胶东罗山金矿床成矿流体来源:蚀变岩型和石英脉型矿石载金黄铁矿稀土与微量元素特征约束

罗山金矿床是胶东玲珑金矿田最大的金矿床之一,同时发育蚀变岩型矿化和石英脉型矿化。本研究在系统的野外和镜下工作基础上,利用电感耦合等离子体质谱(ICP-MS)技术分析了载金黄铁矿的微量和稀土元素,对比了蚀变岩型和石英脉型矿石载金黄铁矿稀土和微量元素特征,探讨了成矿流体的性质与来源。黄铁矿稀土总含量较低,多呈较明显的"右倾"式稀土配分模式,总体表现出负Eu异常,基本无Ce异常; Hf/Sm、Th/La、Nb/La值均<1,推断成矿流体为富Cl的还原性流体。Co/Ni比值范围在0. 08～3. 77,平均值为1. 09; Co/Ni值以及Co、Ni、Bi、Cu和Zn含量均与变质热液型金矿平均含量相近; Y/Ho比值范围总体在21～32之间,与中国东部大陆地壳Y/Ho比值(20～35)基本重合;结合个别样品的弱正Eu异常以及前人的研究成果,推断成矿流体与变质热液类似,主要来源于古太平洋板块俯冲板片脱水和脱碳作用,且可能有长英质岩浆流体和地壳流体的混入。蚀变岩型和石英脉型矿石内的载金黄铁矿的稀土、微量元素组成没有明显区别,Y/Ho、Nb/Ta和Zr/Hf比值变化范围均很小,表明两类矿石的载金黄铁矿为同一期热液活动作用的产物。

Source of Ore-forming Fluids in the Luoshan Gold Deposit,Jiaodong:Constrains from REE and Trace Element Features of Auriferous Pyrite in the Altered-rock Type and Auriferous Quartz Vein Type Ores

The Luoshan gold deposit, one of the biggest gold deposits in the Linglong goldfield, develops both altered-rock type and auriferous quartz vein type mineralization. Based on detailed field and microscopic work, this study measures the trace elements and rare earth elements of the auriferous pyrite with the method of ICP-MS. The characteristics of REE and trace elements in pyrites from the two ore types are compared, and the nature and source of the ore-forming fluids are discussed. The total content of rare earth elements is low, and the REE distribution reveals an obvious light REE enrichment pattern, with negative Eu anomalies and absence of Ce anomalies. The Hf/Sm, Nb/La and Th/La ratios are less than 1, indicating the ore-forming fluids in the Luo-shan gold deposit might be Cl-rich reduced fluids. The Co/Ni ratios of auriferous pyrite range from 0.08 to 3.77, with an average value of 1.09. The Co/Ni ratios and contents of Co, Ni, Bi, Cu and Zn of the pyrite are close to average values of those from metamorphic-hydrothermal type gold deposit. The Y/Ho ratios generally range from 21 to 32, coincident with the continental crust of East China. Combined with weak positive Eu anomalies in few samples, and previous studies, the ore-forming fluids are presumed to be similar to the metamorphic fluid which mainly derived from the dehydration and decarbonization of the subducting paleo-Pacific plate, and may be mixed with felsic magmatic fluid and crustal fluid. There are no obvious differences of REE and trace element composition in the auriferous pyrite from both altered-rock type and auriferous quartz vein type ores, with small Y/Ho, Nb/Ta, and Zr/Hf ranges, which indicate the pyrite from both types of ores was formed in the same hydrothermal activity.