额尔古纳地块七一牧场北山银铅锌矿床地质特征及其成因分析

Geological Characteristics and Genesis of the Qiyimuchangbeishan Silver-Lead-Zinc Deposit in the Erguna Massif,Inner Mongolia

内蒙古七一牧场北山矿床是近年来在额尔古纳地块新发现的一个中型银铅锌矿床。本文在野外地质勘查和室内综合整理分析的基础上,对该矿床的基本地质特征及成因进行了初步研究。该矿床银铅锌矿体赋存于中侏罗统塔木兰沟组安山质火山岩和上侏罗统满克头鄂博组流纹质火山碎屑岩中,呈脉状、细脉浸染状,受北西向、近南北向断裂构造控制,其形成与晚侏罗世花岗斑岩、钾长花岗岩具有密切的时空联系。成矿作用在空间上表现出一定的分带性,随着赋矿深度的增加,成矿元素呈现出Pb→Pb、Zn、Ag→Zn(Cu)的变化特点。结合硫、铅同位素及流体包裹体特征,初步认为该矿床应为晚侏罗世-早白垩世伸展环境下形成的与火山-岩浆作用有关的浅成-超浅成中低温热液脉型银铅锌矿床。

The Qiyimuchangbeishan deposit in Inner Mongolia is one of the medium-size silver-lead-zinc deposits found in the Erguna Massif recent years.Based on field investigations and exploration,this paper studies the geological characteristics and genesis of this deposit.Results suggest that its Ag-Pb-Zn orebodies are hosted in the andesitic volcanic rocks of the Middle Jurassic Tamulangou Formation and rhyolitic pyroclastic rocks of the Upper Jurassic Manketouebo Formation,appearing as veins and veinlet-dissemination shapes which are controlled by northwest-and north-trending fault zones,spatially and temporally associated with the emplacement of granitic porphyry and potassic granite.The mineralization has a feature of zoning in space,with increasing depth,the major mineralizing elements transform in the sequence of Pb→Pb,Zn,Ag→Zn(Cu).Considering the features of the sulfur isotope,lead isotope compositions and fluid inclusions,this work suggests that the deposit can be attributed to the volcanic-magma mesothermal and epithermal vein Ag-Pb-Zn type which formed in an extensional tectonic setting during Late Jurassic to Early Cretaceous.