1

A RESEARCH CARRIED OUT

BY

AGBAJE TITUS MAYOWA

Email address: feelmayor@gmail.com.

AT THE UNIVERSITY OF ILORIN, KWARA STATE, NIGERIA

COAL DEPOSIT IN MAMU

FORMATION, ANAMBRA BASIN

2

OUTLINE

INTRODUCTION……………………………………………………………………………………………… 3

GEOLOGY OF THE BASIN………………………………………………………………………………… 4

STRATIGRAPHY OF ANAMBRA BASIN…………………………………………………………….. 6

EVOLUTION HISTORY OF ANAMBRA BASIN……………………………………………………. 9

PALEOENVIRONMENTAL CHARCATERISTICS OF MAMU FORMATION……………. 10

EXPLORATION HISTORY OF ANAMBRA BASIN……………………………………………….. 11

ECONOMIC GEOLOGY OF COAL IN MAMU FORMATION……………………………….. 13

MINING AND MARKET…………………………………………………………………………………… 14

REFERENCES………………………………………………………………………………………………….. 15

3

INTRODUCTION

Coal, is organic in origin; however, it contains some inorganic matters called

Macerals. Most of the Macerals contained in coal occur in the form of mineral

inclusions, and they constitute the bulk of the non-combustible portion of coal

which, on burning is left behind as ash (Diesel, 1992).

Nigeria is endowed with a large coal deposits most of which are reported to be

within the Benue Trough (Carter et al., 1963 and Obaje et al., 1994). The Benue

Trough of Nigeria which is subdivided into Lower, Middle and Upper portions

contains a thick folded sedimentary pile ranging in age from Albian to Recent

(Kogbe, 1976; Petters, 1982, and Ojoh, 1992). The coal deposits of the Anambra

Basin, located in southeastern Nigeria, appear to contain the largest and most

economically viable coal resources. This basin covers an area of approximately 1.5

million hectares and is constrained by the Niger River on the west, the Benue

River on the north and the Enugu Escarpment on the east. The coal is

predominantly in one seam that outcrops along the eastern side of the basin at

the base of the Enugu Escarpment and dips gently toward the center of the basin.

De-Swardt and Casey (1963) later reported the occurrence of coals in the Nsukka

Formation (formerly called the ‘Upper Coal Measures’), located 4 miles north of

Okaba town. Lignites and sub-bituminous coals are distributed within the coal

measures of the Maastrichtian Mamu and Nsukka Formations in the Lower Benue

Trough (Akande et al., 1992a). The Nigerian coals are sub-bituminous (black coals)

of Campanian – Maastrichtian age, and Lignites (brown coals) of Tertiary age.

4

GEOLOGY OF THE BASIN The geology and stratigraphic descriptions of sediments in the Benue Trough of

Nigeria have been generally discussed and widely reviewed by many authors

(Carter et al., 1963; Reyment, 1965; Petters, 1982; Offodile, 1976; Benkhell, 1989;

Obaje et al., 1994; Omada and Ike, 1996; Obaje, 2009).

Lignites and sub-bituminous coals are distributed within the coal measures of the

Maastrichtian Mamu and Nsukka Formations in the Lower Benue Trough (Akande

et al., 1992a) and in the Campanian – Maastrichtian Gombe Sandstone Formation

in the Upper Benue Trough. The coals in the Lower Benue outcrop mainly in

Enugu area where four mines: Iva Valley, Onyeama, Okpara and Ribadu are being

worked by the Nigerian Coal Corporation.

5

Figure 2: Geology sketch map of Anambra basin

6

STRATIGRAPHY OF ANAMBRA BASIN

Figure 3: Stratigraphic successions in the Anambra Basin

Sedimentation in the Lower Benue Trough commenced with the marine Albian

Asu River Group, although some pyroclastics of Aptian – Early Albian ages have

been sparingly reported (Ojoh, 1992). The Asu River Group in the Lower Benue

Trough comprises the shales, limestones and sandstone lenses of the Abakaliki

Formation in the Abakaliki area and the Mfamosing Limestone in the Calabar

Flank (Petters, 1982). The marine Cenomanian – Turonian Nkalagu Formation

(black shales, limestones, siltstones) and the interfingering regressive sandstones

of the Agala and Agbani Formations rest on the Asu River Group. Mid-Santonian

deformation in the Benue Trough displaced the major depositional axis westward

which led to the formation of the Anambra Basin. Post-deformational

7

sedimentation in the Lower Benue Trough, therefore, constitutes the Anambra

Basin.

