Nigeria is endowed with varieties of solid minerals in addition to the abundant
oil and gas reserves that have been driving the country’s economy
since the mid-70s. About 35 minerals of proven reserves abound in the country.
Due to the vastness of these resources, there is the need to establish
a database that would enhance and optimize their exploration and exploitation
with the aim of deriving maximum benefits from such venture.
The study area, Igarra, is located in Edo State, southwestern Nigeria. While
the northern part is underlain by crystalline rocks of Precambrian age, the
southern part is covered by Cretaceous to Tertiary sedimentary rocks. Landsat-7
ETM imagery was utilized in ILWIS® environment to delineate lithological
boundaries in the study area. Field observations were carried out at 37 localities
in order to evaluate the rock/mineral type and mining activity at each locality.
Finally, a Geographic Information System database of the mineral resources
of the study area was established, and utilized to carry out a digital update
of the existing geological map. This is expected to contribute accurate and
up-to-date metadata to Nigeria’s National Geospatial Data Infrastructure
(NGDI) which is at its formative stage.
For many centuries, maps were prepared in analogue form which were very difficult
to store and preserve. This is because such papers continued to deteriorate
with age, thus defacing the content. In the past few years, experience
has shown that maps which were hitherto available on request from custodian
agencies were either eaten by rodents or termites, outdated or out of stock.
This has continuously made desk studies for many aspects of investigation
difficult if not impossible, because existing information on the study
area may be dispersed, poorly catalogued or no longer in existence. However,
with the invention of the computer and its rapid transformation, many aspects
of the geoscience profession are being speedily computerized.
Geological surveys are established basically to collect information on the
mineral resources of countries in which they are situated. The Geological
Survey of Nigeria Agency, in pursuit of its mandate, has strived to carry
out geological mapping of most parts of the country since the early 1960s.
It has, over the years, made major contributions to the development of the
solid minerals sector, and has been a source of information through its publications.
For example, such published geological maps and bulletins form an indispensable
guide to geologists and mineral prospectors in Nigeria. Until recently, these
maps and reports were traditionally kept in various file cabinets, shelves,
drawers, loose-leaf binders and folders. This method of data management is
fraught with a lot of drawbacks, some of which are:
Loss to animal and insect attacks over time;
Availability of data to only a limited number of users;
Data storage in incompatible formats and scales, thereby creating difficulty
in transfer and integration of data from various sources;
Duplication of efforts in data collection. Even when there are no duplications,
data may be so scattered that access becomes difficult, if not impossible.
With the widening of scientific horizon consequent on new technological
developments, the need to provide information in digital format has risen
tremendously. According to Culshaw et al. (2006), the key strategies that
geological surveys should adopt for their information resources include,
Managing data responsibly as a long-term asset;
Converting as much analogue data as possible to digital format; and
Working routinely in three-dimensional space rather than in two.
In order for any geological survey to be relevant in procurement and sharing
of data, it must improve the interoperability of data so as to facilitate
integration with data from other sources. Adegoke and Ajayi (2003) emphasized
the need for the integration of GPS and GIS into geo-exploration efforts
in order to considerably reduce the time required to acquire and interpret
geological and mineral exploration data. Since these are rather new innovations,
it is incumbent on the geology profession in Nigeria as in other parts of
the world to establish a platform for the entrenchment of the GIS concept
and successfully combine such with the experience of the older generation.
This is one of the basic requirements for establishing a geospatial data
The Study Area
The Igarra area lies within Latitudes 7o00’N-7030’N and Longitudes
6o00’E-6o30’E at the northern fringe of Edo State, Nigeria (Figure
1). It is underlain in the north by Precambrian Basement Complex, and in
the south by Cretaceous and Tertiary sediments. The northern part is rich
in industrial and metallic minerals which are currently at various stages
of exploitation (Table 1). The area has been sufficiently one of studied
by Odeyemi, 1977, 1988, 1990; Rahaman, 1976, 1988) due to the relatively
unweathered and well-exposed outcrops (Figure 2).
Figure 1: Location map of the study area.
Figure 2: The geological map of the study area (modified after Odeyemi, 1977)
Table 1: Some of the mineral deposits in the study area
Rahaman (1988) grouped the rocks of the basement complex into six:
Younger metasediments, commonly referred to as the schist belts;
Charnockitic, gabbroic and dioritic rocks;
Volcanics and hypabyssal rocks; and
Unmetamorphosed dolerite dykes, basic dykes and syenite dykes.
The Precambrian Basement Complex in Igarra area is made up of a metasupracrustal
suite comprising of quartzites, quartz-schists, metaconglomerates, marble
and calc-silicate rocks. Within this area is the Igarra schist belt A detailed
study (Odeyemi, 1988) shows that the said schist belt can be classified into
Quartz-biotite schist with intercalated quartz-pebble conglomerate;
Calc-silicate gneiss and marble;
Polymict metaconglomerate; and
Phyllites and muscovite schists.
All the above groups of rocks have undergone various degrees of deformation
with the adjacent migmatite-gneiss-quartzite complex. There have also been
a lot of migmatization and granitization in some places as a result of emplacement
of Pan African granite plutons which marks the last of the Precambrian activities
to affect the Igarra area (Odeyemi et al., 1999). Anifowose (2004) was of
the opinion that the granitic emplacement was probably controlled by fractures
within the basement, and also showed outcrop pattern indicating that the
Older Granites cut across all other structures with sharp and chilled contacts.
The dominant structural trend in the study area is approximately N-S, and
this is defined by mineralogy, lithology, axial planes and cleavages.
