承德牛圈银金多金属矿床硫化物Rb-Sr年龄和成矿物质来源分析

An analysis of geological age and materials source of the Niujuan Ag-Au polymetallic deposit in Chengde

在对牛圈矿区实地踏勘、野外观察的基础上,通过岩(矿)石样品同位素、稀土元素及流体包裹体均一温度、成分的测试分析,认为牛圈银金多金属矿床的成矿物质来源于花岗岩。岩(矿)石样品稀土元素分析结果表明,矿石与花岗岩稀土元素配分模式相似,均显示出轻稀土元素分馏较强,重稀土元素分馏较弱,二者均有较强的Eu负异常分布特征,表明矿石与花岗岩之间存在密切的成因联系,即成矿物质来源于花岗岩。石英包裹体中氢氧同位素的研究结果显示,成矿流体具有多来源特征,是岩浆水和循环的大气降水的混合。利用单矿物闪锌矿和共生矿物组合黄铁矿与方铅矿Rb-Sr等时线方法测定了牛圈矿床成矿年龄,测试结果显示矿石矿物的形成年龄为(154.1±2.6)Ma,属于燕山中期,推断与燕山期的岩浆岩侵入有密切关系,上述认识为矿床成因类型厘定提供了理论依据。

On the basis of field reconnaissance,field observation,rock （ore）sample analyses and the application of such means as isotope geochemistry,REE,fluid inclusion homogenization temperature and composition,the authors hold that the ore-forming materials of the Niujuan Ag-Au deposit were derived from guanite.The analytical results of REE from rock （ore） show that the chondrite-normalized REE patterns of rocks and ores from the Niujuan Ag-Au deposit are similar to each other,both assuaming LREE enrichment,HREE depletion and obvious Eu negative anomalies.These characteristics demonstrate that the ore-forming materials of the Niujuan Ag-Au deposit were derived from granite.Researches on hydrogen and oxygen isotopes show that the oreforming fluids were of multiple sources,being the mixture of magrnatic water and circulated atmospheric precipitation.According to the composition of ore minerals,the authors used the Rb-Sr isochron method for monomineral sphalerite and paragenetic mineral assemblage of pyrite and galena to determine the ore-forming age,and the result shows that the age of ore mineral is （154.1±2.6） Ma,belonging to middle Yanshanian period.On such a basis,it is deduced that the formation of the deposit was closely related to Yanshanian magmatite intrusion.The results obtained by the authors provide a theoretical basis for the determination of the genetic type of the ore deposit.