NANKA FORMATION

The Eocene Nanka Sands mark the return to regressive conditions. The Nanka

Formation offers an excellent opportunity to study tidal deposits. Well-exposed,

strongly asymmetrical sand waves suggest the predominance of flood-tidal

currents over weak ebb reverse currents. The presence of the latter are only

suggested by the bundling of lamine separated from each other by mud drapes

reflecting neap tides. A good outcrop of the Nanka Formation is the Umunya

section, 18 km from the Niger Bridge at Onitsha on the Enugu – Onitsha

Expressway.

NSUKKA FORMATION

The Nsukka Formation and the Imo Shale mark the onset of another transgression

in the Anambra Basin during the Paleocene. The shales contain significant amount

of organic matter and may be a potential source for the hydrocarbons in the

northern part of the Niger Delta (Reijers and Nwajide, 1998). In the Anambra

Basin, they are only locally expected to reach maturity levels for hydrocarbon

expulsion.

AJALI SANDSTONE

The Ajali Formation (Middle to Late Maastrichtian) a sandy tidal deposit lies above

and the Late Maastrichtian to Danian Nsukka Formation, also a paralic coaly

sequence completes the succession (Obianuju, 2005).The fluviodeltaic sandstones

of the Ajali and Owelli Formations lie on the Mamu Formation and constitute its

lateral equivalents in most places. The converging littoral drift cells governed the

sedimentation and are reflected in the tidal sand waves which are characteristic

for the Ajali Sandstone.

8

MAMU FORMATION

The coal-bearing Mamu Formation and the Ajali Sandstone accumulated during

this epoch of overall regression of the Nkporo cycle. The Mamu Formation occurs

as a narrow strip trending north–south from the Calabar Flank, swinging west

around the Ankpa plateau and terminating at Idah near the River Niger The Ajali

Sandstone marks the height of the regression at a time when the coastline was

still concave. The Mamu Formation is best exposed at the Miliken Hills in Enugu,

with well-preserved sections along the road cuts from the King Petrol Station up

the Miliken Hills and at the left bank of River Ekulu near the bridge to Onyeama

mine.

NKPORO/ENUGU SHALE

Sedimentation in the Anambra Basin thus commenced with the Campanian-

Maastrichtian marine and paralic shales of the Enugu and Nkporo Formations,

overlain by the coal measures of the Mamu Formation. In the Paleocene, the

marine shales of the Imo and Nsukka Formations were deposited, overlain by the

tidal Nanka Sandstone of Eocene age. Down dip, towards the Niger Delta, the

Akata Shale and the Agbada Formation constitute the Paleogene equivalents of

the Anambra Basin. The Enugu and the Nkporo Shales represent the brackish

marsh and fossiliferous Pro-delta facies of the Late Campanian-Early

Maastrichtian depositional cycle (Reijers and Nwajide, 1998). Deposition of the

sediments of the Nkporo/Enugu Formations reflects a funnel-shaped shallow

marine setting that graded into channeled low-energy marshes. The best

exposure of the Nkporo Shale is at the village of Leru (Lopauku), 72 km south of

Enugu on the Enugu – Portharcourt express road, while that of Enugu Shale is at

Enugu, near the Onitsha-Road Flyover.

9

EVOLUTIONAL HISTORY OF ANAMBRA BASIN

The Benue Trough was formed by rifting of the central West African basement,

beginning at the start of the Cretaceous period. At first, the trough accumulated

sediments deposited by rivers and lakes. During the Late Early to Middle

Cretaceous, the basin subsided rapidly and was covered by the sea. Sea floor

sediment accumulated, especially in the southern Abakiliki Rift, under oxygen-

deficient bottom conditions. In the Upper Cretaceous, the Benue Trough probably

formed the main link between the Gulf of Guinea and the Tethys Ocean

(predecessor of the Mediterranean Sea) via the Chad and Iullemmeden Basins.

