|Platinum Group of Elements (PGE)|
|Platinum is an extremely rare metal, occurring as only 0.003 ppb in the Earth’s crust, and is 30 times rarer than gold. If all the world’s platinum reserves were poured into one Olympic-size swimming pool, it would be just deep enough to cover one’s ankles. Gold would fill more than three such pools.|
|The platinum group (alternatively, the platinum group metals or platinum metals) is a collective name sometimes used for six metallic elements clustered together in the periodic table. The six platinum group metals are ruthenium, rhodium, palladium, osmium, iridium, and platinum. They have similar physical and chemical properties, and tend to occur together in the same mineral deposits. Platinum Group of Elements/Metals (PGE/PGM) (Pt, Pd, Rh, Ru, Os, Ir) are the rarest of precious metals in the earth’s crust. These metals are recovered from a few primary deposits and as byproduct in Ni-Cu production. In recent years, PGE are gaining worldwide importance in view of their increasing application in modern technology.|
|Sperrylite (platinum arsenide, PtAs2) ore is a major source of this metal. A naturally occurring platinum-iridium alloy, platiniridium, is found in the mineral cooperite (platinum sulfide, PtS). Platinum in a native state, often accompanied by small amounts of other platinum metals, is found in alluvial and placer deposits in Colombia, Ontario, the Ural Mountains, and in certain western American states. Platinum is also produced commercially as a by-product of nickel ore processing. The huge quantities of nickel ore processed makes up for the fact that platinum makes up only two parts per million of the ore. South Africa, with vast platinum ore deposits in the Merensky Reef of the Bushveld complex, is the world’s largest producer of platinum, followed by Russia.|
|Iridiosmium is a naturally occurring alloy of iridium and osmium found in platinum-bearing river sands in the Ural Mountains and in North and South America. Trace amounts of osmium also exist in nickel-bearing ores found in the Sudbury, Ontario region along with other platinum group metals. Even though the quantity of platinum metals found in these ores is small, the large volume of nickel ores processed makes commercial recovery possible.|
|Metallic iridium is found with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include osmiridium and iridiosmium, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing.|
|Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario and in pyroxenite deposits in South Africa. Ruthenium is commercially isolated through a complex chemical process in which hydrogen is used to reduce ammonium ruthenium chloride yielding a powder. The powder is then consolidated by powder metallurgy techniques or by argon-arc welding.|
|The industrial extraction of rhodium is complex as the metal occurs in ores mixed with other metals such as palladium, silver, platinum, and gold. It is found in platinum ores and obtained free as a white inert metal which is very difficult to fuse. Principal sources of this element are located in river sands of the Ural Mountains, in North and South America and also in the copper-nickel sulfide mining area of the Sudbury Basin region. Although the quantity at Sudbury is very small, the large amount of nickel ore processed makes rhodium recovery cost effective. However, the annual world production of this element is only 7 or 8 tons and there are very few rhodium minerals.|
|Palladium is found as a free metal and alloyed with platinum and gold with platinum group metals in placer deposits of the Ural Mountains, Australia, Ethiopia, South and North America. However it is commercially produced from nickel-copper deposits found in South Africa and Ontario. The huge volume of nickel-copper ore processed makes this extraction profitable in spite of its low concentration in these ores.|
|PLATINUM RESOURCES IN INDIA|
GSI accordingly laid due emphasis on search and assessment of PGE/PGM in the country. The primary deposits are likely to be located in orthomagmatic deposits. Only some occurrences are known in epigenetic hydrothermal type of environment. The following geological domains are favourable for PGE mineralization and the target areas for exploration are:-
Plutonic and hypabyssal layered intrusives of Archaean as well as Early Proterozoic ages in Singhbhum, Dharwar and Bastar Craton. Layered, differentiated mafic-ultramafic complexes with chromite and titaniferous vanadiferous magnetite in greenstone belts and komatiite in greenstone belt.
Mafic-ultramafic layered sequences within Proterozoic Mobile belt skirting cratonic block.
Hydrothermally altered high Mg-volcanic rocks in Proterozoic fold belt.
Ophiolite belts of Cenozoic age in the Extra Peninsular India and Andaman-Nicobar islands.
The belts with differentiated layered complexes which would deserve special attention are:-
North Kanara schist belt, Karnataka.
Nuggihalli schist belt, Karnataka.
Kushalnagar area, Coorg district, Karnataka and Usgaon area, Goa.
Sandur schist belt, Karnataka.
Sittampundi Layered Complex, Tamil Nadu.
Mettupalem-Velliankadu area, Tamil Nadu.
Ultramafic rocks in Attapadi and Nilambur valley, Kerala.
Chimalpad-Chimakurthi-Kondapalli in Andhra Pradesh
West Singhbhum district in Jharkhand
In Orissa, chromite and titaniferous – vanadiferous magnetite are hosted by ultrabasic and basic members respectively of the stratiform intrusions which are exposed in several partially developed stratigraphic sections. These constitute the prime targets of PGE. Sukinda ultramafic chromite belt, Baula-Nausahi chromite belt, Betei-Pindbasa-Nilgiri sector show analogous set-ups of early magmatic ultramafic sequence which gave anomalous values for PGE.