Human Exposure to Arsenic and Other Potentially Toxic Metals in Some Waters of Biu Volcanic Province, North-Eastern Nigeria: The effect of leaching from rocks into surrounding waters

Contents

CHAPTER ONE: GENERAL INTRODUCTION
1.1 INTRODUCTION
1.2 LOCATION, EXTENT AND ACCESSIBILTY
1.3 RELIEF AND DRAINAGE
1.4 CLIMATE AND VEGETATION
1.5 SETTLEMENT AND LAND USE

CHAPTER TWO: LITERATURE REVIEW
2.1 INTRODUCTION
2.2 EFFECTS OF TRACE ELEMENTS IN VOLCANIC AREAS

CHAPTER THREE: DETAILED GEOLOGY AND HYDROGEOLOGY OF THE STUDY AREA
3.1 DETAILED GEOLOGY
3.1.1 INTRODUCTION
3.1.2 PORPHYRITIC AND AMYGDALOIDAL VARIETY
3.1.3 LARGE PHENOCRYSTS OF ZONED LABRADORITE
3.1.4 AGGLOMERATES, TUFFS AND BROWNISH RED BASALTIC SCORIA
3.2 HYDROGEOLOGY OF THE STUDY AREA
3.2.1 INTRODUCTION
3.2.2 SURFACE WATER
3.2.1.1 LAKE TILA
3.2.1.2 PERENNIAL STREAM WATER
3.2.1.3 GROUNDWATER IN THE BASALTS
3.2.3 DATA COLLECTION
3.2.4 DATA PROCESSING
3.2.5 INTERPRETATION OF GROUNDWATER MAP
3.2.6 STRUCTURES
3.2.7 JOINTS

CHAPTER FOUR: HYDROGEOCHEMISTRY
4.1 INTRODUCTION
4.2 METHODOLOGY
4.2.1 SAMPLE COLLECTION AND PRESERVATION
4.2.2 WATER SAMPLE PREPARATIONS
4.2.3 SOIL SAMPLE PREPARATIONS
4.3 ANALYTICAL TECHNIQUE

CHAPTER FIVE: PRESENTATION OF RESULTS/DISCUSSIONS
5.1 PRESENTATION OF RESULTS
5.1.1 Water Sample
5.1.2 MAJOR ELEMENTS
5.1.2.1 Calcium (Ca)
5.1.2.2 Potassium (K)
5.1.2.3 Magnesium (Mg)
5.1.2.4 Sodium (Na)
5.1.3 TRACE ELEMENTS
5.1.3.1 Arsenic (As)
5.1.3.2 Barium (Ba)
5.1.3.3 Cadmium (Cd)
5.1.3.4 Chromium (Cr)
5.1.3.5 Copper (Cu)
5.1.3.6 Iron (Fe)
5.1.3.7 Iodine (I)
5.1.3.8 Manganese (Mn)
5.1.3.9 Molybdenum (Mo)
5.1.3.10 Nickel (Ni)
5.1.3.11 Lead (Pb)
5.1.3.12 Antimony (Sb)
5.1.3.13 Selenium (Se)
5.2 Soil Sample Analysis Results
5.2.1 MAJOR ELEMENTS
5.2.2 TRACE ELEMENTS
5.2.2.1 COBALT
5.2.2.2 CHROMIUM
5.2.2.3 COPPER
5.2.2.4 NICKEL
5.2.2.5 LEAD
5.2.2.6 ZINC
5.3 DISCUSSION OF RESULT
5.3.1 MAJOR ELEMENTS IN SOIL AND WATER SAMPLES
5.3.1.1 SOIL
5.3.1.2 WATER
5.3.2 TRACE ELEMENTS IN SOIL AND WATER SAMPLES
5.3.2.1 SOIL
5.3.2.2 WATER
5.3.2.2.1 Arsenic
5.3.2.2.2 Selenium
5.3.2.2.3 Antimony
5.3.2.2.4 Lead
5.3.2.2.5 Cadmium
5.4 Trace Element Exposure and Human Health
5.4.1 Introduction
5.4.2 Trace Element Exposure
5.5 Trace Elements and Human Health Impact

