1. 1 OLUSEGUN A. OLATINPO (2015)
A PART OF RESEARCH CARRIED OUT BY
OLATINPO, OLUSEGUN AYOBAMI
14/68ET003
AT THE UNIVERSITY OF ILORIN, ILORIN
ON SOME SELECTED MINERAL DEPOSITS IN NIGERIAN
SEDIMENTARY BASIN
IRON ORE DEPOSIT IN AGBAJA FORMATION,
SOUTHERN BIDA BASIN, NIGERIA
ADVANCED SEDIMENTOLOGY COURSE (GEM 690)
2. 2 OLUSEGUN A. OLATINPO (2015)
OUTLINE
1.0 INTRODUCTION
2.0 REVIEW OF THE GEOLOGY OF THE AREA
2.0.1 STRATIGRAPHY OF THE BASIN
2.0.2 TECTONIC HISTORY OF THE BASIN
2.0.3 PALEOENVIRONMENT OF THE AREA
3.0 ECONOMIC SIGNIFICANCE OF AGBAJA IRON ORE
4.0 LEVEL OF EXPLORATION OF THE RESOURCES
5.0 REFERENCES
3. 3 OLUSEGUN A. OLATINPO (2015)
1.0 INTRODUCTION
In today’s competitive world, identifying and exploit your areas of comparative advantage is the
key to survival. The solid minerals industry holds the greatest potential apart from the
Agricultural sector towards the attainment of the vision 20:2020 which is geared at placing
Nigeria amongst the top 20 economies of the world by the year 2020 because of the rich mineral
deposit in commercial quantity scattered in different parts of the country.
One of such mineral in Nigeria is Iron ore. There are over 3 billion tones of iron ore found in
Kogi, Enugu, Niger, Zamfara, and Kaduna States. The large deposit of oolitic iron ores of Kogi
and Enugu States are yet to be fully explored. Iron ore is used for making steel, transformer, and
motor cars, ferrous sulphate from waster liqueur of the steel picking process or by the direct
reaction, metals for electrical shielding, electro-magnetic devices, electric bells, electric fan cage,
equipment rack, instrument body, engineering works, hydrated salt, iron oxide pigments, various
salts of iron and ferrites and chemicals.
The Agbaja Formation hosts an extensive, shallow, flat-lying channel iron deposit and Mineral
Resources currently estimated at 586 million tonnes at 41.3% Fe (within EL12124) (Agbaja
Mineral Resource). The majority of the Mineral Resources are classified as Indicated (466
million tonnes at 41.4% Fe), the balance are classified as Inferred (120 million tonnes at 41.1%
Fe). The Agbaja Mineral Resource is one of the highest grade beneficiable iron ore resources in
West Africa, yet the current resource covers only 20% of the Agbaja town area within EL12124
that is considered prospective for channel iron mineralisation.
4. 4 OLUSEGUN A. OLATINPO (2015)
Table 1: Estimated Iron Ore in Nigeria
The rate of steel consumption of a Nation is a direct reflection of the economical and
technological advancement of such a Nation and if Nigeria is to increase her steel consumption
from its current level, massive investment in the exploitation and processing of iron ore is
required.
The Agbaja town where appreciable amount of ironstone is exposed lies 15 km northwest of the
city of Lokoja in Kogi State, and 165 km south west (highway) from Nigeria’s capital city of
Abuja. Lokoja has reticulated electrical power, cellular telephone networks, primary and
secondary schools, hospitals and other amenities. Abuja, being the political capital of Nigeria is a
well-established and serviced city; it has a large international airport with daily flights to Europe,
the middle-east and other African nations and is connected to Abuja by a well maintained duel
carriageway tarmac road (driving time ~2 hours). Importantly, Agbaja is proximal to existing,
under-utilised river and port infrastructure suitable for the transport of bulk commodities (such as
iron ore concentrate).
Nigeria is one of the richest countries of the world as far as mineral resources are concerned, iron
ore inclusive. The estimated workable iron deposits stand in excess of 2.5 billion tonnes most of
which belong to hematite, magnetite, hematite-geothite and siderite-geothite. (Alafara et al.,
2005) Iron is the sixth most abundant element in the universe and the most abundant metal in the
earth’s crust after aluminum. However, Agbaja iron ore has an estimated reserve of over 1 billion
tones (Alafara et al., 2005). The utilization of Agbaja iron ore is hampered by its poor response
5. 5 OLUSEGUN A. OLATINPO (2015)
to established industrial beneficiation techniques. This is as a result of fine grained texture of the
Agbaja iron ore (Uwadiale and Whewel, 1988).
