PETROGRAPHIC STUDIES OF SELECTED BARIUM SULPHATE DEPOSITS IN BENUE TROUGH OF NIGERIA

 1.0 INTRODUCTION
Barytes is an orthorhombic mineral with chemical composition BaSO4. It possesses one perfect cleavage and two good cleavages, as do the isostructural minerals. The mineral has a specific gravity of approximately 4.5, and it is relatively soft, approximately 3 on Mohs scale. The colour ranges from white to yellowish, grey, pale blue or brown and a thin section is colourless. Barytes (BaSO4) are heavy spar, inert and stable. These properties make them valuable. Barytes, formerly used chiefly as filer and adulterant, is now used in glass and paints industries and the oil well drilling industries which consume 80 percent the world production.
Barytes group minerals include the sulphates (SO42_) of barium (barites or barite), strontium (Celestine) and lead (anglesite). The structure of barite has sulphate group lying on a reflection plane, two oxygen of the sulphate group lie within this plane, and two oxygen and minor images across it. Each barium atom is coordinated by twelve oxygen atoms and seven separate sulphate groups.

Baryte, the most common barium mineral, is abundant in moderate to low-temperature sulphide veins, being associated with fluorite. It occurs mainly as gauge minerals in metalliferous hydrothermal veins and as veins or cavity filling concretion in limestones, sandstone, shale and clay (Dunham 1984)

1.1ORIGIN OF BARYTES
The origin of barite according to Hatch wells (1971) can be supported by the following model:

  • Anatexis
  • Differentiation of basaltic magma from the upper and lower crustal rock by fusion.
  • Carbonitic origin.

Anatexis ; this is the partial melting and recrystallization of pre existing rocks which is attained as high temperature, low pressure and shallow depth (Hatch wells, 1971). The melt composition depends on phase relationships in the solid and the temperature and pressure conditions of melting. (Hatch wells, 1971).
Differentiation of basaltic magma derived from the upper mantle and lower crustal rock by fusion.olivine crystallizes out of the melt due to reduction in temperature.

 

DISCONTINUOUS SERIES                                             CONTINUOUS SERIES
g3High temp. fosterite (18900c                                                  Anorthite (15400c)
g4Fayalite (12050c                                                                        

Pyroxene (orthopyroxene)                                                                       early differentiation
g5g6                                                                                                                 Bytownite
g7g8Mg-Ca clinopyroxene                                                                                   labradonite

g9g10Amphiboles                                                                                         Andesine

g11g12Biotite                                                                                                      Albite   

g13                                              Orthoclase                                                

g14                                                   Quartz                                        pegmatitic stage       

g15                                               Pegmatite                                          late differentiation

                                                   Hydrothermals
Fig 1 schematic diagram of discontinuous and continuous series after Bowen (1970). This involves 3 stages in which minerals will crystallize out according to their temperature.

 

 

STAGE 1; this is the early stage during which Mg/ Fe rich mineral like Olivine crystallize out of the melt, due to reduction in temperature.
STAGE 2; this is the intermediate stage when the rock forming minerals crystallize out of the melt.
STAGE 3; this is the late stage of crystallization during which the residual magma rich in water and volatiles crystallize out. The product of this stage is usually pegmatite rocks in which barite minerals are associated with.
Also in this series minerals higher above, crystallize out of the melt before the ones below and the earlier formed minerals may react with magma to form mineral lower in reaction series.
Iv carbonitic origin; this is divided into 3 main types;

  • Late barite replacement carbonites which are commonly ankeritic, sideritic or maganiferous and also contain fluorite and have contained fluorite and may have RE-Th species.
  • Veins and replacement bodies outside the complex, usually in unaltered wall rock, barites alone, barite plus fluorite or quartz or carbonates.
  • Residual barites accumulation and supergene barites developed by weathering of carbonitic complexes.

