Mineral chemistry of chromite, orthopyroxene and plagioclase of chromitite layers in the Lower and Middle Group of the northwestern Bushveld Complex

This data set contains mineral chemical analyses of chromite, orthopyroxene and plagioclase of five chromitite layers and their immediate host rocks from drill core ZK135 of the northwestern Bushveld Complex. The sampled interval of ZK135 covers the transition of the Lower and Middle Group chromitites (LG6, LG6a, MG1, MG2, MG2 II). Detailed geochemical profiles are presented by data sheets and graphically to reveal small-scale variations in mineral chemistry. Mineral chemical analyses were conducted on drill core material from borehole ZK135 from the Thaba mine, operated by Cronimet Chrome Mining SA (Pty) Ltd. Briefly, each layer is hosted in pyroxenite and comprises a main chromitite layer and in some chromitites additional stringers above or below the main layer. Chromitites are composed of chromite, which are cemented by intercumulus plagioclase and orthopyroxene oikocrysts. A detailed study of the orthopyroxene oikocrysts in MG1 was published by Kaufmann et al. (2018). Additionally, euhedral to subhedral cumulus orthopyroxene is present in the LG6a, MG1 and MG2 layers. Pyroxenitic partings, small layers of pyroxenite within the chromitite, occur throughout the LG6 to MG2 layers. The main mineral phases chromite, orthopyroxene and plagioclase were analyzed by electron microprobe in each layer and the adjacent pyroxenitic host rocks. Major-element compositions of chromite, orthopyroxene and plagioclase were analyzed by electron microprobe at the Museum für Naturkunde Berlin with a JEOL JXA-8500F EMP equipped with a field emission cathode and five wavelength-dispersive spectrometers. For more information please consult the data description file and Kaufmann et al. (2019) to which these data are supplementary material.