Application of liberation analysis in ferromanganese encrustations from South Andaman Sea: An automated mineral identification technique using TIMA

Abstract

Automated scanning electron microscopic studies got exclusive acceptance in identification of various mineral phases; its classification and characterization based on their composition and abundance in semi quantitative manner. Nowadays, these techniques are adopted in understanding various poorly crystalline and amorphous materials to reveal the actual mineral assemblages. Primary mineral phases of five ferromanganese crust and nodule samples collected from West Sewell Ridge and Sewell Rise in South Andaman Sea are studied using automated mineral analyser to understand the mineral assemblages and their micro textures. The internal morphology of these encrustations is densely parallel to sub parallel micro botryoidal textures indicating a precipitated origin from ambient seawater. Since crust and nodules are formed by colloidal precipitation, unclassified materials observed in primary phase analyses may represent the presence of poorly crystalline and amorphous ferromanganese colloidal phases. The liberation analysis, Back Scattered Electron image (BSE), Energy Dispersive X-ray Spectroscopy (EDS), and elemental mapping of the samples revealed occurrence of manganese - iron oxy-hydroxides as alternate laminations/ thin layers along with detrital materials; that forms the composition and internal texture. Major mineral phases identified from liberation analysis using TIMA are todorokite, vernadite, Fe vernadite, cryptomelane, ferrogedrite, glauconite, Fe oxides disseminated, quartz, biotite, orthoclase, illite, plagioclase, amphibole, zinwaldite, and romanechite. Thus, automated mineral identification using TIMA can be effectively adopted for mineral phase identification in ferromanganese encrustations, which is rather difficult using other techniques.