Stones of Zimbabwe (Part: 1)
Minerals of Zimbabwe
Gold mining and exploration in Zimbabwe has been going on from ancient times and it is estimated that a third (about 700 tonnes) of all historical gold production was mined locally from the seventh century until the introduction of mechanised mining methods with the arrival of Europeans about a century ago. There are over 4000 recorded god deposits, nearly all of them located on ancient workings.
It occurs as native silver in association with other minerals such as gold, copper and lead. With the exception of the Osage Mine in Zimbabwe, it is declared as a by-product from the mining of platinum, gold and copper. Gold mines in the Odzi greenstone belt have the highest silver and gold ratios.
Platinum Group of Elements
Platinum Group Metals (PGMs) consist of platinum, palladium, rhodium, ruthenium, iridium and osmium and have a high demand worldwide because of their wide variety of uses in industry. Zimbabwe’s Great Dyke, a linear early Proterozoic layered mafic-ultramafic intrusion trending over 550km at a maximum width of about 11kilometres, has the second-largest platinum reserves in the world after the Bushveld Complex in South Africa. An estimate of 2.8 billion tonnes PGM ore at 4g/t are estimated to lounge on the Dyke. Notably, PGMs are mined as primary metals only in the Bushveld in South Africa and along the Great Dyke in Zimbabwe.
Zimbabwe is located within an exceptionally rich diamondiferous metallogenic province. Large areas of the country are covered by the Archaean Craton and the Archaean Limpopo Belt which are likely to have the best-developed mantle root and diamond potential along with discoveries of the mineralised kimberlites on the Craton (Murowa, Sese, Colossus) and on the Limpopo Belt (River Ranch) which make Zimbabwe an excellent exploration target with potential for economic kimberlites. The diamond exploration success in neighbouring Botswana and South Africa, the greatest producers of gem-quality diamonds has made a positive impact on the diamond prospectively of the country.
Zimbabwe has the 2nd largest high-grade chromium ores in the world after South Africa with reserves of approximately 10 billion tonnes.
Giant crystals of up to 1.5m have been found on the dyke. Chrome is mainly used in stainless steel production, as a metal coat, in the chemical industry and in metallurgical processes.
Zimbabwe has vast high-grade coal deposits occurring as fossilised carbon. It occurs in lower Karoo sediments. The country’s full potential is however yet to be exploited.
In Zimbabwe nickel occurs within the Archean craton in rocks of komatiite composition e.g. at Trojan mine. There are nickel deposits in several serpentinite areas in greenstone belts with igneous complexes around the country. The country has got huge potential in komatiite and laterite and more than 30 nickel deposits are known. Currently, production is at Trojan mine in Bindura.
Asbestos occurs as chrysotile. Zimbabwe was once the world’s 3rd largest producer of asbestos before the demand declined. After gold asbestos was once the largest income producer in the mining sector. Production ceased with the closure of Gates Mine and Shabani Mine.
There are over 70 known deposits in Zimbabwe that have produced copper either as a primary or secondary product. The main producing area has been the Magondi Basin in an area stretching for over 150km.
Zimbabwe has huge iron deposits associated with banded ironstone formations in greenstone belts. Major deposits are estimated to be over 30 billion tonnes of reserves.
Pegmatites which are ubiquitous in several geological environments especially on the edges of green stones and in metamorphic belts are a source of a variety of minerals including tantalite, tin and wolframite, beryl, mica, feldspar, and gemstones such as emerald, aquamarine, chrysoberyl, alexandrite and euclase.
Though Sandawana emeralds are small, they stand out for their beauty and the quality of their colour as one of the most prestigious, beautiful and rarest gemstones in the world, so they retain value well. Their deep green colour comes from chromium.
Larger high-quality Sandawana emeralds are extremely difficult to obtain, and prices are over three times that of diamonds of the same size.
Granites, gneisses, migmatites, gabbro-norites, dolerite, marbles and quartzite, suitable for use as dimension stones, are typical rocks belonging to Zimbabwe’s geological environments.
The most well-known dimension stone in Zimbabwe is black granite ubiquitous in the north-eastern part of the country which has attracted considerate foreign investors.
The majority of stones used in Zimbabwe sculptures are locally sourced and they belong to the Serpentine family of stones. They are sedimentary rocks that are transformed into hard stones over a period of millions of years, due to intense heat and pressure. Serpentines are rich in iron.
Professional sculptures prefer harder varieties such as spring Stones. Dense stones have extremely fine grains and uniform structure and they are ideal raw materials for sculpting. Most of the stones used for sculpting are mined by hands at the Great Dyke.
The mines tend to be small-scale, open cast operations and they are too small to cause any environmental damages. Mining here is a valuable alternative source of income to the rural communities here.