CHAPTER SIX: SUMMARY, CONCLUSION / RECOMMENDATION
6.1 SUMMARY
6.2 CONCLUSION
6.3 RECOMMENDATIONS

REFERENCES CITED

APPENDIX

CHAPTER ONE: GENERAL INTRODUCTION

1.1 INTRODUCTION

Through physical and chemical weathering processes, rocks break down to form the soils on which the crops that constitute the food supply are raised for humans and animals consumption. Drinking water travels through rocks and soils as part of the hydrological cycle and in the process leached elements in solution (Lar, 2009).

Volcanism and related igneous activities are the principal processes that bring elements to the surface from deep inside the Earth. For example, the volcano Pinatubo ejected on the 2nd of June 1991, about 10 billion tonnes of magma and 20 million tonnes of SO2 and the resulting aerosols influenced the global climate for 3 years (Selinus, 2004). This event alone introduced 800,000 tonnes of zinc, 600,000 tonnes of copper, and 1,000 tonnes of cadmium to the surface environment. In addition to this, 30,000 tonnes of nickel, 550,000 tonnes of chromium, and 800 tonnes of mercury were also added to the Earth's surface environment. Volcanic eruptions redistribute some of the harmful elements, such as arsenic, beryllium, cadmium, mercury, lead, radon, and uranium. It is also important to realize that there is an average of 60 sub aerial volcanoes erupting on the surface of the Earth at any given time, releasing various elements into the environment. Submarine volcanism is even more significant than that at continental margins, and it has been conservatively estimated that there are at least 3,000 vent fields on the mid ocean ridges (Selinus, 2004).

Almost all metals present in the environment have been biogeochemically cycled since the formation of the Earth. Human activity has introduced additional processes that have increased the rate of redistribution of metals between environmental compartments, particularly since the industrial revolution. However, over most of the Earth's land surface the primary control on the distribution of metals is the geochemistry of the underlying local rocks. Fundamental links between chemistry and mineralogy lead to characteristic geochemical signatures for different rock types. As rocks erode and weather to form soils and sediments, chemistry and mineralogy again influence how much metal remains close to the source, how much is translocated greater distances, and how much is transported in solutions that replenish ground and surface water supplies. In addition, direct processes such as the escape of gases and fluids along major fractures in the Earth's crust, and volcanic related activity, locally can provide significant sources of metals to surface environments, including the atmosphere and sea floor. As a result of these processes the Earth's surface is geochemically inhomogeneous. Regional scale processes lead to large areas with enhanced or depressed metal levels that can cause biological effects due to either toxicity or deficiency if the metals are, or are not, transformed to bioavailable chemical species (Selinus, 2004).

Many elements are essential to plant, human and animal health, but this depends on the dose. Most of these elements are taken into the human body via food, water, in the diet and in the air we breathe.

The naturally occurring elements are not distributed evenly across the surface of the Earth, and problems can arise when element abundances are too low (deficiency) or too high (toxicity). The inability of the environment to provide the correct chemical balance can lead to serious health problems. Approximately 25 of the naturally occurring elements are known to be essential to plant and animal life in trace amounts, including Ca, Mg, Fe, Co, Cu, Zn, P, N, S, Se, I, and Mo. On the other hand, an excess of these elements can cause toxicity problems. Some elements such as As, Cd, Pb, Hg, and Al have no or limited biological function and are generally toxic to humans (Selinus, 2007).

Those living on lands with heavily impoverished soils, have such a low intake of essential elements that a very large percentage of the population suffers from a variety of diseases caused by severe mineral imbalances. Likewise, in areas, where there is excess intake of elements due to the abundance of certain minerals in the environment, may leads to high incidences of toxicity.

