滇东北茂租热液型铅锌矿床矿物组合共生分异的热力学Eh—pH相图

摘要

滇东北地区广泛分布的热液型铅锌矿床具有普遍的矿物组合分带特征,研究矿床矿物组合的共生分异特征,是了解该类型矿床的成矿流体在演化过程中,成矿元素迁移和沉淀的核心问题之一,通过共生矿物的热力学Eh—pH相图可以有效的诠释成矿流体中成矿元素在迁移、沉淀过程中的物理化学条件.本文以滇东北茂租铅锌矿床为例,对滇东北热液型铅锌矿床的金属矿物共生组合在时间、空间分带特征进行热力学相图分析,选取373K、423K、473K、523K四个温度截面对金属矿物共生组合稳定存在的Eh—pH范围进行计算,相图显示成矿流体中矿物迁移、沉淀机制主要是由于成矿流体的Eh、pH值双重制约:Eh值的变化控制着硫化物沉淀的时间分带,成矿流体从深部向浅部运移,Eh值将会逐渐增大,主要矿物从黄铁矿→方铅矿→闪锌矿依次开始析出;pH值控制硫化物的空间分带,随着pH值的增大,成矿元素从离子的形式转变为硫酸盐矿物进行迁移.研究表明,控制成矿流体中硫化物迁移、沉淀的物理化学条件除了温度、压力、金属离子浓度及流体的氧硫逸度之外,流体的酸碱度及氧化还原电位同样是控制矿物组合共生分异的重要影响因素,此研究对该类型矿床的成矿流体的演化和成矿机制提供了一定的理论依据.%Objectives:The hydrothermal type lead and zinc deposit in northeast Yunnan It has certain mineral assemblage zoning characteristics,the research is lower in this area,this paper for the example of the Maozu lead and zinc deposit of in the northeast of Yunnan province,we use of Eh—pH phase diagram research the balance conditions and change trends of various kinds of metallogenic substances among,from this point of thermal equilibrium condition of Eh—pH,probes the mechanism and characteristic of certain mineral assemblage zoning characteristics of hydrothermal type lead and zinc deposit in northeast yunnan,enriching and improving the physical chemical condition this type of ore deposits origin through this research for the mechanism of metallogenic fluid evolution and mineralization it provides some theoretical basis.Methods:Through field investigation and indoor research,think the northeast hydrothermal type Pb—Zn deposit metallogenic process belongs to the typical solid—liquid phase reactions in mineral balance of thermodynamics,built within the stability of the water balance equation of mineral assemblage of the deposit,using research mineral thermodynamic equilibrium and thermodynamic data calculation and drawing Eh—pH phase diagram of Maozu Pb—Zn deposit Fe—S—Pb—Zn—H—O system,to discuss this Eh—pH among physical chemical condition of ore-forming fluid.Results:Through the phase diagram show that mineral assemblage zoning characteristics,be due to pH and Eh dual control,when the Eh value is above 0.5V the metallogenic elements exist in the form of ions or sulfates,when the Eh value below 0.5V the sulfide happen reduction and precipitation.as the pH increases,the metallogenic elements shift in the form of sulfates removal,from the diagram the range of stability of Pyrite,lead ore all contains the range of stability of sphalerite the stability of the sphalerite is significantly broad than the between,it shows that when the precipitation of pyrite and lead ore is precipitated in different time and space,the sphalerite can continue to move and deposit.on the other hand,this phenomenon explains the macrogeological characteristics of the hydrothermal type lead—zinc deposit in the northeast of yunnan province with lead,zinc,iron symbiosis and zinc as the main proportion Conclusions:The method of Eh—pH phase diagram has been successfully applied to the hydrothermal type lead and zinc deposit in northeast yunnan restriction physical chemical condition of metallogenic migration and precipitation the metallic mineral assemblage characteristics of ore deposit are controlled by Eh and pH,the phase diagram reflect the zoning pattern to with the geological characteristics of the ore deposit are matched.