吉林省和龙地区鸡南BIF型铁矿床含矿建造地球化学特征及形成时代

鸡南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接壤的龙岗地块北部，是东北地区发现较早的BIF型铁矿床之一。该矿床铁矿体主要呈层状、似层状、扁豆状赋存于鞍山群鸡南组上段中部层位，含矿岩石以黑云斜长片麻岩、角闪黑云斜长片麻岩、黑云角闪斜长片麻岩及斜长角闪岩为主，为角闪岩相的中低级区域变质岩系；主要矿石类型为条带状磁铁石英岩型和块状磁铁角闪岩型。为确定该矿床含矿建造的原岩、变质时代及构造背景，重点对含矿岩系中的斜长角闪岩进行了岩石地球化学和锆石U-Pb年代学研究。结果表明：斜长角闪岩的地球化学特征表现为富集大离子亲石元素、轻微富集重稀土元素；主量元素质量分数与中性-基性岩类基本相似，结合原岩恢复图解，判断其原岩类型为亚碱性玄武岩（拉斑玄武岩），形成于弧后盆地背景；LA-ICP-MS锆石U-Pb年代学研究中，2个较老的锆石测点年龄分别为（2 468±15）和（2 469±9）Ma，代表区内峰期变质年龄（约2 460 Ma），26个锆石测点的测年数据较为集中，加权平均年龄为（2 275±25）Ma，代表区内退变质年龄。通过与国内外典型BIF型铁矿床的对比研究认为，区内的鸡南铁矿与官地铁矿同属Algoma型铁矿床。

Geochemistry and Geochronology of Ore-Bearing Formation in Jinan BIF-Type Iron Deposit in Helong Area,Jilin Province

Jinan iron deposit is one of the BIF-type of deposits discovered early in the Northeast China, which is located in the north part of Longgang massif, at the joint of the North China craton and the Xing'an-Mongolia orogenic belt. The layered, stratified, and lenticular iron orebodies are mainly hosted within the metamorphic rocks of Jinan Formation, Anshan Group. The ore-bearing rocks mainly include biotite plagioclase gneiss, amphibole biotite plagioclase gneiss, biotite amphibole plagioclase gneiss, and amphibolite, which experienced amphibolite facies regional metamorphism. The ore types are mainly comprised of BIF-type and massive magnetite amphibolite type. To determine the tectonic setting of ore-bearing formation of Jinan deposit, the geochemical analysis and LA-ICP-MS were conducted for the intermediate-basic rocks. The geological and geochemical features, together with the protolith re-constrution diagrams, indicate that the protolith of the amphibolite is sub-alkaline basalt (tholeiite) formed in the back arc basin. The LA-ICP-MS zircon U-Pb dating of the amphibolite shows that the ages of two old metamorphic zircons are (2 468±15) and (2 469±9) Ma, representing the peak metamorphism age in this area (~2 460 Ma). The concentrated ages of 26 metamorphic zircons were (2 275±25) Ma, representing the retrograde metamorphic age in the area. A comprehensive comparison with the typical BIFs both at home and abroad indicates that Jinan and Guandi iron deposit in Helong area belongs to Algoma-type.