甘肃和政大峡铜金矿床闪长岩锆石SHRIMP U-Pb法同位素定年及其地质意义

大峡铜金矿床位于中秦岭前陆盆地构造区,即西秦岭北部断褶带与中部裂陷槽之间的过渡部位,属于典型的秦岭复合型大陆碰撞造山带的组成部分。矿体呈扁豆体状或透镜体状产出于闪长岩岩体围岩接触带的矽卡岩带内及闪长岩岩体内部张性裂隙中,矿石中金属矿物主要为黄铁矿、黄铜矿。黄铁矿为主要的载金矿物,矿石以块状、星散浸染状、脉状构造为主。对与成矿有关的闪长岩样品中锆石的12个测试点用SHRIMP锆石U-Pb法得出206Pb/238U加权平均年龄值为（219.1±2.1）Ma,表明闪长岩成岩时代为中—晚三叠世的印支末期,岩体形成于印支末期中酸性岩浆活动。结合矿床地质特征和前人的研究成果认为,大峡铜金矿床具有造山型金矿床的成矿特点,为与印支末期造山作用有关的矽卡岩型—石英脉型铜金矿床。

U-Pb isotopic determination by SHRIMP method for zirconium in diorite of Hezheng Daxia copper-gold deposit in Gansu Province and its geological significances

Hezheng Daxia copper-gold deposit locates in foreland basin structure area of middle Qinling Mountains,i.e.the transition part between the fracture fold belt of northern west Qinling Mountains and the collapsed geosyncline of middle-west Qinling Mountains,belonging to a part of typical Qinling complex collisonal orogenic belt.The pisolitic and lenticular orebody occurs in skarn belt that distributes in contact zones linking dioritic rock with country rock and within the tensile fractures inside dioritic rock.Pyrite and chalcopyrite are the main metallic mineral composition in ore.Pyrite is the main carrier of gold mineral,taking form of block structures,scattered,disseminated structures and vein structures.Based on the U-Pb dating of zircon by SHRIMP on 12 test points of zircons from a dioritic sample that is related with the metallogenic process,a weighted average 206Pb/238U age of（219.1±2.1）Ma was obtained,showing that the dioritic diagenetic era was in end indosinian age of middle-late Triassic.The rock mass originated in acid magmatic intrusive movement in end Indonisian movement period.Associating geological characteristics of ore deposit and predecessors＇ research,the paper considers that there are geological features of orogenic gold deposits in Hezheng Daxia copper-gold deposit and the deposit is a skarn-quarts vein type copper-gold deposit that is related to orogeny in end Indonisian period.