Comparison of the chemistry and mineralogy of ilmenite concentrates sourced from fluvial (Brahmaputra River) and beach placer (Cox’s Bazar) deposits, Bangladesh

Abstract

Bangladesh has known concentrations of heavy mineral (HM) sand resources in shoreline placer deposits along the southern and eastern coastlines and also within river sand bar placer deposits associated with the extensive river systems throughout the country. The high-grade Cox’s Bazar beach placer deposits are in populated and environmentally sensitive areas making the future of mineral sands exploitation uncertain. In comparison, the Brahmaputra fluvial deposits are less rich in total HMs but constitute a potential major resource.The recovery of Ti-rich ilmenite from beach placer deposits is widespread but rare from fluvial deposits however many river systems in Bangladesh are annually dredged to maintain open waterways offering a new source of heavy minerals. Exploitation will depend on the quality of the ilmenite compared to existing commercially traded material. In this study, ilmenite concentrates derived from fluvial deposits (Brahmaputra River) and beach placer deposits (Cox’s Bazar) were compared using XRF, XRD and EPMA techniques.The level of impurities associated with the Brahmaputra River ilmenite was higher than in the equivalent Cox’s Bazar fractions suggesting possible issues with liberation or the properties of the associated gangue minerals reacted differently to the separation conditions, or both. Ilmenite from both regions exhibited texturally alike grain types and chemically similar compositions with detrital ilmenite from Cox’s Bazar characterised by TiO2 contents ranging from 49–53 wt-% (average 51 wt-%) while the range for the Brahmaputra River was 44–53 wt-% (average 49 wt-%). The slightly higher and much narrower range in TiO2 for the Cox’s Bazar material was consistent with this material having been subject to more chemical weathering resulting from a longer transit time and reworking through wave action. Based on the major and minor element compositions of ilmenites from both sources, the most likely route for processing the ilmenite-rich component would be via the sulphate route to pigment.