Developing mineralogical and geochemical discrimination methods to classify Li-barren and Li-prospective pegmatites at the Chebogue lithium prospect, southwestern Nova Scotia, Canada

Abstract

The parental magma composition that produces a plutonic rock is what gives the lithium-bearing pegmatite its distinct elemental composition. Lithium, a sought-after incompatible element, is challenging to detect through most routine analytical techniques. It occurs in abundance commonly bonded within aluminosilicate minerals such as in spodumene (LiAlSi₂O₆).<br> This study focuses on comparing mineralogical, petrographic, and geochemical characteristics of the lithium bearing Brazil Lake pegmatite (BLP) with Li-barren pegmatitic float to identify correlations that may help identify unexposed Li endowments. The main objective is to investigate if the chemical composition and mineralogy of chemically-developed rocks can be used to differentiate between economic and sub-economic lithium rocks in the absence of spodumene. Thin section and SEM analysis identified major and accessory minerals to classify the samples of this study (Zone A, north of Brazil Lake). Whole-rock geochemical assay data was used to analyze trace element composition, and LA-ICP-MS analysis of spodumene and muscovite to compare the trace element concentrations of Zone A to LCT pegmatites in North America. Finally, muscovite fractionation modelling was conducted to discover the extent of fractionation of the samples and explore their origin.<br> Based on the Nb/Ta ratios from whole-rock assay data and the composition of the samples, Zone A pegmatites match the LCT classification suggested by Čern&yacute; (1991). Pegmatites with high Li content also correspond to specific ranges in trace elements. The composition of Zone A spodumene is most similar to the BLP, suggesting a common source. This is further supported through muscovite fractionation modeling, which suggested a similar amount of fractionation, due to a low K/Rb ratio and high Cs concentration shown in Zone A and BLP.<br> Overall, this research intends to find a way to facilitate lithium detection and to more reliably uncover lithium prospective deposits.