Distribution and characterization of heavy minerals in Meghna River sand deposits, Bangladesh

Abstract

Heavy mineral (HM) concentrations in sand bar deposits of the Meghna River were evaluated using optical microscopy, X-Ray Diffraction (XRD), X-Ray Fluorescence spectrometry (XRF), Scanning Electron Microscopy (SEM) and Electron Probe Microanalysis (EPMA) to determine the mineralogy, geochemistry and likely source rocks of the sands, and to examine the distribution and HM potential of the valuable heavy minerals, ilmenite and garnet. The Meghna sands were dominated by the light minerals quartz and feldspar and grainsize analysis results showed that>78 wt.% of the sand population fell within the size range of fine to very fine sand (−250 + 63 μm). The HM component made up around 9 wt.% and consisted mainly of amphibole (∼17–46 wt.%), epidote (∼7–30 wt.%) and garnet (∼3–21 wt.%). Fe-Ti oxide minerals including ilmenite, rutile, and titanomagnetite were present at levels of 0.7–7 wt.% with the magnetite content at 0.9–7 wt.%. The textures (moderate sorting, sub angular) and significant feldspar (6–15 wt.%) content in the sands indicated low degrees of hydraulic sorting and low amounts of alteration/weathering. The HM assemblage indicated a likely mixed source area of varying metamorphic grade (low to high) facies and igneous rocks. EPMA results from the detrital ilmenites and garnets showed that for ilmenite, TiO2 contents were between 42.9 and 54.5 wt.% (ave. 51 wt.%), with overall low impurities, while the garnet compositions were dominated by Fe-rich, almandine types. From the chemical analysis of individual garnet and ilmenite grains, it is likely the Meghna River sands have good potential for commercial extraction of garnet and ilmenite.