X-Ray Diffraction Study of Mineralogical Composition of Mudstones from Eastern Gadaref Area, Sudan

SD9800025

X-RAY DIFFRACTION STUDY OF MINERALOGICAL COMPOSITION OF MUDSTONES FROM EASTERN GADAREF AREA, SUDAN

YASS1N AHMED A. KA8JMEL01K

A THESIS SUBMITTED FOR THE PARTIAL FULFILEMENT OF THE DEGREE OF MASTER OF SCTENCE INFHYSICS

PHYSICS DEPARTMENT FACULTY OF SCIENCE UNIVERSITY OF KHARTOUM SEPTEMBER 1996 We regret that some of the pages in this report may not be up to the proper legibility standards, even though the best possible copy was used for scanning

ABSTRACT

X-RA Y DIFFRACTION STUDY OF M1NERAL0GICAL COMPOSITION OF MUDSTONES FROM EASTERN GADAREF AREA, SUDAN M.Sc. by YASSIN AHMED ABDELGADIR KARIM ELDIN 1996

This study reviews the theoretical and experimental aspects of Xray diffraction (XRD) technique. Moreover, the mineralogical composition of some mudstones from Gadaref region has been investigated using DIFFRAC-AT software package, by means of searching and matching procedure in the standard XRD patterns edited by the International Center for Diffraction Data (ICDD).

The X-ray diffraction analysis of the Gadaref mudstones revealed that quartz, kablinite and tridymite are the major mineral constituents of these rocks. Whereas other minerals like alunite, coalingate, cristabolite, gutsvechite, hematite, meta-alungen, minamite, monteponite, samarskite , chlorie, illite and smectite represent minor constituents in some samples.

Most of the mudstone samples investigated have kaolinite content between 71-100 % This most probably indicates that these rocks were subjected to intense weathering and leaching under warm humid climate. These conditions seem to be less favourable for the formation of clay minerals chlorite, illite and smectite. Generally, the clay mineral types, abundances and distribution appear to be influenced mainly by source rock geology, the local environment and climate. Moreover, the high silica content of the mudstones reflects the influence of both hydrothermal and weathering processes.

The high kaolinite content of these mudstone might suggest a good potential for economic exploitation of the kaoline deposits. Further studies, however, might be needed to investigate other technical properties.

Suggestions for further work by XRD are given, and include further additions to the refinement procedures and the purchasing of new computer's facilities.

(i) VsJ'

M-Jai .ij^J' l^N1 J_^ ^yUill JSLiJl LL^ jl^Ji ^y*-"—J

(DIFFRAC-AT)

. (ICDD) ijJ-\ ol;U Jjj

J (tridymite) OJUJO^'J (kaolinite) c~»LJji53i (quartz), yjj—^J

,(alunite) C-JI Jjili J ^ OJI «ii j—»

,(gutsvechite) CJIL~V (cristabolite) , O-J^I^—j

^ ,(minamite) cu-L-u^ ,(meta-alungen) uy^yyil - iv ,(hematite) CJU

A_«J ^y iLu* y,i\i. Jic (samarskite) C-JISL.JL.L- J <. (monteponite) C-J

-v \ J_-J (kaolinite) C-JLJJL_T (^^-IP t^ci- oLu*)i «J_ft (Jijc 01

^4 i^jj] o-vby«j' Lf»l ^^ J_JA-A)I eJL* J-b" 01

oJ_P J S 1>JL_-Jl o!_j_ji<' 0' .r-

i jJJ; JS- v'di 4JJI>-I OLLAJI J Ju^swdl yl ,/«• Lc.j iJuJl(silica)

J LA oi Ji js-io yJaJi jU^-Vi »iA iJuJi (kaolinite) C-JLJJ15^JI OL.^- OI

IJL*

(ii) Several individuals have helped in one way or another during the preparation of this study. If I decide to enumerate, the listing will definitely be lengthy. However, 1 must mention certain people whose help was certainly invaluable.