Figure 1: Extraction of Iron Ore
The channel iron deposit of the Agbaja mine is located within the sub-horizontal to very shallow
east dipping Late Cretaceous Agbaja Formation, which is made up of an upper unit hosting
ferruginous sandstone and oolite/pisolite material (Laterite unit).
The Agbaja Ironstone studied covers some part of Koton-karfe sheet 227 SE and lies within
latitudes 8° 7′ 00′′ - 8° 10′ 30′′ N and longitudes 6° 48′00′′E - 6° 52′00′′E. It occurs within the
upper cretaceous sedimentary sequences of the Bida basin.
2.0 REVIEW OF THE GEOLOGY OF THE AREA
The Bida Basin, also known as the Mid-Niger or Nupe Basin, is located in west-central Nigeria
(fig. 2). Bida Basin is a linear intracratonic sedimentary basin located in central Nigeria
6. 6 OLUSEGUN A. OLATINPO (2015)
extending from Kontagora in Niger State of Nigeria to areas slightly beyond Lokoja in the south
(fig. 3). It trends NW – SE and lies approximately perpendicular to the Benue Trough. It is
separated from the basal continental bed of the Sokoto Basin by a narrow outcrop of the
crystalline basement rocks in the west and it is adjacent to the Anambra Basin in the east (fig. 2).
Often, experts working in the area have divided the basin geographically into northern and
southern Bida basins probably due to rapid facies changes across the basins. The wrench fault
tectonic model of which postulated the Bida Basin as strike slip feature is based on facies
distribution and evidence of syn-depositional basin floor lowering. The northern and southern
Bida (fig. 3) basins comprises of about 3km thick Campanian to Maastrichtian continental to
shallow marine sediments.
Figure 2: Geological Map of Nigeria Showing Bida Basin (Obaje 2009)
7. 7 OLUSEGUN A. OLATINPO (2015)
Figure 3: Geology and location of the Bida Basin and Environs
(Obaje et. al., 2011)
8. 8 OLUSEGUN A. OLATINPO (2015)
Figure 4: Geological map of the southern Bida Basin (Modified from Ojo and
Akande, 2009)
2.0.1 STRATIGRAPHY OF THE BASIN
The stratigraphic succession of Bida basin, collectively referred to as the Nupe Group
(Adeleye, 1974) comprises a twofold Northern Bida sub - basin and Southern Bida sub - basin or
Lokoja Sub- Basin (fig. 10). The basin fill comprises a northwest trending belt of Upper
Cretaceous sedimentary rocks that were deposited as a result of block faulting, basement
9. 9 OLUSEGUN A. OLATINPO (2015)
fragmentation, subsidence, rifting and drifting consequent to the Cretaceous opening of the South
Atlantic Ocean.
2.0.1.1 Southern Bida Basin
2.0.1.1.1 Lokoja Formation
Lithologic units in this formation range from conglomerates, coarse to fine grained sandstones,
siltstone and claystones in the Lokoja area. Sub-angular to sub-rounded cobbles, pebbles and
granule sized quartz grains in the units are frequently distributed in a clay matrix. Both grain
supported and matrix supported conglomerates form recognizable beds at the base of distinct
cycles at outcrops. The sandstone units are frequently cross-stratified, generally poorly sorted
and composed mainly of quartz plus feldspar and are thus texturally and mineralogically
immature. The general characteristics of this sequence especially the fining upward character,
compositional and textural immaturity and unidirectional paleocurrent trends, suggest a fluvial
depositional environment dominated by braided streams with sands deposited as channel bars
consequent to fluctuating flow velocity. The fine grained sandstones, siltstones and clays
represent flood plain overbank deposits. However, Petters (1986) reported on the occurrence of
some diversified arenaceous foraminifers from clayey intervals of the Lokoja Formation
indicating some shallow marine influence. These foraminifera microfossils identified by Petters
(1986) are however more common in the overlying Patti Formation where shallow marine
depositional conditions are known to have been more prevalent.
