Application of CCSEM to heavy mineral deposits: Source of high-Ti ilmenite sand deposits of South Kerala beaches, SW India

For the characterization of sediments, Computer Controlled Scanning Electron Microscopy (CCSEM) is a powerful method in obtaining chemical data on individual mineral grains and modal analysis of the heavy mineral fraction of sediment samples. Here we show how the CCSEM method can be used to evaluate ilmenite ore grade as well as a tool to investigate the source of heavy mineral deposits. The heavy mineral rich deposits in beach sands around the town of Chavara in SW India are characterized by ilmenite with elevated TiO2 contents, often exceeding 60 wt.%. In order to determine the origin of these high-TiO2 ilmenite deposits, we collected a series of beach sediment samples (22) from a c. 800 km long stretch of coastline from northern Kerala state to well within the Tamil Nadu state. A set (7) of river sediments was also taken, roughly covering the catchment area to the beach samples. The data show that the sediments in the Chavara high-Ti ilmenite deposit are distinguished by minor elements in ilmenite, garnet chemistry and heavy mineral assemblage: Chavara ilmenite has high MgO and low MnO contents; garnets have low grossular components and the heavy mineral assemblage is dominated by sillimanite–kyanite in addition to ilmenite. These features correlate with basement geology in the hinterland, and with sediments from rivers, draining the basement. Based on these observations we conclude that high-Ti ilmenite from Chavara beaches originates in the khondalite belt of high-grade metasediments. Our study demonstrates rapid mineral analyses in sediments by CCSEM to be efficient in the characterization of mineral compositions and assemblages in sediments, in the identification of possible source regions and thus ultimately in exploration for industrial mineral resources.