西藏甲玛超大型矿床南坑厚大矽卡岩矿体的成岩-成矿-构造耦合关系

The diagenesis-mineralization-structure coupling relationship of South-Pit skarn thick ore body in the Jiama super large-sized deposit,Tibet

甲玛是西藏冈底斯成矿带规模大、品位富的超大型矿床,也是勘查和研究程度最高的矿床之一。其中,南坑矿段由于富含高品位的矽卡岩型铜铅锌矿石,且具大型规模,已被纳入矿区首采矿段之一,然而关于其控岩控矿机制以及其与主矿段的耦合关系却仍不明确。本次基于详细的钻孔编录和野外地质证据,判定其成矿作用与中新世的花岗闪长斑岩等中酸性斑岩体有关,结合高精度的U-Pb年代学分析,厘定含矿花岗闪长斑岩结晶年龄为(15.5±0.3)Ma,与辉钼矿成矿年龄(15.23±0.22)Ma一致。南坑矿段作为甲玛矿床多中心复合成矿作用模型的重要组成部分,其矽卡岩矿体主要产于林布宗组角岩与多底沟组大理岩之间的层间接触带,属于中新世岩浆热液活动的产物。矿体形成后,受滑覆构造及次级断裂影响,矿体发生错断或破坏。对于南坑矿段后续的勘查评价,应注意与含矿斑岩和矽卡岩的蚀变与矿化分带特征,定位致矿热液中心。

The Jiama deposit is one of super large-sized deposits with high grade and one of the most explored and studied deposits in the Gangdese metallogenic belt of Tibet.Because the South-Pit segment host large-sized skarn Cu-Pb-Zn ore bodies with high-grade,it has been given priority to mining.However,its diagenesis,mineralization and the relationship with main segment are still unclear.Based on detailed borehole logging and field geological evidences,it is determined that the mineralization is related to intermediate-felsic porphyries.The high-precision U-Pb dating of ore-bearing granodiorite porphyry yields the age of 15.5±0.3 Ma,which is consistent with the Re-Os age of molybdenite(15.23±0.22Ma).As the important part of Jiama polycentric complex mineralization model,the skarn ore body in South-Pit segment is mainly distributed on the contact between marble and hornfels.The skarn should be the result of Miocene magmatism and destroyed by the slide nappe fault and secondary faults.For the future exploration in South-Pit,more attention should be paid to the study of alteration and mineralization of ore-bearing porphyry and skarn,and to the locating of the ore-related fluid center.