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

Abstract: 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 by arsenopyrite, 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.