Towards the end of this period the basin rose above sea level, and extensive coal

forming swamps developed, particularly in the Anambra Basin. The trough is

estimated to contain 5,000 m of Cretaceous sediments and volcanic rocks.

A common explanation of the trough's formation is that it is an aulacogen, an

abandoned arm of a three-armed radial rift system. The other two arms

continued to spread during the break-up of Gondwana, as South America

separated from Africa. The two continents seem to have started to split apart at

what are now their southern tips, with the rift extending up the modern

coastlines to the Benue Trough, then later split along what is now the southern

coast of West Africa and the north eastern coast of South America. As the

continents were wedged apart, the trough opened up. When separation was

complete, the southern part of Africa swung back to some extent, with the

sediments in the Benue Trough compressed and folded. During the Santonian

age, around 84 million years ago, the basin underwent intense compression and

folding, forming over 100 anticlines and synclines. The deposits in the Benue

Trough were displaced westwards at this time, causing subsidence of the

Anambra basin.

10

PALEOENVIRONMENTAL CHARACTERISTICS OF MAMU

FORMATION

The Campanian Maastrichtian stratigraphic succession in the Anambra Basin

begins with Nkporo Formation, which are predominantly marine shales of

Campanian age overlain by the Mamu Formation (Early to Late Maastrichtian),

paralic sandstones, mudstones and coals.

Umeji (2002) subdivided the Mamu Formation into three litho logic units which

are:

i). black carbonaceous marine shales which are overlain by more sandy units

(shore face deposits), showing typical heterolithic wave rippled, flaser bedded,

fine, white sandstones interlaminated with dark or grey mudstones;

ii). the coal-bearing facies;

iii). an upper unit composed of fine to medium-grained sandstone, with climbing

ripple-lamination. The studied section lies within the upper part of the coal-

bearing facies.

The sandstones are fine to medium grained and yellow in color. The Shale and

Mudstones are dark blue or grey and frequently alternated with the Sandstone to

form a characteristically striped rock. Coal seams vary in thickness from a few

inches to 12ft (Reyment 1965, Simpson 1956 and Whiteman 1982).

11

EXPLORATION HISTORY OF COAL IN ANAMBRA BASIN

Anambra Basin in Lower Benue Trough is a major coal producing basin in Nigeria

where intensive exploration and exploitation activities have been on since 1916.

Coal was first discovered in 1909 in Udi near Enugu by the Mineral Survey of

Southern, Nigeria. It was discovered in the Mamu Formation (formerly called the

\lower coal measures) of the Anambra Sedimentary Basin (Simpson, 1954). In

1950, the Nigerian Coal Corporation (NCC) was formed and given the

responsibility for exploration, development and mining the coal resources. The

NCC is 100% owned by the Federal Government and is headquartered in Enugu.

NCC has operated two underground mines, Okpara and Onyeama, and two

surface mines, Orukpa and Okaba, located on the eastern edge of the Anambra

Coal Basin.

Between 1950 and 1959, coal production in the Enugu mines increased annually

from 583,487 tonnes to a peak of 905,397 tonnes. After 1959, production

decreased significantly each year including the Civil War period of 1966 to 1970

when no coal production was reported.

Production in the 1980s was less than 100,000 tonnes annually and decreased

further in the 1990s. Much of this production was utilized by the railroad and

some smaller tonnages were exported. NCC has not operated any coal mines for

several years.

12

Figure 4a: Part of Coal Measure in Mamu formation, Lower Benue Trough

exposed in Okaba Area.

Figure 4b: Coal in Okaba Area, Lower Coal Measure

13

ECONOMIC GEOLOGY OF COAL IN MAMU FORMATION

A large coal reserve probably in excess of 1,000 Million tonnes is believed to occur

within the Mamu formation at depth over 600m in Amangiodo area of Enugu

State. Nigeria estimates its coal reserves at more than 2 Billion tonnes with

approximately 650 Million tonnes proven.

