藏东主要岩金矿床类型基本特点及其找矿前景

The types and prospects of the gold deposits in eastern Xizang

藏东地区是西南三江复合造山带有色金属、贵金属成矿带的重要组成部分,也是三江带中北段新生代强烈陆内变形区,具有金和金银金属矿产成矿的优越条件。已发现的众多岩金矿(化)点反映出藏东有多种岩金矿床成因类型,其中以斑岩型和破碎带充填交代型两种类型最为重要。前者以新生代浸源偏碱性斑岩为成矿母岩,矿(化)体赋存于斑岩、隐爆角砾岩内部、接触带及外接触蚀变带中,主矿化元素为金、银、铅、锌,少数还有铜、钨;后者的矿(化)体一般赋存于多期活动的区域性大断裂侧次级断裂、派生断裂、层间破碎带及节理、劈理发育带内,主矿化元素亦为金及银、铅、锌、铜,个别有锑、汞等。成矿时代以新生代及白垩纪—新生代为主。文中还对藏东构造单元和新生代偏碱性岩带进行划分,对两种金矿床类型的一般矿化特征、矿源层、蚀变和化探异常与矿化关系、找矿标志及找矿方向作了简要论述。

The eastern Xizang area is an important part of nonferrous and precious metallogenic zone, and a highly deformed area during the Cenozoic in the central and northern parts of the NujiangLancangjiangJinshajiang area, where the gold and silver deposits are preferentially hosted. A lot of the gold deposits in eastern Xizang have been recognized, including sedimentary (gold placer), sedimentarydiagenetic, volcanic, porphyrytype, fractured fillingmetasomatic, qartzvein and porphyry copperassociated gold deposits, of which the porphyrytype and fractured fillingmetasomatic are most common. The parent rocks of the porphyrytype gold deposits consist of the Cenozoic partially alkaline porphyries. The orebodies occur generally in porphyries, cryptoexplosion breccias, contact zones and outer contactalteration zones. The main oreforming elements are composed of gold, silver, lead, zinc, copper and tungsten. The latter orebodies appear commonly in the secondary faults, derived faults, interformational fractured zones and joint and cleavage development zones close to the regional rifts. The main oreforming elements consist of gold, silver, lead, zinc, copper, antimony and mercury. The mineralization ages are represented by the Cenozoic and Cretaceous-Cenozoic times. The present paper deals also with the division of the tectonic elements and Cenozoic partially alkaline rock belts in eastern Xizang, with the emphasis on the mineralization, source rocks, alteration, geochemical anomaly, indicators and prospects of the two types of gold deposits cited above.