山东胶东地区盘子涧金矿成矿流体He-Ar同位素地球化学特征

He-Ar Isotope Geochemical Characteristics of Ore-forming Fluids for Panzijian Gold Deposit in Jiaodong Area of Shandong,China

盘子涧金矿地处山东胶东地区蓬莱—栖霞金成矿带南部,是典型的石英脉型金矿,Au品位高,目前对该矿床成矿流体来源的研究尚不深入。在详细的矿相学观察及黄铁矿显微结构研究基础上,对盘子涧金矿主成矿阶段(石英-黄铁矿(绢云母)阶段和金-石英-多金属硫化物阶段)的载金黄铁矿进行了流体包裹体He-Ar同位素组成分析。结果表明:盘子涧金矿载金黄铁矿中流体包裹体的3He丰度为(3.49~8.50)×10^-14 cm^3 STP·g^-1,4He丰度为(2.46~5.06)×10^-8 cm^3 STP·g^-1,3He/4He值为0.8 Ra^1.2 Ra(Ra为大气3He/4He值,Ra=1.39×10^-6),成矿流体表现出以富集地幔为主导的壳幔混合特征;40Ar丰度为(1.02~2.65)×10^-7 cm^3 STP·g^-1,40Ar/36Ar值为896.3~1724.1,是大气饱和水40Ar/36Ar值的2~3倍,与中国东北部幔源岩样品40Ar/36Ar值相近,推测成矿流体主要来源于富集地幔,成矿流体中存在着一定量的地壳放射性成因40Ar,表明地壳流体参与了成矿作用。综上所述,推断山东胶东地区盘子涧金矿成矿流体为以富集地幔流体为主导的壳幔混合流体。

Panzijian gold deposit is located in the southern of Penglai-Qixia gold metallogenic belt,Jiaodong area,Shandong,which is a typical quartz vein type of gold deposit with high gold grade.However,the source and characteristic of ore-forming fluid are still controversial.Based on the theory of mineral microscopy and microstructure of pyrite,He-Ar isotopic composition of fluid inclusions from gold-bearing pyrite at the main metallogenic stages(quartz-pyrite(sericite)and gold-quartz-polymetallic sulfide stages)in Panzijian gold deposit was measured.The results show that the abundances of 3He of fluid inclusions from gold-bearing pyrite in Panzijian gold deposit are(3.49-8.50)×10^-14 cm^3 STP·g^-1,the abundances of 4He are(2.46-5.06)×10^-8 cm^3 STP·g^-1,and 3He/4He ratios are 0.8 Ra-1.2 Ra(Ra is 3He/4He ratio in air,Ra=1.39×10^-6),indicating that the ore-forming fluid exhibits crust-mantle mixing characteristics dominated by enriched mantle;the abundances of 40Ar are(1.02-2.65)×10^-7 cm^3 STP·g^-1,and 40Ar/36Ar ratios are 896.3-1724.1,which are 2-3 times of the ratio of atmospheric saturated water,but similar to the ratios of samples from mantle-derived rocks in the northeastern China,indicating that the ore-forming fluid mainly comes from enriched mantle,and the crustal fluid also participates in mineralization,because there is a certain amount of 40Ar of crustal radioactivity in the ore-forming fluid.Therefore,it is believed that ore-forming fluid in Panzijian gold deposit is a crust-mantle mixed fluid dominated by enriched mantle fluid.