Environmental pollution arising from the distribution elements by natural or anthropogenic processes distorts geochemical systems. The natural geochemical composition of rocks and soils that make up the environment where we live may become direct risks to human health and may be the underlying cause of element deficiency and toxicity (lar, 2008).

Because of the increasing concern on the negative effects of excess or lack of trace elements to Humans and Animals an attempt will be made to study trace elements concentration in the soils, surface and underground waters of some part of Biu volcanic province.

1.2 LOCATION, EXTENT AND ACCESSIBILTY

The study area covers some parts of the Biu Plateau. The area is located in the standard sheet 133SW. Lying between longitude 12 ̊ 07ˈE and 12 ̊ 15ˈE and latitude 10 ̊ 31ˈN and 10 ̊ 38ˈN. Biu Town is located at the centre of the Plateau. The towns bordering the area include Damaturu to the North, Mubi to the South and Damboa to the East and Gombe to the West figure1.

The area is fairly accessible and has relatively good network of roads and foot paths. There is a trunk ‘A’ road in the area that stretches from Biu-Damboa road and Biu-Garkida road that give good access for sample collection.

1.3 RELIEF AND DRAINAGE

Topographically, the Biu Plateau stands at an altitude of about 600-800m above sea level, forming a flat top in some areas, it slopes gradually to the north and has steep precipitous escarpment to the south. To the west and east it has steep slopes. There are however gently undulating plains of the buried basement and cretaceous rocks particularly in the western and southern part of the Plateau. The Basement rocks are often deeply weathered, and where the protecting basalt cover has been removed, gullies and rough topography often develop (Du Preeze, 1949).

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Figure 1: Map of Nigeria showing the location of the study area (Modified after Falconer, 1911)

In the northern part around Miringa area it is characterized by the presence of volcanic cones, which formed many flat top hills. The topography can be observed from the extinct volcanoes in line from north to south along side with Biu-Damboa road, and to the west and east near Zagu.

In the southern part of the area from Kinging to Marama and Lokoja the topography steadily increases and decreases at some interval but generally maintains an average altitude of about 450-600m above sea level. Many hills here have well developed craters with branched rims and steep sided feature. A number of volcanic cones rise above the plain; some appear well preserved but are deeply weathered.

At the south-eastern parts of the Plateau near Kwajaffa there is a sudden drop in the altitude to about 150m above sea level.

Numerous tributaries of the Gongola River including the Hawal, Ruhu, Gungeru, and Ndivana rivers rise on the plateau and deeply dissect its surface. All rivers in the study area are seasonal, displaying dendritic drainage patterns that are both structurally and morphologically controlled (figure 2). While Biu’s southern and western sides are quite steep, the plateau slopes more gradually in the north onto the Bauchi Plains and the Chad Basin (Du Preeze, 1949).

1.4 CLIMATE AND VEGETATION

Biu Plateau falls within the Guinea Savannah climatic zones of Nigeria. There are two types of seasons in this area. They are wet and dry season. The wet season starts around April to September while the dry season sets in from September to March (Falconer, 1911).

The month of October to February witness the cold period with extensive cold and dusty cloud. The dry season is influenced by the tropical continental NE trade wind (harmattan), while the wet season with its torrential rains occasionally accompanied by hail storm is induced by the tropical maritime SW trade wind. The plateau receives approximately 1,000 mm (40 in) of precipitation from April to September, the rainy season lasts 140days (Falconer, 1911).

The vegetation of the study area could be best described as Sudan type. It is characterised by trees of about 6- 8 meters high interspersed with tall trees and plain grasses. Vegetation is thicker along the river channels and streams.

Temperature alters very much as it attains about 34̊C during the day while in the night it could drop significantly to 8̊C.

Relative humidity is generally low, ranging from as low as 13 per cent in the driest months of January and February to the highest values of seventy to eighty per cent in the rainy season months of May and September (Falconer, 1911).

