THE RESPONSE OF PORPHYRY COPPER DEPOSITS TO IMPORTANT GEOLOGICAL EVENTS IN XIZANG

Yulong porphyry copper belt, Gangdise porphyry copper belt and Bangong Co porphyry copper belt occur in tectonomagmatic belts of the same names in Xizang, respectively. Among them, the Bangong Co copper porphyry belt has been poorly studied and assessed, with only Dobzha porphyry Cu-Au deposit discovered in the northwest of Gerze. However, in the neighboring countries some large porphyry copper deposits, such as Saindak in Pakistan and Sar Cheshmeh in Iran, have been found out. The research on paleoclimate since 70 Ma ago indicates that the continent-continent collision between the Indian and the Asian plates after the closure of the Neo-Tethys was accompanied by three accelerated processes of subduction which occurred during 40～35 Ma, coinciding with mineralization epoch of the Yulong porphyry copper belt; during 18～12 Ma, coinciding with mineralization epoch of the Gangdise porphyry copper belt; and at 3.6 Ma, coinciding with mineralization age of the hot springs and Cs-Au-Sb deposits in Yangbajain, respectively. Thus, the spreading of the Indian Ocean, the continent-continent collision, and the Ampferer subduction were responsible for the mineralization of porphyry copper deposits in Xizang. The first accelerated subduction resulted in the formation of a series of Himalayan pull-apart basins on the eastern margin of the Qinghai-Xizang Plateau and in the emplacement of mantle-derived porphyry magma, forming a series of porphyry-skarn type Cu, Cu-Mo and Cu-Au deposits in the Yulong porphyry copper belt. The second accelerated subduction was characterized by the compression in the depth and the extension in the shallows, which resulted in the emplacement of mantle-derived porphyry magma, forming a series of porphyry-skarn type and epithermal Cu-Mo, Cu-Au and polymetallic deposits in the Gangdise porphyry copper belt. And the third accelerated subduction was characterized by the compression in the depth and the extension in the shallows in the whole Qinghai-Xizang Plateau, which resulted in the formation of numerous hot springs and hydrothermal Cs-Au-Sb deposits in south Xizang, Gangdise and north Xizang.