自2004年以来,在内蒙古东部地区发现或探明了众多钼多金属矿,位于二连浩特红格尔地区的乌花敖包矿是新近发现的钼矿。到目前为止,前人对该矿研究较少。文中对该矿的野外地质特征、火成岩组合及其特征、LA-ICP MS锆石U-Pb年代学等开展研究,指出成矿火成岩分别为石英斑岩、花岗斑岩及隐伏的细粒二长花岗岩,地表出露的花岗闪长岩等为围岩。成矿火成岩在TAS图上均为亚碱性系列,在SiO2-K2O图上为高钾钙碱系列,σ在1.91～3.29,平均为2.44,A/CNK在0.876～1.013,表现出偏铝质岩石的特征。微量元素相对富Rb和K,而亏损Ba和Sr;在高场强元素中,相对富集Th、La、Ce、Nd、Zr、Ta、Hf、Tm、Tb和Yb,而相对弱亏损P、Sm和Nb,强烈亏损Y,反映出有强烈的结晶分异作用存在。LREE/HREE比值在6.52～14.76,普遍高于一般花岗岩（1～1.2）,轻稀土相对富集,说明轻重稀土间存在着分馏作用。铕异常δEu在0.43～0.91,具有明显的负Eu异常,说明本区花岗岩岩浆形成演化过程发生了斜长石的分离结晶作用或岩浆源区残余相含斜长石。石英斑岩LA-ICP MS锆石U-Pb测年显示该斑岩的形成年龄为（139.2±3.4）Ma,MSWD为1.9。基于上述分析研究和构造环境判别,结合区域对比,推测乌花敖包的钼矿应当形成于早白垩世,即燕山造山运动晚期蒙古微大陆同西伯利亚板块沿蒙古—鄂霍茨克地带拼合的同碰撞阶段。%Several Mo-polymetallic ores have been explored and verified in the eastern Inner Mongolia area since 2004.The Wuhuaaobao Mo deposit in Honggeer area of Erlianhot is one of the new found ores.But,till now there are few studies about this ore deposit.The present paper deals with the geological features,the characteristics of igneous rock assemblages and the results of LA-ICP MS zircon U-Pb dating.We propose that the metallogenic igneous rocks are quartz porphyry,granite porphyry and concealed fine-grained adamellite.The granodiorite exposed on the surface is the surrounding rock.In TAS diagram,metallogenic igneous rocks are plotted in sub-alkaline areas and in SiO2-K2O diagram,belong to high-potasstic calc-alkaline series.They are metaluminous with σ between 1.91-3.29(average is 2.44) and A/CNK between 0.876-1.013.Trace element abundances show enrichment in Rb,K and depletion in Ba,Sr.High field strength elements show enrichment in Th,La,Ce,Nd,Zr,Ta,Hf,Tm,Tb,Yb and relatively depleted in P,Sm,Nb and extremely depleted in Y.It reflects the process of obvious crystallization-differentiation and proves that there is fractional distillation in LREE and HREE and LREE/HREE is 6.52-14.76 which is much higher than average.According to δEu ranges in 0.43-0.91,we inferred that there must have happened plagioclase fractional crystallization during the process of granitoid magma evolution or there were plagioclase remnants in source region.The LA-ICP MS zircon U-Pb dating of quartz porphyry yielded an age of 139.2±3.4 Ma with MSWD of 1.9.All above,combined with tectonic setting discrimination and regional geological correlation,it is reasonable to conjecture that the Wuhuaaobao Mo deposit was formed in Early Cretaceous,namely,in the syn-collisional stage of Mongolia microcontinent when merging with Siberia plate along the Mongolian-Okhotsk zone in Late Yanshan Epoch.
展开▼
