Research Paper, 2007, 82 Pages
Chapter 1 Introduction
Chapter 2 Literature Review
Chapter 3 Materials and Methodology
Chapter 4 Interpretation of Results
Chapter 5 Discussion, Conclusion and Recommendation
Gombe Inlier is a Basement dome within the Gongola Basin which exposes most of the Stratigraphic sequence (Bima Sandstone, Yolde Formation, Pindiga Formation and Gombe Sandstone). Most of the works done in that area are on the exposed Stratigraphic sequence at the flank of the inlier.
Barite Mineralization was reported from Gombe inlier but no detailed work has been done to study the Barite along side other accessory minerals. The fracture systems hosting the Barite on the Gombe inlier was also least understood because it has not been studied in detail let alone to understand the chemistry and the economic implication of the Barite Mineralization and the accessory minerals. The relationships between the fractures hosting the mineralizations and the strike slip fault that affacts the inlier is also least understood.
Only unregistered miners patronize the Barite in Gombe inlier and so the impact of the mineralization on the economy is almost in-assessable.
This research is aimed at determining the origin and economic potentials of the Barite within the Gombe inlier. Samples from various locations and veins on the inlier have been analyzed to determine the chemical composition of the Barite in order to evaluate the origin and economic potential. Structural analysis of the trend of the Barite veins have been carried out using the stereographic projection to plot S-pole diagram in order to determine the origin and nature of the structures hosting the Barite.
The research is also aimed at generating baseline data on chemistry and petrography of all mineralizations by means of a chemical analysis as well as detailed macroscopic and microscopic study of the minerals and rocks of the inlier and subsequent production of a geologic map.
The mapped area is located in Gombe Local Government of Gombe State. It covers an area of 126km sq. on the topographic map of Gombe N.W sheet 152 with a scale of 1:50,000 and is located between Latitudes 11o11′
20.4” and 11o14′ 37.4” and Longitudes 10o16′ 20.8” and 10o19′ 16.0” (Fig. 1a).
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The area is easily accessible through Dadin Kowa road which is a major tarred road that passes through Gombe town. The untarred motorable road from the railway and foot paths makes the outcrop easily accessible.
The mapped area lies between 29.8704 to 670.5600 meters above sea level based on the contour lines. The topography is defined by the prominent inlier and relatively high igneous body with gentle and steep slopes and undulating sedimentary rocks surrounding it, making it an inlier.
The drainage of the area is controlled by the inlier. The inlier has no dissections except along the strike – slip fault, water flows down the rock in tributaries, some of which flow into River Magaria (Fig. 1).
The climate of the study area can be described as bi-seasonal. The dry season is comparatively longer (November – March) than the rainy season (mid-May – September).
Rainfall distribution is the major factor influencing vegetation cover although topography and ground water condition are also significant. In terms of vegetation, the mapped area can be described as exhibiting the characteristics of the Sahel Savannah type of vegetation (Falconer, J.D, 1911). The vegetation comprises mainly of different types of grasses.
The soil type to a large extend controls the type of vegetation that may dominate a given locality.
The study area has been mapped in detail using the topographic map of Gombe N.W sheet 152 with a scale of 1:50,000. Samples were collected from the veins and from different locations and GPS and attitude readings were taken. .
Samples from the field are studied macroscopically to evaluate texture and colour. Thin sections are prepared in the laboratory using both rocks and mineral samples. The slides are examined with a petrographic microscope and optical characteristics observed in each sample noted. The attitude readings of the fractures hosting the veins were used to plot S-pole diagram were plotted on the stereonet to determine the nature and origin of structures hosting the Barite. Geochemical analyses were carried out on the samples to ascertain their chemical composition.
The S-pole diagrams, the petrographic studies and the geochemical analysis were merged to evaluate the origin of the Barite, the nature and origin of the structures hosting the Barite and the economic potential of the Barite within the Gombe inlier.
The Benue Trough of Nigeria within which the study area is located is the most important of all the Cretaceous sedimentary basins of Nigeria. It is an elongated rift approximately 1000km long and 50 – 150km wide tending NE – SW and overlying the pre-Cambrian shield of the West African Mobile Belt (Benkhelil, 1989, Guiraud, 1990).
The trough is an elongated partly fault-bounded depression occupied by up to 6,000m of marine and fluvio-deltaic sediments that have been compressionally folded into a non-orogenic shield environment (Carter et al, 1963, Wright, 1976 and 1981).
