Melt-Fluid and Fluid-Fluid Immiscibility in a Na_(2)SO_(4)-SiO_(2)-H_(2)O System and Implications for the Formation of Rare Earth Deposits  

作　　者：CUI Hao ZHONG Richen XIE Yuling WANG Xiaolin CHEN Huan 

机构地区：[1]School of Civil and Resource Engineering,University of Science and Technology Beijing,Beijing 100083,China [2]State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China

出　　处：《Acta Geologica Sinica(English Edition)》2021年第5期1604-1610,共7页地质学报（英文版）

基　　金：funded by the National Natural Science Foundation of China(Grant nos.41930427,41872078,and 41502069);the Young Elite Scientists Sponsorship Program by CAST(Grant no.YESS20180143);the Fundamental Research Funds for the Central Universities(Grant nos.FRF-TP-18-017A3 and FRF-IDRY-19-001)。

摘　　要：Liquid-liquid immiscibility has crucial influences on geological processes,such as magma degassing and formation of ore deposits.Sulfate,as an important component,associates with many kinds of deposits.Two types of immiscibility,including(i)fluid-melt immiscibility between an aqueous solution and a sulfate melt,and(ii)fluid-fluid immiscibility between two aqueous fluids with different sulfate concentrations,have been identified for sulfate-water systems.In this study,we investigated the immiscibility behaviors of a sulfate-and quartz-saturated Na_(2)SO_(4)-SiO_(2)-H_(2)O system at elevated temperature,to explore the phase relationships involving both types of immiscibility.The fluid-melt immiscibility appeared first when the Na_(2)SO_(4)-SiO_(2)-H_(2)O sample was heated to~270℃,and then fluid-fluid immiscibility emerged while the sample was further heated to~450℃.At this stage,the coexistence of one water-saturated sulfate melt and two aqueous fluids with distinct sulfate concentrations was observed.The three immiscible phases remain stable over a wide pressure-temperature range,and the appearance temperature of the fluid-fluid immiscibility increases with the increased pressure.Considering that sulfate components occur extensively in carbonatite-related deposits,the fluid-fluid immiscibility can result in significant sulfate fractionation and provides implications for understanding the formation of carbonatite-related rare earth deposits.

关 键 词：geochemistry liquid-liquid immiscibility high sulfate concentration sulfate melt hydrothermal fluids 

分 类 号：P618.7[天文地球—矿床学]