1.1.2 CHEMISTRY OF BARYTES
Specimen of barites are generally nearly pure BaSO4. Barium (Ba) can be replaced by strontium (Sr) in a continuous solid solution series from barites to Celestine. Members of this series with a preponderance of Ba, molecule are called strontibarytes and these near the Sr end are called baryto-celestine (Heinrich and Vian, 1996). Appreciable replacement of Ba by Pb or by Ca is uncommon and it has been shown that at room temperature only about 6% CaSO4 can enter into solid solution in barites structure. The solubility of barite in water is very slight but it is increased by heating and by the presence of chlorides. When gently heated some crystal of barite deprecipate giving of H2S (Dunham, 1984).
1.1.3 GENERAL PROPERTIES OF BARITE
The properties of barite can be best described under these following headings namely; physical, optical, chemical and calculated properties.
1.1.3.1 PHYSICAL PROPERTIES
CLEAVAGE;(010)perfect(210)perfect(010)imperfect.
COLOUR;white, yellowish white, grayish white, brownish white, dark brown
DENSITY;4.48
DIAPHANIETY;  Transparent to translucent to opaque.
FRACTURE; uneven-flat surface (not cleavage) fractured in an uneven pattern
HABIT; massive-fibrous-distinctly fibrous fine grained forms
HABIT; prismatic-crystals shaped like slender prisms (eg tourmaline)
HABIT; tabular-form dimensions are thin in one direction
HARDNESS; 3-3.5 calcite-copper penny
LUMINESCENCE; phosphorescent
LUSTER; vitreous (Glassy)
STREAK; White
1.1.3.2 OPTICAL PROPERTIES
na=1.636
nβ=1.637
nγ=1.647
δ=0.012
2v=370+ve
OAP is parallel to (010)
Col    colourless
H      clusters of tabular crystals common massive
Cl      Basal cleavage (001) is perfect, as (210); imperfect, on (010)
R        moderate
A        Alteration-Barite may alter to witherite or be replaced by a large number of minerals
B        Birenfringence-low, first order yellowish or mottled colours seen
IF        Interference figures Bx2 figure seen on (100) section, with two good cleavages present
1.1.3.3 CHEMICAL PROPERTIES
CHEMICAL FORMULAR; BaSO4
COMPOSITION; Molecular weight= 233.39gm
Barium; 58.84%  Ba;65.70% BaO
Sulfur; 13.74%      S; 34.30% SO3
Oxygen; 27.42%   O;
EMPIRICAL FORMULAR; Ba(SO4)
1.1.3.4 CALCULATED PROPERTIES
ELECTRON DENSITY; Pelectron=3.99gm/cc
Note: Pbarite=4.48gm/cc
FERMION INDEX: Fermion index=0.89398
PHOTOELECTRIC: P.Ebarite=265.56barus/electron
U=PEBarite x Pelectron=1,060.27bara/cc
1.1.3.5 CRYSTALLOGRAPHY OF BARYTE
CRYSTAL SYSTEM; Orthorhombic
CLASS; (H-M)mmm(21m21m21m)- Diapyramidal
SPACE GROUP:PNMA (P2. 1n2, 1m2, 1a)
CELL PARAMETERES: a=8.664 (2) A0,b=5.457(3) A0, C=7.157 (2) A0
RATIO:A;B:C=1.628:1:1.312
UNIT CELL VOLUME: V 346.97(3)
A03 (Calculated unit cell)
1.1.3.6 MORPHOLOGY
Usually thin to thick tabular (001) bounded by (210) alone or in combination with (101), (101) or other form. Also flattened (001), and elongated to prismatic (010) or (100) more rarely prismatic (001), or equant. Often aggregates or clusters of tabular crystals with edges projecting into crest-like forms, or as rosettes. Also, form massive material, compact, laminated or concretionary; and in fibrous, stalactic, and earthy masses
1.2 AREA OF STUDY
The area studied is within the Guma Local Government of Benue state between latitude 07035’06’’ and 08012’56’’N and longitude 23’02’’ and 009007’52’’E, within the lower part of the middle Benue trough that contains cretaceous sediments.
1.2.1 CLIMATE
The climate is tropical with seasonal variations classified as wet and dry seasons, the middle Benue has a more prolonged wet season within early march to mid October while dry season is between late October and early march.
The wet season fluctuated more but generally lies between late April to early October while dry season lies between early October and late April at upper Benue
Temperatures are generally high between March and April and October to early February. However in some years when harmatan is severe the dry season last longer
1.2.2 TOPOGRAPHY
The middle Benue is generally characterized by a gently undulating topography which is punctuated by few hills. As one ascends the Benue trough through the middle to upper part of the trough the topography becomes rough. At the upper Benue, relief is exaggerated by hills like the lamudes and ligri, which rise up to 600m above the sea level.
1.2.3 VEGETATION
The vegetation of the middle Benue is of the guinea savannah and is made up the shrubs, tall grasses, scattered coconut and palm trees and a lot of mango and citrus trees
1.2.4 DRAINAGE
The Benue trough is drained by river and it tributaries meandering from north to south. Most of the river channels dry up during the dry season. The pattern is generally dendritics in the area studied.
1.2.5 GEOLOGY OF BENUE TROUGH
The Benue trough is defined as an intercontinental cretaceous basin about 1000km in length stretching in a NE-SW direction and resting unconformable upon the Precambrian basement (Barber, 1957). It is commonly subdivided into three main domains corresponding to both geological and geomorphological portion.

  • The upper Benue trough is the northeastern Y-shaped part of the basin and can  be sub divided into three domain, the Yola-Garua branch trending WNW-ESE, the Gongola branch and the Muri-Larnide domain trending NSS’’E
  • The lower Benue rough shifted south west includes two main structural units, the N 600E trending Abakaliki antclinorium flanked by the Anambra syncline trending N300E
  • The middle Benue trough is the linear part of the basin