The northern limit of the trough is the southern boundary of the Chad Basin, which is in turn separated from the trough by an anticlinal feature called the Dumbulwa-Bage Highs (Zaborski, 1997) while the southern limit of the trough is the northern boundary of the Niger-Delta ( Zaborski et al, 1997). Marine and fluvio-deltaic sediments infill the entire Benue Trough ranging from Late Aptian to Paleocene in age (Adegoke, et al, 1978, Allix, et al, 1981).
There has been systematic variation in the depositional environment within the trough over time such that, continental lacustrine or fluviatile sediments occur at the base through various marine transgressive and regressive beds to immature continental sandstones at the top.
The Benue Trough runs through the NE – SW central parts of Nigeria from the Niger Delta in the SW right up to the Borno Basin in the NE of Nigeria. It is subdivided arbitrarily into lower, middle and upper portions. Although no concrete or clear outline can be drawn to demarcate the individual subdivided portions, some major localities (towns or settlements) which constitute the major depo-centers of the different portions have been well documented by Petters, (1982), Nwajide, (1990), Idowu and Ekweozor (1983) (Fig. 2).
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FIG. 2. Geological Sketch Map of Benue Trough (Maluski et al, 1995)
The depo-centers of the Lower Benue Trough comprises mainly of the areas around Nkalagu and Abakaliki, while those of the Anambra Basin centers are around Enugu, Awgu, Akwa and Okigwe. The Middle Benue Trough comprises of areas around Makurdi through Yandev, Lafia, Obi, Jangwa to Wukari. In the Upper Benue Trough, the depo-centers comprise of areas around Tula, Jessu, Dukul, Numanha and Lamja (in the Yola Arm of the trough) and Pindiga, Gombe, Nafada, Ashaka (in the Gongola Arm of the trough).
The study area falls within the Gongola Arm of the Upper Benue Trough. (Fig. 2)
The Upper Benue Trough comprises of the area extending from the Bashar – Mutum Biyu line as far north as the ‘Dumbulwa-Bage High’ of Zaborski et al, 1998 which separates it from the Borno Basin. It includes an E – W trending Yola Arm and a N – S trending Gongola Arm which are separated by an area structurally dominated by four major NE – SW trending sinistral strike-slip faults, the Gombe fault, Bima-Teli fault, Kaltungo fault and Burashika fault. Carter et al, (1963) referred to the median zone as Zambuk Ridge (Fig. 3).
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Fig. 3. Simplified Geological Map of the Upper Benue Trough (after Zaborski et al, 1997)
The Cretaceous succession in the Upper Benue Trough comprises of early Cretaceous continental clastics, the Bima Group, Yolde Formation, Pindiga Formation and lateral equivalents in the Yola Arm which are the Dukul Formation, Jessu Formation, Sekule Formation, Numanha Shale and Lamja sandstone, sandy members of the middle part of the Pindiga Formation in the Gongola Basin, Gombe Sandstone, Kerri-Kerri Formation and Neogene to Quanternary Basalts.
The continental Bima Group comprises the oldest sediments in the Upper Benue Trough which directly and unconformably overlie the crystalline Basement rocks. Several workers described the Bima Group however; Guiraud (1990a, 1991a) provided the most detailed account and described its three parts as:
The Upper Bima Sandstone (B3); a fairly homogeneous, relatively mature, fine to coarse grained sandstone characterized by tabular cross- bedding with sets of a few tens of centimeters to a few meters thick. Convolute bedding and overturned cross bedding are common. Its thickness ranges from 500 – 1500m. It has no direct dating but on account of stratigraphic position, an Albian (to Early Cenomanian?) is probable.
The Middle Bima Sandstone (B2) which is widely distributed, fairly uniform unit consisting of fining upward cycles each 5 – 10m thick. It has trough and tabular cross bedding and clays and palaeosols may occur at the top of individual cycles. Overall thickness ranges from 100 – 500m. Guiraud (1991a, 1991b) reported fossil wood, silicified Metadopocarpoxylon libanoticum (Edwards) to which a Late Aptain age was assigned.
