内蒙古东珺铅锌银矿床质量平衡计算与围岩蚀变特征

Wall rock alteration characteristics and mass balance calculation of Dongjun Pb-Zn-Ag deposit in Inner Mongolia

为研究内蒙古东珺铅锌银矿床围岩蚀变类型与蚀变分带地球化学特征,将近矿、远矿蚀变围岩与紫红色安山岩进行对比,以Al_2O_3为惰性组分,利用标准化Isocon图解法对围岩蚀变过程中物质组分带入、带出进行质量平衡计算;分析微量元素的迁移机制。研究结果表明:蚀变的空间位置关系自内向外可以划分为3个蚀变带即钾硅化-绢云母化带、绢英岩化带、青磐岩化带,其中与矿床成矿关系最为密切的是绢英岩化带;岩浆热液沿裂隙侵位交代围岩,近矿蚀变围岩中各组分质量变化都非常明显,Mg O,P2O5,TFe2O3,Ca O和Na2O组分都在蚀变时随热液大量迁出,而SiO_2和K2O则在热液对围岩进行交代过程中保留下来;近矿蚀变围岩多发生硅化、钾化、绢云母化、黑云母化蚀变;近矿蚀变围岩中明显减少的组分TFe2O3,Mg O和P2O5在远矿蚀变围岩中都略有增加,Ca O质量分数显著上升,SiO_2质量分数减少;远矿蚀变多发生绿帘石化、绿泥石化、碳酸盐化;近矿蚀变围岩轻重稀土分馏最强,远矿蚀变围岩轻重稀土分馏减弱;近矿蚀变围岩主要富集U和Th等高场强元素,多强烈亏损Ba和Sr等大离子亲石元素,其中La,Ce,Sr,Nd,Zr,Sm和Y元素从近矿围岩中组分流失而在远矿围岩处相对富集,具备火山—次火山热液矿床地球化学与围岩蚀变特征。

To study the types and geochemical characteristics of wallrock alternation in Dongjun Pb-Zn-Ag deposit,Inner Mongolia,altered near-ore or far-ore wallrock and purplish red andesite were compared.Al2O3 was used as the inert component,and mass transfer in the process of wallrock alteration was calculated by normalized Isocon diagram method.In addition,migration mechanism of trace elements was analyzed.The results show that there exist three alteration zones from the inside to the outside,i.e.,K-silication-sericitization zone,phyllic alteration zone and propylitization zone.The phyllic alternation zone displays the closest relationships with mineralization.The components in the altered near-ore wallrock fluctuate obviously.A great amount of MgO,P2O5,TFe2O3,CaO and Na2O move out along with hydrotherm during alternation,while SiO2 and K2O are preserved in the process of metasomatism of magmatic hydrothermal along fracture emplacement.Potassic,silicified,sericite and biotite alterations are common in the altered near-ore wallrock.Contents of TFe2O3,MgO and P2O5 increase slightly in altered far-ore wallrock,which all reduce dramatically in altered near-ore wallrock.There is an obvious increase in CaO mass fraction,but a decrease in SiO2 mass fraction in far-ore alternation zone in which epidotization,chloritization and carbonatization are easy to be found.Rare earth elements(REE)fractionation of altered near-ore wallrock is the strongest,and REE fractionation of altered far-ore wallrock is weakened.High field strength elements(e.g.U,Th)are enriched in altered near-ore wall rock,while large ion lithophile elements(e.g.Ba,Sr)are depleted.Elements(e.g.La,Ce,Sr,Nd,Zr,Sm,Y)run from near-ore wallrock and relatively enrich in far-ore wallrock,which shows the geochemical and wallrock alternation characteristics of volcanic-subvolcanic hydrothermal deposit.