The geological complexity of the study area is therefore not in doubt. This
probably has been responsible for the existence of diverse rock and mineral
types, particularly industrial minerals that are being exploited by several
industries providing employment for hundreds of people. For example, the
area has some of the largest deposits of marble in Nigeria.
Materials and Methods
A Landsat-TM imagery over the study area was acquired courtesy of the Regional
Centre for Training in Aerospace Survey (RECTAS), Obafemi Awolowo University
Campus, Ile-Ife, Nigeria. The imagery was georeferenced and processed by
combining the spectral values of Bands 4, 5 and 6 in order to enhance the
structural and lithological features. Information retrieval was based on
tone, colour, texture, structure, rock associations and spectral characteristics
exhibited by different rock types. ILWIS 3.3 Academic® was employed
in digitizing different features from the image. Existing geological and
topographical maps were used for checks to ensure proper tying of points
since the geology of the area is sufficiently known through fieldwork to
permit a sound interpretation and correlation with the Landsat image. All
the detected geological features in addition to drainage and cultural features
were subsequently digitised as individual layers.
The Digital Elevation Model (DEM) of the study area was produced by creating
a sub-map of the digitised topographic map (Figure 3). According to Banerjee
and Mitra (2004), the draping of satellite imagery over DEM enables the identification
and subsequent delineation of geological features. In the mapping of lithological
boundaries using remote sensing technique, it has been observed that there
is only a little difference between the technique and field mapping (Hennier
and Spang, 1983; Banerjee and Mitra, 2004) but complementing with DEM has
improved the map information quality particularly in the study area with
rugged terrains with ridges and valleys. Therefore such DEM data will form
part of the required metadata in NGDI for mineral exploration purposes. Also,
this method can be conveniently extended to areas where there are no geological
maps. This technique was adopted in order to generate a surface for draping
and visualization of the terrain it represents.
The field survey was based on 1:50,000 geological map of the project area
produced by Odeyemi (1977), the 1:100,000 topographical map (Auchi Sheet
266), and the 1:250,000 geological map of Lokoja Sheet No. 62. During the
fieldwork, a total of 37 localities were visited to investigate the economic
rocks and minerals within the study area in terms of lithological/mineralogical
characteristics, the state of exploration, lateral extent of each occurrence,
type of mining activity and the company involved. These attributes were created
and linked to the digital mineral map (Figure 4). The two datasets that were
generated (Landsat image interpretation and fieldwork data) were input into
the GIS to generate thematic maps based on each mineral occurrence. GPS enables
accurate reading of geographical coordinates of mineral occurrences, which
can then be combined with other datasets mentioned above to form a Geographical
Information System (GIS) database.
Figure 4: Mineral map draped over the geological map of study area
The use of GIS database in mineral resources data management has been found
to be an improvement over the conventional resource management technique.
Thematic maps that were generated indicate the results of the field survey,
remote sensing image analysis and interpretations as well as the result
of some data analysis that were carried out. The thematic maps generated
to show the mineral occurrences reveal the accurate location of each of
the rock/mineral outcrops. The result of the study shows that marble, calc-gneiss,
granites, vein quartz and kaolin occur in large quantities at different
localities within the study area.
There is no gainsaying the fact that geospatial information technology has
contributed a lot to sustainable development in developed countries. According
to Boroffice and Akinyede (2005), over 80% of environmental management decisions
in developed countries are based on quality and accurate geospatial information
collected from different facets of human activities on the Earth. On the
other hand, Africa has been lagging behind in the collection and archiving
of reliable spatial data and this has significantly resulted in the failure
of development projects on the continent.
With the launching of NigeriaSat-1 Earth observation satellite in September
2003, the Nigerian scientific community finds it less difficult having access
to satellite imageries. Also, the periodical liberalization of satellite
data access for scientific purposes has made them available to African scientists
who are using the opportunity to develop some strategies in tackling the
problem of sustainability in response to the New Partnership for Africa’s
Development (NEPAD) initiative. In this regard, a series of pilot projects
are being implemented with focus on boosting food production, mineral and
water resources management, deforestation, desertification and land use/cover
In view of the fact that all sustainable development issues require geospatial
data utilization and management, it became imperative for countries to establish
national geospatial data infrastructure (NGDI). The United Nations Economic
Commission for Africa (UNECA) considered that the development of NGDI be
mandatory for all African countries. This geared the necessary government
agencies towards the establishment of better data collection and archiving
techniques in preparation for a geospatial data infrastructure policy. Sequel
to this, a meeting was convened by the National Space Research and Development
Agency (NASRDA) in February 2003 with the objective of charting a road map
for the implementation of an NGDI for Nigeria. Nigeria’s Earth Observation
Satellite, NigeriaSat-1, is in a good stead to provide the stream of image
data for the NGDI. The details of the project, which is being anchored by
NASRDA, have been well documented in terms of implementation and update.
The draft policy Nigeria’s NGDI was said to be at the final stage of
presentation to the National Assembly that is expected to pass a bill on
it (Agbaje, 2006). This would consolidate the availability and standardization
of data for sustainable national development.
This study has revealed that there is improvement in mineral resources data
management in the study area compared with the conventional resource management
technique. With the creation of a GIS database of the mineral resources
in the study area, accurate representation of locations of mineral deposits
and their characteristics can be provided and can be easily updated over
time. This will put an end to the problem of inadequate mineral resources
database that has discouraged local and foreign private investment in the
solid minerals sector of Nigeria’s economy. Also, with the eventual
legislation of Nigeria’s Geospatial Data Infrastructure policy, the
country will be in a good stead to tackle the problems generally associated
with data collection and access for planning purposes and decision making.
The first author is grateful to the Federal University of Technology, Akure
for offering teaching assistantship during this study.
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