Lower Bima Sandstone (B1) is a highly variable unit with an overall thickness of 0 – 1500m. Individual lithofacies distribution was controlled by synsedimentary tectonic activity which created a number of sub-basins with associated volcanism. Lithofacies association within a sub-basin consist of conglomeratic alluvial fan or debris flow deposits, adjacent to active basin – forming faults, grading laterally into fining –upward fluvial sequences into lacustrine deposits with interbedded clays, fine - grained sandstones and calcareous sandstones. In the sector of the Gombe Inlier, the Bima Group is greatly attenuated. It is represented by pebble conglomerates and poorly sorted arkosic sandstone similar to the lower Bima Formation elsewhere. Radiometric ages from intercalated lavas suggest an age from Albian to close to Jurassic- Cretacous boundary, (Guiraud1991a).
The name Yolde Formation was proposed by Carter et al, (1963) for the transition beds recognized earlier by Falconer (1911) and Barber et al, (1954) between the Bima Group and the Pindiga Formation. A type section was designated in the Yolde stream in the western part of the Yola Arm. The
Yolde Formation gives rise to a subdued topography often with sparse vegetation cover and is poorly exposed in most part of the Gongola basin.
The Yolde Formation is indeed a transitional sequence between the continental Bima Group and the marine deposits of the lower part of the Pindiga Formation. The lower sandstone - mudstone portion of the Yolde Formation is interpreted to be of fluvial origin, the upper portion with more thinly and regularly bedded bioturbated sandstones and low diversity bivalve faunas at the top is of shallow marine origin. Lawal (1982) and Lawal and Moullade (1986) suggested a Late Albian to Late Cenomanian age for the Yolde Formation on the basis of its palynofossils.
The name Pindiga Formation was proposed by Carter et al. (1963) for the calcareous beds and clay shales previously described by Barber et al, (1954). The nature of the Pindiga Formation is best understood by regarding it as consisting of five members.
The name ‘Kanawa Formation’ was proposed by Thompson (1958) for a sequence of shales and intercalated limestone outcropping around Kanawa to the east of Gombe. It corresponds only to the lower shale-limestone member of the Pindiga Formation and provides an excellent stratigraphical mark horizon between the sandy units above and below. The Kanawa Member was formed during the Late Cenomanian to Early Turonian transgression, which affected the entire Benue Trough and also the Sahara region of the north (see example, Busson, 1972, Reyment, 1980, Meister et al, 1992). It has a wide spread occurrence in the Upper Benue Trough and a greater part of it consist of shaly mudstone, irregular thin lenses and discontinuous layers of diagenetic gypsum also occur. Its age equivalent in the Yola Arm, the Dukul Formation has similar lithology of shaly mudstone with intercalated limestone. The Kanawa member has been extensively studied due to the rich faunas of its limestone beds.
The name ‘Gulani Sandstone’ was proposed by Carter et al, (1963, pp. 52 – 53) who regarded it as a member of the Pindiga Formation and provided the only significant previous description. Numerous exposures of the Gulani Member occur in the Gulani-Jang area, where the contact with the Kanawa Member has not been seen but appears to be sharp. The Gulani Member contains relatively thinly bedded coarse to very coarse-grained pebbly sandstones with purple, brown and white laminated mudstone interbeds. The sandstones are frequently ripple-marked and the mudstone occasionally displays desiccation cracks. The age is described alongside with the Dumbulwa Member.
The name ‘Deba - Fulani Member’ is proposed mainly for the sandy beds occurring in the middle part of the Pindiga Formation. Its unit has not previously been differentiated. The Deba – Fulani Member appears to pass laterally into the Dumbulwa Member, south of the Dumbulwa-Bage High. Exposures of the Deba Fulani member are rare and no complete section has been found. Limited sections showing sequences of sandstone and siltstone in beds of 5 – 150m thick are present in streams around, especially to the west of Deba Fulani which is proposed as the type area. The age is described along side with the Dumbulwa Member.
The Dumbulwa Member is a new name proposed for a unit which appears to be the same as the upper sandstone-shale portion of the Gongila Formation of Carter et al. (1963). There has been some doubt concerning this view, the term ‘Gongila Formation’ being inappropriate for these beds because Gongila Village itself lies upon the lower Bima Formation. In the light of the criticism concerning the name ‘Gongila Formation’, the name ‘Dumbulwa Member’ was proposed for the sandstone and shale sequence in the middle part of the Pindiga Formation in and around the Dumbulwa-Bage High. The proposed type unit which is in the Dumbulwa Hill consists of fining-upward cycles. The Dumbulwa Member reaches its greatest thickness of about 200m in the Dumbulawa and Bage Hills.
