江西相山西部地区深部多金属矿化矿石组构学、矿物学研究及其地质意义

Ore fabric and mineralogy of polymetallic mineralization in western Xiangshan uranium orefield,Jiangxi Province

江西相山铀矿田西部地区实施的铀矿科学深钻3号孔在深部-700 m发现大量铅锌多金属矿化脉,垂向上呈"上铀下多金属"的分布特征。文章对深部多金属矿化进行了详细的矿物学和矿石组构学研究,并对其成因进行了探讨。研究表明,矿石结构主要有中细粒及微粒结构、自形晶粒状结构、他形晶粒状结构、填隙结构、包含结构、镶边结构、固溶体分离结构、碎裂结构、环带结构等;矿石构造主要有脉状构造、细脉状构造、条带状构造、角砾状构造、致密块状构造、稠密浸染状构造等。矿化类型主要有石英-毒砂-黄铁矿(锡石、黄铜矿)型、黄铁矿型、闪锌矿-方铅矿-黄铁矿型、闪锌矿-方铅矿-碳酸盐(菱铁矿-方解石)型,在空间上具有明显的分带性。根据矿物组合和穿插关系,矿化过程经历了成矿前期的碱性流体作用,形成矿前期绿泥石、锡石和金红石。铅锌成矿期经历了石英-毒砂阶段、黄铁矿化阶段、铅锌矿化阶段、铅锌银碳酸盐阶段等多期叠加。成矿后期以形成碳酸盐-石英脉为特征。综合分析认为,相山深部多金属矿化具有浅成、中低温特征,是与次火山岩有关的低硫化型浅成中低温热液多金属矿化。目前已经发现的铅锌多金属矿化很可能是深部矿化的一个端员,深部很有可能存在与成矿有关的次火山岩体,且具有寻找斑岩型多金属矿化的成矿潜力。

The Xiangshan uranium orefield, the largest hydrothermal uranium orefield in China, is hosted in Early Cretaceous felsic volcanic rocks. In recent years, through deep drilling exploration, a discovery of hidden lead-zincsilver mineralization in the depth was achieved in the west of the Xiangshang uranium orefield. In this paper, the deep polymetallic mineralization was studied in detail in the aspects of mineralogy and ore fabric. Studies show that ore textures mainly include fine and medium particle texture, idiomorphic grain texture, xenomorphic grain texture, filler texture, poikilitic texture, and solid solution separation texture and fracture texture, and ore structures mainly include vein structure, band structure, brecciated structure, dense block structure, and dense disseminated structure. According to the mineral assemblage and the intercalation relationship, four types of mineralization were recognized: quartz-arsenopyrite-pyrite(cassiterite, chalcopyrite) vein, pyrite vein, sphalerite-galena-pyrite vein, and sphalerite-galena-carbonate(siderite-calcite) vein. Furthermore,according to mineral assemblage and intercalation relationship, mineralization process experienced alkaline fluid action in the early stage of mineralization, with characteristics of forming chlorite, cassiterite and rutile. The metallogenic stage of lead and zinc experienced multiple stages such as quartz-arsenopyrite stage, pyritization stage, lead-zinc mineralization stage and lead-zinc carbonatization stage. The latest mineralization period was characterized by the formation of carbonate-quartz veins without mineralization. Based on comprehensive analysis, the authors hold that the polymetallic mineralization in the depth of Xiangshan orefield genetically belongs to epithermal type related to subvolcanic magmatism. The polymetallic mineralization is likely to be a low-sulfur end-member of deep mineralization,which implies that there is great potential of finding porphyry polymetallic mineralization in Xiangshan orefield.