胶东辽上金矿床C、O、S、Pb同位素组成及矿床成因

C,O,S and Pb isotopic compositions and genesis of the Liaoshang gold deposit in Jiaodong Peninsula

辽上金矿床是胶莱盆地东北缘地区近年来新发现的一处特大型金矿床,以黄铁矿、白云石为载金矿物而区别于"焦家式"、"玲珑式"金矿床。为探讨新类型金矿床成矿流体特征和成矿物质来源,对该矿床载金白云石C、O和黄铁矿S、Pb进行了同位素分析。结果显示,载金矿物白云石中δ13CV-PDB值为-4.60‰~-3.60‰,δ18OV-SMOW值集中在9.6‰~10.6‰;黄铁矿δ34S值为+7.2‰~+9.4‰,均值为+8.2‰;黄铁矿206 Pb/204 Pb、207Pb/204 Pb与208 Pb/204 Pb值分别为17.027~17.576、15.435~15.503、37.706~38.205。结合胶莱盆地构造-岩浆演化背景,认为辽上金矿床C-H-O含矿流体主要源于地幔,上升过程中有大气降水参与及壳源成矿物质混入,具有壳幔混合特征,成因类型为含金黄铁矿碳酸盐脉充填型低温热液金矿床。

The Liaoshang gold deposit is a newly discovered superlarge gold deposit on the northeast margin of Jiaolai Basin,which is different from"Jiaojia-type"and"Linglong-type"old deposits by unique gold bearing minerals of pyrite and dolomite.The isotopic analysis of C,O for Au-bearing dolomite and S,Pb for Au-bearing pyrite from this deposit was carried out in order to identify the source of ore-forming materials and fluids for this new type gold deposit.The results show that theδ13CVPDB and theδ18OV-SMOW values of dolomite range from-4.60‰to-3.60‰and 9.6‰to 10.6‰,respectively.Theδ34S values of Au-bearing pyrite vary from+7.2‰to+9.4‰with an average of+8.2‰.The results of Pb isotope from Au-bearing pyrite vary from 17.027 to 17.576,15.435 to15.503,and 37.706 to 38.205 for 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb ratios,respectively.Combined with the tectono-magmatic evolution in the Jiaolai Basin,the authors hold that the ore-bearing C-H-O fluids of the Liaoshang gold deposit mainly originated from the mantle.Furthermore,the meteoric water and crustal ore-forming materials were involved during the ascending process of ore-forming fluids,resulting in the characteristics of crustmantle mixing.In conclusion,the genetic type of Liaoshang gold deposit should be the pyrite-carbonate vein type low temperature hydrothermal gold deposit.