Geology and Geochemistry of Muyexe Magnesite Deposit, Giyani Greenstone Belt, Limpopo Province, South Africa

Abstract

Muyexe magnesite deposit is situated in the Giyani Greenstone Belt in South Africa. Despite mining activities currently taking place at Muyexe magnesite deposit, little information is available about the geology and geochemistry of the deposit. This has resulted in a gap of information about the nature and character of magnesite, namely; its geology, mineralogy, geochemistry and mode of occurrence. Consequently, there is a need for further investigation of the magnesite deposit. The main objective of the study was to establish the geology and geochemistry of the Muyexe magnesite deposit and to ascertain its mode of occurrence. Further work involved undertaking detailed geological mapping, magnesite and rock sampling for petrographic and geochemical studies using petrographic microscopy and X-ray fluorescence spectrometry and identification of minerals in rocks and magnesite through X-ray diffractometry. A total of 20 magnesite and 4 host rock samples were collected from the Muyexe magnesite deposit. Furthermore, 62 rock samples were collected during geological field mapping of which 16 representative samples were selected for further analysis. X-ray fluorescence spectrometry was conducted on all selected samples of magnesite and rocks. XRD analysis was conducted on 12 rocks and 2 magnesite samples. Mineralogy of the rocks was also confirmed using petrographic microscopy. Detailed geological map of the Muyexe area revealed that the area is dominated by metamorphic ultramafic and mafic rocks. Basalt and peridotite are intrusions within the rock. The serpentinites and peridotites were found to be the source rock for magnesite mineralization, while the peridotite is the source rock for serpentinites rocks. XRD analysis revealed that magnesite in the Muyexe magnesite deposit is associated with silica and dolomite, while XRF data revealed that the following major oxides are present in magnesite as impurities; silicon dioxide (SiO2), calcium oxide (CaO), and iron oxide (Fe2O3). These oxides reduce the quality of magnesite, thus, their removal is necessary during processing. Magnesite of this deposit was found to be of good quality, with an average value of 54.02 wt. %. Magnesite at Muyexe was formed due to precipitation of Mg2+ along the fractures of serpentinites and peridotites due to CO2rich hydrothermal fluids. Magnesite occurs as a cryptocrystalline of the Kraubathtype.