1.2.5.1 UPPER BENUE TROUGH
In the upper Benue trough the lithostratigraphic pile includes a lower continental unit formed by the Bima sandstones series deposited in a lacustrine-deltaic environment above a marne sequence of shales. With interbedded carbonates represent the Turonian and Seninian stages
YOULDE FORMATION; Youlde Formation transitional between the continental Bima sandstone and the succeeding marine Formation falcona (1911) recognized such a transitional Formation between the muris sandstone and the marine Turonian and described it as the passage bed (Reyment 1955)
DUKULL FORMATION; this is the limestone shale series recognized by falconer (1911). The type locality is at Dukull where beds of shales interbeded with thin limestone and with a total thickness of up to 100m. This marks the beginning of a widespread shallow marine transgression, which covered most of the NE during Turonian time
JESU FROMATION; while in the North;( Gombe area marine transgression continued with the deposition of the Pindga Formation in the south a breed regressive phases resulting in deposits of sandstone, sandy, mudstone and shales of the Jesu Formation were in operation (Carter et al 1983)
SEKULE FORMATION: is the similar to the older Dukul formation and has been described elsewhere as the upper limestone (Barber et al, 2004) it is a sequence of shale and limestone, the shales being much thicker
1.2.5.2 MIDDLE BENUE TROUGH
The lithostratigraphic unit ranges in age from Albian to Coniacian. Locally the Maastrichtian stage is represented by the continental Lafia Formation. The oldest rocks known in the middle Benue trough belong to the Asu river group deposited in a marine environment linked n the south to the lower Benue trough. A tectonic phase of compression has turned the cretaceous into a set of long and regular folds with an incipient fracture cleavage in the core of the main keane anticline . The sequence are discussed below

  • Lower cretaceous group as in the southern Benue valley, sedimentation started here in the lower cretaceous with the deposition of the Albian glacier and limestone of the Asu river group. The rock type; is similar to that of lower Benue valley
  • Upper cretaceous, the Asu group is immediately overlain by the keana sandstone that has been assigned by a number of workers to the Cenomanian.

1.2.5.3 LOWE BENUE TROUGH
Two major structural units are distinguished in the lower Benue trough; the Anambra syncline and the Abakaliki anticlinoria. The lithostratigraphic pile include shale, siltstones and limestone occurrence Asu river group deposited in a shallow marine environment during the Albian times, the shales are dominant lithology in the Abakalik anticlinoria structure
Lithologic succession n lower Benue consists of Ezeak/ Makurdi Formation, Tunonian is better known with the occurrence of the Ezeaku  shales and the Makurdi Formation. The Ezeaku shale  consists of thick flaggy calcareous and non calcareous shale, sandy or shelly limestone and calcareous sandstone. Around Makurdi Formation and overlie the Albian shale if consists of thick mass of current bed coarse grained ( Cratchley and Jones 1965)
AWGU FORMATION; up in the Senonian stage, the Agwu Formation was deposited, these consists of marine fossiliferous grey-blue shale associated with subordinate limestone and calcareous sandstone.

  • UKPORO SHALE; the Awgu Formation is succeeded by the Nkporo shales which are 65found in the south sedimentary basin to constitute marine shale, whereas in the southwest parts of the Benue valley they are, infact mainly arenaceous sandstones eg Otobi sandstone.
  • MAMA FORMATION; consist mainly of sandstone, carbonaceous shale, sand , shales and some coal seems
  • AJALI FORMATION; Overlying the Mamu Formation; it consists of about 330m of coarse-grained characteristically current bedded sandstone.
  • NSUKKA FORMATION; This Formation is marked by the deposition of carbonaceous, shale, sandstones and sometimes coal seam. The uppermost unit been recorded as containing Paleocene fauna in southern Nigeria (Cralchley and Jones 19)

1.3 ECONOMIC GEOLOGY OF BENUE TROUGH
Apart from barite there are other industrial minerals that occur in the Benue trough they are;

  • Lead-zinc deposits, which extend from Abakaliki area in a narrow belt to Zurak in the northeast.
  • Brine occurs at Awe AND Keana lakes and springs.
  • Limestone which is special throughout the trough.
  • Coal, which occur in Gombe area.
  • Gypsum, which occur at Oturkpo area.

1.4 ECONOMIC IMPORTANCE OF BARITE
As earlier stated, most of the industrial applications of barites are based on their exceptionally high specific gravity. Therefore barite is widely used as weighing agent in the production of drilling mud in petroleum industry (RMRDC, Abuja 2005). About 91% of barites produced worldwide are mainly used for this purpose
Barite is also used in the manufacture of white paint especially to give weight to paper (Gribble,1988).
1.5 AIM OF THE STUDY
To determine the petrographic properties of some selected barites which was taken from Benue trough of Nigeria with a view to determine their distinguishing features.

 

 

 

 

 

 

 

REFERENCE
BOWEN 1970 continuous and discontinuous series
CATER 1983; The geology of parts of Adamawa, Bauchi and Bornu province in northeastern. Bull. Geol. Surv. Nigeria, 30, 109P
CRATCHELY, C.R. and JONES, G.P.1965; An interpretation of the geology and gravity anomalies of the Benue valley Nigeria. Overseas Geol survey geophysics. Paper no 1, 26Pp
DUNHAM, 1984; Geology of Northern pennie ore field, Pp.168-170.
FALCONER J.P. (1911); The geology and geography of the Northern Nigeria Macmillan and Sons Ltd London. Pp 59-75
HATCH WELLS, 1971;Igneous petrology (6th Ed) Pp. 68-72
REYMENT R.A 1965; Aspects of Geology of Nigeria, Ibadan