1.5 SETTLEMENT AND LAND USE

The Biu Plateau’s thin soils, scarcity of water in the dry season, and relative inaccessibility have discouraged human settlement there. Several ethnic groups (Babur, Bura, Tera, Margi, Hina, and Fulani), make their home on the Biu Plateau, the largest being the Bura people. The Biu plateau has a generally low population density, except for urban pockets in the south. Biu, a regional administrative and commercial centre, is the largest town. Roads link Biu to north-eastern Nigeria’s largest cities Maiduguri, Yola, and Gombe. The Biu plateau provided a place of refuge for small, militarily weak groups, who resisted the expansion of the powerful Fulani Sokoto Caliphate, which controlled most of northern Nigeria in the 19th century (Falconer, 1911).

The volcanic soils are naturally fertile but also thin and stony. Small, hand-tilled farms are the mainstay of the region’s economy. Sorghum, millet, maize (corn), beans, cotton, and peanuts are the main crops. Some farmers grow crops in terraced plots on the slopes of valleys. Rice is cultivated in some valley bottoms.

Most inhabitants in the region keep cattle, goats, sheep, horses, and donkeys; and Biu town is the chief trade centre (sorghum, millet, peanuts [groundnuts]) on the Plateau. The town, site of the emir’s palace, has several (government Health offices and a Dispensary. The Church of the Brethren operates a teacher-training college at nearby Waka Biu (Falconer, 1911).

illustration not visible in this excerpt FigFigure 2: Drainage map of the study area (present study)

CHAPTER TWO: LITERATURE REVIEW

2.1 INTRODUCTION

Not much work has been done on trace element Hydrogeochemistry in volcanic environment in Nigeria. The present study is the first of its kind and will relate the distribution of trace elements from soils into surface and ground waters in the study area to the possible health impact in humans. However, the effects of trace elements in volcanic environment on Human, Animals and Plants have been studied considerably around the world by various authors.

2.2 EFFECTS OF TRACE ELEMENTS IN VOLCANIC AREAS

In the western United States, groundwater with elevated arsenic concentrations is known to be associated with intermediate to felsic volcanic rocks and associated sediments (Welch et al., 1988). Volcanic rocks and sediments derived from them are also associated with elevated arsenic levels in ground water. This may be true not because volcanic rocks contain more arsenic than other types of rocks, but because the arsenic is more readily mobilized from volcanic rocks and derived sediments.

Volcanic rocks and derived sediments in the north-eastern half of the Tucson basin, where sediments are derived largely from granitic rocks, arsenic concentrations in ground water are generally less than 2 parts per billion (ppb). In contrast, in the south-western half of the basin, underlain by sediments derived substantially from volcanic rocks, arsenic is found in much higher concentrations in groundwater (Spencer, 2000). Volcanic rocks and derived sediments, especially where altered to clay minerals, may be especially prone to yielding arsenic to groundwater under such conditions.

The problem of fluorosis related to volcanic activity was first recognised in Japan were this pathology was called “Aso volcano disease” (Kawahara, 1971) due to the fact that fluorosis was widespread in the population living at the foot of this volcano. Water intake being the main route of fluorine into the human body, fluorosis in volcanic areas is generally associated to elevated fluoride content in surface- and ground-waters.

High fluoride concentrations (greater than the WHO guideline value of 1.5 mg/l) are found in the Rift Valley of western Uganda and in the volcanic areas of the east (Mbale, Elgon, Moroto areas). The incidence of fluorosis is known to be high as a result. The crater lakes of western Uganda often have high concentrations (e.g.4.5 mg/l F in Lake Kikorongo; Mungoma, 1990) and concentrations in ground waters having interaction with these lake waters are likewise expected to be high (and the waters correspondingly saline). High fluoride concentrations are particularly noted in groundwaters from the Rwenzori Mountains on the western border and the Sukulu Hills in eastern Uganda (WRAP, 1999). In the Sukulu Hills, fluoride may also be associated with occurrences of phosphate minerals which are currently being investigated for mining development.

