内蒙古苏尼特右旗毕力赫大型斑岩型金矿床辉钼矿Re-Os同位素年龄及其地质意义

Molybdnite Re-Os isotope age of Bilihe large-size porphyry gold deposit in Sunid Right Banner of Inner Mongolia and its geological significance

内蒙古苏尼特右旗毕力赫大型斑岩型金矿的发现在华北板块北缘尚属首例。为了查明该斑岩型金(铜)矿化发生的时间,作者采集了斑岩体内6件辉钼矿样品进行铼-锇同位素测试,获得等时线年龄为(272.7±1.6)Ma(MSWD=0.57)。毕力赫晚古生代金矿成矿地质事件的厘定,为华北板块北部晚古生代汇聚板块构造体系提供了新证据,促使对华北北部一些基础地质问题重新进行认识,对中亚造山带中东段晚古生代岩浆弧环境寻找浅成低温-斑岩型金多金属矿床具有启示意义。

Situated in Sonid Right Banner of Inner Mongolia,the Bilihe gold deposit lies within the Caledonian hyperplasia orogenic belt sandwiched between North China north margin（Kangbao-Chifeng）fault and Wenduermiao-Xilamulun fault in the middle-eastern section of the Central Asian orogenic belt.The host rock in the Bilihe gold deposit is a set of neutral-acidic volcanic rocks-sedimentary rocks,which can be divided into andesites in the lower part and rhyolites with related clastic rocks in the upper part.The concealed gold-bearing sub-volcanic intrusive complex composed mainly of granodiorite porphyry-monzogranite porphyry is closely related to the minera-lization.Four types of mineralization have been identified,namely quartz vein type,tectonic fracture zone altered rock type,explosion breccia type and porphyry altered rock type.The first three mineralization types are controlled by faults,breccia pipes（veins）and volcanic bodies as well as their supporting structures.The gold deposit belongs to the（sub）volcanic hydrothermal type,which has been subjected to intense erosion and hence only partially preserved.The most important mineralization type is the porphyry alteration type,and the proven resources of this type of mineralization account for more than 90% of the total resources of the mining area.The porphyry type mineralization occurs in the inner-and exo-contact zone between hypo-volcanic complex body and overlying volcanic rocks as well as volcanic clastic rocks,especially in the inner-contact zone.It is the first time that a large-sized porphyry gold deposit was found in the northern margin of North China plate,i.e.,the Bilihe large-size porphyry gold deposit in Sunid Right Banner of Inner Mongolia.In order to identify the porphyry gold（copper）metallogenic age,the authors used Re-Os isotope to test 6 molybdnite samples collected from the porphyry,which yielded the isochron age of（272.7±1.6）Ma（MSWD=0.57）.Redefinition of the late Paleozoic ore-forming geological event of the Bilihe gold deposit has provided new evidence for the convergent plate structural system in the northern part of North China in late Paleozoic,recognized some basic geological problems of the northern part of North China,and given enlightenments in search for low temperature shallow-seated porphyry gold-polymetallic deposits in the magmatic arc environment of the middle-east segments of the Central Asian Orogenic Belt in late Paleozoic.