Geochemistry and genesis of Silica sand deposits, Marakkanam area, Tamil Nadu, India

Abstract

White sand (the commercial name of Silica sand) was thoroughly investigated on the basis of the geomorphology, sedimentology, geochemistry, light and heavy mineral study to find out the origin of deposit present in the study area. The geomorphology of the study area indicates that most of the landforms are aggradational and are oriented along the coast line with the formation of three lagoons namely Kaliveli, Yedayantittu Kaliveli and Mudaliyarkuppam Lagoons. The economically viable Silica sand is deposited in front of the sea and acted as a barrier to form these lagoons. The over all geology suggests that the study area is made up of sedimentary deposits from Cretaceous to Recent. The polymodality of frequency curves of silica sands indicate the multi source of deposition. With the presence of paleo channels and lagoon in the study area, the sediments might have been transported by river and deposited under barrier, beach and lagoonal environments. The bivariate plots indicate the silica sand samples were probably deposited in the beach and fore shore environment. The Visher diagram of the samples of the study area is characterized by traction, saltation and suspension population. The CM pattern shows the samples of the study area leading to the transportation of sediments by rolling. In the study of Heavy and Light minerals, the monocrystalline quartz is found to be of a dominant (90-95 %) followed by polycrystalline quartz (3 ? 10 %) and feldspars (2 ? 4 %). The heavy minerals of the study area are very meager in quantity showing a very good amount of diversification. The heavy mineral assemblages consist of zircon, rutile, tourmaline, topaz, kyanite, epidote, garnet, chlorite, hypersthenes and pyroxenes. The SEM studies of the silica sand grains show various surface solution features, rounded crescent like pits, net like sutures, V shaped pits, concoidal fractures and crack like features. Few well rounded grains are also noticed may be due to long transportation mostly by rolling.