James Macdonald
Graduate Student, University of Manitoba

Emplacement mechanisms of rare element pegmatites, Separation Lake greenstone belt, northwest Superior Province

The prevailing theory regarding the Li-bearing pegmatites of the Separation Lake greenstone belt (SLGB) is that the dykes intruded in one event at ~2640 Ma and that the Li-bearing minerals were recrystallized by solid-state deformation, however recent investigations suggest that these rocks intruded over a ~50 Ma period (ca. 2649 to 2601 Ma) and that the distribution of minerals within them was controlled by magmatic, rather than deformational, processes. In the current study field mapping, detailed textural analysis, electron back-scattered diffraction (EBSD) and in-situ U-Pb geochronology are applied to the pegmatites and their host rocks to correlate the mechanics and timing of pegmatite emplacement in the tectonic framework of the western Superior Province. Our preliminary results show that granitic intrusions predating the Li-bearing pegmatites record textures indicative of regional scale deformation and suggest that emplacement of the mineralized dykes operates under a mechanism similar to fluidization, in which localized deformation may be imparted on the country rocks upon dyke emplacement.


James Macdonald originated in Pinawa, Manitoba and completed his BSc degree in Honours Geology at the University of Manitoba in 2017. James researched the trace element and stable isotope characteristics of igneous carbonate minerals as part of an undergraduate thesis with Dr. Anton Chakhmouradian and following graduation he spent four years working in the mineral exploration industry, primarily exploring for gold within the Red Lake camp of northwest Ontario. Most of this time was spent working with Rimini Exploration and Consulting, where James was fortunate to experience the progression of the Dixie Lake project from greenfield exploration through to advanced exploration and resource delineation. In 2021 James realized the increasing importance of domestic critical metals and decided to undertake a master’s program with Dr. Alfredo Camacho at the University of Manitoba where he is currently studying the emplacement mechanisms associated with the rare-element pegmatites of the Separation Lake greenstone belt in northwest Ontario.