内蒙古西乌珠穆沁旗布敦乌拉银多金属矿床地质特征、成因与成矿预测

Geological characteristics,genesis and metallogenic prediction of Budunwula Ag polymetallic deposit,West Ujimqin,Inner Mongolia

内蒙古西乌珠穆沁旗布敦乌拉银多金属矿床位于大兴安岭南段多金属成矿带白音查干银矿床的北侧,是一座中型银矿床,目前矿区内估算(121b+122b+333)矿石资源储量为523.93万t,银金属量859.84 t,平均品位(Ag) 164.11×10^(-6),伴生金属为Pb、Zn、Cd及Ga等4种元素。矿体赋存于二叠系大石寨组流纹岩及流纹质凝灰岩中,矿脉受北东向断裂构造控制,矿化与硅化、绢云母化、绿泥石化和碳酸盐化碎裂岩带关系密切;成矿热液期可分为3个阶段,分别是石英-黄铁矿阶段(Ⅰ)、银多金属硫化物阶段(Ⅱ)和方解石-石英阶段(Ⅲ),其中II阶段为主成矿阶段,形成辉银矿、辉锑银矿、银黝铜矿、闪锌矿和方铅矿等多种硫化物。从空间、矿化元素分带来看,白音查干和布敦乌拉多金属矿床成因关系密切,均产在花岗斑岩岩体周围,在垂向上由下向上,平面上围绕成矿岩体由内向外,蚀变矿物组合从电气石±石英±萤石变化为较低温的含萤石±绢云母±绿泥石±方解石±高岭石组合,成矿元素分布依次为Sn-Cu→Ag-Pb-Zn,两矿区可以联合构成与早白垩世石英斑岩相关的岩浆热液型多金属成矿系统。根据控矿因素与找矿标志,建立成矿找矿模型,进而得出布敦乌拉矿床深部具有勘查Sn-Cu矿化或Ag-Pb-Zn矿化的潜力,白音查干矿床石英斑岩南侧为勘查脉状Ag-Pb-Zn矿化的远景区。

The Budunwula Ag polymetallic deposit in West Ujimqin,Inner Mongolia is a medium-sized silver deposit,located in the north of Baiyinchagan deposit,southern Great Xing an Range polymetallic metallogenic belt.At present,the total estimated ore reserves of Budunwula deposit is 5.2393 million tons(121b+122b+333),with 859.84 tons of silver,164.11×10-6 of Ag average grade,and associated metals of Pb,Zn,Cd and Ga.The orebodies is controlled by NE trending faults and occurs in rhyolite and rhyolitic tuff of Permian Dashizhai Formation.Mineralization is closely related to silicification,sericitization,chloritization and carbonation.Field and textural relationships indicate three hydrothermal paragenetic stages,which are represented by quartz-pyrite stage(Ⅰ),Ag polymetallic sulfide stage(Ⅱ)and calcite-quartz stage(Ⅲ),of which stage II is the main ore-forming stage,forming a variety of sulfides such as argentite,antimonite,silver tetrahedrite,sphalerite and galena.The genesis of Baiyinchagan and Butunwula polymetallic deposits are closely genetic related.The metal elements are distributed from Sn-Cu to Ag-Pb-Zn around the ore-forming rock body from inside to outside,and the altered mineral assemblage is changed from tourmaline±quartz±fluorite to fluorite±sericite±chlorite±calcite±kaolinite.The two deposits can be accounted as a complete magmatic hydrothermal polymetallic metallogenic system,caused by Early Cretaceous porphyry.According to the ore controlling factors and ore prospecting criteria,the genetic model and ore-forming prediction is established for this deposit.It is considered that the deep part of Butungula deposit has the potential to explore Sn-Cu mineralization or Ag-Pb-Zn mineralization.The south side of quartz porphyry in Baiyinchagan deposit is the prospective area for exploring vein-type Ag-Pb-Zn mineralization.