Na-metasomatism and its contributions to REE enrichment in alkaline granite systems
Alkaline igneous rock is one of the main sources of rare earth resources in the world,especially heavy rare earth resources.Until now,there is a lack of comprehensive and systematic research on key scientific questions such as the super-enrichment mechanism of rare earth(REE)and some high field strength elements(HFSE)in alkaline granite systems and their controlling factors.This paper focuses on Na-metasomatism in the alkaline magmatic-hydrothermal systems,and discusses the mineral replacement reaction processes and the remobilization and migration processes of rare earth elements in the hydrothermal replacement processes,such as albitization,arfvedsonization and aegirinization.In alkaline systems,alkali amphiboles and pyroxenes are considered to be the significant carriers of REE and HFSE,and are also effective tracers of magmatic differentiation and evolution.Taking the Nianzishan alkaline granite in NE China as an example,the late magmatic-hydrothermal metasomatism will lead to the evolution of alkali amphibole and pyroxene from calcium-rich minerals to sodium-rich mineral phases,which will lead to the remobilization and transferring of REE and HFSE in the late hydrothermal stage.In particular,REE and HFSE would be released into the metasomatic fluids,which may be the key controlling factors leading to the super-enrichment and mineralization of these key metal elements in the late hydrothermal stage.Therefore,the sodium index[Na#=Na/(Na+Ca)molar ratio]of the alkali amphiboles and pyroxenes may be a potential mineral geochemical index,which will provide a new proxy for REE exploration in the alkaline-peralkaline plutons.
Critical metalsAlkali amphibolesNa-metasomatismREE and HFSENa-index(Na#)
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维普