COMBUSTION

The calorific value of an air dried sample of Nigerian coal is usually between 7,000

and 8,000 kca/kg (Orajaka et al., 1990). Mackowsky (1982) in his work found out

that the calorific value of Onyeama, Orukpa, Okaba and Gombe coals ranges

between 7,000 – 8,000 kcal/kg, while that of the Obi/Lafia coal ranges between

7,500 – 8,500 kcal/kg. These are high and optimum calorific values for

combustion. It can be used as a domestic fuel. It gives a gas of high calorific value

and produces exceptional yields during low-temperature carbonization processes.

The combustibility, grind ability, calorific values and ash properties are genetically

linked to one another and they all depend on the coal rank and Maceral

composition (Mackowsky, 1982). And based on combustion properties (calorific

value, grind ability and ash properties) the most optimum coals for combustion

are those from the upper part of the Onyeama mine, lower part of the Orukpa

mine, Okaba whole mine and the sub-bituminous series of the Gombe coal

deposits.

14

GASIFICATION

Coal-based vapor fuels are produced through the process of gasification.

Gasification may be accomplished either at the site of the coalmine or in

processing plants. In processing plants, the coal is heated in the presence of

steam and oxygen to produce synthesis gas, a mixture of carbon monoxide,

hydrogen, and methane. This synthesis gas (syngas) can then be converted into

transportation fuels like gasoline and diesel through the Fischer – Tropsch

process. Currently, this technology is being used by the SASOL Chemical Company

of South Africa to make gasoline from coal and natural gas. Alternatively, the

hydrogen obtained from gasification can be used for various purposes such as

powering a hydrogen economy, making ammonia, or upgrading fossil fuels.

On-site gasification is accomplished by controlled, incomplete burning of an

underground coal bed while adding air and steam. To do this, workers ignite the

coal bed, pump air and steam underground into the burning coal, and then pump

the resulting gases from the ground. Once the gases are withdrawn, they may be

burned to produce heat or generate electricity. Or they may be used in synthetic

gases to produce chemicals or to help create liquid fuels.

In these regards, Enugu, Orukpa and Okaba coals in the Lower Benue Trough are

optimum for gasification while the high-volatile bituminous coals in the Middle

Benue Trough (Obi/Lafia coals) are sub-optimum for this purpose.

LIQUEFACTION

Liquefaction processes convert coal into a liquid fuel that has a composition

similar to that of crude petroleum. Coal can be liquefied either by direct or

indirect processes. However, because coal is a hydrogen-deficient hydrocarbon,

15

any process used to convert coal to liquid or other alternative fuels must add

hydrogen. Four general methods are used for liquefaction:

(1) Pyrolysis and hydro carbonization, in which coal is heated in the absence of air

or in a stream of hydrogen;

(2) Solvent extraction, in which coal hydrocarbons are selectively dissolved and

hydrogen is added to produce the desired liquids;

(3) Catalytic liquefaction, in which hydrogenation takes place in the presence of a

catalyst; and

(4) Indirect liquefaction, in which carbon monoxide and hydrogen are combined

in the presence of a catalyst.

MINING AND MARKET

Coal seams can be mined by surface/underground method. The choice of mining

method is dictated by both technical and economic factors. The most important

technical factors are the thickness of the coal seam, the depth of the coal seam,

the inclination of the seam and the surface topography.

Coal is the most widely available and well-distributed fossil fuel in the world and

is the second largest primary source of energy after crude oil in consumption

terms, and the largest in terms of reserves. Global consumption of coal is forecast

to increase significantly between 2010 and 2020.

The mined coal will be largely sold to international parties, however, there is

increasing domestic demand for coal. Nigeria has over 160 million people, the

required energy consumption has been estimated to be over 120,000 MW,

however, and at present Nigeria can only supplies 3,500 MW. Nigeria is also

changing from hydropower generation to coal fired power plants.

