Review of Geology, Geochemistry and Origin of Gypsum Mineralization in Chad Basin (North Eastern Nigeria)

Origin of Gypsum Mineralization by Brine Mixing Hypothesis

Travail de Recherche , 1998 , 80 Pages , Note: Research

Sciences de la Terre / Géographie - Géologie, Minéralogie, Pédologie

A field trip was conducted in order to evaluate the geology, geochemistry and origin of gypsum mineralization in the Nigerian sector of Chad Basin, part of which is the research area. The gypsum mineralization underlain the whole area of about 2247.75km2 within the Chad Basin and comprises of five different forms; Detrital, Balatino – Laminated, Selenite, SatinSpar, and Alabaster. The thickness of the gypsum forms increases with depth, and they are emplaced at various depths. All the gypsum forms retained traces of former lamination except detrital gypsum therefore lamination is a primary structure.The chemical composition of the gypsum forms showed that they are all high grade (over 70% CaSO4 . 2H2O). The moisture content could be used to show fractured areas where circulation of water is easier. Alabaster gypsum is the heaviest as such more suitable for cement works. The chemical composition of all the gypsum forms revealed high trace elements content which could be the product of the brine mixing phenomenon. The petrographic studies of the Balatino, Selenite, SatinSpar and Alabaster gypsum forms revealed that they all recrystallized from the primary laminations during the early diagenesis. The recrystallization appeared to be perpendicular to the primary laminations. There are dissemination of anhydrite in the matrix of the gypsum forms which shows the effect of incomplete rehydration after upliftment. The origin of gypsum mineralization in Chad Basin is both sedimentary and diagenetic, so based on high trace element content and primary lamination, a brine mixing hypothesis was proposed for the origin of the gypsum mineralization in the Chad Basin.

TABLE OF CONTENTS

Chapter 1 Introduction

Chapter 2 Literature Review

Chapter 3 Materials and Methods

Chapter 4 Results

Chapter 5 Discussion of Results

Chapter 6 Conclusion and Recommendation

References

CHAPTER ONE: INTRODUCTION

1.1 Necessity of Gypsum

Gypsum mineralization is one of the pivot for Nigeria’s industrial revolution for a self reliant and durable economy especially in the building and agricultural and construction industries.

The cement industries, as well as chemical, ceramic, pharmaceutical, paints and may other industries in Nigeria need gypsum as one of the most important raw material for their productions. However, prior to the 1990s, gypsum mineral has been imported from Spain and Morocco. Nigeria spent about[illustration not visible in this excerpt]900 million annually on the importation of gypsum for her cement Anonymous (1996).

The earliest work on evaporates in the North Eastern region was done by Vischer (1910) in a geographical account of an early expedition into the areas of the Chad Basin and immediate environment. The author described two classes of evaporate mineral deposits. Namely;

(a) The magma salt (an admixture of sodium carbonate and bicarbonate, sodium sulphate and sodium chloride in concentrations of approximately equal magnitude)
(b) Magma natron (mainly sodium carbonate with subordinate amount of sodium sulphate and sodium chloride).

The earliest reconnaissance traverse of the area was made by Falconer (1911) during the Mineral survey of northern Nigeria in the first decade of the century. Gypsum occurrence in North Eastern Nigeria was first reported by Carter et al., (1963) as occurring within a sequence of blue black shales, containing few, thin, impersistent limestone beds and occasional interbedding with thin siltstone beds and lava flows. Reyment (1965) confirmed this by reporting the Fika Formation as consisting of blue-black shales, occasionally gypsiferous with a thickness exceeding 430 meters. Maglione (1981) also confirmed the presence of gypsum mineralization in well drained, well aerated environments within the Nigerian sector of Chad Basin (part of which is the research area). Gypsum occurrence at Nafada Bajoga areas was reported by Orazulike (1988).

All these workers confirmed that the Fika shales are gypsiferous. Since then, not much work has been done in this area to determine the economic viability of the gypsum mineralization at various depths and in various places within the Chad Basin. Only the illegal miners patronized the gysiferous areas.

1.2 Objectives

This research work is in line with the renewed interest in the search for gypsum in various parts of the country in order to feed the Nigeria’s industrial sector like, cement, chemical and ceramics industries. This would help to attain maximum utilization of gypsum resources by the said industries in order to hasten development in Nigeria.

Another objective of the study was to conduct a detailed investigation on the gypsum mineralization in the research area (Fig.1). the detailed research entails studying the geology, geochemistry, origin, as well as the mineralogical and textural evolution of the gypsum prospects in order to assess it’s economic significance.

