甘肃和政大峡金矿床闪长岩锆石SHRIMP法U-Pb同位素定年及其地质意义

U-Pb Isotopic Determination by SHRIMP Method for Zirconium in Dioritic of Hezhengdaxia Gold Deposit in Gansu Province and Its Geological Meaning

和政大峡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中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。黄铁矿为主要的金的载体矿物,矿石以星散浸染状、脉状构造为主。对一件闪长岩样品中锆石的12个测试点用SHRIMP锆石U-Pb法得出^(206)Pb/^(238)U加权平均年龄值为219.1±2.1 Ma(MSWD=1.8),因此,认为闪长岩成岩时代为中—晚三叠世的印支末期,岩体的形成应源于印支末期中酸性岩浆热液的侵入活动。结合矿床地质特征和前人的研究成果,讨论后认为和政大峡金矿床具有造山型金矿床的成矿特点,为与印支末期—燕山早期造山作用有关的矽卡岩型—热液脉型金矿床。

Hezhengdaxia gold deposit locates in front mainland basin structure area of middle Qinling,the transition part between fracture fold belt of northern west Qinling and collapsed geosyncline of middle west Qinling.Belongs to a part of the typical Qinling compex collisonal orogenic belt.The pisolitic and lenticular orebody produce in skarn that distributes in zones of dioritic rock contacte with country rock and inside tensile fracturesd of dioritic rock.Pyrite and chalcopyrite are the main minerals composition in ore,pyrite is the main carrier gold mineral.Small vein disseminated and vein structures are the main structures of ore.Based on the SHRIMP zircon U-Pb chronologic study of 12 test points of zircons from a dioritic sample obtained a weighted average ^(206)Pb/^(238)U age of(219.1±2.1) Ma(MSWD =1.8).Therefore,the dioritic diagenetic era was in end Indonisian movement period.The rock mass originated in intermediate and acid magmatic intrusive movement in end Indonisian movement period.Combined with geological characteristics of ore deposit and predecessors' researching results,There are the orogenic gold deposit geological features in Hezhengdaxia gold deposit,and deduced it is a skarn-hydrothermal vein type gold deposit that related to orogeny in end Indonisian-early Yanshan period.