首页|Scavenging and release of REE and HFSE by Na-metasomatism in magmatic-hydrothermal systems
Scavenging and release of REE and HFSE by Na-metasomatism in magmatic-hydrothermal systems
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Exploitable or potentially exploitable deposits of critical metals,such as rare-earth(REE)and high-field-strength elements(HFSE),are commonly associated with alkaline or peralkaline igneous rocks.However,the origin,trans-port and concentration of these metals in peralkaline systems remains poorly understood.This study presents the results of a mineralogical and geochemical investigation of the Na-metasomatism of alkali amphiboles and clinopyroxenes from a barren peralkaline granite pluton in NE China,to assess the remobilization and redis-tribution of REE and HFSE during magmatic-hydrothermal evolution.Alkali amphiboles and aegirine-augites from the peralkaline granites show evolutionary trends from sodic-calcic to sodic compositions,with increasing REE and HFSE concentrations as a function of increasing Na-index[Na#,defined as molar Na/(Na+Ca)ratios].The Na-amphiboles(i.e.,arfvedsonite)and aegirine-augites can be subsequently altered,or breakdown,to form hydrothermal aegirine during late-or post-magmatic alteration.Representative compositions analyzed by in-situ LA-ICPMS show that the primary aegirine-augites have high and variable REE(2194-3627 ppm)and HFSE(4194-16,862 ppm)contents,suggesting that these critical metals can be scavenged by alkali amphiboles and aegirine-augites.Compared to the primary aegirine-augites,the presentative early replacement aegirine(Aeg-Ⅰ,Na#=0.91-0.94)has notably lower REE(1484-1972)and HFSE(4351-5621)contents.In contrast,the late hy-drothermal aegirine(Aeg-Ⅱ,Na#=0.92-0.96)has significantly lower REE(317-456 ppm)and HFSE(6.44-72.2 ppm)contents.Given that the increasing Na# from aegirine-augites to hydrothermal aegirines likely resulted from Na-metasomatism,a scavenging-release model can explain the remobilization of REE and HFSE in peralkaline granitic systems.The scavenging and release of REE and HFSE by Na-metasomatism provides key insights into the genesis of globally significant REE and HFSE deposits.The high Na-index of the hydrothermal aegirine might be useful as a geochemical indicator in the exploration for these critical-metals.
Critical metalsAlkali amphibolesNa-metasomatismREE and HFSENa-index(Na#)
Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China
CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,China
Department of Geology,Lakehead University,Thunder Bay,ON P7B 5E1,Canada
国家自然科学基金国家自然科学基金Key Research Program of the Innovation Academy for Earth Science,CAS中国科学院青年创新促进会项目广东省科技计划GIGCAS
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