PROSPECT OF GEMSTONES OF INDIA IN 21ST CENTURY

Diamond occurs in both primary (kimberlite/lamproites) and secondary (conglomerate and gravel) deposits in three distinctive provinces namely the South Indian Diamond Province in Dharwar Craton, the Central Indian Diamond Province in Bundelkhand Craton and the Eastern India Diamond Provincein Bastar and Singhbhum Cratons. About 184 kimberlite and lamproite bodies have so far been located. The only diamond mine is located on Majhgawan lamproite, Panna Diamond Belt, Madhya Pradesh.

Coloured gemstones, mainly ruby, occur in the western margin of Eastern Ghats within the Transition zone with Bastar Craton in Kalahandi district, Odisha. Blue sapphire occurs in kaolinised pegmatite/plumasites traversing the lenses of actinolite-tremolite rocks in Sumjam area, Jammu & Kashmir. Occurrences of star ruby/translucent ruby have been noted in the Karur-Kangayam belt of the Southern Granulite Terrain (SGT). Sporadic occurrences of emerald are found associated with pegmatites traversing ultramafics along the Aravalli ridge between the towns of Udaipur and Ajmer in Rajasthan. Aquamarine (with or without topaz and tourmaline), occur associated with pegmatites traversing gneisses and mica schist in parts of Tamil Nadu, Karnataka, Odisha and Rajasthan. The gem varieties of chrysoberyl (Cat’s Eye and alexandrite) occurs in pegmatites intruding ultramafics and its contact zones in the western and northern margins of Eastern Ghats Mobile Belt (EGMB). Amethyst and agate occur in different parts of Deccan volcanic province. Many small occurrences of gem varieties of garnet (almandine-rhodolite and hessonite), iolite, zircon, spinel, tourmaline, sillimanite, apatite, kyanite, etc have been reported mainly from highgrade metamorphic terrain of EGMB and SGT.

The current emphasis is focused on the direct assessment of all the discovered/ reported kimberlite/ lamproite bodies for their actual micro-diamond contents and systematic exploration within the Proterozoic platform deposits bordering Dharwar, Bastar and Bundelkhand cratons. The zones of metamorphic/ metasomatic/ pegmatitic activities in the protoliths or reactive zones covering western part of EGMB and in and around Palghat-Cauvery Shear Zone in SGT in Kerala and Tamil Nadu hold good prospect for coloured gemstones and for plate tectonic gemstones like ruby.