胶东邢家山大型钼矿地质地球化学特征及成因意义

Geological-geochemical characteristics of the Xingjiashan Mo deposit in Jiaodong and their geological significance

邢家山钼矿床是胶东唯一达大型规模的矽卡岩型钼(钨)矿,本文在详细野外调研的基础上,划分了成矿期次,通过元素地球化学及同位素地球化学示踪成矿物质来源及形成时代并结合区域成矿背景探讨了成矿机制。该矿床成矿过程可划分为岩浆热液期(包括早期矽卡岩阶段、中期硫化物阶段和晚期碳酸盐岩阶段)和表生氧化期,钼矿化主要发生于中期硫化物阶段,辉钼矿主要赋存于石榴石透辉石矽卡岩和透辉石符山石矽卡岩中,为岩浆热液交代作用过程产物。成矿母岩幸福山岩体中SiO2、Al2O3和Fe2O3等物质迁出,为矽卡岩矿物形成提供了丰富的物源,矽卡岩和花岗岩的稀土和微量元素配分相似,显示二者具有成因关系,稀土明显富集LREE;钼矿化矽卡岩中δEu、δCe的变化较小,离矿区较远的铅锌矿化大理岩中δEu显示较小的负异常、δCe显示较弱正异常。C-O同位素测试数据显示,大理岩中C来源于海相碳酸盐岩,而热液方解石脉中C主要来源于岩浆岩;辉钼矿中Re含量较低指示着成矿物质来源于下地壳。该矿属于形成于燕山早期的岩浆接触交代矽卡岩型钼矿床。

The Xingjiashan Mo-W deposit is the only large-size molybdenum deposit in Jiaodong,which is well known for numerous gold orefields.In order to find out the ore-forming mechanism of this deposit,the authors conducted systematic geological survey and geochemical analysis in the Xingjiashan Mo deposit.The results show that the Xingjiashan Mo deposit has experienced magmatic hydrothermal period （comprising skarn stage,quartz-sulfides stage and carbonates stage） and supergene oxidation period.Molybdenite mainly occurs in garnet-vesuvianite skarn of the quartz-sulfidies stage.Geochemical data indicate that substances like SiO2,Al2O3,TiO2 and Fe2O3 migrated into the skarn from Xingfushan monozie granite,while CaO and MgO were brought outward.The migration of oxides provided enough substance for the formation of skarn minerals.The obvious similarity of REE patterns and spider diagrams between skarn rocks,stock and marble implies a closely genetic link between them.Besides,the values of δEu and δCe rising from ores to remote Pb-Zn mineralization marble might record the environment change from reducing to oxidizing in the post-ore stage.The C-O isotopic compositions of calcite veins also show the granitic origin features.In addition,the low Re content in molybdenum of this deposit may indicate that Mo was derived from the lower crust.The Xingjiashan Mo deposit is a typical contact metasomatic skarn deposit formed in early Yanshanian period.