Geological Overview

Geological Mining Kenya

Geological Mining Kenya

The geology of Kenya may generally be grouped into the following five major geological successions: Archean (Nyanzian and Kavirondian), Proterozoic (Mozambique Belt and Bukoban) Palaeozoic/Mesozoic sediments, Tertiary/Quaternary volcanics and Tertiary/Quaternary sediments

Quaternary:

Soils, alluvial beach sands, evaporates, fossil coral reefs and sandstones at the coast: alluvial and lacustrine sediments of the Rift Valley. There are also volcanic rocks of the rift valley from the younger volcanoes.

Tertiary:

Coastal sediments, Late Miocene and Pliocene volcanics, Terrestrial and lacustrine inland sediments. There are Early Tertiary formations not represented at surface.

Palaeozoic/Mesozoic:

(Cretaceous, Jurassic, Triassic, Permian and Carboniferous): The Karroo formations of the coastal hinterland, including the basal sedimentary formation in north-east Kenya.

Proterozoic:

  • Kisii series (Bukoban system): Volcanics with sediments
  • Mozambique Belt:quartzites, biotite/hornblende gneisses, schist, granitoid gneisses, amphibolites, migmatites.
  • Intrusives:syntectonic granites

Archean:

  • Kavirondian system: Mudstones, Sandstones, Conglomerates,Granitic intrusions
  • Nyanziansystem:Shales,cherts,ironstones,Pyroclastics, Rhyolites, Andesites, Basalts.

The Nyanzian Shield

The Nyanzian and Kavirondian systems forming the Nyanza Craton are the oldest rocks in the country with ages over 2,500 million years.

The Nyanzian system is mainly composed of lavas and pyroclastics with minor sediments and banded ironstones. The Kavirondian, which rests unconformly on the Nyanzian, consists of grits, sandstones, greywackes and conglomerates. Both the Nyanzian and Kavirondian svstems are isoclinallv folded about axes that have an east-westerly trend.

Kavirondian, is only slightly younger than Nyanzian but folding in the two systems has similar orientation. Numerous granitic bosses and batholiths have intruded the Nyanzian and Kavirondian. The Kavirondian intrusions were more but the pre-Kavirondian were also widespread and the two systems are discernible.

Mozambique Belt

The Mozambique belt is a structural unit within which a wide variety of meta-sedimenta-ry and meta-igneous rocks are found showing a broad concordance of structural style and metamorphic history. In most of these rocks, the degree of deformation is intense and is of high metamorphic grades. They were thus referred to earlier in literature as the basement system rocks, due to high degree of metamorphism and deformation.

Recent work on the Mozambique Belt has shown that rocks can be sub-divided into groups of contrasting lithology, structure and composition of igneous rocks content. These groups are being studied in greater detail in order to come up with proper chronostrati-graphic terminology.

Within the Mozambique Belt basic igneous complexes are found and range in size from bosses to small dykes. Thev occur both east and west of the Rift Valley. Some of the older basic intrusions have undergone deformation and metamorphism to give ortho-amphibo-lites and charnockitic gneisses.

Basic and granitic intrusions are known in the Mozambique Belt. The most characteristic feature of the Mozambique Belt is its structural trend which is more or less north-south in its entire belt.

Variations of the northerly trend are minor and, when observed, can be explained and are localised. The majority of Mozambique Belt rocks have been placed in upper Precambrian (Proterozoic).

Palaeozoic and Mesozoic Formations

Palaeozoic and Mesozoic formations in Kenya are found near the coast and in north-east part of Kenya. The earliest of these rocks are Permo-Carboniferous which are mostlv sand-stones and shales that form the Duruma series. This is equivalent to the Karroo system in Southern Africa. The local formations are Taru; Maji-ya-Chumvi; Mariakani and the Mazeras. They extend for about 100 kilometres from Taru to Mazeras, west of Mombasa. The rocks dip very gently towards the ocean and are heavily faulted in places.

Mesozoic rocks occur in two separate areas, in the north-east part of Kenya and along the Coast belt. The stratigraphy and fossils in the two areas are very distinct and it is likely that the sedimentary basins in the two areas were connected. Revision mapping in the area has come up with interesting lithological units that have revised lithological names.

Tertiary and Quaternary Vblcanics

Volcanic rocks cover the central parts of the country from south to north, occurring in the floor of the Rift Valley and on the peneplains west and east of the valley.

The oldest of the volcanics are of Lower Miocene age and comprise the eroded lavas and pyroclastic piles of South Nyanza. Late in Miocene times, Kapiti and Yatta phonolites were erupted and flowed to great lengths.

