closely related to the complex arc magmatic geological processes resulted from the subduction of paleoAsia ocean crust under KazakhstanYili plate, which happened mainly from the middle Devonian to the late Carboniferous (D2C2).

Key words: metallogenetic epoch, Almalyk porphyry copper deposit, geological significance, Uzbekistan, western Tianshan