Scandium enrichment and release in pyroxene driven by melt and fluid metasomatism: Insights from East Gondwana, Antarctica

Abstract Mafic-ultramafic intrusions represent the primary source of global scandium (Sc) resources worldwide. These intrusions typically originate from fertile mantle sources in arc systems. While fluid- and melt-driven metasomatism are widely recognized as crucial mechanisms for Sc enrichment in the mantle, key aspects, including the precise composition of these metasomatic agents and their operating conditions remain poorly constrained. To address these knowledge gaps, we conducted a comprehensive investigation of Sc enrichment and release using clinopyroxene and orthopyroxene chemistry from charnockites and mafic granulites in East Antarctica’s Prydz Bay Belt. We reveal a multi-stage Sc evolution pathway within the accretionary belt that is initiated by dehydration of carbonate rocks, generating reduced carbonatite melts which trigger mantle metasomatism and significantly enrich Sc in the pyroxene. This enrichment is followed by post-peak decompression melting at 800-1000 °C and 6.5-12.8 kbar, which triggers metasomatism by an oxidized silicate melt, facilitating Sc release from both orthopyroxene and clinopyroxene. The subsequent arc accretion stage involves interaction with an external, oxidized, and likely phosphorus-rich aqueous fluid, leading to Sc release. The findings of Sc-rich pyroxene in mafic granulite and charnockite, together with the presence of CO₂-rich fluid inclusions in East Gondwana (Antarctica), collectively indicate that scandium enrichment may be a regional event. This study provides further implications for the exploration of Sc deposits in metamorphic rocks.