甘肃花牛山铅锌矿床闪锌矿LA-ICP-MS微量元素组成及其地质意义

LA-ICP-MS Trace Element Analysis of Sphalerite in Huaniushan Pb-Zn Deposit in Gansu Province and Its Geological Significance

天山—北山铅锌成矿带位于中亚造山带、塔里木板块和华北板块的交汇地带,是我国西北地区重要的金属资源产地之一。花牛山铅锌矿是天山—北山地区具典型成因意义的铅锌矿床,矿床成因机制一直存在争议。本文通过LA-ICP-MS对其闪锌矿微量组成进行分析,结果表明:该矿床闪锌矿形成于中—高温环境,以富集Fe、Mn、In、Cd、Cu等元素,贫Ga、Ge、Ni等元素为特征,其中Fe、Mn、In、Cd、Cu以类质同象的形式赋存于闪锌矿中,Ag、Pb以显微包裹体的形式赋存于闪锌矿中;其微量元素组成与岩浆热液为主导的矿床(都龙、黄岗梁、孟恩陶勒盖、赤土店)类似,除此之外,闪锌矿Tl元素质量分数以及Cd/Fe和Cd/Mn值均显示岩浆热液属性,在微量元素判别图中样品也落入岩浆热液区域。野外调研发现,矿体底部未见角砾状和网脉状矿体,矿体均发育在岩性界面及层间破碎带中。结合矿床地质特征、闪锌矿微量元素地球化学特征,认为花牛山铅锌矿床成因类型属于中高温岩浆热液型。

Tianshan-Beishan Pb-Zn metallogenic belt is located in the intersection of Central Asian orogenic belt,Tarim Craton,and North China craton,which is one of the important metal resources in Northwest China.Huaniushan Pb-Zn deposit is a typical genetic deposit in Tianshan-Beishan area.The results of LA-ICP-MS analysis on the trace element composition of sphalerite show that the sphalerite was formed in the medium-high temperature environment and characterized by rich in Fe,Mn,Cd,In,Cu and poor in Ga,Ge,Ni.Among them,Mn,Fe,In,Cd,Cu are in the lattice of sphalerite in the form of isomorphism,whereas Ag and Pb may exist in the form of micro-inclusions.The trace element composition is similar to that of the magmatic hydrothermal deposits(Dulong,Huanggangliang,Meng’entaolegai,Chitudian);in addition,the mass fraction of Tl element and the values of Cd/Fe and Cd/Mn of sphalerite show magmatic hydrothermal properties,and the trace element discrimination figure also falls into magmatic hydrothermal region.The field investigation shows that there are no brecciated or reticular ore bodies at the bottom of the deposit,and the ore bodies are developed in the lithologic interfaces and interlayer fracture zones.Based on the geological characteristics of the deposit and the geochemistry of sphalerite,it is conclude that the genetic type of Huaniushan Pb-Zn deposit belongs to magmatic hydrothermal type formed at medium-high temperature.