Metallic Mineral Deposits

Abstract

Iron, and hence iron ores, have played a very important role in the history of human civilization, because of which the latter has been named “Iron Age”. The principal types of iron ores are variously enriched hematite-dominated banded iron formation (Superior type) and variously modified magnetite-dominant banded iron formation (Algoma type). The Superior type deposits mainly formed during late Archean-early Proterozoic period. Algoma type is somewhat older. India’s iron ore deposits, with an estimated reserve of 28 Gt, are concentrated in South India, Central India, and Eastern India. Mn ores, principally oxides to hydroxides, formed during separate events from early Proterozoic to recent (Mn-nodules) in South Africa, Brazil, Ghana, Gabon, India, and countries of previous USSR. Genetically the deposits are hydrothermal, sedimentary (-diagenetic), and of supergene enrichment. Chromium, obtained from chromite, is essentially magmatitic (orthomagmatic) in origin and chromite deposits are commonly associated with mafic–ultramafic rocks. Out of India’s reserves of 139 Mt of chromite ores, >90% is located in eastern India and the rest in south India. Bulk of gold in nature forms in the “native state”, which does not mean 100% purity in reality. Alloying with Ag (and Hg) is common. Most ores form from hydrothermal fluids of primary and secondary origin and as placers (and nuggets). Gold is reported from different parts of India, but the largest yield came from the Kolar gold field in Karnataka amounting to 800 t Au. Copper mineralization was recorded from the Singhbhum copper belt, occurring in association with altered volcanic rocks, now interpreted by some to represent an IOCG situation. Khetri copper deposits are associated with metasediments. Malanjkhand Cu(–Mo) deposit is associated with calcalkaline granitic rocks. SEDEX-type Pb–Zn deposits of Rampura-Agucha, Rajpura-Dariba, and Zawar belt were deposited in Paleoproterozoic sediments of Rajasthan. All these deposits are regionally metamorphosed in grades varying from granulite to upper greenschist facies. Total reserves of Pb–Zn ores were estimated to be 685.59 Mt in 2010. Mineralization of Sn, W, Nb, Ta, Li, Be, F, and REE occur in the pegmatites of Bastar-Malkangiri belt, Bihar mica belt and Rajasthan-Gujarat areas. Monazite in the beach sands of South India is a good source of REE. The same sands are also endowed with large Ti resource in the form of ilmenite and rutile. India is one of the five major Al-ore containing countries of the world. Bauxite is of residual origin produced from Al-rich rocks. In India, the principal belts of bauxite are located along the East coast, Central India, and the West coast. Warm and wet climate with good drainage favor bauxitization.