Characterization of pegmatites in the La Motte Batholith area, Preissac-La Corne Plutonic Suite, Abitibi Subprovince and its implications for exploration

Abstract

This project focuses on the study of pegmatite characteristics in the La Motte Batholith (LMB) sector in the Abitibi Subprovince, located between the cities of Rouyn-Noranda and Val d'Or, and approximately 30 km west of the North American Lithium mine (101.9 Mt @ 1.06 % Li₂O; Sayona Québec). The study area hosts mineralizations in critical and strategic minerals, most notably the Authier deposit, which are exclusively associated with Li-Cs-Ta pegmatites. The aim of the study is to characterize the mineralogical and geochemical properties of the pegmatites in the sector to better target lithium exploration. This characterization enables the subdivision of various families of pegmatites in the LMB sector, ranging from barren pods to spodumene-rich dykes. Within the LMB, the pegmatitic facies exhibit chemical characteristics similar to those of intersecting pegmatite dykes, suggesting a genetic link between the La Motte Batholith monzogranite and the different pegmatite families despite a possible age difference of several million years. The results also confirm that elemental ratios from whole-rock analyses (K/Rb, K/Cs, Nb/Ta, Mg/Li, and Zr/Hf) within lithium-bearing dykes show the lowest values compared to other dykes, regardless of the sampling location within the same dyke. Potassium feldspar and muscovite microprobe analyses from different pegmatites also reveal K/Rb and K/Cs ratios similar to whole-rock analyses, thereby strengthening the assessment of the fractionation degree of the LMB pegmatites. These ratios thus allow for targeting sectors hosting highly fractionated dykes even where spodumene has not yet been identified.