Mineralogical Variability of the Whabouchi Pegmatite and its Effect on the Li Concentrations

The Whabouchi pegmatite, located in the James Bay area of Québec, is a lithium-cesium-tantalum pegmatite of albite-spodumene type. In order to evaluate the mineralogical and geochemical variability of the pegmatite, 168 samples were collected from drill core and analyzed for their whole rock geochemistry and mineralogy. The pegmatite is composed of quartz, albite, K-feldspar, spodumene, and muscovite, with trace amounts of spessartine garnet, apatite, beryl, tourmaline, and oxides. It is mostly homogenous, showing greatest variability with respect to the minerals albite, K-feldspar, and spodumene. The Li2O concentration varies between 0.03 and 4.46 wt.%, for an average of 1.53 wt.% and an estimated variability of 53%. Modal mineralogical data showed an inverse correlation between spodumene and the feldspars (albite + K-feldspar), which could also be observed when comparing the Li2O content with the sum of Na2O and K2O. To improve on this relationship, correlation matrices comparing all geochemical components were constructed and allowed the development of an equation able to estimate the Li2O content of the samples within 0.5 wt.% of the measured value. The applicability of the equation to other albite-spodumene type pegmatites was verified with samples collected from the Georgia Lake area of northwestern Ontario. The calculation provided a good approximation of the Li2O content of the samples, with 92% of the data showing a difference of 0.5 wt.% Li2O or less; however, it has an impact on the statistical mean of the data set, the data being recalculated to return an average closer to 1.5 wt.% Li2O. Considering the difficulty in analyzing lithium content of an in situ sample, this relationship could facilitate estimation in the field using portable X-ray fluorescence with the capability of analyzing all required components.