Mineralogical and petrogenetic characterization of the Witkop pegmatite, Northern Cape

Pegmatite, which forms in various tectonic environments and crystallizes through developed magma, is a significant source of green energy transition metals like Li-Cs-Ta and REEs (Müller et al., 2022). Lithium is one of the most important metals for making high-energy batteries and battery storage systems (Müller et al., 2022). It is also the lightest metal on the periodic table and has unique properties that make it ideal for use in batteries.

In Africa, Li is mined from hard rock deposits such as pegmatites. These deposits are often small, covering only a few hundred square meters, and are usually found in Li-Cs-Ta pegmatites (London, 2018). The main Li-bearing minerals in these pegmatites are spodumene, petalite, and lepidolite (Müller et al., 2022). Li-Cs-Ta pegmatites are typically hosted in metamorphosed rocks formed under upper greenschist to lower amphibolite facies conditions (Bradley et al., 2017). However, the origin of the melt or fluid responsible for forming Li-Cs-Ta pegmatites is poorly understood. It is still unclear whether this melt formed through extreme fractionation of a cooling parental granite or came directly from the dehydration of metasedimentary rocks during metamorphism (Müller et al., 2017). To better understand the origin of the Li-rich melt and why some pegmatites contain Li-Cs-Ta minerals while others do not, this study will combine trace element analysis with SIMS insitu oxygen isotope data from quartz. Preliminary trace element results suggest some crustal origin; however, this will be tested more by the oxygen isotope work. The study focuses on pegmatites in the Richtersveld Subprovince, part of the Namaqua Metamorphic Belt in South Africa.

This area is of particular interest because it contains both Li-mineralized and non-mineralized pegmatites. The pegmatites are hosted by both metasedimentary and igneous rocks in the amphibolite facies and are part of a belt bordered by LCT and NYF pegmatites. This research will help explain the processes that control Li mineralization in pegmatites in this region.

References

Bradley, D.C., et al., 2017. Mineral-deposit model for lithiumcesium-tantalum pegmatites. In: Mineral Deposit Models for Resource Assessment. U.S. Geological Survey, Reston, Virginia, pp. 1–48. https://doi.org/10.3133/sir20105070O.

London, D. (2018) ‘Ore-forming processes within granitic pegmatites’, Ore Geology Reviews, 101, pp. 349–383. Available at: https://doi.org/10.1016/j.oregeorev.2018.04.020.

Müller A., et al., 2017. The Sveconorwegian Pegmatite Province – thousands of pegmatites without parental granites. Canadian Mineralogist , 55, 283–315, https://doi.org/10.3749/canmin.1600075.

Müller, A. et al., 2022. GREENPEG–exploration for pegmatite minerals to feed the energy transition: first steps towards the Green Stone Age. Geol. Soc. London Spec. Publ. 526, 27. https://doi.org/10.1144/SP526-2021-189