摘要
矿床形成深度及成矿后的变化与保存是目前深部找矿亟待解决的关键问题.选取4个成矿年龄均为130Ma左右的典型玢岩铁矿,分别为宁芜盆地中矿体已经出露地表并经受过剥蚀的东山铁矿和矿体埋藏距地表40m以下的梅山铁矿,庐枞盆地中矿体埋藏距地表400m以下的罗河铁矿和矿体埋藏距地表600m以下的泥河铁矿,采用双重定年技术对这4个矿床主成矿阶段矿石矿物组合中的磷灰石进行了裂变径迹研究.结果显示:(1)东山铁矿AFT合并年龄为106.3±5.4Ma,梅山铁矿为94.2±4.0Ma,罗河铁矿为81.3±4.0Ma,泥河铁矿为79.1±3.3Ma,且AFT年龄和围限径迹长度随样品埋藏深度减小而增大,分别更接近成矿年龄和原始径迹长度,显示4个矿床成矿后差异抬升剥蚀作用导致磷灰石样品通过部分退火带时的冷却速率存在差别;(2)热史模拟反映这4个矿床成矿后均经历了早期短暂快速冷却和后期长期缓慢冷却2个阶段,两阶段之间的拐点温度接近,对应深度为1.7～1.8km,结合其他证据证明宁芜、庐枞盆地玢岩铁矿成矿深度均为2km左右.说明这4个矿床现今埋藏深度的差异主要是由于成矿后的抬升、剥蚀作用导致.(3)自110Ma以来宁芜盆地的整体抬升剥蚀幅度大于庐枞盆地,导致宁芜盆地大部分玢岩铁矿矿体接近或暴露地表.2个盆地早期抬升剥蚀作用与区域性黄桥事件同步.
The metallogenic depth and post-mineralization uplift and denudation are the key issues in deep prospecting,which have been weak in the study of mineral deposits due to the absence of effective technology.The authors select Dongshan,Meishan porphyry-like iron deposits in Ningwu basin and Nihe,Luohe porphyry-like iron deposits in Luzong basin formed about ~130 Ma as the study subjects for the metallogenic depth and post-mineralization uplift and denudation of porphyry-like iron deposits,with the help of AFT analysis of apatites in ore mineral assemblages.The results suggest:(1) the pooled AFT ages(1σ) of the four deposits are 106.3±5.4 Ma,94.2±4.0 Ma,81.3±4.0 Ma and 79.1±3.3 Ma,respectively,showing the ore bodies of four deposits passed the PAZ successively.The AFT ages and confined track lengths decrease with the increase of buried depth of samples and become close to the mineralization ages and the initial confined track length,which are possibly controlled by diverse uplift and denudation after mineralization leading to the different cooling rates while the samples passed the PAZ.(2) The thermal histories of AFT modeling reflect that there are two different cooling stages,namely the rapid cooling progress caused by losing of heat source and the slow cooling progress caused by uplift.The temperature inflection points between the two stages of the four deposits are probably identical,corresponding to a depth of 1.7 to 1.8 km.(3) Since 110 Ma,the uplift and denudation rate of the Ningwu basin have been greater than those of Luzong basin,so that most ore deposits in Ningwu basin buried shallowly or even exposed to the surface.The early uplift and denudation were controlled by the regional Yellow Bridge tectonic event.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2012年第5期966-980,共15页
Earth Science-Journal of China University of Geosciences
基金
全国危机矿山找矿典型矿床研究专项(No.20109904)
