Till geochemical characterization of the Kaustinen lithium province of Finland: Implications for lithium targeting.

Lithium is a critical mineral resource for development of hi-tech green energy technologies. Finland is one of the few EU countries with high potential for lithium mineral resources. Presence of significant lithium ore reserves within the rare-element granitic pegmatites classified as LCT (Li-Cs-Ta) pegmatites in the Kaustinen lithium province in Finland, makes it a substantial region for lithium resources in Europe. Hence the present study presents geochemical characterization of the Kaustinen lithium province for lithium exploration targeting. Results of multivariate statistical analysis applied to till geochemical data are presented. These map the geochemical signatures of (a) major lithostratigraphic units and (b) lithium-bearing spodumene pegmatites and differentiate them from the geochemical signatures of other potentially lithium enriched rocks such as mica schists, mica gneisses and granitoids in the region. Two unsupervised clustering algorithms are employed, namely principal component analysis (PCA) and factor analysis (FA). The results indicate that each lithostratigraphic unit is characterized by a distinct geochemical signature which is distinguishable in the factor and PC maps derived. The boundaries of the lithostratigraphic units in the PC and factor maps conform to the units mapped from the geophysical datasets.

This study demonstrates that FA and PCA of till geochemical data can be used for mapping bedrock lithology in poorly exposed terrains. Additionally, the factor analysis maps also differentiate the Li signature of the mica schists and gneisses of the basement complex from that of pegmatitic granite units, which are interpreted to be the source rocks of the spodumenepegmatite generating fluids. The FA highlights the spatial association of spodumene pegmatites with the mafic metavolcanic lithological units within the Evijärvi-Himanka thrust zone, indicating that the compressional regime during the Svecofennian orogeny in this region provided the structural architecture as well as pre-existing permeable pathways for the parental fluids of the spodumene pegmatites; while at the same time the competency contrast between mafic metavolcanic rocks (amphibolite) and surrounding schists in a compressional regime is interpreted to be one of the controls on the channelization and emplacement of the pegmatitic melts.