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), bt rm crest (BM), backshore (BS), dune (DU), and beach ridge or strandline (SL), upto I tn depth, at fifteen stations, spaced at a distance of approximately 10 km interval. Out of four size ranges (-420 to +350 mu, -210 to +177 mu, -105 to +88 mu and the fraction consisting of the highest percentage in the sediment - first mode), the +88 mu 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 21.95%. This concentration may be due to the winnowing by wave action and selective sorting processes. Erosion exposes one of the stations in the bench 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 pincer 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.