蒙古国阿林诺尔钼矿床赋矿花岗岩年代学及地球化学特征

The Geochronology and Geochemical Features of Ore-hosting Granite in the Aryn nuur Molybdenum Deposit,Mongolia

蒙古国阿林诺尔钼矿床赋存于细粒黑云母花岗岩体中,整体呈平卧的柱状大矿体,矿床蚀变发育。本文报道了该矿床赋矿花岗岩SHRIMP锆石U-Pb年龄,并对其进行了元素地球化学研究。SHRIMP锆石U-Pb年代学研究表明,阿林诺尔赋矿花岗岩侵位于229.0±2.2Ma(MSWD=1.16),为中三叠世,与他人测定该矿床辉钼矿Re-Os等时线年龄(227±3.1Ma,MSWD=0.07)在误差范围内一致,表明矿床与赋矿花岗岩体的岩浆作用有着密切的成因联系,成岩成矿的年龄也与该区蒙古-鄂霍次克残余洋盆消减作用处于同一时期。元素地球化学研究显示,岩体具有过铝质高钾钙碱性特征,富集Rb、Ba、Th以及K等大离子亲石元素,亏损Nb、Ta以及Ti等高场强元素,具有Climax型斑岩钼矿的特征,其形成过程可能与俯冲板块上方地壳伸展作用过程中高钾钙碱性岩浆活动有明显的联系。阿林诺尔钼矿赋矿岩体的成岩成矿作用是蒙古-鄂霍次克残余洋盆向两侧大陆俯冲构造体制下地壳伸展作用的产物。

The Aryn nuur molybdenum deposit is located in East Mongolia and occurs as a wholly prostrate cylindrical ore body in highly altered fine-grained biotite granite.For the purpose of accurate determination of the age of the ore-bearing fine-grained granite,the authors employed the zircon SHRIMP dating technique,which yielded a concordant age of 229.0 ± 2.2 Ma（MSWD=1.16）.This age represents the intrusion age of the ore-bearing granite,which is consistent with the molybdenite Re-Os age of the ore deposit.The age data show that molybdenum mineralization was genetically related to the intrusion of the ore-bearing granite.Element geochemistry demonstrates that the ore-bearing granite rocks are of peraluminous and high-K calc-alkaline nature and show Rb,Ba,Th and K enrichment relative to light REE and high field strength elements in the primitive mantle normalized spidergrams.These features are typical of Climax-type porphyry molybdenum deposits.Combined with the late Palaeozoic-early Triassic tectonic setting of East Mongolia,the authors hold that the formation of the ore-bearing granite and the ore-forming process of the Ary nuur molybdenum deposit were both related to the subduction of the relaxation and extension of crust above the Mongol-Okhotsk subduction zone.