2.0.1.1.2 Patti Formation
Outcrops of the Patti Formation occur extensively on the Agbaja Plateau and Ahoko and
Abaji on the Lokoja-Abuja expressway. This formation consists of sandstones, siltstones,
claystones and shales interbedded with bioturbated ironstones. Argillaceous units predominate in
the central parts of the basin. The siltstones of the Patti Formation are commonly parallel
stratified with occasional soft deformational sedimentary structures (e. g. slumps), and other
structures as wave ripples, convolute laminations and load structures. Trace fossils (especially
Thallasinoides) are frequently preserved. Interbedded claystones are generally massive and
kaolinitic, whereas the interbedded grey shales are frequently carbonaceous. The subsidiary
sandstone units of the Patti Formation are more texturally and mineralogically mature compared
10. 10 OLUSEGUN A. OLATINPO (2015)
with the Lokoja Formation sandstones. The predominance of argillaceous rocks, especially
siltstones, shales and claystones in the Patti Formation requires suspension and settling of finer
sediments in a quiet and low energy environment probably in a restricted body of water (Braide,
1992). The abundance of woody and plant materials comprising mostly land-derived organic
matter, suggests prevailing fresh water conditions. However biostratigraphic and paleo-ecologic
studies by Petters (1986) have revealed the occurrence of arenaceous foraminifers in the shales
of the Patti Formation with an assemblage of Ammobaculites, Milliamina, Trochamina and
Textularia which are essentially cosmopolitan marsh species similar to those reported in the
Lower Maastrichtian marginal marine Mamu Formation (the lateral equivalent) in the adjacent
Anambra Basin (Gebhardt, 1998). Shales of the Mamu Formation on the southern side of the
Anambra Basin are commonly interbedded with carbonates and overlain by bioturbated
siltstones, sandstones and coal units in coarsening upward cycles toward the northern side of the
basin (Akande et. al., 2006). This sequence is overlain by herringbone-cross-bedded mature
sandstones of the Ajali Formation (Middle Maastrichtian) in the northern fringes of the basin
hence providing strong evidence for shallow marine, deltaic to intertidal depositional
environments for the Maastrichtian sediment of the Anambra Basin. The Patti formation,
therefore, appears to have been deposited in marginal shallow marine to brackish water condition
identical to the depositional environments of similar lithologic units of the Mamu and Ajali
formations in the Anambra Basin (Ladipo, 1988; Nwajide and Reijers,1996). The more marine
influences in the adjacent Anambra Basin is probably related to the nearness of that basin to the
Cretaceous Atlantic ocean prior to the growth of the Niger Delta.
2.0.1.1.3 Agbaja Formation
This formation forms a persistent cap for the Campanian-Maastrichtian sediments in the
southern Bida basin as a lateral equivalent of the Batati formation on the northern side of the
basin. The Agbaja formation is best exposed on the Agbaja Plateau where it overlies
successively the Lokoja and Patti formations. The Agbaja formation consists of sandstone beds
in this region. The sandstones and claystones are interpreted as abandoned channel sand
overbank deposits influenced by marine reworking to form the massive concretionary and oolitic
ironstones that had been mapped in some details (Ladipo et al., 1994). Minor marine influences
11. 11 OLUSEGUN A. OLATINPO (2015)
were also reported to have inundated the initial continental environment of the upper parts of the
Lokoja sandstone and the Patti formation (Braide, 1992; Olaniyan and Olabaniyi, 1996). The
marine inundations appear to have continued throughout the period of deposition of the Agbaja
ironstones in the southern Bida basin (Ladipo et al., 1994).
2.0.2 TECTONIC HISTORY OF THE BASIN
The inland basins of Nigeria constitute one set of a series of Cretaceous and later rift
basins in Central and West Africa whose origin is related to the opening of the South Atlantic
(Figure. 11). The upper Cretaceous Bida basin of central Nigeria is sandwiched between the
Precambrian schist belts of the Northern Nigeria massif and the West African craton. Of interest
is the southern part of the basin, which developed in a continental setting, because the facies
architecture of the sedimentary fill suggest a close relation between sedimentation dynamic and
basin margin tectonics (Sokari, 1990). This relationship is significant to an understanding of the
basin`s origin, which has been controversial. A simple sag and rift origin has been suggested, and
consequently dominated the negative thinking on the hydrocarbon prospects of the basin, which
were considered poor. Although distinguishing pull-apart basins from rift basins, based solely on
sedimentological grounds, may be difficult, the temporal migration of the depocenter, as well as
the basin architecture of repeatedly upward-coarsening, show a strong tectonic and structural
overprint that suggests a tectonic framework for the southern Bida basin similar in origin to a
pull-apart basin which was based solely on the sedimentological evidence proved to be a difficult
mechanism (Sokari, 1990).
