Scandium and gallium in weathered basalts as unconventional resources

Abstract

Being critical metals, both scandium (Sc) and gallium (Ga) are in high demand because of their usage in advanced technologies. Yet economically viable Sc and Ga deposits are scarce in the world. New and alternative resources are now urgently needed to ensure a stable supply. Cenozoic basalts in East China are voluminous and comprise a volcanic belt for more than 4000 km long. These basalts have geochemical affinities of ocean island basalts (OIB) with variably enriched LREE relative to HREE with average contents ∼ 19 ppm Sc, and ∼ 21 ppm Ga. We report here Sc- and Ga-enriched regolith of basalts in the Lei-Qiong region, the southernmost part of this volcanic belt. These basalts are strongly weathered under the tropical climate and regolith profiles range in thickness from a few meters to 30 m. The weathered basalts have Sc and Ga concentrations ranging from 19 to 50 ppm and 18 to 47 ppm, respectively, up to 2 times higher than the fresh protolith. They are also variably enriched in Nb (8.1 to 126 ppm) and Ti (1.3 to 4.9 wt%). Preliminary estimates suggest a minima of ∼ 0.3 million tonnes each of Sc and Ga in the Lei-Qiong region. Thus, the weathered products of basalts are potentially important sources of Sc and Ga. Although present in low concentrations, Sc and Ga of the regolith could be viable sources of these elements due to ever-increasing demand and easy and cost-efficient mining. If combined with Nb and Ti, the regoliths would have more even more values. Therefore, weathered basalts could become a potentially important source of these metals, which could ultimately contribute to the maintenance of a reliable and stable source of Sc and Ga in the future. Such unconventional resources may impact the global commercial aspects of Sc and Ga in the future.