| Firstly, my Supervisor, Dr O.man Mahmoud Abdullatif who takes i most of the gratitude for his constant Iv.'lp and guidance throughout the £ course of this project. I Secondly, I would like to record my deep appreciation, to Dr. \ Osman Dawi Eisa who is my former supervisor. \ Thirdly, I would like to express my gratitude to Dr. M.H.Shaddad I for the installation of DIFFRAC-AT from which I learned quite alot in ? relation to the software package, lam particulrly grateful to my colleagues | Mr.H.H.Idris who helped me also in the installation of DIFFERAC-AT. ? Fourthly, lam particulrly grateful to Computer Laboratory Group for I providing Laser Jet III printer which matches the DIFFRAC-AT package, * for making this study possible by giving me access to the Department's I resources. Also my great thanks are extended to Mr. Hosham, Miss. Mona H and Miss. Hyfa working for Gortas Computer Service for rearrangements I and decorations. I Fifthly, on behalf of the Physics Department, Faculty Of Science, I University Of Khartoum, I would like to pay tribute to the following | International Organizations: The International Atomic Energy Agency (IAEA) for donating the diffractometer and it's accessories, the International Program in Physical Sciences(IPPS) for their generaous gift, the DIFFRAC-AT software.

At last but not least, members of my extended family have, of course, been extremely supportive and they all deserve a special word of my thanks. Of all, I would like to acknowledge the role of my parents (specially my mother) for encouraging me to take this endeavour. lam also deeply indepted to my brothers Moatasim, Mohammed for their generous financial assistance, without which this research would have been impossible to carry out. Also, my great thanks go to my uncle Dr. KarimEldin for his moral support and the peaceful atmosphere he provided to me.

(iii) DEDICATION

To my father and specially to the soul of my mother,

Mariam (Mimi), whose sudden departure on 7 November

1996 has surely deprived me of the felicity of

accomplishing this work with her and whom I will never forget for such a moment .

iv) Page No.

ABSTRACT i ACKNOWLEDGEMENTS iii DEDICATION iv

CHAPTER 1 1

INTRODUCTION 1

1-0 Introduction 1 1-1 Objectives 2

1-2 Methods 2

CHAPTER II 4

THEORETICAL BACKGROUND 4 II-O Introduction 4 II-1 The Crystalline Solid 4 11-2 The Unit Cell 4 11-3 The Crystal Lattice 5 11-4 Crystallographic Notation "Miller Indices" 8 II-5 The Reciprocal Lattice 10 11-6 X-Ray Diffraction 11 11-7 Detennination of d-spacing and Intensities 14 H-8 The Intensity of Diffraction 15 II-8.a. Scattering by an Electrons 15 II-8.b. Scattering by an Atom 16 II-8.C. Scattering by a Unit Cell 19 II-8.d. The Temperature Factor 19 II-8.e. The Absorption Factor 21

CHAPTER HI 22

EXPERIMENTAL TECHNIQUE AND DATA PROCESSING 22 III-O Introduction 22 III-l Production of X-Rays 22 III-2 The X-Ray Generator 26 III-3 The Cooling System 26 III-4 The Goniometer 28 III-5 The Detector 28 III-6 TheDACO-MP 28 III-7 Mode of Operation of The Diffractometer 30 III-8 Data Processing with the DACO-MP 32 III-8 a. The Peak Search 32 III-8.b. The Extended Operations 33 II[-9 Data Processing with DIFFRAC-AT V3.1 34 111-10 Samples Separation and Preparation 36 III-11 Data Collection of Mineral Samples 36 Using D500 Measuring Routine

CHAPTER IV 37

GEOLOGICAL LITERATURE REVIEW 37

IV-0 Introduction 37 IV-1 Mineralogical Compositions 37 IV-2 Clay Minerals 37

IV-3 Regional Geology 41

CHAPTER V 43

RESULTS, INTERPRETATION AND DISCUSSIONS 43

CHAPTER VI 70

CONCLUSIONS AND RECOMMENDATIONS 70 REFERENCES 71 CHAPTER

INTRODUCE sj, 1-0 Introduction:

X-ray diffraction (XRD) is the t efficient method for the ; detemiination of the mineralogi: alconv on rocks and especially fine grained minerals with complex structur ke -lay minerals, which occur mostly in sedimentary rocks such as sai ones, mudstones, claystones and limestones (Tucker, 1988, 1991).

