Buried Placer Mineral Deposits along the East Coast Between Chennai and Pondicherry

Along the east coast of India between Chennai and Pondicherry, 163 sediment samples were collected from different sub-environments of the beach representing low water mark (LWM), foreshore (FS), berm crest (BM), backshore (BS), dune (DU), and beach ridge or strandline (SL), upto 1m depth, at fifteen stations, spaced at a distance of approximately 10 km interval, Out of four size ranges (-420 to +350μ, -210 to +177μ, -105 to +88μ and the fraction consisting of the highest percentage in the sediment - first mode), the +88μ size range shows rich concentration of heavies (8.26 to 96.6 %). The heavy mineral content in the bulk sediment samples ranges from 0.55 to 22.95 %. This concentration may be due to the winnowing by wave action and selective sorting processes. Erosion exposes one of the stations in the beach ridge, up to 4 m depth from the surface and shows a higher concentration of heavy minerals. This information, along with analytical results of the stations from the surface upto one metre depth, indicating heavy mineral concentration of 8%, suggests the possibility of buried placer deposits at about 2 to 4 m depth along the beach ridge. Based on this prognostication, a random station was selected i.e. near Mahabalipuram and manual boreholes were drilled. These boreholes have confirmed the existence of buried placer deposits having concentration of 8 to 88 % of heavy minerals around 1.5 to 4 m depth of beach ridge. R mode and Q mode factor analyses indicate the possible environmental parameters prevailing at the time of deposition as well as under the present conditions in the stations.