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The carbonatite melt – granite wall-rock interaction: A case study on the Bulhoek carbonatites, South Africa

The study aims to provide valuable insights into the dynamics of the interaction between carbonate melts and silicate wall-rocks during ascent and emplacement of carbonatitic intrusions. A specific focus is given to potential processes leading to rare earth element (REE) enrichment. It can be assumed that the interaction of silicate rocks with carbonate melt is diverse. Therefore, a study of granites interacting with a carbonatite melt was used to carefully assess the effects of a specific lithology.

The research centers the Bulhoek carbonatite complex, a bi-partite intrusion (Bulhoek North and South) situated in the eastern central region of the Bushveld Complex, approximately 35km west of Pilanesberg (South Africa), where it intruded the Nebo-granite (an integral part of the Bushveld Complex). The key characteristics of this intrusion are reflected by volcanic breccia, finitized Nebo-granite and beforsite (fine-grained magnesio-carbonatite) containing abundant apatite and strongly disaggregated granite xenoliths. Textural evaluation indicates that the element budget of the granites was resorbed by the carbonate melt. An integrated analytical approach, involving scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), and whole-rock analysis, is currently in progress to reveal the intricacies of the carbonate melt – granite interaction. While previous field studies have touched upon the fenitization of the Nebo-granite, a comprehensive understanding of the entire (and mutual) interaction remains a significant research gap. This study bridges this gap and will deepen our knowledge of carbonatite formation.


Ole L. F. Sauter1, Johannes R. Giebel2, Benjamin F. Walter3
1Technische Universität Berlin, Germany; 2Technische Universität Berlin, Germany;University of the Free State, South Africa; 3Karlsruhe Institute of Technology
GeoBerlin 2023