From a geological point of view the knowledge of mineralogy is highly important for rock classification and the determination of origin and depositional environments of rocks. Moreover, the mineralogy is helpfull in geological prospecting, exploration and evaluation of the economic potential : of mineral deposits. This depends primarily on accurate identification of the I minerals, knowledge of the composition and association in which they occur j. in nature. Therefore, it is important to study the characteristic of the deposits f qualitatively.

' Genetically, minerals are natural chemical compounds and are natural \ products of various physico-chemical processes going on in the earth crust, '. including the products of the life activity of various organisms.

Clay minerals are the most abundant minerals on the surface of the | earth.This is illustrated by the fact that they are the essential constituents of | fine sedimentary rocks, such as mudstones, claystones, and shales making up jj to 75 % of the total sediments composition. They are hydrous a-lumino ; silicates with specific sheet or layered structures.Common clay minerals include kaolinite, illite, smectite and chlorite. Clay minerals are attributed to three origins: (i) inheritance, (ii) neoformation and (iii) transformation ', (Tucker, 1991).

The samples investigated are collected from several outcrops from eastern Gadaref area. These samples are mainly mudstones and siltstones rocks belonging to what is known in Sudan as the "Nubian Sandstone Formation . The age of these rocks is of Cretaceous age and the depositional £>YWivonments of these rocks is of fluvial river origin (Omer, 1983). I (0 1-1 Objectives:

The objectives of this work are, first, to review the theoretical and experimental aspects of XRD technique and, second, to characterize and determine the mirteralogical composition of some mudstones and to assess their potential in kaolin industry.

1-2 Methods:

The nmdstone samples were prepared by crushing, disaggregation and sieving. Then, the XRD analyses were carried out on whole powdered samples. Methods and approaches followed in this study are shown in Fig.I-1.

The format of this thesis will be as follows :

The elementary theory of crystal lographic notatioh and XRD theory will be discussed in chapter II.In chapter III the experimental set up, data processing with DIFFRAC-AT software, samples preparation and collection are given .The geological literature review are given in chapter IV. Chapter V deals with the data analysis and the results obtained using DIFFRAC-AT routine facilities, and finally the conclusions and recommendations are given in chapter VI.

(2) Fig.I-1 A flow diagram to show the overall approach to study.

Introduction

Theoretical Samples Analysis Experimental

Unit cell Preparation Production Of X - rays

{. XRD Separation

\ Introduction XRD analysis DIFFRAC-AT Of * Diffraction 1

Conclusions and Recommendations

(3) \.- .-.'ILake Atba.-a

"iAlluviums, wadi fills, terraces L; delta and swamp deposits ^ Tertiary tor . •„;. •••; Umm RawabRawaba FormatioFormation '+ Quaternary!. I-.- — -.;(unconsolidate( d sands with * 'gravels, clays and shales Mesozoic i [^Vj Basic volcanics. mainly bass toTertiaryi r^ ^Acidic and intermediate vole ' I X 'mainly rhyolites and tracny:

VCretaceous! ...-•jGedaref Formation (conglom _i_Jsandstones,siltstones and muc

Upper I Shist group, undifferentiatec ?roterozoicL Gedaref C*l*ZvtjGranites, undifferent iated . v \/ V V V » intrusives, mainly gatv •,AV V ^^ ^ Proterozoic Ultrabasic rocks and serper

•-'. •'.' s v v .v Gneiss Group, undifferentiat study- fault area jand fracture. International boundary

Railway

Main road 50 Km

-Q,): Geological map of the Gedaref region showing the Study area. CHAPTER II

THEOERTICAL BACKGROUND:

11-0 Introduction:

In this chapter the theoretical aspects of crystal notation are briefly reviewed, namely : the crystalline solid, the unit cell, the crystal lattice, Miller indices, the reciprocal lattice, Bragg law, the intensity of diffraction as well as the factors affecting it. The theoretical aspects have been revealed extensively in the literatures (Animalu, 1978; Nuffield, 1966;). Practical application of X- ray diffraction and method:; of minerals identification and estimation hare been provided by Tucker, (1988); Carol, (1970); Thorez, (1976) and Zussman, (1977).

