东升庙多金属硫化物矿床主要含矿岩系地质地球化学特征及对矿床成因的指示意义

Geological and geochemical characteristics of the main ore-bearing rock series in the Dongshengmiao superlarge polymetallic sulfide deposit and their implications for ore genesis

东升庙矿床是内蒙古狼山-渣尔泰山成矿带上最大的锌多金属矿床,主要含矿岩系是狼山群第2岩组。通过对矿区地质现象的野外观察和钻孔样品地球化学特征的研究,结合国际上同类矿床最新研究进展,对东升庙矿床主矿体的成矿过程提出了新观点。岩、矿石样品的岩相学研究结果显示,不同岩段的岩、矿石有不同的组构特征:第4岩性段中部菱铁矿矿石为典型的细粒镶嵌结构和块状构造,具明显的化学沉积特征;第4岩性段底部2号矿体中的闪锌矿矿石具半自形-它形晶粒结构或溶蚀结构,多为角砾状构造或块状构造,有明显的充填-交代现象;第3岩性段以绢云石墨片岩为主的黑色岩系网脉状矿化普遍,常见后期热液充填现象。岩矿石样品的地球化学研究结果显示,菱铁矿矿石和闪锌矿矿石有相似的微量元素富集特征和稀土元素配分曲线,可能具有同一物质来源。而第3岩性段的绢云石墨片岩有不同的微量元素富集特征和稀土元素配分曲线,可能是多期热液活动作用的结果。值得一提的是,在2号主矿体硫化物矿石中不但发现有来自于矿体下部的有一定磨圆度的绢云石墨片岩碎屑角砾,还有一些来自上部围岩的含炭质白云大理岩角砾。此类碎屑角砾可能是交代残余或者交代过程中垮塌的产物,无法用同时沉积解释。综合分析认为第3岩性段的网脉状矿化是后期热液充填的结果,而第4岩性段底部的2号矿体是含矿热液选择性交代碳酸盐地层而成矿,菱铁矿矿体是富铁热液运移到海底后沉积生成。相对于传统的喷流沉积成矿方式,本文认为交代作用对东升庙主矿体的形成起到了关键作用。

The Dongshengmiao deposit is a superlarge lead zinc polymetallic deposit occurring in the LangshanZhaertaishan metallogenic belt of Inner Mongolia,and the main ore-bearing rock is the second Formation of Langshan Group.In this paper,the authors combined the study of multiple suites of core samples which cover the main ore-bearing rock series with the recent study of hydrothermal deposits abroad,and arrived at some new understanding of the major orebody of the Dongshengmiao deposit.The rock and ore in different lithologic members have different fabric characteristics：in the middle of the fourth lithologic member,siderite ores show fine mosaic texture and massive structure,with obvious characteristics of chemical sedimentation; at the bottom of the fourth lithologic member,sphalerite ores of the No.2 orebody exhibit hypautomorphic-allotriomorphic crystalline granular texture or dissolution texture,and mostly show massive,banding or brecciated structure,with obvious filling-metasomatic phenomenon; stockwork mineralization is generally existent in the third lithologic member which is sericite-grapholite based,with very common later hydrothermal filling phenomenon.In addition,geochemical study of the rock and ore indicates that siderite ore shares similar trace element enrichment and REE distribution pattern to sphalerite ore,so they may have had the same provenance.However,sericitegrapholite in the third lithologic member has different trace element enrichment features and REE distribution curves,probably resulting from multi-stage hydrothermal activity.It is worth mentioning that we can find dolomitemarble fragment breccia which belongs to upside wall rock and they are different from sericitegrapholite fragment breccia.The dolomite-marble fragment breccias resulted probably from replacement.Comprehensive analysis shows that stockwork mineralization in the third lithologic member was caused by later hydrothermal filling,while the No.2 orebody at the bottom of the fourth lithologic member might have resulted from ore-bearing hydrothermal selective replacement of carbonate strata,and siderite orebody＇ s mineralization might be attributed to the migration of the iron-rich hydrothermal solution to the bottom of ocean and the subsequent precipitation.Ore-bearing hydrothermal replacement played a key role in the ore-forming progress of the major orebody in the Dongshengmiao deposit.The result achieved by the authors has deepened the understanding of the SEDEX deposit.