钦杭成矿带金山造山型金矿成矿年代学研究

Geochronological Study on the Jinshan Orogenic Gold Deposit in the Qinhang Metallogenic Belt

华南钦杭成矿带位于扬子地块与华夏地块的构造拼贴带,其北东段以发育铜金铅锌银多金属矿床为特色。金山金矿是该带金储量最大的金矿床,目前针对该矿床的成因模式和形成时代都还存在很大争议。选取金山金矿的石英脉型金矿体,在详细的矿床地质和流体包裹体研究基础上,开展石英流体包裹体Rb-Sr同位素定年工作。研究结果表明:阳山矿段石英脉型V5金矿体和湾家坞矿段石英脉型V7金矿体的石英流体包裹体Rb-Sr等时线年龄分别为(751±98)Ma和(754±62)Ma,二者在误差范围内保持一致。此外,金山金矿含金石英脉中87Sr/86Sr同位素初始比值较低,为(0.7056±0.0039)^(0.7103±0.0025),指示运移金的成矿流体主要来自于低成熟度的基底地层。上述同位素证据支持金山金矿是新元古代的造山型金矿,而不是加里东期或燕山期构造岩浆的产物。

Qinhang metallogenic belt is located along the suture zone between Yangtze and Cathaysia blocks in South China,and its northeastern section is featured by large scale Cu-Au-Pb-Zn-Ag polymetallic deposits.Jinshan gold deposit is one of the largest gold deposits in this belt,the ore genesis and formation age remain in dispute.On the basis of detailed ore deposit geology and fluid inclusion studies,the quartz vein type orebodies was selected to conduct quartz fluid inclusion Rb-Sr isotope dating.The results show that samples from the V5 gold orebodies give a quartz fluid inclusion Rb-Sr isochron age of(751±98)Ma,and those from the V7 gold orebodies yield a quartz fluid inclusion Rb-Sr isochron age of(754±62)Ma.Two ages are consistent with the error ranges.In addition,the initial 87Sr/86Sr values of fluid inclusions hosted in auriferous quartz are(0.7056±0.0039)^(0.7103±0.0025),suggesting that the ore-forming fluids were derived from the low maturity basement strata.To sum up,Jinshan gold deposit belongs to the Neoproterozoic orogenic gold deposit,instead of Caledonian or Yanshanian periods of tectono-magmatic products.