滇东北矿集区茂租铅锌矿床地球化学特征

C,O,Sr Isotope and REE Geochemistry of Maozu Pb-Zn Deposit in Northeastern Yunnan Mineral Concentration Area

茂租铅锌矿床位于扬子地台西南缘,是滇东北矿集区内的一个大型矿床,矿体主要呈似层状产于震旦系灯影组白云岩中;矿石矿物以闪锌矿为主,次为方铅矿;脉石矿物主要为白云石、方解石和萤石。本文对该矿床中与铅锌矿密切共生的团块状白云石、方解石和萤石以及围岩灯影组白云岩的REE地球化学特征和C、O、Sr同位素进行了对比研究。结果表明:团块状白云石和方解石的稀土配分模式、C同位素和Sr同位素比值与围岩灯影组白云岩比较接近,表明形成团块状白云石和方解石的成矿流体主要来源于围岩灯影组白云岩的溶解;但这两种矿物的稀土总量ΣREE高于灯影组白云岩,说明成矿流体除了主要由围岩提供REE外,还有部分其他富含REE流体的加入。萤石则具有LREE亏损和分配曲线相对平缓的稀土配分模式特征,表明萤石形成于成矿的晚阶段,有更多的外部流体的加入。团块状白云石、方解石和萤石表现出明显的Eu正异常,且团块状白云石和方解石的O同位素低于灯影组白云岩,反映了存在较高温度的流体活动,这3种脉石矿物是由高温热液流体形成的。灯影组白云岩和3种脉石矿物都具有明显的Ce负异常,说明成矿流体可能主要来源于地层循环水,继承了围岩的Ce负异常特征。方解石和萤石的Sr同位素比值高于围岩震旦系灯影组白云岩和峨眉山玄武岩,但小于基底岩石昆阳群和会理群,说明成矿流体主要由赋矿围岩等沉积地层中的循环流体与流经了基底岩石的深部流体混合形成。

The Maozu Pb-Zn deposit is a large deposit located in the northeastern Yunnan metallogenic province at the southwestern margin of the Yangtze plate.The ore-bodies are stratified and hosted in dolostone of Sinian Dengying Formation.The ore minerals are primarily sphalerite and galena,and the gangue minerals are mainly dolomite,calcite and fluorite.The C,O,Sr isotopes and REE geochemistry of the massive hydrothermal dolomite,calcite,fluorite and surrounding rocks were analyzed.The results show that the chondrite-normalized curves,δ13 C and 87 Sr/86 Sr values of the massive hydrothermal dolomite and calcite are similar to those of the Sinian dolostone,indicating that C,O and Sr were mainly derived from the dissolution of the host rock.The massive hydrothermal dolomite and calcite have higherΣREE than those of the surrounding rocks,implying that some other fluid with much higherΣREE joined the ore-forming fluid.Fluorite is characterized by LREE depletion,and the chondrite-normalized curve is quite consistent,indicating that fluorite was formed at a later stage with more other fluid joined.The massive hydrothermal dolomite,calcite and fluorite show that positive Eu anomalies,and theδ18 O values of the massive hydrothermal dolomite and calcite are lower than those of the host rock of the Sinian dolostone,indicating that these three gangue minerals might have been formed by high temperature fluid.The Sinian dolostone and the three kinds of gangue minerals show obvious negative Ce anomalies,implying that the ore-forming fluid might mainly come from Sinian Dengying Formation,which inherited the characteristics of the surrounding Sinian rocks.The 87 Sr/86 Sr ratios of calcite and fluorite are higher than those of the Permian Emeishan basalt and surrounding rocks of Sinian dolostone,but lower than those of the Proterozoic basement rocks(Kunyang and Huili Group).So,it is likely that the ore-forming fluid might mainly come from the surrounding rocks of Sinian Dengying Formation and other strata,and then mixed with the fluid that derived from or flowed through the Proterozoic basement rocks.