ZaneAldeen Rahabi, PhD
Z. Rahabi1, D. Lentz1, T. Martins2, L. Groat3
1Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick, Canada
2Manitoba Geological Survey, Winnipeg, Manitoba, Canada
3Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada
High-purity quartz is essential for the production of semiconductors, optical fibers, photovoltaics, electric lights, computer chips, and laboratory equipment. Most high-purity quartz worldwide is extracted from large-volume (>100,000 m3) pegmatites, alaskite granites, metamorphic quartzites, or vein quartz, with zoned pegmatites being a common source due to their largely monomineralic quartz cores. The Tanco pegmatite, southeastern Manitoba, has a volume of 21,850,000 m3 and contains several zones of massive monomineralic quartz. Furthermore, the Tanco mine is a historical Li and Ta producer and current Cs producer, with an on-site ore processing facility. The global need for high-purity quartz therefore presents a potential economic opportunity for the Tanco mine. Samples of quartz from the Tanco pegmatite were analyzed by thin section petrography, and the majority of samples were found to contain abundant micro-scale inclusions of needle-like tourmaline crystals, which have not previously been reported at this locality. Tourmaline needles are commonly aligned parallel to fluid inclusion trails and perpendicular to elongated subgrains defined by undulose extinction in the host quartz. While tourmaline needles are generally evenly disseminated throughout the quartz, in some samples they are clustered into linear trends along the contacts of quartz subgrains. Preferential orientation of tourmaline micro-inclusions relative to fluid inclusion trails and quartz subgrains has implications for both pre- and post-crystallization strain dynamics in the Tanco pegmatite. The presence of these tourmaline inclusions also has implications for potential metallurgical processing of quartz, as they would prove difficult to remove by traditional processing methods due to their small size and ubiquity. Finally, their presence additionally suggests that boron contents in the silicate melt which gave rise to the Tanco pegmatite’s quartz cores may have been higher than previously thought, with implications for crystal fractionation processes in the pegmatite as a whole.