东秦岭钼多金属成矿带夜长坪斑岩-矽卡岩型钼钨矿床磁铁矿成因类型与指示意义  

Genesis types and indications of magnetite in Yechangping porphyry-skarn type Mo-W deposit,East Qinling Mo polymetallic metallogenic belt

作　　者：晏国龙[1] 祁小军[1] 肖淳[1] 蒋昊原 Yan Guolong;Qi Xiaojun;Xiao Chun;Jiang Haoyuan(Geological Corporation of China Gold Group;China National Gold Group Co.,Ltd.)

机构地区：[1]中国黄金集团地质有限公司 [2]中国黄金集团有限公司

出　　处：《黄金》2024年第11期34-44,共11页Gold

基　　金：中国黄金集团有限公司地质科研项目(ZJZY-2023-KY02)。

摘　　要：夜长坪超大型斑岩-矽卡岩型钼钨矿床位于东秦岭钼多金属成矿带,保存了完整的矽卡岩形成演化及成矿作用的重要信息。通过详细的野外地质调查及镜下鉴定,将夜长坪钼钨矿床中的磁铁矿划分为3种类型:晚矽卡岩阶段形成以他型粒状或以聚合体形式与黑云母、绢云母、黏土等矿物共生的Mt1型磁铁矿;氧化物阶段形成半自形至自形与石榴子石、透闪石、阳起石等矿物共生的Mt2型磁铁矿;呈稠密浸染状与辉钼矿等硫化物共生,或产出在石英多金属硫化物脉中的Mt3型磁铁矿。电子探针及LA-ICP-MS原位测试分析结果显示:Mt1~Mt3型磁铁矿FeO平均含量逐渐升高,Mt1型磁铁矿富Si、Mg、Na等元素,具有最高的V、Cr、Ti、Al和Mo含量。Mt2型磁铁矿Ti元素含量明显降低,Si含量略有下降,具有最高含量的Mg和Mn。Mt3型磁铁矿中Ti、Si、Na、Ca元素含量均最低。磁铁矿元素变化特征显示,Fe元素易被Si、Ca、Al等元素替换;随磁铁矿的结晶,成矿流体中逐渐富集Mo等成矿元素。磁铁矿成因判别图解显示,Mt1型磁铁矿与另外2种磁铁矿形成物质来源略有不同,Mt1型磁铁矿更偏向于岩浆热液成因,Mt2型磁铁矿和Mt3型磁铁矿则更偏向于变质热液成因,随着Mt2型磁铁矿的形成,赋矿围岩参与成矿的程度逐渐增强。从早期较高温的Mt1型磁铁矿至晚期较低温的Mt3型磁铁矿,V和Ti具有较为明显的正相关关系;流体-岩石作用程度判别图解显示交代作用逐渐增强。因此,在夜长坪钼钨矿床氧逸度的变化和流体-岩石作用程度的逐渐增强是控制成矿的主要因素。Yechangping super-large porphyry-skarn type Mo-W deposit,located in the East Qinling Mo polymetallic metallogenic belt,preserves crucial information on skarn formation evolution and mineralization.Through detailed field geological surveys and microscopic identification,magnetite in Yechangping Mo-W Deposit is classified into 3 types:Mt1 magnetite,formed during the late skarn stage,is granular or in aggregates associated with biotite,sericite,clay minerals,etc.;Mt2 magnetite,formed during the oxide stage,is semi-euhedral to euhedral and associated with garnet,tremolite,actinolite,etc.;and Mt3 magnetite,densely disseminated and associated with molybdenite or occurring in quartz polymetallic sulfide veins.Electron probe and LA-ICP-MS in-situ trace element analysis show that the average FeO content increases progressively from Mt1 to Mt3 magnetite.Mt1 magnetite is rich in elements such as Si,Mg,and Na,and has the highest content of V,Cr,Ti,Al,and Mo.Ti content in Mt2 magnetite decreases significantly,with a slight reduction in Si content and the highest levels of Mg and Mn.Mt3 magnetite has the lowest content of Ti,Si,Na,and Ca.The changes in magnetite element characteristics suggest that Fe is easily replaced by Si,Ca,and Al elements,with Mo and other ore-forming elements gradually enriching in the ore-forming fluids during magnetite crystallization.Genesis discrimination diagrams of magnetite indicate that Mt1 magnetite has a different source material compared to Mt2 and Mt3,tending more toward a magmatic-hydrothermal origin,while Mt2 and Mt3 are more metamorphic hydrothermal in nature.The host wall rock participated more in the mineralization with the formation of Mt2 magnetite.From the higher temperature early Mt1 magnetite to the lower temperature late Mt3 magnetite,V and Ti show a clear positive correlation.Discrimination diagrams for fluid-rock interaction indicate that metasomatism intensifies progressively.Therefore,changes in oxygen fugacity and the increasing degree of fluid-rock interaction in Yechangping

关 键 词：矿物学 斑岩-矽卡岩型 钼钨矿床 磁铁矿 LA-ICP-MS 成因类型 东秦岭 钼多金属成矿带 

分 类 号：TD11[矿业工程—矿山地质测量] P632[天文地球—地质矿产勘探]