The petrogenetic link between Kiruna-type ore deposits and their host silicic igneous rocks: the Vergenoeg Fe-F-REE deposit in the Bushveld large igneous province (South Africa).

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Silicic large igneous provinces (SLIPs) frequently contain important Fe (±Cu, ±REE, ±U, ±P, ±F) ore deposits. The formation of such ore deposits, especially the relative roles of magmatic versus hydrothermal/metasomatic processes, is under debate since decades and the deposits are mostly classified as iron oxide-copper-gold (IOCG)-type or Kiruna-type deposits. In this study, we propose to reconstruct the petrogenetic evolution of the Vergenoeg F-Fe-REE deposit in South Africa, one of the largest F deposits of the world. The Vergenoeg deposit is situated within one of the largest SLIPs of the world, the volcanic Rooiberg Group, which is part of the Bushveld large igneous province and is dominated by rhyolites. Several contradicting petrogenetic models have been proposed for metal enrichment in Vergenoeg, which can be grouped into magmatic versus hydrothermal approaches. We will study melt inclusions trapped in quartz, feldspars, fayalite, magnetite, and apatite of the hosting felsic rock types (Rooiberg rhyolites and Bushveld granitoids) and the ore body in order to identify the source for ore formation at Vergenoeg, i.e., immiscible Fe-rich melt vs. Fe-F-REE rich granitic melt (hydrothermal formation of the ore by expulsion of Fe-F-REE-rich fluids). These investigations will be complemented by Fe and O stable isotope analyses of the ore and the host rocks. Major and trace element analysis of the main ore phases magnetite, fayalite, fluorite and apatite will provide insight into the partitioning of elements (especially the REE) between immiscible melts and/or their behavior during hydrothermal solution, enrichment and re-precipitation processes. The results of the study will provide important data allowing to elucidate the role of magmatic and/or hydrothermal processes on the formation of Fe (±REE, ±F) ore deposits in SLIPs and will contribute to a better understanding of the petrogenetic link between these Fe-F-REE and either IOCG-type or Kiruna-type ore deposits.