滇东北矿集区茂租铅锌矿床热液白云石稀土元素特征

摘要

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、萤石和方解石.矿床的矿化蚀变分带明显,从围岩到矿体,矿化蚀变分带分别为:斑点状白云石化带、脉状白云石化带、星点状矿化带、细脉浸染状矿化带和矿体.白云石是该矿床的重要脉石矿物,除了震旦系灯影组的微晶-细晶白云石外,与成矿热液活动有关的白云石主要有斑点状白云石、脉状白云石和团块状白云石.文章对茂租铅锌矿床3种热液白云石及围岩灯影组白云岩的稀土元素地球化学特征进行了对比研究.结果表明:3种热液白云石与灯影组白云岩的稀土元素配分模式比较接近,总体上具有稀土元素总量低、轻稀土元素富集和Ce元素负异常的特征,这些相似的稀土元素特征表明3种蚀变白云石与围岩之间存在着成因联系.灯影组白云岩ΣREE含量较低,具有Eu元素负异常,而脉状和团块状热液白云石具有明显的Eu元素正异常,反映了存在较高温度的流体活动,热液蚀变白云岩是由高温热液流体形成.斑点状热液白云石Eu元素异常不太明显,可能是由于蚀变强度较弱,继承了原岩Eu元素负异常的特征.团块状白云石ΣREE和w(Y)、w(Sm)较高,表明有其他REE富集流体的加入.3种热液白云石是由高温流体形成,流体主要来源于地层,并有其他富含REE流体加入.%The Maozu Pb-Zn deposit is a large-sized deposit,which is located in the northeastern Yunnan metallogenic province,on the southwestern margin of the Yangtze Plate.The orebodies are stratiform and hosted in dolostone of the Sinian Dengying Formation.The ore minerals are primarily sphalerite and galena,and the gangue minerals comprise dolomite,fluorite and calcite.The mineralization and alteration zonation of this deposit is very obvious:from the surrounding rock to the orebody,it can be divided into spotted dolomitization,vein dolomitization,star-like mineralization,veinlet-disseminated mineralization and orebody.Dolomite is one of the most important gangue minerals.There are spotted,vein and massive hydrothermal dolomites,in addition to the microcrystalline and finegrained host rock of the Sinian dolostone.These three hydrothermal dolomites were related to the ore-forming fluid.The REE geochemistry of these three hydrothermal dolomites and surrounding rocks was analyzed.The results show that the chondrite-normalized curves of the three types of hydrothermal dolomite and the surrounding rocks of Sinian dolostone are quite consistent.Both the hydrothermal dolomite and surrounding rocks show obvious negative Ce anomalies,and their REE content is not high with LREE enrichment.These similar REE geochemical characteristics indicate that the three types of hydrothermal dolomites were related to the surrounding rocks of Sinian dolostone.The surrounding rocks of Sinian dolostone have low REE content and show obvious negative Eu anomalies,whereas the vein and massive hydrothermal dolomites show obvious positive Eu anomalies.This indicates that the hydrothermal dolomite might have precipitated from a relatively high temperature fluid.The positive Eu anomalies of spotted hydrothermal dolomites are not obvious.The alteration was not strong and inherited the characteristics from surrounding rocks of Sinian dolostone.The massive hydrothermal dolomites have higher ΣREE,Y and Sm values,implying that other fluids with much higher ΣREE took part in the hydrothermal fluid.So,it is probable that the three types of hydrothermal dolomites might have precipitated from a relatively high temperature fluid.Dengying dolostones might have served as the main material source and,in addition,other fluid with much higher ΣREE also provided some material source.