Provenance and Implications of Heavy Minerals in the Beach Sands of India's Central West Coast

Shalini, G.; Hegde, V.S.; Soumya, M., and Korkoppa, M.M., 2020. Provenance and implications of heavy minerals in the beach sands of India's central west coast. Journal of Coastal Research, 36(2), 353–361. Coconut Creek (Florida), ISSN 0749-0208.The heavy mineral assemblage and mineral chemistry of the beach sands of Mulki, Karnataka, central west coast of India, are discussed in this paper to understand their provenance. The study is based on the seasonal modification in shoreface profiles and identification of heavy minerals under binocular microscope followed by electron probe micro-analysis. The heavy mineral assemblage of the Mulki estuarine beach sands includes ilmenite, magnetite, zircon, rutile, hornblende, epidote, kyanite, and tremolite. There are two generations of ilmenite. The older generation is characterized by porous ilmenite that shows TiO2/FeO between 1.32 and 8.09. The second generation of ilmenite is characterized by fresh, rounded to angular grains that have relatively lower TiO2/FeO ratios (<1.25). Rutile also shows two types: one with TiO2 >97% and another with TiO2 <94%. The presence of two generations of ilmenite and rutile suggests reworking of the older generation, probably derived from the offshore region or a paleobeach brought by the combined action of alongshore current and waves to the present beach, and a second generation brought by the modern drainage system. The heavy mineral assemblage and mineral chemistry suggest mixed provenance consisting of basic igneous rocks, acidic rocks, and high-grade metamorphic rocks. Mafic and acidic source rocks are indicated by the presence of two types of ilmenite, one with Cr2O3 and the other devoid of Cr2O3, and two types of hornblende, one rich in MgO and the other poor in MgO. High-grade metamorphic source rocks are indicated by the presence of rutile, kyanite, and tremolite. The Mulki-Pavanje River drains from a low-grade metamorphic terrain. Therefore, high-grade metamorphic minerals are attributed to an external source brought by alongshore drift.