CHAPTER TWO: LITERATURE REVIEW

2.1 Fika Shales

The name Fika Shales was assigned by Raeburn and Brynmor (1934) to the Limestone – Shale group which also includes the Gongila and Pindiga Formations of the present work. The Fika Shles is a sequence of blue – black shales occasionally guypsiferous and containing one or two thin impersistent limestone beds (Carter et al., 1963). The Formation underlies a broad belt of country in the north-western part of the Mutwe plain extending westwards to Fika and south-westwards to form the narrow outerop which strikes southwards from Nafada. Although the beds are poorly exposed, sections are known from wells, boreboles and stream channels (Carter et al., 1963)

The shales contain abundant fish fossils and also crocodile remains and Chelonian fragments. The blue-black nature of shale may be indicative of attendant reducing conditions at the time of deposition of the unit. The blue- blackk shales were deposited during the middle Cretaceous world-wide marine transgression in both the Benue Trough and Chad Basin (Petters, 1978). These sediments feature sparse population of benthic foraminifera assemblages as well as high organic matter content suggesting deposition under anoxic conditions (Petters and Ekweozpr, 1982b).

However, blackness of sediment can also be due primarily to high abundance of pyrite and may not necessarily signal high organic content. Ekweozor et al., (1989) analyzed many shale cuttings from the Fika Shales and reported that they contain fluffy, biodegraded humic matter (non- fluorescent amorphous organic matter, humosapropelinite showing intergrowth of micrinite and framboidal purite in some places. This organic matter is inferred to have been derived mostly from oxic paralic swamp or lacustrine depositional environment.

The relative abundance of arenaceous benthic foraminifera within Fika Shales point to the prevalence of near – shore environment. Petters (1983) dated Fika Formation as Coniacian to early Maastrichtian. The thickness of Fika Shales overlies the Gongila Formation and underlies the Gombe Sandstone in the Chad Basin, Table 1.

Table. 1 Stratigraphic succession of Chad Basin, Zambuk Ridge and Upper Benue Basin

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Lower Palaeozoic To Pre-cambrian Crystalline Baseme`nt

(After Carter et al., 1963)

2.2 Chad Basin

The Chad Basin which is the largest intracratonic area of inland drainage basin in Africa (Raeburn and Brynmor, 1934) and (Barber, 1965) occupies an area of about 230, 000km2 in the central Sahara and southern Sudan. The western limit is the water divide which divides the Niger and the Chad drainage systems and the southern limit is the water – shed between the Chad and Benue systems. About one tenth of the basin is situated in the northern part of Nigeria which lies between latitude 10⁰N-14⁰N and longitude 10⁰E – 13⁰E.

The Chad Basin is endoreic i.e. it does not drain to the outside. It is separated from Upper Benue by a basement dome (Zambuk Ridge) and it also contains Albian-recent sedimentary rocks among which are the Fika Shales that host gypsum mineralization. Some of the sedimentary rocks; Bima Sandsone, Gongila Formation and Fika Shales have been folded and uplifted during the Maastrichtian orogenic event which trends NW-SE at right angle to Santonian orogenic event which trends NE – SW (Benkhelil, 1982).

CHAPTER THREE: MATERIALS AND METHOD

3.1 Field Work

The field work was conducted in the first half of the month of June, 1997. Seven mining sites were visited. The mode of mining in all the mining sites are pitting,( ranging from 0.2 to 13m depth (Table 2, Fig.1) and trenching. In most of the mining sites, the carrierbeds (Fika Shales and Mudstone) area shallow, so the pits are not very deep. The mineralization is continuous with minor discontinuities as such it is intercepted by the different mining pits in different mining sites. The sections are shown in Fig.2. The continuity suggests a uniform depositional environment over a wide region.

While on the field, observations were made on the gypsum samples along the following lines:

(a) different gypsum forms and their various carriers beds
(b) structural and textural relationship between the different gypsum forms.

The mining sites are confined to stream slopes and areas liable to flood near stream channels between the villages. The streams are part of the tributaries of the River Gongola which drain 90% of the water in the region, Fig.1. Table 2 summarizes the measurement in different mining sites and Fig.2. gives the measured section in the different mining sites.

The following are the findings based on the field work:

(i) Five different gypsum forms are recognised: Detrital, Balatino, Selenite, SatinSpar and Alabaster.
(ii) The changes in gypsum forms is vertical with depth and not horizontal with distance
(iii) The thickness and deformation of the gypsum forms increases with depth
(iv) All the different gypsum forms at any depth have peculiar carrier beds.

