钦杭成矿带南段盘龙铅锌矿成矿体系环境分析--来自矿石组构的限定

Metallogenic Conditions of the Panlong Pb-Zn Deposit in the Southern Section of the Qinhang Metallogenic Belt: Constraint from Ore Fabric

盘龙铅锌矿位于钦杭成矿带南段,为近年来新发现的大型喷流-沉积(SEDEX)型铅锌矿床。矿体严格受控于泥盆纪上伦组白云岩。本文基于岩相学研究,系统分析了盘龙铅锌矿矿石组构特征,识别出SEDEX原生成矿阶段形成的条带状、条纹状、浸染状、草莓状、(变)胶状沉积构造,后期改造的网脉状、角砾状、环带构造以及交代、压力结构。本研究认为,成矿包括原生沉积期、活化改造期和地表氧化期,其中原生沉积期又可分为白云石-黄铁矿阶段和硫化物沉淀阶段。扫描电镜(SEM)分析显示,盘龙铅锌矿多数硫化物颗粒很细小,黄铁矿存在草莓状、胶状、五角十二面体的不同形貌特征,重晶石存在浑圆细粒状、放射状、脉状三种形貌,表征盘龙铅锌矿的成矿过程中体系环境经历了温度先升后降,p H先降后升,氧化性逐渐降低的变化。

The Panlong lead-zinc deposit,located in the southern section of the Qinhang metallogenic belt,is a large-scale one discovered in recent years.Its ore bodies are hosted in the Lower Devonian Shanglun Formation dolostone with stratiform,lenticular and brecciform textures.The observation of ores and thin section shows that sulfides were preserved with layered-banded,disseminated,colloidal,and framboidal structures which formed in the primary sedimentary and stockwork,zonal,metasomatic,and pressure structures in the late stage of reformation.Then three metallogenic stages are recognized：（1）primary sedimentary stage,（2）reformed stage,and（3）surface oxidation stage.The observation of SEM shows that the sulfide is small-sized.Three types of morphology of pyrite with framboidal,colloidal,and pyritohedron are identified,i.e.,rounded-,rosette-and vein-type barites.We infer that the Panlong lead-zinc deposit during the ore-forming process experienced temperature increase and then decrease,p H decrease and then increase,and gradual oxidation decrease.Taken regional evolution into consideration,the Panlong Pb-Zn deposit is defined as a reformed SEDEX one.