延边地区官地铁矿床形成时代及其构造意义

官地铁矿床位于吉林省和龙地区,地处华北克拉通北缘与兴蒙造山带东段接合带附近的和龙地块北部。主矿体呈层状、似层状、透镜状赋存于鞍山群甲山组下段;含矿岩石以磁铁石英岩、长英片麻岩、云母片岩、斜长浅粒岩为主,其变质程度为绿片岩相-角闪岩相的中低级区域变质;主要矿石类型为条带状铁建造。为确定矿床的形成时代,重点对含矿变质岩系中的斜长浅粒岩开展了LA-ICP-MS锆石U-Pb年代学研究。结果表明,官地铁矿床含矿变质岩的原岩(酸性火山岩)形成于(2551±44)Ma,在(2525±48)Ma经历区域变质作用,随后又受古元古代构造热事件的改造。官地铁矿床与华北克拉通内鞍山地区铁矿床具有相似的成矿地质条件、矿床特征和形成时代,同属于鞍山式(阿尔戈马型)沉积变质型铁矿床。根据测年结果,并与邻区的锆石年龄对比分析,认为和龙地块应归属华北克拉通,这为索伦-西拉木伦-长春缝合带的东延问题研究提供了新的证据。

Formation age and tectonic significance of Guandi iron deposit in Yanbian area, Jilin Province

The Guandi iron deposit is located in Helong area of eastern Jilin Province, at the north part of the Helong massif which is sandwiched between North China Craton and the Xing''an-Mongolia orogenic belt. The iron orebodies, exhibiting stratoid and lenticular forms, are mainly hosted in the metamorphic rocks of Jiashan Formation, Archean Anshan Group. The ore-bearing rocks mainly include magnetite-quartzite, quartz-feldspathic gneiss, plakite, and plagioclase leucoleptite, which underwent greenschist to amphibolite facies regional metamorphism. The major ore type is banded iron formation (BIF). In order to determine the formation age of the iron deposit, the authors carried out the LA-ICP-MS zircon U-Pb dating of plagioclase leucoleptite. The results indicate that the protolith, which was acid volcanic rock, formed at (2551±44) Ma and experienced the regional metamorphism at (2525±48) Ma. Afterwards, it was influenced by the Paleoproterozoic thermo-tectonic event. Because the Guandi iron deposit is similar to the Anshan-type iron deposit in North China Craton in such aspects as metallogenetic geological conditions, deposit characteristics and formation age, it can be classified as the Anshan-type sedimentary-metamorphic iron deposit. The Helong massif should belong to the North China Craton based on a comparison of the zircon ages with the adjacent areas, and this may be new evidence for the eastward termination of the Solonker-Xar Moron River-Changchun Suture in the Yanbian area.