西藏沙拉岗锑矿控矿构造及成矿时代约束

Ore-control structural and geochronologic constrain in Shalagang antimony deposit in southern Tibet, China

西藏沙拉岗锑矿床位于中国北喜马拉雅地区然巴杂岩穹窿的东南部40km。该地区至少有4种矿床类型被发现:(1)金矿;(2)金锑矿;(3)锑矿;(4)铅锌(银,锑)矿。沙拉岗是该地区代表性的一个以辉锑矿为主要矿石矿物的脉状锑矿床。赋矿围岩为下白垩统甲不拉组板岩、粉砂岩、硅质岩以及辉长岩和闪长岩等侵入体。主要的矿体受控于近东西向和近南北向断裂构造。近东西向的断裂构造多为低角度浅层次的层间断裂,在成矿前和成矿后均有活动。近南北向的构造多为高角度的断裂,切割了矿区的近东西向断裂,闪长岩和辉长岩,是主要的导矿构造和成矿要素,连通了深部含矿热液和浅表近东西向断裂构造。当近东西向和近南北向的构造发生交汇,沿断裂构造分布的蚀变和矿化的规模随之扩大,往往存在较大规模的工业矿体。锆石SHRIMPU-Pb分析说明辉长岩形成于23·6Ma左右,近南北向断裂构造及其伴随的锑矿化的时间,至少要晚于23·6Ma。

The Shalagang Sb deposit is located at 40km southeast of the Ranba complex dome at the Northern Himalaya area in China. At least four mineralization styles are recognized in Northern Himalaya： （1） Au deposits; （2） Sb-Au deposits; （3） Sb deposits and （4） Pb-Zn （Ag, Sb） deposits. Shalagang is one of representative vein type antimony deposits that have stibnite as the only mineral of economic interest. The country rocks are consisted of slate, siltstone, and silicalite of Lower Cretaceous Jiabula Formation, gabbro and diorite dike. The main ore bodies are controlled by E-W striking faults and N-S striking faults. The E-W striking faults are low angle and shallow lever interlayer fault, and were in activity during pre-mineralization and post-mineralization. The N-S striking faults are high angle faults. It cut the E-W faults, diorites and gabbros, and connected the deep lever ore-forming fluids with the shallow lever faults, resulting in stibnite deposition along the E-W faults and N-S faults. The place, where E-W striking faults jointed with N-S striking faults, has stronger alteration and Sb mineralization along these faults. Larger economic ore body could exist along these jointed faults. Zircon SHRIMP U-Pb analysis showing that the age of diorite is around 23.6Ma, indicated that the N-S striking faults and Sb-mineralization within it, which cut the diorite, are formed later than 23.6Ma.