湖南道县正冲稀有金属矿床云英岩地球化学特征及对成矿的约束

Geochemical characteristics and mineralization of greisen in Zhengchong rare metal deposit of Daoxian,Hunan

正冲矿床复式花岗岩体顶部云英岩富集Li、Rb、Cs、W、Sn等元素,是一处富F、稀有多金属云英岩型矿床。不同演化阶段花岗岩和云英岩地球化学分析结果显示：对比花岗岩,云英岩中K_2O、Na_2O、MnO、TiO_2和Fe_2O_3~T呈突然分离变化;Rb、Th呈突然升高而Ba、Sr呈突然降低变化;K/Rb、Zr/Hf、La/Sm和（La/Yb）N值呈突然降低变化。地球化学特征暗示云英岩是岩浆不混溶作用形成的,并且F与不混溶作用共同制约云英岩的成因及成矿作用：当F含量〈3%时,以石英-钾长石-铁锂云母-黄玉云英岩为主,Li、Rb、Cs、Nb、Ta在此阶段开始富集成矿;F含量〉3%时,以黄玉-铁锂云母-石英云英岩为主,Li、Rb、Cs进一步富集,而Nb、Ta元素含量降低。

The Zhengchong ore deposit,a greisen-type deposit enriched with Li,Rb,Cs,W,Sn and F greisen,is located at the top of composite granite mass. XRF and ICP-MS are used to obtain the geochemical characteristics of the granite and greisen in various stages. Compared with granite,greisen geochemical characteristics are as following： K_2O,Na_2O,Mn O,TiO_2 and Fe_2O_3~T exhibitsed a separating state. Rare elements and rare earth elements of greisen are characterized by Rb and Th increase suddenly,whereas Ba,Sr,K / Rb,Zr / Hf,La / Sm ratios and（ La / Yb）Nratios decrease suddenly. All of these geochemical characteristics indicate that the origin of greisen belongs to liquid immiscibility. Moreover,F and liquid immiscibility play important roles in the rare metal mineralization process. When F 3%,the enrichment of Li,Rb,Cs,Nb and Ta will be due to the quartz-potash feldspar-topaz-zinnwaldite lithofacies greisen formation. When F〉3%,greisen lithofacies is composed mainly of topaz-quartz-zinnwaldite. In this stage,Li,Rb and Cs are enriching further whereas Nb and Ta decreasing.