Aknur Zhakanova, BSc
A. Zhakanova1, A. Yessenaly1, A. Zeinisheva1, G. Khabiyeva1
1Department of Geology, Nazarbayev University, Astana, Astana, Kazakhstan
Weathering crusts that have formed on granitoid rock are now being considered more and more a possibility for the extraction of rare earth elements (REE), especially in situations where supergene processes are favorable for the migration and keeping of the secondarily formed REEs. Northern Kazakhstan is home to the Souktal Plutonic Complex, which has thick weathering profiles lying on Proterozoic granite-gneisses, but still, there is not enough of an understanding of the inner mechanisms that control the distribution of REE in these profiles. This study is mainly geared towards evaluating the REE resolution of Souktal weathering crusts through a process oriented, predictive framework as opposed to a deposit confirmation approach. It adopts a process-oriented framework based on archived drill cores, focusing on weathered intervals (30-43 m) from cores C-15 and C-18, where granitic gneisses are transformed into clay-rich assemblages dominated by quartz, kaolinite, feldspars, muscovite, and minor Fe hydroxides.
The study aims at pinpointing the mineralogical, geochemical, and vertical zoning characteristics that rule REE retention and also those that lead to REE being separated and their being increased across different levels of weathering. Ion-exchangeable REE were quantified using a two-step sequential leaching procedure with hydroxylamine hydrochloride (0.2 mol NH₂OH·HCl) and sodium hydroxide (1 mol NaOH), followed by ICP-MS analysis of REE, Y, and Sc. Total extracted REE range from 4.1 to 7.8 ppm, indicating a measurable ion-adsorbed REE pool. Light REE dominate over heavy REE, and La/Yb ratios increase between leaching steps. The features are consistent with ion-adsorption-type REE systems and suggest that deeper drilling is warranted to evaluate higher-grade zones and the future REE potential of the Souktal weathering crust.