辽东五龙金矿鸡心岭断裂的年代学约束及其对成矿潜力的指示
The chronological constraint of Jixinling fault and its implication for metallogenic potential in Wulong gold deposit, Liaodong peninsula, China
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摘要: 五龙金矿是辽东地区形成于早白垩世的代表性石英脉型金矿, 与胶东地区"玲珑式"金矿相似。胶东地区早白垩世金矿受北东向断裂控制且规模宏大, 五龙金矿已知矿体主要赋存于北西向和近南北向断裂内, 其北东向断裂研究程度较低、成矿潜力尚不清楚。针对五龙矿区的鸡心岭断裂开展了地质调查, 对侵位其中的岩脉和热液白云母进行定年, 为断裂内构造-岩浆-热液活动提供年代学约束。调查发现, 鸡心岭断裂整体为脆性变形, 具有多期活动的特征, 依次有煌斑岩、含白云母石英脉和闪长岩脉侵入其中。测年结果显示, 煌斑岩的锆石206Pb/238U年龄加权平均值为132.1±1.7 Ma, 热液白云母的40Ar/39Ar坪年龄为126.8±0.5 Ma, 闪长岩的锆石206Pb/238U年龄加权平均值为112.9±1.4 Ma。年龄数据指示, 鸡心岭断裂在132 Ma之前形成, 在132~113 Ma之间经历了岩浆-热液活动, 依次对应区域上的早白垩世初期北北西-南南东向挤压和早白垩世中期北西-南东向/北西西-南东东向伸展背景。从现有调查程度看, 鸡心岭断裂较胶东地区北东向断裂具有序次低、规模小、构造和流体活动较弱的特征。辽东地区燕山期金矿找矿应注意关注更高序次的低角度断裂, 五龙一带的北东向断裂找矿工作应优先评价断裂走向变化、深部由陡变缓的部位。Abstract: Wulong gold deposit is a typical quartz vein-type ore deposit formed in the Early Crataceous in Liaodong peninsula, similar in many aspects to the Linglong-type gold deposit in Jiaodong area.The gold deposits in Jiaodong area mainly occurred in the NE trending fault.However, most of orebodies in the Wulong deposit are controlled by the NW and N-S trending fault.The study of the NE trending fault are limited within the Wulong deposit and their ore-potential are still unclear.Geological survey were conducted for Jixinling fault, and chronology study of dikes and hydrothermal muscovite in the fault were also carried out.Jixinling fault, being brittle, experienced multi-stage of structural motion, was intruded by lamphoryrye dikes, muscovite-bearing quartz veins and diorite dikes sequentially.U-Pb dating of the zircons from the lamprophyre and the diorite yields 206Pb/238U mean age of 132.1 ±1.7 Ma and 112.9 ±1.4 Ma, respectively.The hydrothermal muscovite gives a 40Ar/39Ar plateau age of 126.8 ±0.51 Ma.It is indicated that, Jixinling fault was formed before 132 Ma, and magma and hydrothermal motion occurred in the fault during 132~113 Ma.The Jixinling fault fracturing, the intrusion of dikes and veins were probably correlated to the NNW-SSE compression in the earlier time of Early Crataceous, NW-SE/NWW-SEE extension in the middle of Early Crataceous, respectively.Jixinling fault was formed in a lower order than NE trending fault in Jiaodong area, with less structural intensity, smaller fracture zone and alteration range.The further exploration for NE trending faults of Early Crataceous gold systems in Liaodong peninsula should focus on low-angle faults with higher order, and more attention should be paid to the area where the faults' attitude switches suddenly for the NE trending faults in the Wulong orefield.