Further eruptions accompanied by faulting persisted and also gave rise to the Rift Valley and the volcanic piles of Mounts Kenya, Elgon and Kilimanjaro.

Quaternary volcanism was mostly within the Rift Valley and has given rise to the craters and cider cones that are found in the floor of the valley e.g. Longonot, Menengai and Suswa.

Tertiary and Quaternary Sediments

There are many deposits of sediments in various parts of Kenya. They usually occur at the base of volcanic succession, intercalated with it or occurring in tectonic troughs.

The repeated faulting of the Rift Valley floor and the numerous volcanic eruptions created many short-lived basins of internal drainage in which lacustrine and fluviatile sediments accumulated. Most of these sediments are unfossiliferous, but a few are of interest as they contain deposits that bear artefacts and interesting fossils that have been studied extensive-

The more important sediments of middle Pleistocene are the Olorgesaillie lake beds, a lacustrine series with much diatomite, mammalian fossils and artefacts. This is also comparable to the Kariandusi sediments near Gilgil and the Kanjera Beds in the Kavirondo Gulf off Lake Victoria. Olorgesaillie beds and Kariandusi sediments are in the Rift Valley.

MINERAL OCCURRENCE

A wide range of minerals, both metallic and non-metallic (industrial), are known to occur in the country. These include barite, gypsum, gold, silver, lead, talc, titanium, salt, a variety of gemstones, (mainly ruby and several varieties of garnet) dimension stones, silica sand, heavy mineral sands, manganese, zinc, wollastonite, graphite, kaolin, copper, nickel, chromite, pyrite, various clays, rare earth elements and pyrochlore.

The Geological environments for the mineralization can be summarised as follows:

  • The Archean Nyanzian Craton area of Western Kenya where metallic mineralization of base and precious metals are known to occur: gold, copper and silver have been mined in the past. They are also potential for ferrous and no-ferrous metals. Kimberlitic bodies have also been reported.
  • The Proterozoic Mozambique Belt that is most extensive in Central Kenya north to South in which minerals such as kyanite, corundum, graphite, wollastonite, marble, asbestos, fluorspar, magnesite, kaolin and a variety of gemstones are found together with minerals associated with basic and granitic rocks.
  • The sedimentary rocks of Palaeozoic to Quaternary are widespread. These rocks are sources and hosts of limestones, gypsum, clays, manganese and construction materials and possibly hydrocarbons. Base metal mineralization, lead-zinc-barite and copper are known to occur in the sedimentary basin along the coastal belt.
  • Heavy mineral sands also occur along the coastal beach sands and recently deposits of about 3.2 billion tons of titanium bearing have been discovered.
  • The volcanic rocks associated with Rift System host a variety of minerals and construction materials. The volcano-sedimentary accumulations have deposits of clays, evaporites, trona (soda ash), diatomite, natural carbon dioxide, kunkar and gypsum. Gem quality rubies have also been discovered recently.

The geothermal fields are found in the area and some have been exploited, currently producing 57 MW of power to the national grid.

Carbonatites are known to be host of several minerals found in the Nyanzian shield area, around Lake Victoria shores and in the southern part of the coastal sedimentary basin. Mrima, one of the carbonatites known for potential of niobium and rare earth elements (REE) is found in the coastal basin, south of Mombasa.

CURRENT ACTIVITIES

Exploration

A number of international companies, including, Tiomin, AfriOre and Kansai/Mid-Migori are currently carrying out exploration activities for gold. Tiomin Resources Inc. has recently completed exploration for heavy mineral sands and has been issued with a Mining Lease. A fiscal agreement providing for incentives has also been signed.

Mining

The Kenya Mining industry is dominated by production of non-metallic minerals which are mainly: soda ash (trona), fluorspar, diatomite, vermiculite, natural carbon dioxide, kaolin, barytes, a variety of gemstones, limestone and lime products including various construction materials.

In the case of metallic minerals, some quantities of gold are being produced. Iron ore is produced from localised small deposits and is utilised in the manufacture of cement in the country.

Mineral Products

Soda ash is produced from the mineral trona that occurs at Lake Magadi which is situated within the Great Rift Valley. The commodity is produced by the Magadi Soda Company Limited in one of the biggest known natural sources of trona in the world. The bulk of the soda ash is exported but a good deal of the commodity is used in various local industries as well. The annual production during the year 2005 was valued at US$ 38million.

Trona occurs together with common salt and Lake Magadi is also a major source of crude salt.

Fluorspar is mined to the east of the town of Eldoret within the Rift Valley system. The Kenya Fluorspar Company Limited operates the mine. The mine produces acid grade Fluorspar of which the bulk is for export.The annual production for the year 2005 was valued at US$ 14million.