The Bida basin is a gently down-warped trough whose genesis may be closely connected
with the Santonian orogenic movements of south eastern Nigeria. The basin is a NW-SE trending
embayment, perpendicular to the main axis of the Benue Trough and Niger Delta Basin. It is
frequently regarded as the north-western extension of the Anambra Basin, both of which were
major depocentres during the third major Transgressive cycle of southern Nigeria in Late
Cretaceous. Interpretations of LandSat images, borehole logs, as well as geophysical data across
the entire Bida Basin suggest that the basin is bounded by a system of linear faults trending NW-
SE. Gravity studies also confirm central positive anomalies flanked by negative anomalies as
shown for the adjacent Benue Trough and typical of rift structure (Ojo, 1984; Ojo and Ajakaiye,
1989). The Benue Trough is a failed arm of a triple junction (aulacogen) that existed beneath the
12. 12 OLUSEGUN A. OLATINPO (2015)
present position of the Niger Delta during the Cretaceous. The trough is filled with over 5000m
of predominantly Aptian to Maastrichtian sediments in the lower, middle and upper Benue
geographical regions. The Lower Benue Trough which includes the Anambra Basin is
considered as the southern extension of the Bida Basin. Initial gravity studies in the Bida Basin
put the maximum thickness of the sedimentary successions at about 3.5 km (Ojo, 1984) in the
central axis. Although the hydrocarbon potential of the basin has not been fully tested; the basin
remains undrilled. Both ground and aeromagnetic studies by several workers have outlined the
basin's configuration (Adeniyi, 1985; Udensi and Osazuwa, 2004). A recent spectral 99 analysis
of the residual total magnetic field values over several sections of the basin reveals an average
depth to the basement rock to be approximately 3.4km with sedimentary thickness of up to
4.7km in the central and southern parts of the basin (Udensi and Osazuwa, 2004). In general,
sediment thickness decreases smoothly from the central portion to the flanks of the basin.
Figure 5: Regional tectonic map of western and central African rifted basins showing the
relationship of the Muglad, Doba and East Niger Basins to Nigerian inland basins. Location of
13. 13 OLUSEGUN A. OLATINPO (2015)
regional shear zones (marked with half-arrow) and major zones extension (complete arrow) are
shown. (Adapted from Schull, 1988).
2.0.3 PALEOENVIRONMENT OF AGBAJA FORMATION
The Campanian-Maastrichtian Agbaja Ironstone Formation of the Bida basin, Nigeria, forms a
major part of the about 2 billion tons of iron ore reserves of the Middle Niger Embayment. The
ironstone deposits were previously reported to be similar to the Minette-type ironstones because
of their depositional patterns, composition and inferred origin. Four rock-types are recognized
within the Agbaja Ironstone Formation: ooidal pack-ironstone, pisoidal pack-ironstone, mud-
ironstone and bog iron ore. In the ironstones, kaolinite of both the groundmass and the
ooids/pisoids is of lateritic origin (figure 6), whereas the associated quartz, mica and heavy
minerals are of detrital origin.
Figure 6: Ironstone Bed at Agbaja Area
Ironstone
Bed
14. 14 OLUSEGUN A. OLATINPO (2015)
Ooids and pisoids were formed by mechanical accretion of platy kaolinite crystals by rolling on
the sea floor in a near-shore environment, and were subsequently transported and deposited
together with a fine-grained kaolinitic groundmass. Pyrite (mainly framboidal) and siderite (both
exclusively occurring as pseudomorphs of goethite and/or hematite) are diagenetic whereas
goethite is post-diagenetic in origin, resulting from the ferruginization of the kaolinitic precursor.
Crandallite-gorxeicite-goyazite, bolivarite and boehmite are also post-diagenetic in origin.
