Biotite chemistry and mineral association as an indicator of redox conditions in the iron oxide Cu-Au (IOCG) system: Constraints from the Khetri Copper Belt, western India

•Biotite and uraninite related to IOCG mineralization are associated with redox sensitive minerals such as magnetite, ilmenite, and graphite.•Calculation of Fe3+ in biotite using methods of Dymek, 1983, Guidotti and Dyar, 1991•Mineral association, Fe3+ content of biotite, and U/Th ratio of uraninite point to redox conditions reaching below the Fayalite-magnetite-quartz (FMQ) buffer.•The presented method could be useful for magnetite-poor IOCG systems.