The Dumbulwa, Deba Fulani and Gulani Members are lateral equivalents therefore their ages and environments of deposition can be conveniently considered collectively. No direct dating is currently available for them.
In the Yola Arm, the Dukul Formation which is Early – Middle Turonian at the top is overlain by the Jessu Formation which is interpreted by Allix (1983) as of a less marine nature than either the Dukul or the overlying Sekule Formation. Ciolopoceras occurs in this area again (Barber, 1957) demonstrating marine Upper Turonian.
The Fika Member comprises of the ‘Fika Shales’ of Carter, et al, (1963) and the equivalent of the upper shale member recognized by authors in the Pindiga Formation. There was a mis-mapping due to the failure to recognize the Deba Fulani thrust and the subsequent interpretation of the base of the Deba Fulani Member south as the base of the Gombe Formation. The Fika Member produces a low featureless topography and its outcrop can be recognized from the black shrinking clay soil. No type section has been
designated, only borehole records provide the nature of the unit. The exposures that occur mostly reveal shaly mudstone, lack macrofossils and contain irregular lenses and bonds of gypsum.
In the Gombe Inlier, three oolitic sandstone beds 40, 15 and 13cm thick from lowest to highest are present in the upper part of the Fika Member which are separated by 1.5 and 1m of shales respectively. Variable thickness of 600m has been reported by authors for the Fika Member and a number of paleontological observations give information on the depositional environment and age. The Fika Member has lower limits around the Middle – Upper Turonian boundary and upper limits close to the Campanian - Maastrichtian boundary. Carter et al, (1963), Lawal (1982) and Allix et al, (1984) believed that it represented a continuous period of deposition from Turonian to Maastrichtian. Structural dips shown by the Gombe Formation are frequently only about half of those in the nearest exposed pre-Campanian beds. This is not strange since the outcrop of Gombe Formation is same distance from the main deformed zones close to the system of strike-slip faults occurring along the axial part of the Upper Benue Trough. This relationship is also present in the Gombe Inlier where all the Cretaceous sediments have been deformed.
The Gombe Formation corresponds to the name ‘Gombe Sandstone’ which was proposed by Carter et al (1963) for the ‘Gombe grits and clays’ previously identified by Falconer (1911). A type section was designated by Carter et al, (1963) in the Kware Stream on the southern outskirts of Gombe town. The Gombe Formation is restricted to the western part of the Gongola Basin. It weathers to produce a ferruginous capping. This resistant material, along with ironstone weathered out of the sequence is responsible for the rugged and hilly topography characterizing much of its outcrop. The Gombe Formation has a marked angular unconformity between it and the Kerri-Kerri Formation and is made up of three major lithofacies which may prove recognizable as separate members. At the base, the Gombe Formation consists of rapidly alternating thin beds of silty shales, sometimes with plant remains and fine to medium grain sandstones with some intercalated thin flaggy ironstones. Bioturbation is common in this facies, mainly horizontal feeding burrows of Thalassinoides type. This lithofacies is repeated in the Gombe Inlier above few tens of meters of strata belonging to the bedded facies. Dike (1995) has reported coal horizons in the upper part of the Gombe Sandstone encountered in the boreholes penetrating the subcropping part of the formation.
Gombe Formation was interpreted by Carter et al (1963) as deltaic and estuarine deposits. Lawal (1982) found a marked decrease in marine microfossils (foraminifera, dinoflagellates and acritarchs) at the boundary of the Pindiga Formation and the Gombe Formation, the pollens in the Gombe Formation indicated a Maastrichtian age.
The Cretaceous Gongola Basin is concealed to the west by the Kerri- Kerri Formation and to the extreme east by the basalts of Biu Plateau.
The continental clastics of the Kerri-Kerri Formation with thickness of over 320m have been described by Adegoke et al (1986) and Dike (1993). The Formation has scanty age data. Paleocene pollens have been recovered (Adegoke et al, 1979) but Eocene beds may also occur (Adegoke et al, 1986). The irregular topography of the unconformity surface that separates the Kerri- Kerri Formation from the Gombe Formation is exposed on the northern outskirts of Gombe town.
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