Texture development in titaniferousmagnetites found in Layer 21 in the Bushveld Igneous Complex, South Africa

Abstract

Very limited studies have been conducted on titaniferous-magnetite exsolution textures and the conditions needed for the formation of these textures. Published research surrounding the exsolution textures consider only a particular element of the oxide, or a specific condition. The Upper Zone of the Rustenburg Layered Suite in the Bushveld Igneous Complex boasts 25 magnetite layers. The 21st layer counted from the Main Magnetite layer is called Layer 21, which is the uppermost titaniferous-magnetite layer in the Upper Zone. Uncommon exsolution textures in the titaniferous-magnetite grains were studied in order to gain a greater understanding of the formation of oxide exsolution textures. The exsolution texture presents itself as a three-dimensional framework of ulvöspinel-rich lamellae together with magnetite prisms. This is called a cloth texture exsolution. The data collected for this investigation included Scanning Electron Microscope (SEM) images, elemental weight percentage data, and SEM line scans. Previous studies do not show exsolution textures that are exactly similar to the exsolution textures seen in Layer 21, although the same basic type of microtexture can be seen. This indicates that conditions such as temperature, pressure, and oxygen fugacity, as well as the bulk mineral chemistry, plays a large role in the formation of the exsolution texture. A rough model has been provided that considers all of the information collected in previous studies in order to start the development of a complete model. Another model has been provided explaining the physical appearance of the cloth texture exsolution. The exsolution textures need to be investigated on a three-dimensional basis in order to develop a more accurate understanding of why the titaniferous-magnetite exsolution textures are different from location to location.