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Fig. 1 Map of the Research Areas Showing Mudflat areas (Shoreline

Environment) hosting the Gypsum Mineralization within the exposed Fika Shales. (modified after Carter et al., 1963)

3.2 Geochemical Analysis

Ten samples were analyzed using X-Ray Fluorescence analytical technique. This was done to determine the chemistry and hence assess the quality of the gypsum.

3.2.1 Sample Preparation

Gypsum samples were cleaned and ground into powder using agate mortar and piston. Agate mortar was used to prevent silica contamination. For every sample ground, the agate mortar was washed and dried before grinding another sample. This was also done to prevent contamination of samples. When dealing with samples containing heavy elements in the light (low density) matrix, which is often the case in gypsum, the grain size effect can be an additional source of error in XRF analysis. This was overcome by grinding to very fine particles.

The – 60 mesh sieves was used to ensure that the powdered particles are in size. The sieve was made of nylon as iron and steel sieves can introduce Zn, Pb, Ag, Cu or Co contamination into the sample during sieving. 2g of the sample was weighed using a sensitive digital scale.

The 2g of the sample was placed into a pelletizer device for pelletization. No binder was added to the ground gypsum powder because the water of crystallization act as a binder. The pelletizing device compacted the 2g of the powdered sample into pellets and the pellets were used directly for the XRF analysis. The analysis was conducted at the laboratory of the Centre for Energy Research and Training (CERT), ABU Zaria.

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Fig.2 Flowchart for Gypsum Sample Pelletization

3.3 Petrographic Studies

Four different gypsum forms were studied in hand and thin section to assess their textures and textual evolution.

3.3.1 Sample preparation

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Fig.3 Flowchart for sample preparation

CHAPTER FOUR: RESULTS

4.1 Field Studies

The results of the field studies are summarized in Table 2 and all the information and findings in Table 2 are plotted in Fig. 2:

Table 2: Summary of the Field Studies.

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Mining Site 1 Daura

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Thin mudstone containing disseminated detrital gypsum crystals

Grey shales and mudstone containing detrital gypsum crystals

Blue – black shale containing satinspar gypsum

Mining site 2 Kwayaya Mainamaji

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Mudstone containing laminated and detrital gypsum Grey shales containing selenite gypsum

Blue – Black shale containing Satinspar

Mining site 3 Kanwaram

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Mudstone containing disseminated detrital gypsum

Mudstone & Grey shales containing laminated gypsum

Blue-Black shales containing SatinSpar gypsum

Fig. 4 cont’d

Mining Site 4 Alangafe

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Mining site 5 Balagaye

Thin layer and mudstone grey shale containing selenite

Grey shales containing Satinspar

Blue-Black shales containing massive Alabaster gypsum

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Laminated gypsum and disseminated detrital gypsum in Mudstone

Selenite gypsum in Mudstone and grey shales Satinspar in Blue – Black shales

Enterolithic satinspar in Blue – Black shales Marine Alabaster gypsum in Blue-Black shales

Mining site 6 Nyakire

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Fig. 4 cont’d

Mudstone containing laminated gypsum and disseminated detrital gypsum crystals

Blue-black shales containing Satinspar gypsum Blue black alabaster gypsum

Mining site 7 Turmi – Malori

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Mudstone containing laminated gypsum and disseminated detrital gypsum

Mudstone, grey shale containing Selenite gypsum Blue-Black shales containing Satinspar gypsum

Blue-Black shales containing massive Alabaster gypsum

Mining site 8 Garin Ali – Zangaya

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Thin Mudstone

Grey shales containing Selenite gypsum

Blue-Black shales containing Satinspar gypsum

Blue-Black shales containing massive Alabaster gypsum

Mining site 9 Fika

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Fig. 4 cont’d

Thin Mudstone

Grey shales containing Selenite gypsum

Blue-Black shales containing Satinspar gypsum

Blue-Black shales containing massive Alabaster gypsum

• Université: Abubakar Tafawa Balewa University (Geology Programme)
• Cours: Economic Gelogy/ Mineral Exploration
• Note: Research
• Auteur: Dr. Ahmed Isah Haruna (Auteur)
• Année de publication: 1998
• Pages: 80
• N° de catalogue: V212437
• ISBN (ebook): 9783656413851
• ISBN (Livre): 9783656414544
• Langue: anglais
• mots-clé: review, geology, geochemistry, origin, gypsum, mineralization, chad, basin, north, eastern, nigeria, brine, mixing, hypothesis