Effect of Tsunami in the ilmenite population: An examination through X-ray diffraction, scanning electron microscopy and inductively coupled plasma atomic emission

Abstract

Kerala state in the SW part of Indian subcontinent hosts one of the best beach placer deposits in the world. The near shore deposit is ~140Mt and is very rich in heavy minerals, often up to 70%, and ilmenite forms its chief constituent. The seasonal enrichment of this deposit takes place through monsoonal activity and the recent tsunami (24 December 2004) had significantly contributed its share. Mineralogical and chemical variation of the surface (pre- and posttsunamigenic) as well as subsurface ilmenites (4-5m depth) of this deposit has been investigated. SEM examination on ilmenites of pre-tsunamigenic period conveys that the micromorphology represents mostly of mechanical activities rather than chemical and solution activities. Both post-tsunamigenic and subsurface ilmenites were influenced dominantly by solution and chemical alteration. The pre-tsunamigenic (surficial) ilmenite grains consist only of rutile as an altered product with a small FeO – Fe2O3 ratio. However, the presence of considerable altered products such as rutile and pseudorutile in the post-tsunamigenic and subsurface ilmenite indicates that the ilmenite alteration is in an advanced state. Regarding trace element composition, it was found that Al, Mg, Na, Ca, Cd, Co, K, Sr and Pb have higher contents in both core and post-tsunamigenic ilmenite than the pre-tsunamigenic ilmenite. These elements play an important role in understanding the behavior of the minerals during beneficiation and further processing. The relative lesser content of such elements in the onshore pre-tsunamigenic ilmenite grains reveals that the chemical leaching has not been active compared to the ilmenite concentrates from the shallow sea that have been brought by the tsunami and also to that have been deposited earlier and now seen underneath up to a depth of ~5m.