西藏斑岩铜矿对重大地质事件的响应

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

西藏已有 3个构造岩浆带发现斑岩铜矿 :玉龙成矿带、冈底斯成矿带和班公错成矿带。其中班公错成矿带还少有研究和找矿评价 ,目前仅报导在改则西北发现多不杂斑岩铜金矿 ,但该带的邻国已发现大型斑岩铜矿 ,例如巴基斯坦的赛恩达克 (Saindak)和伊朗的萨尔切什梅 (SaiCheshmeh)等。据青藏高原 70Ma以来的古气候研究 ,在新特提斯洋闭合之后 ,印度板块与亚洲板块陆陆碰撞 ,曾有过 3次加速 :第一次为 4 0～ 35Ma ,与玉龙矿带的成岩成矿年龄相吻合 ;第二次为 1 8～ 1 2Ma ,与冈底斯矿带的成岩成矿年龄相吻合 ;第三次为 3.6Ma以来 ,与羊八井等热泉和铯金锑成矿年龄相吻合。故西藏斑岩铜矿为印度洋扩张和陆陆碰撞“A”型 (Ampferersubduction)俯冲的产物。第一次加速在青藏高原的东缘三江地区产生一系列喜马拉雅期走滑拉分盆地 ,导致幔源斑岩岩浆上侵 ,形成玉龙等一系列斑岩型夕卡岩型铜铜钼铜金矿 ;第二次加速使冈底斯深部挤压而浅部拉张 ,导致幔源斑岩浆岩侵位 ,形成冈底斯一系列斑岩型夕卡岩型浅成热液型铜钼铜金多金属矿 ;第三次加速使青藏高原整体深部挤压而浅部拉张 ,在藏南。

Yulong porphyry copper belt, Gangdisê 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 Gangdisê 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 Gangdisê 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, Gangdisê and north Xizang.