西藏改则县波龙斑岩型铜金矿床地球化学特征及成因浅析

波龙铜金矿床是喜马拉雅特提斯成矿域班-怒成矿带西段产出的大型铜金矿床,是多龙铜金矿集区的重要组成部分,找矿潜力巨大。波龙矿区内的含矿斑岩体基本上全岩矿化,矿体呈不规则筒柱状产于早白垩世花岗闪长斑岩体中及其与下侏罗统曲色组砂岩的接触带内。目前控制矿体长度1200m,向深部延伸大于1000m(倾向200o),最大连续厚度为473.47m,未穿透矿体。矿体平面投影呈似椭圆状,面积约1.2km2。本文通过对波龙铜金矿床地质、矿床地球化学特征的研究,认为该矿床的形成与斑岩体侵位、岩浆期后成矿流体的演化有关,矿床类型属于斑岩型铜金矿。矿石构造为斑岩铜矿典型的细脉-浸染状构造。金属矿物以黄铜矿为主,次为黄铁矿、斑铜矿、辉钼矿、磁铁矿、镜铁矿等,非金属矿物有石英、长石、绢云母、黑云母、硬石膏等。通过硅酸盐分析,里特曼组合指数—戈蒂里图解表明波龙斑岩型铜金矿的花岗闪长斑岩属钙碱性系列,形成于岛弧环境;稀土元素地球化学特征反映以岩浆热液成矿作用为主。

Geochemical Characteristics and Genesis of the Bolong Porphyry Copper-Gold Deposit in Gerze County, Tibet

The Bolong Cu-Au deposit with great prospecting potential is a large ore deposit in the western part of the Bangong Co-Nujiang River Metallogenic Belt of the Himalayan Tethyan metallogenic domain,and also an important part of the Duolong ore concentration area.The ore-bearing porphyries of the Bolong ore field were basically mineralized.The ore body in the irregular pipe columnar form was in early Cretaceous granodiorite porphyry and the contact zone with Lower Jurassic Quse Formation sandstone.The ore body is 1200 m in length and greater than 1000 m in downward extension(dipping 200°),and its maximum continuous thickness is 473.47 m.The ore body hasn’t been penetrated by drilling.The planar projection of the ore body is oval-shaped and its area is approximately 1.2km 2.The authors studied geological and geochemical characteristics of the Bolong Cu-Au deposit and found that the formation of this deposit was related to porphyry emplacement and magmatic evolution of the ore-forming fluids.This deposit is a copper-gold porphyry deposit.Ore structure is typical porphyry copper veinlets-disseminated structure.Metallic minerals are mainly chalcopyrite and secondarily pyrite,bornite,molybdenite,magnetite,and specularite,whereas non-metallic minerals are quartz,feldspar,sericite,biotite,anhydrite,etc.The Bolong porphyry copper-gold deposit was formed in an island arc environment and its granodiorite porphyry was calc-alkaline series,as evidenced by silicate analysis and Rietmann combination index-Gotti graphic table.REE geochemical characteristics suggest that the mineralization was mainly magmatic hydrothermal mineralization.