Manganese industry in Nigeria
Introduction
This paper reviews available information on manganese in Nigeria, provides additional useful data and examines the prospects of developing a manganese mineral industry in Nigeria.
Geological setting of Nigeria
Approximately one half of Nigeria is underlain by rocks of the Precambrian Basement Complex [granites, gneisses, migmatites, gabbro, basalt, schist among other rocks]. The other half comprises sediments in a number of basins, the key ones being the Sokoto Basin, the Chad Basin, the Benue Trough and the Niger Delta Basin. The sediments are Late Jurassic to Recent. The Younger Granites [consisting of ring dykes] were intruded into the Pre-Cambrian Basement, during manganese minerals have been recorded both in the crystalline rocks and the sediments.
However, there has been no detailed information on the characteristics of the manganese such as tectonic setting, depositional environment, geological setting, host rocks mineralogy, resources, reserves. Some of the manganese occurrences mentioned turn out to be flash in the pan.
Manganese on a global context
Manganese minerals occur in host rocks which may be crystalline or sedimentary.
However, sedimentary marine deposits predominate as sources of manganese on a global scale. High grade ore [40% and above] with reserves of over 100 million tones found in a few countries South Africa, Australia, Brazil and Gabon. There are deposits elsewhere with smaller reserves and an average 30% Mn. In Precambrian terrain, rhodochrosite, manganiferous quartzites, gondites are common host rocks. Sedimentary marine manganese deposits are most commonly hosted by dolomite, limestone, chalk, calcareous sandstones and black shales.
Other features
i) Minerals
manganese minerals are varied oxides, carbonates and silicates.
They include:
– Pyrolusite MnO2
– Braunite 3Mn2O3:MnSiO3
– Ramsdellite MnO2
– Hausmannite
– Manganite MnO(OH)
– Kutnohorite Ca (Mn, Mg, Fe) (CO3)2
Also of some importance are:
– Rhodochrosite
– Psilomelane
– Cryptomelane
– Gondite
– Mnganocalcite
– Manganolite [rock] a general term for rocks containing manganese especially manganese oxide
End use
Steel and iron making [consumes most of the manganese produced]
Upgrading ferroalloys
In dry cell batteries, animal feed, fertilizers
In some aluminum alloys
Pigments
Colorants
Chemicals
Manganese Industry in Nigeria In Retrospect
Preamble
The brief review of the global manganese industry is of great relevance. Since mining is a global industry mineral resources may yield revenue in the international market or be used in domestic industry. The use of some locally produced minerals in domestic manufacture of goods should be part of a new frontier which emphasizes accelerated industrial development in Nigeria in this regard. Manganese with a variety of end uses, is a very attractive commodity.
Manganese occurrences
A negative feature in the extractive minerals industry in Nigeria is that the true geological picture’ is hardly ever given i.e. a clear indication of the status’ of the mineral being described occurrences, resources/reserves etc. There are instances where investors sought for what could be best referred to as flash in the pan.
It appears that to date all references to manganese occurrences are yet to be adequately investigated. Vigorous exploration programmes are imperative.
Exploration Guide
Genetic Models
The empirical models indicate that manganese occurrences are associated with crystalline and sedimentary rocks. The recorded occurrences of manganese in the rocks of Precambrian Basement Complex, the metasedimentary rocks of the north-western Nigeria and rocks in the Zaria area and Calabar Flank/Oban Massif. The indicated grades are from 10% to 25% Mn.
Nwabufo-Ene [2004, 2005, and In Press] discussed the potentials of manganese in the Calabar Flank/Oban Massif. In some areas manganese has been removed from host rocks and may have been adequately concentrated to form deposits. The favourable host rocks include manganiferous carbonate [rhodochrosite], manganiferous quartzites, garnetiferous quartzites as well as gondite. Some of the pyrolusite occur with cryptomelane and are probably intermediate rather than end products. The products may have been facilitated by the highly acidic and potassic environment.
This feature ought to be noted during exploration of special economic interest is the supergene manganese formed by the action of groundwater. Groundwater dissolved Mn from the host rock in reducing conditions in an upper groundwater body. Subsequently the Mn was precipitated as Mn4+ bearing minerals by interaction with an oxygenated lower groundwater body.
Assays of over 40% Mn have been indicated.
The foregoing emphasizes that exploration will benefit by mapping the host rocks and searching for possible supergene deposits. The host rocks and a number of other characteristics of the Mn in the Calabar Flank/ Oban Massif are very similar to those in some countries in West Africa.
– Nsuta deposit, Ghana
– Mokta deposit Coite Ivoire
Sedimentary manganese
Nwabufo-Ene [2005, In Press] described occurrences of manganese in the Gidan Bauchi, Black Shale Member, Dange Formation, Palaeocene, Sokoto Basin. The occurrences may be related to the intersection of oxidation reduction interfaces with epicontinental sediments. In general the tectonic setting for sedimentary manganese deposits.
Shallow marine environments [shorelines, continental shelf and interior basins (such as the Benue Trough) preferably in sheltered sites. Black shale pinchouts are abundant in Nigeria and may be favourable sites.
Other favourable environments
Bauxites and other ores formed by weathering i.e. Laterite type deposits may be of interest. Sites of supergene manganese enrichment should be primary targets. Geophysical techniques have in general not been found to be useful except the use of self-potential to locate supergene capping.
Economics
The potential for a non-export’ manganese industry in Nigeria is high. Special interest may be taken by investors on manganese of:
i) Battery grade
ii) Chemical grade
High grade of the manganese is generally essential the best option is to locate zones of supergene enrichment. It is important to note that export of manganese may compete with production of high grade Mn deposits such as those in South Africa, Australia, Brazil and Gabon [grade of ore approximately 36 to 54% Mn- supergene enrichment has produced up to 70% Mn]. The manganese oxides may be amenable to simple refining process and used in local industries such as batteries and chemicals.
Conclusion
Well- planned exploration using the scientific method [ore deposit models, mineral deposit models effective exploration models] may define economically important Mn deposits. The data available indicates an emphasis on the zones of supergene enrichment. Investors are encouraged to take an interest in a domestic manganese industry. There should be a dynamic balance between the extractive and Non-extractive sectors.
References
Nwabufo-Ene 2004 Manganese in Nigeria genesis and exploration methods Trammel Open files circ. 10 15p
Nwabufo-Ene 2005 Reflections on the economic equations in the minerals industry in Nigeria Paper presented to the Nigeria Mining and Geosciences Society, Nnamdi Azikiwe University Awka -10pp
Nwabufo-Ene [In Press Economic Equations in the minerals Industry
