SUBDUCTION,COLLISION,DEEP FRACTURE,ADAKITE AND PORPHYRY COPPER DEPOSITS

Participation of oceanic crust-derived or upper mantle-derived material is essential for porphyry copper deposits which are formed by pre-collisional B-type subduction and post-collisional A-type subduction.Initial Sr isotopic(~(87)Sr/~(86)Sr) ratio for a porphyry copper deposit must be less than 0.708.The initial Sr isotopic ratio of more than 0.708 is characteristic of porphyry Mo deposits or porphyry W-Sn deposits because of participation of continental crust-derived material.Porphyry copper belts are often parallel to deep fracture zones which cut through crust,and are confined to the hanging wall of the deep fractures where small granitic porphyry masses are often developed.Granitic porphyry is crust-mantle mixture-derived and mainly mantle-derived in material origin.Copper-bearing porphyry and adakite probably result from subduction and metasomatism.These two rocks have the same features,but they become different in late subduction stage.The present paper deals with the relationship of subduction,collision and deep fracture zone with porphyry copper deposits exemplified by Gandese porphyry Cu(Mo,Au and polymetallic) ore belt.Meanwhile,the development of porphyry Mo deposits other than porphyry Cu deposit in the central collision orogens in China indicates that participation of upper mantle-derived material is of great importance for porphyry Cu(Au) deposits.