Geochemical sampling in Kaustinen, Finland – Indications of new lithium sources

Abstract

Indications of undiscovered lithium resources in the Kaustinen region of Finland were investigated through bedrock and till sampling using percussion drilling. The area belongs to the Paleoproterozoic Ostrobothnia Schist Belt, till deposition was in the Quaternary Period. Local spodumene pegmatites are classified as lithium‑cesium‑tantalum (LCT) pegmatites, particularly albite-spodumene types. Sampling in Leviäkangas area covered 2175 m along 11 lines, samples every 25 m. The targets were selected to cross some of the previously mapped spodumene boulder fans. Total of 98 rock-chip and 139 till samples were analyzed using ICP-MS and ICP-OES methods, with four-acid and aqua regia dissolutions. Elevated lithium >143 mg/kg as twice the background was identified in 30 rock-chip samples (150–527 mg/kg). Metasediments were visually identified as mica schist. Granite discoveries, a lithium rich (Li 350 mg/kg) and a lithium-poor type (Li 40), displayed LCT characteristics based on Mg/Li, K/Rb, and Nb/Ta ratios. Halos, enriched in Li, Be, Nb, Rb and Sn extended 25–75 m around granites, while lithium-enriched tills reached several hundred meters. Bottom tills contained 20–161 mg/kg Li (four-acid leaching), while surface tills ranged 17–109. Tills from excavator made pits contained spodumene in heavy mineral studies. Glacial flows have been from NE (040°) or NW (340°). The geochemistry of metasediments showed indications of undiscovered Li deposits, while the utilization of till samples in mapping Li-enriched halos would have required a more comprehensive knowledge of stratigraphy and glacial flow directions.