湖南瑶岗仙石英脉型钨矿床顶部的横向交代作用

Characteristics of layer alteration at the top of the quartz vein in the Yaogangxian tungsten deposit, Hunan Province

湖南瑶岗仙钨矿床的陡倾黑钨矿石英脉沿燕山早期花岗岩顶部接触带两侧发育,石英脉在岩体中延深>1000m,岩体外延深>500 m。岩体上部的沉积岩包括寒武纪变质细砂岩、泥盆纪砂岩以及三叠纪含炭泥砂岩。毒砂黄玉层发育于三叠系与泥盆系角度不整合接触面上方的砂岩中,顺层分布,下方为陡倾含钨石英脉(宽0.3 m)。地质地球化学研究显示,毒砂黄玉层主要为一套由石英砂岩遭受强烈硅化,伴随毒砂、黄玉、白云母等蚀变形成的交代岩。蚀变岩中迁入的组分与含矿石英脉的成分一致,富Si、F、B及成矿元素W、Mo、Bi等,蚀变的流体与形成石英脉的成矿流体相同。瑶岗仙钨矿的垂向分带不同于"五层楼",顶部不发育细脉带和线脉带,而是以缓倾斜顺层分布的毒砂黄玉层直接发育于陡倾的石英中脉带之上,构成脉型钨矿床另一种成矿形式,即"上层下脉"的双层结构。这种模型的认识对脉型钨矿找矿有一定意义,即在富含毒砂-黄玉-白云母等强烈硅化的顺层状蚀变岩层下方,应重视寻找陡倾斜黑钨矿石英脉。

The steeply- dipping wolframite- quartz veins occur on both sides of the top contact zone of early Yanshanian granite,extending about 1000 m in the granite and about 500 m in sediments within the Yaogangxian tungsten deposit of Hunan Province.The sedimentary rocks overlying the granite consist of Precambrian metamorphic sandstone, Devonian sandstones and Triassic carbonaceous siltstone. Arsenopyrite topaz rocks（layers）occur along the sandstone overlying the Triassic-Devonian unconformity,and the tungsten- bearing quartz vein under the rocks（layers）is about 0.3 m in width. The studies of geology and geochemistry show that arsenopyrite- topaz rock mainly originally consists of quartz sandstone, with strong silicification, accompanied byarsenopyrite, topaz, muscovite and some other minerals, suggesting an altered rock. The rocks rich in Si, F, B and ore- forming elements such as W, Bi and Mo are similar to features of quartz veins. The fluid of alteration is the same as ore-forming fluid of quartz vein. The vertical zoning of the Yaogangxian tungsten deposit is different from the ＂five floor model＂ of wolframite-quartz veins. There are not veinlet and linear vein zones at the top of the model, but the arsenopyrite-topaz rock layer directly and gently dips over the steeply dipping quartz wide vein（0.3 m）. A new metallogenic model for the tungsten bearing quartz vein deposit is suggested in this paper, i.e.,＂layer in the upper part and vein in the lower part＂. This model is of significance for the exploration of vein-type tungsten deposits, i.e., under the strongly silicified bedding alteration rocks with arsenopyrite, topaz and muscovite, there might occur steeply dipping wolframite-quartz veins.