Hematite was formed from the dehydration of goethite, whereas gibbsite (restricted to the upper
part of the deposit) is of recent and in situ lateritic origin. The presence of newly formed
authigenic pyrite and siderite (now replaced by hematite and goethite) are indicators of a
reducing environment during diagenesis.
The absence of diagenetic chamositic clay minerals, evidently caused by a low Mg
concentration, suggests that fully marine conditions were not established during sedimentation.
This is supported by the lack of fossils, brecciated shell materials and bioturbation features in the
deposit. Reworking and redeposition of the primary constituents are inferred from broken
pisoids, nuclei of pisoidal/ooidal fragments in pisoids and high iron concentrations present in the
pisoids and ooids compared to that of the groundmass. These observations indicate that the
Agbaja ironstone deposits of the Lokoja study area exhibit some environmental and
mineralogical characteristics that are markedly different from other known deposits of Minette-
type, where primary chamositic clay minerals generally form the protore for the ironstones. The
recognition of kaolinite as the precursor constituent and the occurrence of similar deposits of the
same age (Late Cretaceous) in Nigeria, Sudan and Egypt have implications for the
paleoenvironmental interpretations of Phanerozoic ironstone deposits.
3.0 ECONOMIC SIGNIFICANCE OF AGBAJA IRON ORE
Kimberly (1994) defined ironstone as any sedimentary rock with total iron content greater than
15%. High grade iron is obtained from ironstone deposits around the world. Iron ores are usually
found in the form of magnetite (Fe3O4), haematite (Fe2O3), goethite (FeO(OH), limonite
(FeO(OH).n(H2O) and siderite.( FeCo3 ). Iron ore is the raw material used to make pig iron
which is one of the main raw materials of steel. Ninety-eight percent (98%) of the iron ore mined
globally is used to make steel (Wikipedia, 2010). The deficiency in iron content shown by many
ores is due to the presence of impurities. These impurities include silica, phosphorous, sulphur
15. 15 OLUSEGUN A. OLATINPO (2015)
and titanium. Sulphur and phosphorous are deleterious impurities in iron and steel industry
(Onyemaobi, 1998). Silica is objectionable because it displaces iron and so much lime is required
to flux it. Titanium is undesirable because it drives much of the iron in a furnace to the slag.
Magnetite iron ore deposits generally grade around 25-40% Fe, however the Agbaja Mineral
Resource is a unique sedimentary hosted magnetite deposit with a resource grade averaging
41.3% Fe, which with selective mining of higher grade material will provide a feed head grade of
45.7%, ranking it in the top quartile of magnetite projects world-wide with respect to resource
grade.
Magnetite deposits are typically found in banded ironstone formations (BIFs), however Agbaja is
unique in that it is a channel iron deposit (CID), with only two known similar deposits of this
kind in the world. Typical BIF magnetite deposits require large amounts of energy intensive
grinding to liberate the iron from its associated natural matrix, however the Agbaja CID material
is relatively soft and friable and only requires moderate grinding, simple magnetic separation,
and only a coarse grind particle size to liberate the iron. Consequently mining and processing
costs for the Agbaja project are relative low compared to other magnetite projects. Agbaja
estimated total operating costs rank in the bottom quartile when compared to operating costs of
all other magnetite projects.
4.0 LEVEL OF EXPLORATION OF THE RESOURCES
Kogi Iron Limited (Kogi, Kogi Iron or the Company) is an Australian company with the
objective of becoming an African iron ore producer through the development of its 100% owned
Agbaja iron ore project located in Kogi State, Republic of Nigeria, West Africa (Agbaja or
Agbaja Project). The Company holds 17 iron ore exploration licences in Kogi State, with the
main focus being EL12124, which covers more than half of the Agbaja Plateau and within which
is the Agbaja iron ore deposit. This Preliminary Feasibility Study (PFS) assesses the technical
and economic viability for the development of an iron ore mining and processing operation at
Agbaja to produce 5.0 million tonnes of upgraded iron ore concentrate per annum.
The project includes the development of an iron ore mining and processing operation capable of
producing five million tonnes (Mt) of upgraded iron ore concentrate per annum. The mine life is
estimated to be 21 years. Environmental and social impact assessment for the project was
16. 16 OLUSEGUN A. OLATINPO (2015)
completed in January 2014. The production of iron ore concentrate from is anticipated to start by
the end of 2016 or early 2017.
