湖南锡田锡钨多金属矿床成矿构造特征及其找矿意义

锡田矿床内发育近SN向花岗岩穹窿伸展构造、NE向复式褶皱和NE或NEE向走滑伸展构造系统。穹窿构造主要由印支期和燕山期侵入的花岗岩和古生代地层及不连续的环形滑脱断层组成,控制燕山期花岗岩与围岩接触带矽卡岩型矿体的分布;复式褶皱为古生代地层组成的NE向复式向斜,在矿区中部被锡田复式花岗岩体切割。严塘复式向斜与小田复式向斜中的背斜核部,尤其断层叠加的部位常控制一些构造破碎带型钨锡富矿体的分布。NE向或NEE向走滑伸展构造系统包括NE向右行(伸展)走滑断层、NE向或近EW向右行次级的走滑伸展断层、近SN向左行走滑断层和NW向伸展断层,控制了锡田矿区内的不同方向构造蚀变岩型、石英脉型和云英岩脉型锡钨多金属矿床的分布。花岗岩锆石U-Pb、白云母40Ar-39Ar和辉钼矿Re-Os同位素测年表明锡田地区燕山期构造活动、岩浆作用与成矿响应时间非常接近,介于150～160Ma。岩体与地层(灰岩)接触带、岩体中的NEE向断裂带以及被NE向断裂叠加的背斜轴部是重要的成矿区域,可作为下一步矿产勘查工作重要靶区。

Structural Characteristics and Prospecting Significance of the Xitian Tin-Tungsten Polymetallic Deposit, Hunan Province, China

The Xitian tin-tungsten deposit, an important deposit discovered recently in the Nanling ore-forming province, occurs in the contact zone of the Late Devonian dolomitic limestone and Jurassic to Cretaceous (Yanshanian) granitoids. The main ore types of the deposit are skan-, structural skan-, structural altered rock- and quartz-greisen vein types. There is a SN-trending extensional structure of granite dome, a series of NE-trending multiple folds and NE or NEE-trending strike-slip tectonic system developed in the Xitian deposit. The dome structure is composed of Indosian and Yanshanian granites, Paleozoic strata and Mesozoic discontinuous ring detachment faults, which controls the distribution of skarn orebodies. The complex fold is a NE-trending complicated synclines, which consists of Palaeozoic strata, and is cut by strike-slip faults in the anticlinal core. Some structural fracture zone type ore bodies are controlled by both the coaxial overprinted fold of two periods, which belong to Yantang and Xiaotian complicated syncline, and the ductile brittle shear faults. The strike-slip system consists of the first-order NE-trending right lateral strike-slip faults, secondary P-orientation shear faults, SN-trending left laterial strike-slip faults and NW-trending stretch faults. The strike-slip system controls the distribution of quartz-vein- and greisen vein type tin-tungsten polymetallic orebodies. Zircon SHRIMP and LA-ICPMS U-Pb dating of the Xitian granites and 40Ar-39Ar ages of muscovites from the greisenization type tungsten-tin orebodies as well as Re-Os isochron age of molybdenites from the quartz-vein type tin-tungsten ore bodies demonstrate that the time of tectonic activity, magmatism and metallogenesis in Xitian tin- tungsten deposit is basically consistent with those of the large-scale metallogeny in Nanling ore-forming province (150 Ma ~160 Ma). There exist many metallogenic areas favorable for future exploration, such as contact zones of granites and limestones, NEE- or NE- trending fault zones in the granite dome, and anticlinal cores overprinted by the Yanshanian NE-trending strike-slip faults in the strata.