H-I The crystalline solid :

A crystal may be defined as a solid composed of atoms arranged in a pattern periodic in three dimensions. As such, crystals differ in a fundamental way from gases and liquids because the atomic arrangement in the latter do not possess the essential requirement of periodicity.

H-2 The Unit Cell:

Imagine space to be divided by three sets of planes, the planes in each set being parallel and equally spaced.This division of space will produce a set of cells each identical in size and orientation to its neighbours. Each cell is a parallelpipcd.

A set of points so formed has an important property : it constitutes a point lattice, which is defined as an array of points in space so arranged that each point has identical surroundings. By "identical surroundings" we mean that the lattice of points when viewed in a particular direction from one lattice point, would have exactly the same appearance when viewed in the same direction from any other lattice point.

Since all the cells of the lattice are identical, the size of the unit cell can in turn be described by the three vectors a, b, and c drawn from one (4) corner of the cell taken as origin (fig.II-1). These vectors define the cell and are called the crystallographic axes of the cell.

They may also be described in terras of their lengths (a,b,c) and the angles between them (a,p,y). These lengths and angles are the lattice constants or lattice parameters of the unit cell.

The vectors a, b, c define, not only the unit cell, but also the whole point lattice through the translations provided by these vectors (Animalu, 1978).

11-3 The Crystal Lattice ;

An ideal crystal is the one without structural defects such as vacancies, impurities, or grain boundaries. The distribution of atoms (or group of atoms) in such a crystal may be represented by lattice points in space, defineAby an infinite set of lattice vectors (Animalu, 1976),

1 = 1^+1^+1,0, (II-l) where l\,l2, and h are the integers (positive, negative, or zero) (fig 11-2.a). If there is only one species of atoms, it may be possible to place these on the lattice sites so that lattice vectors correspond to the positions of atoms, this is named the Bravais lattice( figJ-2a). More frequently, however, there may be group of atoms in a crystal, a lattice site may be associated not only with one atom but with a set of atoms, the lattice is said to have a basis ( fig. II-2b) (Animalu, 1978).

(5) rig. 11-1 A Unit Cell.

(6) Fig.II-2 Two dimensional lattice,

(a) Bravais lattice. (b) Lattice with a basis of three atoms.

(a)

o X o X O X tb)

(7) • ':-' .- •;•'-.,- indices"._ ____:

''•>'• i pbne arc sets of integers h,k,l enclosed in . ;. -4L;,;.,;!ion of liic plane relative to the crystal

For a cubic crystal 1 /h,l /k, I /I are the intercepts of the plane (hkl) on the a,, a.7 and a3 axes respectively, so that the equation of the plane may be written as

or P lz=l (H-3)

It follows that the direction cosines of the normal to the planes {hkl) are proportional to h, k, 1 respectively. A direction normal to a plane with Miller indices {hkl) is denoted by [hkl] (with square brackets). If an intercept, say, 1/h, is negative, the Miller Indices become (hkl), with a bar above the negative intercept (Animalu, 1978).

POOR QUALITY ORIGINAL

(B) Fig. 11-3 A plane specified by .the Miller indices (Ml).

(9) H-5 The Reciprocal Lattice :

The Miller Indices of a plane do not define a plane uniquely since all parallel planes have a common normal and hence Miller Indices. Nevertheless, the notation has a simple geometrical significance in atoms of the dual of a lattice, known as the reciprocal lattice.

Geometrically, the analytical equation (II-3) has two interpretations with the (hkf) so considered fixed (x,y,z) variable. With (hkf) fixed, the equation represents a set of points (x,y,z) lying on a plane, and is the reverse ; situation with (x,y,z) fixed and (hkf) variable, the equation represents a set of planes (hkf) passing through a fixed point.