The iron ore mine is located on the Agbaja plateau, approximately 15km northwest of Lokoja
city in Kogi State, and approximately 165km southwest of Abuja, the capital city of Nigeria.
Two mining areas (Stage 1 and Stage 2) have been identified, pits have been designed, and
material movement schedules completed. A proposed processing plant site location has also been
identified; it is in the north east portion of the area covered by the Agbaja Mineral Resource and
was selected based on its central location between the two areas identified for mining operations.
The Stage 1 mining area is approximately 7.2 km2 and is west of the plant site and contains
approximately 158 Mt of Indicated Mineral Resources. Targeting the magnetic fraction of the
Indicated Mineral Resource, the average grade of material identified for mining is estimated at
46.1% Fe, with a corresponding strip ratio of approximately 0.55 to 1. As currently designed this
area will provide processing plant feed for an initial 15 years at the planned concentrate
production rate of 5 Mtpa.
The Stage 2 mining area is approximately 2.2 km2 and is to the east of the plant site. This area
is estimated to contain approximately 66 Mt of the Indicated Mineral Resources. The average
grade of material is estimated at 44.8% Fe, with a strip ratio of approximately 0.56 to 1. This
area will provide processing plant feed for an additional 6 years, bringing the combined plant
feed from the two areas to 21 years (at concentrate production rate of 5 Mtpa).
With a life-of-mine average strip ration of 0.55 to 1 (on Indicated Mineral Resources), mining
costs for the 21 years of operations will be low, a distinct advantage of the project.
Kogi has opted for a mining contractor to conduct all site development, overburden and waste
removal, open-pit mining including site rehabilitation, haulage and ore feed to a primary crusher.
Mining operations will be conducted on a 24/7, 365 days per year basis and it is envisaged that
production drilling and blasting will not be required, as all material is regarded as soft and
friable, and amenable to “free-dig”.
17. 17 OLUSEGUN A. OLATINPO (2015)
5.0 REFERENCES
ADELEYE, D. R., 1974. Sedimentology of the fluvial Bida Sandstones (Cretaceous) Nigeria.
Sedimentary Geology 12, 1-24.
ADENIYI, J. O., 1985. Ground total magnetic intensity in parts of the Nupe Basin and the
adjacent basement complex, Niger State, Nigeria. Nigerian Journal of Applied Science 3,
6778.
AKANDE, S. O., OJO, O. J., ADEKEYE, O. A. AND LADIPO, K. O., 2006. A Geological
Field Guide to the Southern Bida Basin. Nigerian Association of Petroleum
Explorationists (NAPE), 24th Annual Conference and Exhibition, Abuja, 21pp.
ALAFARA, A.B., ADEKOLA F.A.O., AND FOLASHADE A. O., 2005. Quantitative
leaching of a nigerian ore in hydrochloric acid. Journal of Applied science and
Environment, 9(3): 15-20.
BRAIDE, S. P., 1992. Syntectonic fluvial sedimentation in the central Bida Basin. Journal of
Mining and Geology, 28, 5564.
KOGI IRON LIMITED 2014. In-house report on the positive preliminary feasibiliby study of
Agbaja project.
LADIPO, K. O., AKANDE S. O. AND MUCKE, A., 1994. Genesis of ironstones from the
Mid- Niger sedimentary basin: evidence from sedimentological, ore microscopic and
geochemical studies. Journal of Mining and Geology, 30, 161-168.
OBAJE, N. G., 2009. Geology and Mineral Resources of Nigeria. Springer, Heidelberg, 221pp.
OBAJE, N. G. MOUMOUNI, A. GOKI, N. G., AND CHAANDA, M. S., 2011. Stratigraphy,
Paleogeography and Hydrocarbon Resource Potentials of the Bida Basin in North-Central
Nigeria, Journal of Mining and Geology Vol. 47(2), pp. 97–114
OJO, S. B., 1984. Middle Niger Basin revisited: magnetic constraints on gravity interpretations.
Abstract, 20th Conference of the Nigeria Mining and Geosciences Society, Nsukka, pp.
5253
OLANIYAN, O. AND OLOBANIYI, S. B., 1996. Facies analysis of the Bida Sandstone
Formation around Kajita, Nupe Basin, Nigeria. Journal of African Earth Sciences, 23,
253-256.