Acute and chronic fluorosis on grazing animals has been described for many explosive eruptions all around the world [Mt. Hekla – Iceland (Georgsson and Petursson 1972), Lonquimay – Chile (Araya et al, 1990), Nyamuragira – Democratic Republic of Congo (Casadevall, 1995), Mt. Ruapehu – New Zealand (Cronin et al, 2002). Consequences on livestock are due to grazing of grass or drinking water that is Fluoride -contaminated.

High fluorine content in waters derive either from Water-Rock Interaction (WRI) processes in volcanic aquifers (ground waters) or to contamination due to wet or dry deposition of magmatic fluorine (surface waters - reservoirs). Furthermore, paleopathologic studies on human skeletons found in Herculaneum, referable to victims of 79 AD eruption of Mt. Vesuvius, evidenced that fluorosis in this area had the same incidence as in modern times, pointing to the constancy of the geochemical processes responsible for fluorine enrichment of the drinking water in the area over at least the last 2000 years (Morettini and Ciranni, 2000).

Dental fluorosis due to groundwaters enriched by water rock interaction (WRI) in recent or active volcanic areas has been assessed in many parts of the world. Many articles illustrate such cases. Some of them refer to limited areas like Gölcük – SW Turkey (Pekdeger et al, 1992), Mt. Aso volcano, Japan (Kawahara et al, 1971), Island of Tenerife – Spain (Hardisson et al, 2001), Furnas volcano, São Miguel – Azores, Portugal (Baxter et al, 1999), while other evidence a widespread problem throughout entire countries like Mexico (Soto-Rojas et al, 2004), Ethiopia (Kloos and Haimanot, 1999), Kenya (Nyaora et al, 2002), Tanzania (Nanyaro et al, 1984). In these areas, populations as high as 200,000 people could be at risk to develop fluorosis like for example the inhabitants of the Los Altos the Jalisco region in Mexico (Hurtado et al, 2000).

Very acidic lakes in active volcanic systems can also achieve extreme fluorine concentrations not only due to intense WRI processes but also to direct input of F-rich volcanic gases. Lake like Ijen Crater Lake – Indonesia (Heikens et al, 2005) reach concentrations far above 1000 mg/l. Seepage or effluent rivers from these extremely F-rich lakes can easily contaminate ground- or surface waters. It has been estimated that the Ijen Crater Lake discharges daily in the surface and ground waters of the highly populated area of Asembagus about 2800 kg of fluorine (Heikens et al, 2005), which is responsible of the widespread occurrence of fluorosis in the area. Furthermore the fluorine contained in the salts extracted from the shores of the East African Rift Valley lakes and used for cooking purposes represent an additional fluorine source for the local population (Nanyaro et al, 1984).

Ullrey (1981) reported the occurrence of low selenium areas in Arizona and New Mexico where the soil is formed from Tertiary volcanic rock. These areas also tend to correspond to areas where selenium-deficiency disorders such as white muscle disease occur.

Volcanic eruptions that discharge more than a few mega tonnes of sulphur gases into the atmosphere have the potential to cause regional to global scale climate change through complex mechanisms. A well observed and understood phenomenon is the summer cooling and winter warming of Northern Hemisphere continental regions following large, sulphur‐rich eruptions of volcanoes in the tropics. The 1815 eruption of Tambora, Sumbawa Island, Indonesia, responsible for the greatest recorded fatalities due to volcanic activity (Witham, 2005), also released sufficient sulphur into the upper atmosphere to result in widespread cooling during the Northern Hemisphere summer in 1816. This has been linked to epidemic disease in Ireland, the UK, and parts of continental Europe through a combination of socioeconomic factors and the effects of the climatological anomalies on crop yields (Oppenheimer, 2003). In the immediately impacted region, an estimated 61,illustration not visible in this excerpt000 people died during and in the aftermath of the eruption, mostly as a result of famine and epidemic disease.

