Impact of Coastal Features on Beach Placers: A Case Study Using Remote Sensing Data

Abstract

Black and white aerial photographs of the Central West Coast of India for a stretch of about 500 km (Bombay to Goa) were interpreted by mirror stereoscope to study the coastal features. Subsequently ground truth data was also collected to confirm the photographic findings. Altogether 200 representative beach samples were collected from high tide and low tide levels and analysed for its heavy mineral content. Photographic grey tone variation of the beach sediments were correlated to the differential concentration of heavies in the sediments. Impact of lithology, coastal geomorphology and drainage on the concentration of heavies was established. Coast shows marine, fluvial and aeolian features and dendritic drainage pattern. Rivers carry lots of sediment load due to heavy rainfall and high relief in the catchment area. In aerial photographs beach sands show white, greyish white, dark grey and black tone depending upon the percentage of the black minerals. Comparison of the tonal variation with heavy mineral percentage reveals that light minerals show white tone and as the percentage of heavies increases, the tone changes dark grey to black. Mineralogical study indicates that the heavy mineral percentage varies from 0.4 to 98.64%. Where the concentration of heavies is more the rock type along the coast and in the catchment area of the rivers is Deccan basalt with appreciable laterite cover and drainage intensity is high. As drainage intensity decreases and where the rock type is granite and gneisses the concentration of heavies is low or almost negligible.