西藏冈底斯南缘汤白矿区早侏罗世含矿斑岩锆石U-Pb定年及其地质意义

Zircon U-Pb geochronology and geological implication of Early Jurassic ore-bearing porphyry from the Tangbai area on the southern margin of Gangdise,Tibet

汤白矿区位于西藏冈底斯斑岩铜矿带西段南缘,南侧紧邻日喀则弧前盆地。矿区由地表探矿工程控制3条赋存于早侏罗世角闪石英闪长斑岩中的主矿体(1号、2号和3号),在野外地质调查的基础上,对角闪石英闪长斑岩进行LA-ICP-MS锆石U-Pb定年和岩石地球化学测试。研究结果表明:(1)含矿斑岩的成岩年龄为183.3±1.2Ma,形成于早侏罗世;(2)含矿斑岩地球化学特征与大洋岛弧背景下的安山质岩石的地球化学性质一致,表明汤白矿区含矿斑岩形成于大洋岛弧环境;(3)西藏冈底斯斑岩铜矿带具有寻找俯冲期斑岩型矿床的巨大潜力,今后应加强该带俯冲期斑岩型矿床的勘查评价工作,特别是早—中侏罗世斑岩的成矿潜力评价。

The Tangbai ore district, located in the western segment of the Gangdise porphyry copper belt. Its south margin is Xigaze forearc basin. The surface exploration engineering of the mining area revealed that there are three orebodies(No.1, 2 and 3) in Early Jurassic hornblende quartz diorite porphyry. On the basis of field geological investigation, the authors carried out zircon LA-ICPMS U-Pb dating and whole-rock geochemical testing of Early Jurassic hornblende quartz diorite porphyry. The results of the study are as follows. The age of ore-bearing porphyry is 183.3±1.2 Ma, suggesting Early Jurassic;geochemical characteristics of ore-bearing porphyry are similar to those of andesite from the oceanic island arc setting, indicating that ore-bearing porphyry in Tangbai area was formed in the oceanic island arc setting, and the Gangdise porphyry copper belt has huge potential in the search for porphyry deposits of subduction period. It is therefore held that in the future work emphasis should be placed on the subduction stage porphyry deposit exploration and evaluation, especially on the Early-Middle Jurassic porphyry metallogenic potential evaluation.