CHAPTER THREE: DETAILED GEOLOGY AND HYDROGEOLOGY OF THE STUDY AREA

3.1 DETAILED GEOLOGY

3.1.1 INTRODUCTION

Biu Plateau is situated on the structural and topographic divide between the Benue and Chad sedimentary basins (fig. 3). The structural divide is a broad E-W ridge or swell of basement, which extends to the western edge of the Biu Plateau. The two basins are divided by the Zambuk ridge to the west (Carter et al., 1963). Fig 4 shows a simplified geological map of Nigeria.

The basalt of the Biu Plateau mainly overlies Basement rocks. These are predominantly granites, granite-gneiss and Fayalite-quartz, Monzonite, Bauchites (near Wandali at the SW margin of the plateau), hypersthenes diorite, volcanic and sub volcanic rocks of the Burashika group (Turner, 1978). To the west and north, Basalt of the Biu Plateau has spread over cretaceous sediments, mainly the arkosic Bima sandstone. These rocks are folded, with axes to the SW of the Plateau trending NE-SW, the structures extending into the basement rocks as NE-SW faults (Turner, 1978).

The buried landscape consisted of gently undulating plains on both the basement and Cretaceous rocks, which must have been particularly featureless in the NE. (Du-Preez, 1949) discovered that the sub-basalt surface was lateralized. Laterite exposed beneath the basalt near Puba, 4km SW of Kwajaffa consists of about 1.5m of hard pisolitic ironstone overlying residual clays and weathered granite-gneiss.

Two important post depositional processes affect the Poliocene basalts. The first was internal, the crystallization of zeolites and calcite, which are abundant in vesicular and rubbly interflow horizons. The second is surface weathering to clays and laterites. The basalt of the poorly drained northeastern plains is deeply decomposed to clay presumably a continuing process. Much less widespread, but more significant, is the development of laterite on the high Plateau.

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Fig.3: Location MAP of Biu Plateau and other Rock types in Nigeria (adopted from Wright, 1976)

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Figure 4: A Simplified Geological Map of Nigeria (Source: - NGSA, 2004)

The rocks in the Biu Plateau mostly occur as “flood basalts” in a number of flows and in fact cover nearly 85% of the area with its centre around Biu (Turner, 1978). The basalt at some places has built up large number of flows. The dimension of the flows and the marked absence of pyroclastics in and around Biu, Tum, Marama, and Shaffa areas, indicate that the eruption of basaltic magma in these places was not violent. However, the basaltic sequence in the Northwestern part of Biu (Miringa area, fig. 5) is surrounded by several youthful scoria, cinder cones, tephra rings etc, the pyroclastics are generally restricted to the area west of Biu- Damaturu road, suggesting that the eruptions in these places are violent in nature.

The volcanoes are built up by essentially basaltic materials and are of two textural types namely: the Biu type, which is flow basalts, massive with vesicles, and the Maringa type, highly scoraceous and associated with pyroclastic deposits. These two types present the same mineralogy consisting of phenocrysts of both olivine, plagioclase (bytwonite-labradorite), and rarely pyroxene (diopside-augite) set in a groundmass of labradorite laths, magnetite, ilmenite, minor K-feldspars, nepheline and volcanic Glass (Saidu, 2004).

The Basement rocks on which the basalt of the Biu Plateau overlies are predominantly granites and granite-gneisses. The foot of the Basement can be seen in the southern part of Biu (Kwajaffa area), Southwestern part (Wandali area) and Southeastern part (Garkida area). To the North and Western part of the Biu Plateau the basalt spread over Cretaceous sediments, mainly over the arkosic Bima sandstone (Turner, 1978).

Du Preez, (1949), studied the detailed petrology of the Biu basalt; petrologically the basalts are represented by a wide range of rock types such as porphyritic and amygdaloidal variety, large phenocryst of zoned labradorite and agglomerates, tuffs and brownish red basaltic scoriae. The land sat image (fig 6) gives a synoptic view of the study area.

