内蒙古乌尔吉地区大石寨组火山岩地球化学特征及成矿潜力

Geochemical characteristics and metallogenic potential of Dashizhai Formation volcanic rocks in Olji area,Inner Mongolia

乌尔吉地区地处中亚造山带东段,属大兴安岭南段铅锌银铜锡铁成矿带。区内二叠系大石寨组为一套变质火山岩夹碎屑沉积岩组合,火山岩具有典型的不对称双峰式特征,基性峰强。岩石地球化学研究表明,中基性、基性岩类属准铝质钙碱性系列和低钾(拉斑)系列,中性岩类总体属钾玄岩系列,中酸性岩属过铝质钙碱性岩系列,岩石为海西中晚期大陆边缘裂谷盆地的岛弧环境下的产物。大石寨组火山岩总体上富集Ag、Sn、Pb、Zn、Cu等成矿元素,是本区Pb、Ag、Sn、Zn等成矿元素的矿源层之一,成矿潜力较大。结合前人研究认为,大石寨组火山岩是本区寻找火山热液型锡、铅、锌、铜等多金属矿床的有利场所。

Located in eastern Central Asian orogenic zone,the Olji area belongs to the lead,zinc,silver,copper,tin,iron metallogenic zone of southern Da Hinggan Mountains. Permian Dashizhai Formation in the study area is an association of metamorphic volcanic rocks interbedded with clastic sedimentary rocks. The volcanic rocks have the characteristics of typical asymmetric bimodal volcanic rocks,and the basic peak is strong. The study of rock geochemistry indicates that intermediate-basic and intermediate rocks belong to quasi-aluminous and calc-alkaline rock series or low potassium（ tholeiitic） rock series,intermediate rocks belong to shoshonitic rock series,and intermediate-acid rocks belong to peraluminous and calc-alkaline rock series. The rocks were formed in an island arc environment of continental margin rift basin in middle-late Hercynian period. Dashizhai formation volcanic rocks are enriched in Ag,Sn,Pb,Zn,Cu and other metallogenic elements,and constitute the source bed of Pb,Ag,Sn,Zn and other metallogenic elements in the study area. The metallogenic potential of Dashizhai Formation volcanic rocks is huge. Combined with previous research,the authors hold that Dashizhai formation volcanic rocks are the best place in search for volcanic hydrothermal lead-zinc-silver-copper deposits.