内蒙古敖仑花斑岩钼矿床成岩成矿年代学及地质意义

敖仑花钼矿床位于大兴安岭南段,是西拉木伦河断裂北侧多金属矿集区内新发现的斑岩型钼矿床.首次采用SHRIMP锆石U-Pb技术对敖仑花含矿花岗斑岩进行了测年,获得成岩年龄为134±4Ma;采用ICP-MS方法测定敖仑花钼矿床辉钼矿中Re-Os同位素,获得模式年龄在131±2～133±2Ma之间,辉钼矿Re-Os同位素等时线年龄为132±1Ma(MSWD=1.12),成岩与成矿误差范围内基本同时发生,敖仑花斑岩钼矿床为早白垩世构造、岩浆活动的产物.西拉木伦河断裂带内的多金属矿床具有一定的时空分布规律,130～150Ma是带内矿床成矿高峰期,两侧矿床可能具有不同的成矿物质来源.区内独特的成矿特征,与区域经历了古亚洲洋构造域和滨西太平洋构造域的复合演化有关,发生于早白垩世时期的这一大规模成矿事件,是该区经历增生造山和地壳加厚之后,演化为孤后大陆伸展背景时强烈岩浆活动和成矿作用的产物.

Petrogenesis and mineralization chronology study on the Aolunhua porphyry Mo deposit, Inner Mongolia, and its geological implications

Located in the southern segment of the Da Hinggan Mountains,the Aolunhua Mo deposit is newly found as a porphyry molybdenum deposit to the north of the Xilamulun fault.U-Pb dating for zircons from the Aolunhua granitic porphyry by SHRIMP method yields an age of 134±4Ma.Re-Os isotopic dating by the ICP-MS method on molybdenites separated from the Aolunhua molybdenum deposit yields an isochron age of 132±1Ma(MSWD = 1.12),with model ages ranging from 131±2 to 133±2Ma.The ore-forming time of the porphyry Mo deposit represented by the Re-Os isochron age is almost same as the time of petrogenesis,both in early Cretaceous.Our new age data,along with the published age data of the polymetallic deposits in the Xilamulun metallogenic belt,lead us to suggest that 130～150Ma is the main period of ore-formation in this area,and the ore-forming material for the deposits on both sides of the Xilamulun fault were from different sources.The unique metallogenic characteristics of the polymetallic deposits in the Xilamulun metallogenie belt was probably linked to the composite evolution of the Paleoasian and west circum-Paeifie tectonomagmatic domains.The main metallogenic pulse formed responding to the intensive magmatism and minerogenesis in early Cretaceous during which an extensional back-are regime was developed in the Xilamulun area following accretionary orogenesis and thickening of continental crust.