内蒙古额勒根斑岩型钼(铜)矿化区辉钼矿铼-锇同位素年龄及地质意义  

Re-Os isotopic age dating of molybdenite separates from Elegen porphyry Mo (Cu) mineralized area, northwestern Alxa, western Inner Mongolia

作　　者：聂凤军[1] 屈文俊[2] 刘妍[1] 杜安道[2] 江思宏[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]国家地质实验测试中心,北京100037

出　　处：《矿床地质》2005年第6期638-646,共9页Mineral Deposits

基　　金：国家"973"项目(2002CB412606);国家自然科学基金项目(40573025)的联合资助

摘　　要：为了查明额勒根矿化区斑岩型钼(铜)矿化发生的时间,对主要矿化体内5件辉钼矿样品进行了铼_锇同位素分析,所获同位素等时线年龄为(332.0±9.0)Ma(2σ),其MSWD值为0.29。鉴于辉钼矿呈浸染状分布于似斑状花岗闪长岩和花岗闪长斑岩体中,并且与黄铜矿和黄铁矿呈共生结构关系,推测额勒根地区斑岩型钼(铜)矿化体、似斑状花岗闪长岩和花岗闪长斑岩体的形成时间为早石炭世中期,均是海西中期构造_岩浆活动的产物。Located in the southernmost part of the Queershan-Wuzhuergashun terrane along the southern margin of the Siberian block, Elegen is a large-size porphyry Mo （Cu） mineralized area in Alxa, western Inner Mongolia. Porphyry Mo （Cu） mineralization occurs within Hercynian porphyritic granodiorite and granodiorite porphyry stocks as veins, veinlets and disseminated blocks. Re-Os isotopic age dating of five molybdenite separates from the major porphyry Mo mineralized zone gives an isochron age of （332.0 ± 9.0） Ma and model ages ranging from 336.5 to 340.6 Ma, 338.3 Ma on average. As the Re-Os isochron age is in agreement with field geological evidence, and molybdenite is coexistent with chalcopyrite, it is held that the Re-Os isochron age represents the ore-forming time of porphyry Mo （Cu） mineralization within Elegen area. Combined with field geological observations and petrological evidence, it is suggested that the ore-forming materials might have been derived from a mixed source of depleted mantle- and crust-derived magma or fluids. It has been noted that the Re-Os isochron age of molybdenites from the porphyry Mo （Cu） mineralized zone in Elegen is located in the middle of the age range of those unpublished ^40Ar/^39Ar age data for K feldspar separates from monzogranite, tonalite and K feldspar granite bodies. Field geological observations, petrological studies and geochronlogical analyses show that in the hydrothermal environment of Elegen, ^40Ar/^39Ar age of K feldspar separates from the strongly altered intrusions may be partly or even significantly reset whereas Re-Os age records have preserved the primary mineralization event. The Re-Os isochron age of the five molybdenite separates in Elegen indicates that Early Carboniferous island-arc magmatism and relevant porphyry Mo （Cu） mineralization in the northwestern part of Alxa had been active before the Permian collision between the Siberian block and the Kazakhstanian-Beishan plate.

关 键 词：地球化学 铼-锇同位素年龄 辉钼矿 斑岩型钼(铜)矿化体 额勒根 内蒙古 

分 类 号：P618.65[天文地球—矿床学] P597.3[天文地球—地质学]