ABSTRACT The Wekusko Lake pegmatite field in central Manitoba, Canada, is known for its multiple pegmatite dike occurrences, most remarkably its Li-rich pegmatites of economic importance. The Li-rich pegmatites from Wekusko Lake are the focus of this study and belong to the Green Bay group of the Wekusko Lake pegmatite field. These dikes were dated at ca. 1.78 Ga and were emplaced early during the D4 brittle–ductile deformational event. The results presented here describe in detail the pegmatite mineralogy, textures, and zonation of the Li-rich dikes of the Green Bay group, with emphasis on white mica chemistry. The aim of this study is to establish the nature and evolution of white micas from the Li-rich pegmatites of the Wekusko Lake pegmatite field in Manitoba. We aim to understand the differentiation mechanisms that allowed the high level of trace element enrichment observed in the white micas of the studied Li-rich pegmatites. Major and trace elements in white micas from a representative and well studied pegmatite dike were analyzed by electron microprobe and LA-ICP-MS. White mica compositions and textural evidence were used to define two different populations that seem to have been affected by magmatic processes (fractional crystallization) and a secondary episode of metasomatism. Fractional crystallization modeling of a granitic melt can explain some of the trace element enrichment, but extreme Cs enrichment cannot be explained via this mechanism. We interpret that many metasomatic white micas crystallized in boundary layers. Their compositions are controlled by the local melt composition, but aqueous fluids likely contributed to the development of the white mica textures. The substitution mechanisms at play depend on the type of trend and on the stage of evolution. Li enrichment without M2+ enrichment in metasomatic white mica grains is observed, and it is postulated that Fe3+ in white mica explains this behavior. The K/Rb ratio decreases in white micas with fractionation, whereas the concentrations of incompatible elements, such as Cs, Rb, Tl, Ta, and Li, increase. At Wekusko Lake, the Nb and Ta contents seem to be controlled in part by the presence of columbite group minerals and in part by crystallization in boundary layers.

This project investigates the potential use of white micas as an indicator mineral within Li-bearing pegmatites and the potential of field portable techniques, such as Raman spectroscopy and Laser Induced Breakdown Spectroscopy (LIBS) as real-time techniques in exploration. The pegmatites in the Wekusko Lake field, Manitoba, Canada, display five zones of varying mineralization. White micas display two textures in the field (primary igneous and secondary) and four textures were identified by backscattered electron imaging (poor zonation, rimmed, patchy and exsolution). The white micas were analysed by Electron Probe Micro-Analysis (EPMA) and Laser Ablation Induction-Coupled Plasma Mass Spectroscopy (LA-ICP-MS) and the results show a strong correlation in the Li content of the white mica and the whole rock Li2O obtained from the assays of drill core. The K/Rb vs. Cs contents of the white mica indicate that the most prospective dikes contain moderate to highly evolved grains. The use of portable Raman Spectrometer, while useful for mineral identification, was not able to detect a significant Li signature at the concentrations tested (1500-6000 ppm).

Lithium (Li) is one of the latest metals to be added to the list of critical materials in Europe and, thus, lithium exploration in Europe has become a necessity to guarantee its mid- to long-term stable supply. Laser-induced breakdown spectroscopy (LIBS) is a powerful analysis technique that allows for simultaneous multi-elemental analysis with an excellent coverage of light elements (Z < 13). This data paper provides more than 4000 LIBS spectra obtained using a handheld LIBS tool on approximately 140 Li-content materials (minerals, powder pellets, and rocks) and their Li concentrations. The high resolution of the spectrometers combined with the low detection limits for light elements make the LIBS technique a powerful option to detect Li and trace elements of first interest, such as Be, Cs, F, and Rb. The LIBS spectra dataset combined with the Li content dataset can be used to obtain quantitative estimation of Li in Li-rich matrices. This paper can be utilized as technical and spectroscopic support for Li detection in the field using a portable LIBS instrument.

Pegmatite deposits are an important source of lithium, which increasingly is used in battery technologies. The rare-metal pegmatite dikes of the Green Bay group from the Wekusko Lake pegmatite field in Manitoba offer an excellent opportunity to investigate new exploration techniques for lithium pegmatites. The dikes were mapped and sampled during the summer of 2018, and this work revealed that the pegmatite dikes are deformed and folded. The examination of drill core revealed that the pegmatite dikes exhibit five zones, defined by their minerology and grain size: a border zone, wall zone, intermediate zone, central zone and a core zone. The zones vary in width and all zones are not always present in each pegmatite. The crystal habit of muscovite, feldspar and spodumene vary based on the host zone and muscovite mineral chemistry is being examined as a potential vector for Li mineralization. Columbite-group (CGM) minerals are zoned with respect to Nb and Ta values and primary grains have been selected for U-Pb geochronological studies.