Geochemistry

Monazite

Metamorphic rock

Zircon

Placer mining

Geomorphology

Gneiss

Archaeology

Biotite

Sillimanite

Geology

Paleontology

Placer deposit

Kyanite

Quartz

Mining engineering

Geography

Provenance

Heavy mineral

Hornblende

Staurolite

Marine Geology

Heavy-mineral concentrates known as black sands occur in layers and patches along the Kerala beaches, situated on the southwest coast of India. Detailed microscopic studies of 28 beach samples and 32 river bed samples from 16 west-flowing rivers of Kerala were examined. The heavy-mineral suite consists of opaques, hornblende, tremolite-actinolite, hypersthene, clinopyroxene, zircon, monazite, garnet, sillimanite, epidote, staurolite, apatite, etc. Distribution maps of these minerals on the beaches and in river sediments have been prepared. Opaques as high as 96% were noted in some samples on the beach. The minerals are derived mainly from the charnockites, khondalites, granite gneisses, pegmatites or retrograde charnockites from the drainage basins of the different rivers. A combination of two or more characteristic minerals was also identified for the major rivers of Kerala. Five heavy-mineral provinces on the beach were recognised. From north to south they are: (1) mixed mineral province with opaques, zircon, hornblende, garnet, sillimanite, epidote; (2) garnet-hypersthene province; (3) opaque zircon province; (4) hornblende-hypersthene province; and (5) opaque zircon monazite province. Vigorous wave activity during the southwest monsoon, the longshore current and onshore offshore movements played an important role in sorting the heavy-mineral placer sands. A three-stage depositional model of the heavy-mineral placer sands corresponding to the initial, transgressive and regressive stages influenced by wave and current activity is suggested.

The black sand placer deposits of Kerala beach, southwest India