基于低温热年代学技术的胶西北玲珑、焦家金矿床隆升剥露差异对比研究

To determine the exhumation degree of ore deposits is one of the key issues in mineral exploration and prospecting. However, due to lack of effective techniques, this problem has restricted the further improvement of metallogenic prediction level. In recent years, the booming development of low temperature thermochronology may shed light on the issue. Based on our previous studies, the work take the Jiaojia and Linglong gold deposits (two representative deposits from Northwest Jiaodong Peninsula) as the research objects, sample granitic/metamorphic rocks from each seledted levels around - hanging/foot walls of ore-hosted faults, and then perform zircon and apatite (U-Th)/He microscope and fission track dating. Integrating partial retention/annealing zone, age-elevation track, FT fission length and thermal history modeling and combined with the previous recognitions of rocks/ores-forming, regional tectonic-magmatic processes and geodynamic settings, this work aims to 1) determine the motion direction and displacement amount between the hanging- and foot-walls of ore-hosted faults; 2) elucidate the exhumation differences between the two deposits and the exploration potential in deep; 3) reveal the relationship between exhumation and regional geological events; and 4) construct an available methodological system for exhumation assessment and provide a reliable scientific criterion for exploration potential appraisal applied in mineral deposits.

矿床剥露程度是找矿评价的关键问题之一。但是，长期以来由于缺乏有效的技术手段，这个问题一直制约着成矿预测水平的进一步提高。近年来快速发展的低温热年代学技术有可能为这个问题的解决提供一条可行的途径。课题在前期研究基础上，以胶西北地区两个典型金矿床（焦家和玲珑）为研究对象，围绕两个矿床控矿断裂带上、下盘相同高程自上而下系统采集花岗岩/变质岩样品，挑选锆石和磷灰石单矿物，开展锆石和磷灰石微区原位（U-Th）/He和裂变径迹（FT）低温热年代学研究，通过He局部保留带或FT局部淬火带，年龄-高程轨迹，FT裂变径迹长度和热史模拟，结合前人成岩成矿、区域构造岩浆活动和地球动力学背景的研究成果，力图①确定控矿断裂上、下盘运动方向及位移量；②查明两个矿床剥露差异量；③揭示剥露作用与区域地质事件联系；及④构建一套本区可以推广的矿床剥露差异对比研究方法体系，为找矿潜力评价服务。

利用锆石、磷灰石（U-Th）/He和磷灰石FT技术相结合，对胶西北玲珑、焦家两个矿床成矿后隆升剥蚀过程及深部找矿潜力进行对比研究，探索该技术应用于非斑岩型矿床成矿隆升剥蚀研究的应用效果及应用前景。研究结果表明，玲珑、焦家两个矿区锆石ZHe年龄相对集中分布于80 – 100 Ma，磷灰石AFT和AHe年龄较分散，相对集中分布于80 - 100 Ma、55 – 65 Ma、30 – 40 Ma和10 – 20 Ma等多个年龄区间。年龄-高程关系图显示，玲珑矿区不同高程样品ZHe年龄-高程之间没有明显变化趋势，焦家矿区显示上、下台阶状分布，磷灰石AHe年龄-高程之间呈多台阶状分布。热史模拟结果表明两个矿区均先后经历过三次幕式快速构造隆升。结合区域构造运动，认为本区的低温热年龄是对构造运动的直接响应。其中80 – 100 Ma和60 – 65 Ma年龄是对两次板块碰撞构造运动的响应，40 – 45 Ma和20 – 25 Ma是对两次局部构造差异性运动的响应。前两次构造运动被一致记录在不同地区的构造隆升热史演化记录中，但是，后者不同地区各不相同。基于低温热年代学年龄分布特征，认为玲珑矿区成矿后隆升剥蚀程度比焦家矿区多了大约1 Km，因此，焦家矿区深部找矿潜力好于玲珑矿区。与传统矿床隆升剥蚀评价方法相比，该方法具有时空一体定量评估的能力，具有进一步应用前景。