内蒙古兴阿斑岩钼矿床地质特征、成岩时代与岩浆成因研究

Geological characteristics,petrogenic age and magmatic origin of the Xing'a molybdenum deposit,Inner Mongolia

兴阿钼矿床位于内蒙古自治区鄂伦春自治旗境内,是新近发现的一处超大型斑岩型钼矿床.矿体主要赋存于八道沟二长花岗斑岩体及其上的隐爆裂隙中,呈似层状分布,平均厚9.29 m,Mo平均品位0.118％.从岩体向外依次为钾化、硅化、绢英岩化、青磐岩化等斑岩型蚀变分带,围岩蚀变和物化探异常是重要的找矿标志.对矿区赋矿钾长花岗岩、成矿二长花岗斑岩和成矿后闪长玢岩开展了锆石LA-ICP-MS U-Pb定年,结果表明成矿作用发生于131-124 Ma,大约在129 Ma.3类侵入岩锆石Hf同位素研究显示,成矿相关岩浆源自新元古代末亏损地幔增生地壳物质的部分熔融.

The Xing’a molybdenum deposit is a recently discovered giant porphyry deposit in Oroqen county, Inner Mongolia. The orebodies mainly occur in the Badaogou monzogranite porphyry and the cryptoexplosive fractures. The layered orebodies have an average thickness of 9.29 m with an average Mo grade of 0.118%. The deposit shows porphyry-type alteration zoning, ranging outwardly from potassic silication, through silicification and phyllic alteration, to propylitic alteration. The alteration features and geophysical and geochemical anomalies are very significant symbols of exploration. The isotope study of zircon U-Pb dating by LA-ICP-MS for the ore-bearing K-feldspar granite, ore-causative monzogranite porphyry and post-mineralization diorite porphyry were conducted, and the result indicate that the mineralization formed in a time span of from 131 Ma to 124 Ma, roughly at about 129 Ma. The Hf isotope study of these three types of intrusions indicates that the ore-related magmas were originated from partial melting of the juvenile crust sourced from a depleted mantle in late Neoproterozoic.