16

REFERENCES

Akande, S. O., Hoffknecht, A. & Erdtmann, B. D. (1992a). Rank and Petrographic

Composition of Selected Upper Cretaceous and Tertiary Coal of Southern Nigeria.

International Journal Coal Geology 20, 209 – 224.

Benkhell, J. (1989). The Origin and Evolution of the Cretaceous Benue Trough,

Nigeria. Journal Africa Earth Sciences 8, 251 – 282.

Carter, J. D., Barber, W., Tait, E. A. & Jones, G. P. (1963). The Geology of Parts of

Adamawa, Bauchi and Borno Provinces in Northeastern Nigeria. Bulletin

Geological Survey Nigeria, 30, 1 – 108.

Diesel, C. F. K., (1992). Coal Bearing Depositional Systems. Springer Verlag, Berlin,

721pp.

De-Swardt, A. M. J. & Casey, O. P. (1963). The Coal Resources of Nigeria.

Geological Survey of Nigeria Bulletin, 28: 1 – 100.

Kogbe, K. C. (1976). Paleogeographic History of Nigeria from the Albian Times. In:

Geology of Nigeria (Edited by Kogbe, C. A.). 2nd Edn. Elizabethan Pub. Co. Lagos,

pp. 15 – 35.

Mackowsky, M.-Th (1982). The Application of Coal Petrography in Technical

Processes. In: Stach’s Textbook of Coal Petrology (Edited by Stach, E., Mackowsky,

M.-Th., Teichmuller, M., Taylir, G. H., Chandra, D. and Teichmuller, R.), 413 – 483.

Gebruder Borntraeger, Berlin.

Nigeria Coal Cooperation, NCC 1950

Obaje, N. G., Ligouis, B. & Abba, S. I. (1994). Petrographic Composition and

Depositional Environments of Cretaceous Coals and Coal Measures in the Middle

Benue Trough of Nigeria. International Journal Coal Geology, 26, 233 – 260.

Obaje, N. G. (2009). Geology and Mineral Resources of Nigeria. Springer

Dordrecht Heidelberg London New York, 221 pp.

Obianuju, P. U., (2005). Palynological Study of the Okaba Coal Mine Section in the

Anambra Basin, Southern Nigeria. Journal of Mining and Geology. vol. 41, No. 2.

pp. 194

Offodile, M. E. (1976). The Geology of the Middle Benue, Nigeria. Palaentological

Institute, University Uppsala, Special Publication 4: pp 1–166.

17

Ojoh, K. A. (1992). The Southern part of the Benue Trough (Nigeria) Cretaceous

Stratigraphy, Basin Analysis, Paleo-oceanography and Geodynamic Evolution in

the Equatorial Domain of the South Atlantic NAPE Bull 7:131–152.

Omada, J. I. & Ike, E. C. (1996). The Economic Appraisal and Genesis of the Barite

Mineralization and Saline Springs in the Middle Benue Trough, Nigeria. Journal

Mineralogy, Petrology, Economic Geology 91, 109 – 115.

Orajaka, I. P., Onwuemesi, G., Egboka, B. C. E. & Nwanfor, G. I. (1990). Nigerian

Coal. Mining Magazine, pp. 446 – 451.

Petters, S. W. (1982). Central West African Cretaceous – Tertiary Benthic

Foraminifera and Stratigraphy, Palaeontographica Abteilung A 179, 1 – 104.

Reyment, R. A. (1965). Aspects of the Geology of Nigeria. 145p. University Press,

Ibadan.

Simpson A. (1954). The Nigerian Coalfield: The Geology of Parts of Owerri and

Benue Provinces. Geological Survey of Nigeria. Bulletin 24, pp 1 – 85.

Umeji, A. C., (2002). Evolution of the Abakaliki and the Anambra Sedimentary

Basins, Southeastern Nigeria. A report of Shell Chair Project submitted to S.P.D.C.

Nig. Ltd. 155pp.

Whiteman, A.J., (1982). Nigeria. Its Petroleum Geology, Resources and Potential.

Graham and Trotman, London, pp. 39.