3.1.2 PORPHYRITIC AND AMYGDALOIDAL VARIETY

The y occur in the central Plateau around Biu showing the lath of labradorite feldspar, some of which exhibit a rudimentary trachytic arrangement. Large phenocrysts of olivine are common but smaller crystals also constitute an important proportion of the groundmass, in some cases the smaller crystals are completely altered to iddingsite, whereas the phenocrysts are either unchanged or show only marginal alteration effects. Some amygdales are encrusted or completely filled with zeolites such as stilbite, and sometimes with calcite. Pyroxene is present as small elongated crystals in the groundmass and iron oxide is abundant.

3.1.3 LARGE PHENOCRYSTS OF ZONED LABRADORITE

They formed a prominent constituent of the worn volcanic cones near Jaragwol on the Gongola. The groundmass, which consist chiefly of labradorite laths, minutes grain of pyroxene and much iron ore, shows pronounced flow structure, especially around the large feldspar and olivine phenocrysts. The olivine shows extensive serpentinisation. The basalts at Ngulde exhibit a glomero-phorphyritic texture.

The phenocrysts of labradorite and mafic minerals are arranged in clusters, the former usually forming an outer rim enclosing a core of ferro-magnesium minerals consisting chiefly of enstatite. The groundmass sometimes shows an ophitic texture and consists of laths of labradorite together with olivine, clino-pyroxene and some enstatite. Large beautifully zoned labradorite phenocrysts are often present and enstatite is sometimes seen to change into clini-pyronexe.

3.1.4 AGGLOMERATES, TUFFS AND BROWNISH RED BASALTIC SCORIA

They are widely distributed in Babur district. Scoriaceous are not infrequently found inter-bedded with black, fine-grained varieties. The volcanic cones to the west of Biu-Damaturu road are composed of decomposed scoriae, fragments of ropy lava, bombs, tuffs and agglomerate, the latter frequently containing boulders of granite-gneiss

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Fig.5: Geological map on Biu-plateau (adopted from Saidu, 2004)

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Figure 6: Landsat image of the Study Area, insert are craters and Tila Lake (from Google Maps, 2011)

Excellent exposures of bedded tuff dipping at a low angle to the north-west may be seen at Lake Tila. Agglomeratic tuffs form aprons around the prominent volcanic cones one mile north of Miringa. In this locality, masses of agglomerate consisting chiefly of large and small lava bombs, inclusion of ultra-basic rocks and granite-gneiss build picturesque cliffs and crags in which caves have been formed in some places. Similar outcrops are present in many other localities notably at Mount Sagu north of Buratai. Mount Tila is composed of brownish-red Scoriaceous basalts. South of Biu agglomerate are not abundant, there are however, several outcrops of agglomerate near Ngwa and also an interesting occurrence at a much lower level several miles west of Buma on the Hawal. Isolated occurrences, like Mount Biski three miles north-west of Haran in East-Bura district, are sometimes found.

Ultrabasic nodules are an important component of the agglomerates in some areas. West of Miringa they may be up to one foot in diameter. Frequently they form the cores of lava bombs with an outer shell of lava froth. They generally consist essentially of olivine, but diopside is sometimes present. Another interesting type of inclusion observed west of Miringa consists exclusively of pyrope with a network of kelyphitic veinlets. Red grains of pyrope have also been found in the heavy mineral concentrates in the Magzar River some eight miles east of Miringa. One inclusion was seen to consist of pyrope with subordinate olivine in diopside showing definite kimberlitic affinities. Iddingsite nodules were seen in some localities, but in general they are rare. Other bombs containing large crystals of glassy oligoclase and dark green olivine have been noted.

3.2 HYDROGEOLOGY OF THE STUDY AREA

3.2.1 INTRODUCTION

Water is the most important natural resource provided for survival of man by nature. Globally, water is mostly used for domestic, industrial and agricultural purposes. The water resources of the study area can be divided into surface and groundwater resources.

The surface water of this area occurs in the form of streams and lakes. They serve as water supply sources for both drinking and domestic uses. Most of the streams are seasonal. The streams and lakes are recharged by direct precipitation during the rainy season.

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