Diatomite is produced at Gilgil within the Rift Valley, but it is also known to occur in a number of localities within the Rift Valley system. The commodity is produced for both export and local markets. Its potential is large.

Vermiculite is produced from Lodosoit which is in the northern central part of the Rift Valley Province within the pre-Cambrian rocks of Mozambique belt.

Limestone and lime products are produced for the manufacture of cement and other industrial products. Cement and construction industries take the bulk of the limestone mined and quarried. Limestone, marbles and dolomites are widely occurring in the country and a large tonnage of the commodity is known to exist. Along the coastal belt, Bamburi Portland Cement Company Limited exploits kunkar and crystalline limestone in the vicinity

The three cement factories, Athi River, Bamburi and East Africa Portland produce over 1.5 million tonnes of cement to meet local needs.

Natural Carbon dioxide associated with the rift system, is exploited in a number of places and has been marketed by Carbacid (C02 Mfg) Limited for industrial purposes. Other Industrial Minerals exploited include gypsum which is mined in Tana River in the Coastal belt, Kajiado near Nairobi and in Turkana in North Western Kenya. Gypsum is mined and supplied to local cement plants and some is exported to Uganda

Kenya boasts of a wide range of coloured and ornamental stones of gem quality, which are mined in the country These mainly include, in order of importance, ruby, tsavorite, sapphire, various types of garnet, peridot, tourmaline, aquamarine and others.

Lead was being produced from galena, which was being mined in small quantities in the coastal belt, where it was smelted together with scrap lead to manufacture lead batteries.

Gold is known to occur in a number of places in gold bearing greenstone rocks of Nyanzian Craton in Western Kenya. Areas with alluvial gold are being harvested by local miners through conventional panning in the northern part of the country.

Titanium and zirconium production

Substantial deposits (3.2 billion tonnes) of mineral sands containing ilmenite, rutile and zircon along the Kenyan Coast have been established through exploration work by Tiomin Resources Inc. of Canada. These deposits occur in Kilifi, Kwale, Mambarui and Vipingo areas. Tiomin is focusing first on the Kwale deposit owing to its higher grades of the minerals.

The mineralized sand deposits in Kwale amount to 200 million tonnes which is approximately 6% of the total identified deposits in the Coast Province. Tiomin will mine about 140 million tonnes that are economicallv recoverable out of the 200 million tonnes over a period of 14 years. The value of minerals to be extracted at Kwale over this period is approximately US$ 695 million. During the first 6 years output would be more than 330,000 tonnes ilmenite, 75,000 tonnes rutile and 37,000 tonnes zircon per year.

Tiomin estimates that it will spend USS 150 million in construction of the project facilities and another USS 415 million as operating costs during the project’s 14 years life span.

During the first 5 years of production the Government will receive approximately USS 2.5 million as royalty per year and is expected to increase thereafter. The Government will also receive income tax, corporate tax and other taxes. In addition the project will contribute to GDP growth.

During its construction phase the project would create about 1,000 direct jobs with additional employment in the operational phase. A further 1000 jobs would be created indirectly through sub contracting and provision of goods and sendees to the project.

The project would expend about USS 20 million in Coast Province alone every year. Out of this USS 2.0 million will be for salaries and wages. In addition the company will improve infrastructure and construct social amenities in the area. At the resettlement site, Tiomin will construct two primary schools, two secondary schools, two dispensaries, one health centre, two social halls, water supplies at each settlement village and relocate and built churches and mosques that exist at the mine site.

The Company is expected to start the construction phase of the Kwale Project this year after the compensation and resettlement issues have been completed. Production is to commence in 2007.

Mineral commodities contributed about one per cent of the Gross Domestic product (GDP). However, there exists tremendous potential that awaits exploitation. Investors are expected to take up the opportunity presented to them in the form of favourable fiscal reform to invest in mineral exploration and mining.

MINING OPPORTUNITIES

There exist high mineral potential areas i.e. the gold bearing greenstone belt of Western Kenya and Mozambique Belt in Central and Southern Kenya. Several exploration companies have been granted exploration licenses to explore for gold and base metals in these areas. Some of the above high mineral potential areas have been staked by both local and foreign companies. Investors may wish to enter into joint ventures with companies already holding exploration concessions.

Kenya has a well developed transport and communications system, which is progressively being improved and modernized to meet the needs of the expanding economy. A welldeveloped road and air network, seaports, posts and telecommunication facilities provide back-up to industrial development.

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One Response to “ Geological Mining Kenya ”

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