The Reaction Mechanism Study At The Copper Iron(Arsenic)Sulfide Mineral-water Interface

"mineral-fluid" interaction is a common phenomenon in the nature world.The comprehension of the reaction mechanism is a key factor to improve our knowledge of nature process,for example isotopic fractionation,global elemental cycles,chemical weathering,depositions formation and alteration and so on(Putnis,2014;Putnis and Ruiz-Agudo,2013).In order to find out the relationship between copper mineralization and transformation and "mineral-fluid" interaction,we conduct s series of experiments under hydrothermal conditions.And we also analyze the mineral kinds,chemical constituents and interfacial reaction mechanism.We conduct our reaction in Poly Tetra Fluoro Ethylene(PTFE)tube.The volume of the tube is 9 ml.The experiments investigate the effect of reaction temperature,the pH,the ion concentration and reaction time on the "mineral-fluid" interaction.We have used X-ray diffraction(XRD),Laser raman spectrum(RS),scanning electron microscope(SEM)and electron probe microanalyses(EPMA)to investigate mineral kinds,chemical constituents,and texture.We have gete the following results.(1)The results show that the species of the reaction product is different with different temperature,different pH and different reaction time.The main product is chalcopyrite,bornite,digenite,anilite,hematite and magnetite.The hematite can form in different temperature and different pH.There would be more in low temperature and most of the hematite nucleate on the bottom and wall of the PTFE tube.chalcopyrite and bornite can form in mild acid conditions while digenite forms in mild basic conditions.In low temperature(about 100?)the pyrite mainly converts to hematite.(2)The chalcopyrite is unstable in the fluid contain SO2 and H2S.And it can transform to covellite and pyrite.Covellite and pyrite compete for reprecipitation and finally pyrite replaces chalcopyrite with morphology reserved while covellite precipitates on mineral surface and at bottom and inner wall of PTFE tube.(3)We successfully synthesis enargite via "mineral-fluid" interaction in 200?.Previous studies reported that enargite is high temperature polymorphism of luzonite(D' Souza et al.,1971;Skinner,1960).The transformation temperature is 280-320? and enargite is usually used as geothermometer.However,the synthesis temperature of enargite is much lower than previous reported.This means that we can't simply regard enargite as geothermometer.The formation of enargite may be an indicator of high sulfur fugacity and high oxygen fugacity fluid environment.However,the lower limit of enargite forming temperature need more systematic and detailed study.The results show that the pyrite transform to hematite,chalcopyrite,digenite and chalcopyrite transform to bornite,pyrite,enargite are the process of dissolution and precipitation.And the transform process is the coupled interfacial dissolution and reprecipitation mechanism.