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).
Final Report Abstract
1. Fayalite rocks of the world class Vergenoeg magnetite-fluorite deposit preserve a cumulate mineral assemblage of fayalite with rare Ti-rich magnetite, ilmenite, fluorapatite and allanite. The assemblage is interpreted to have formed by accumulation from a reduced, dry and extremely fractionated rhyolitic parental melt that was enriched in Fe, F and REE. 2. High fayalite δ18O values (up to 7.4 ‰), re-calculated REE patterns and broadly coeval Paleoproterozoic formation strongly suggest that the generation of the highly-silicic parental melt is related to the formation of rhyolites of the Rooiberg group. Therefore, these data document a petrogenetic link between the formation of the Vergenoeg deposit and the Bushveld LIP. 3. Primary fluorite formed in an interstitial mineral assemblage together with quartz and a second generation of fayalite, Nb-rich ilmenite and magnetite. 4. Predominantly negative magnetite δ18O values, textural relationships and mineral compositions document that the main formation of magnetite and fluorite in the Vergenoeg deposit occurred during late hydrothermal fluid circulation, related to the release of F-rich fluids from the crystallizing granites of the Bushveld Complex. This suggests that the Vergenoeg deposit may belong to the broad class of IOCG deposits. The overprint led to the extensive replacement of magmatic fayalite and its alteration products by Ti-poor magnetite.
Publications
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(2017). In-situ trace element and Feisotope studies on magnetite of the volcanic-hosted Zhibo and Chagangnuoer iron ore deposits in the Western Tianshan, NW China. Chemical Geology, 453, 111-127
Günther, T., Klemd, R., Zhang, X., Horn, I., Weyer, S.
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(2018). Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa. Contributions to Mineralogy and Petrology, 173, 51
Günther, T., Haase, K., Klemd, R., Teschner, C.
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(2018). Origin of discordant ultramafic pegmatites in the Bushveld Complex from externally-derived magmas. South African Journal of Geology, 121, 287-310
Cawthorn, R.G., Latypov, R., Klemd, R., Vuthuza, A.
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(2018). Oxygen isotope and trace element compositions of platiniferous dunite pipes of the Bushveld Complex, South Africa–Signals from a recycled mantle component? Lithos 310, 332-341
Günther, T., Haase, K., Junge, M., Oberthür, T., Woelki, D., Krumm, S.
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(2020). Formation of the Vergenoeg F-Fe-REE deposit (South Africa) by accumulation from ferroan silicic magma. Journal of Petrology
Brandt, S., Klemd, R., Haase, K., Faßbender, M. L. Vennemann, T.
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(2021): Cumulate olivine: A novel host for heavy rare earth element mineralization. In: Geology 49 (4), S. 457–462
Brandt, S., Faßbender, M. L., Klemd, R., Haase, K.
