Mineral composition of xenoliths of transformed tholeiitic basalts in ore-hosting rocks of the Rudnogorskoe iron ore deposit, Eastern Siberia

Research subject. Variously-altered tholeiitic basalt xenoliths in ore-hosting rocks from the Rudnogorskoe iron ore deposit, the Angaro-Ilim region of Eastern Siberia. Aim. To identify the sequence of mineral transformations during the formation of magnetite ores. Materials and methods. The mineral composition of weakly-altered and hematitized xenoliths of tholeiitic basalts in skarned rocks and relics of basaltic hyaloand lithoclasts in varying degrees magnetitized volcaniclastites were studied. Minerals were identified using a powder X-ray diffractometer with the determination of the quantitative ratios of mineral phases by SHIMADZU XRD-6000 and DRON-2.0 diffractometers and using the microscopic (Olympus BX51) and electron microscopic (Tescan Vega 3 sbu with an Oxford Instruments Xact energy-dispersive analyzer) and IR spectroscopic (Spectrum One IR Fourier-spectrometer and a Multiscope microscope, PerkinElmer) research methods. Results. In xenoliths of weakly-altered tholeiitic basalts, volcanic glass is smectitized and partially replaced by secondary aggregates of chlorite and carbonate. In hematitized xenoliths, the smectite-hematite mineral association contains skarn epidote and garnet. Smectite aggregates, partially transformed into magnetite mass, are present in the magnetitized volcaniclastites. The studied smectites are classified as saponite according to the obtained values of basal reflections d001 in the range of 14.76–15.23 Å and calculated crystal chemical formulas. The differences in the morphology, chemical composition, and IR spectrometric characteristics of smectites reflect the varying degrees of transformation of the tholeiitic basalts in multi-stage ore-forming processes.