“带外脉式”钨矿床成矿模型——以湖南白云仙钨矿田头天门矿床为例

Metallogenic model of outside the cupola style" quartz vein-type tungsten deposit: A case study of Toutianmen deposit,Baiyunxian orefield,Hunan Province

石英脉型钨矿床是南岭钨矿成矿带的主要矿床类型,含钨石英脉产于成矿花岗岩顶部的接触带附近,其中"带外脉式"的石英脉几乎全部产于接触带外侧。湖南白云仙钨矿田头天门钨矿床发育较完整的"带外脉式"钨矿矿化组合和空间分带,主要矿化类型包括花岗岩型和石英脉型,前者分布于岩墙上部,后者发育于上方外侧的砂岩中。笔者研究了头天门钨矿床中花岗岩和各类矿体的地质地球化学特征,探讨了岩浆演化与钨的富集成矿过程。提出头天门钨矿床粗粒斑状黑云母花岗岩→细粒碱长花岗岩岩株→岩墙→云英岩化花岗岩→云英岩→石英脉的岩浆-热液演化-成矿全过程,成矿流体表现出"上液下浆"的分带特点。在岩墙形成前的演化过程中,成矿元素的富集主要受岩浆晚期分异作用的制约,岩墙之后的演化则主要受热液作用的影响。成矿地质体为细粒碱长花岗岩岩株以及上部的岩墙。建立了带外脉式型钨矿床成矿模型,形成机制主要为:在岩浆固结之前,岩浆中的挥发分和H2O在岩体顶部聚集引起围岩破裂,岩浆充填形成岩墙,挥发分和成矿物质在岩墙上部聚集形成花岗岩型(云英岩型)钨矿,并在外侧形成石英脉型钨矿。

The quartz vein type tungsten deposit is the most important type of mineralization in the Nanling metallogenic belt.The veins occur near the top contact zone of the granite cupola.Nevertheless,in the  outside the cupola style ＂ quartz veins-type tungsten deposits,almost all veins occur on the outer side of the contact zone.The complete zoning of mineralization of  outside the cupola style＂ was recognized in the Toutianmen tungsten deposit in Baiyunxian orefield,Hunan Province.The main types of mineralization include granite-type ore in the upper part of the dyke,and quartz vein-type ore in sandstone rocks above the dyke.The geology and geochemistry of the granites and mineralization were studied,and the tungsten enrichment and the ore-forming mechanism were discussed.It is held that there is a complete magma-fluid evolution sequence in order of coarse granite（ batholith） →fine granite（ copula） → granite dyke→greisen granite→greisen to W-bearing quartz vein.The  liquid in the upper part and magma in the lower part ＂ model of the ore-forming fluid in the system was recognized.The enrichment mechanism of the ore-forming elements was mainly controlled by the magmatic differentiation at the late stage of the magma before the formation of dykes,and was mainly controlled by the hydrothermal process after the formation of dykes.The ore material mostly came from the fine grained granite and the dyke.The metallogenic mechanism of the outside the cupola style＂ quartz vein-type tungsten deposit is summarized as follows： The volatile and H2 O gathered at the top of the cupola and led to fracturing of the sandstone rocks before the crystallization and solidification of the magma.The ore-forming material was concentrated at the upper part of the dyke to form the granite-type ore,and hydrothermal solution derived from the dyke filled fractures and formed the W-bearing quartz vein.