Thus, a plane with a set of points on it and a point with set of planes passing through it are said to be dual. It is convenient in most applications to ' think of (hkf) as defining the coordinates of points of another space (the reciprocal lattice space, also called k-space). The points, g, labeling the lattice planes are called reciprocal lattice points and may be defined by the mathematical relation (Animalu, 1976).

g.I = N (II-4)

or exp. (ig.l) = 1 (II-5) r. where N is an integer. The connection of the g's in equation (II-4) with (hkf) of equation (II-3) follows on setting :

and h:k:l» g:<:gy:gz

(10) Ii ti V? (11-5) the g'r can be written in the form

g ~ nib] + 112b?. + 11^3 (II-6)

Where bt (IH, 2, 3) are the primitive translation vectors of the reciprocal lattice as long as the bj's obey the relation

(II-7)

where &j is the Kronecker delta.

Equation (II-7) can be solved to give

2n{a xa ) 2 } (II-8-a) a,-a2

b2 = (II-8-b) a. a,

(a, xa2)

*,=• (II-8-c) xo3

-• The common denominator in each case is

(H-9) :"'t. -a, a.

- the volume of the cell in the lattice. Thus the dimension of the bfs is

), hence the name reciprocal lattice (Animalu, 1978).

Rav Diffraction :

Diffraction is due essentially to the existence of certain phase relations • ^between two or more waves. The phenomenon of X-ray diffraction by crystal f-*has proven the wave nature of X-rays and provided a new method for mgm 01) investigating the fine structure of matter. A, rdinf fo Bragg's presentation the X-ray diffracted beams are found only v n th< reflections are from the parallel planes. Bragg planes are a set of a' s of the crystal wtere the rays interfere constructively (fig.II-4). The scattering is elastic, so that the wavelength of the diffracted photon does not change on reflection.

For a series of parallel lattice planes spa x' qually, d-apart; the path difference for the reflected rays from adjacent planes will be: 2 d sin0,

so that sin 0=xd

let

then

(11-10)

-, Where n is an integer, n = 1, 2, 3riK is a multiple of the wavelength and 9 is ^glancing angle. Equation (II-10) is known as Bragg's law and is used in ivrofk.

(12) 'ig. 11-4 Diffraction of X-Rays by a crystal H-7 Determination of d-spacing and Intensities:

From an X-ray diffractomeUr record, values of 29 are obtained by applying Bragg's law, the d-spacing are obtained from 29-d tabulations for that particular wavelength. V is worthwhile to consider briefly the question, what are the d-spacing because of the confusion which sometimes exists regarding the nature of d-spacing.

From Bragg's equation:

nA- 'Id sin 0

The quantity measured experimentally is:

din = A I (2 sin 0) (11-11)

Which is conventionaltycalled the d-spacing. Evidently any one lattice spacing gives an integral series of d/n of these d-spacing. It is customary to include the order of reflection, n, in the indices of reflection so that, for example, the uP reflection from the basal plane is described as OOn reflection. It would then seem reasonable to index the observed basal reflection as 001, 002, ....and take

However, the true lattice spacing is often a multiple of this apparent d(001) because the unit cell contains more than one structural layer. The question that may be asked:"why not record 26 values or sinG values instead of converting them to d-spacing?".

In the first place, 29 or sin9 depends on the wavelength, A., used and there is no unique A. for a given substance. Secondly, the use of the d-spacing and the associated intensities for the X-rays identification of crystalline materials are the cnes used by the Joint Committee of Powder Diffraction Standards (JCPDS).

(14) II-8 The Intensity of Diffraction :

II-8,a. Scattering by an Electron:

X-rays are scattered in all directions by an electron, the intensity of the scattered beam depends on the angle of scattering.

The characteristic radiation obtained from a dilTraction tube is generally considered to be unpolarized. However, the process of scattering causes the diffracted beams to be partially polarized.i.e. the amount of polarization depends on the angle of scattering (Nuffieid, 1966).

The intensity I of the beam scattered by a single electron at a distance R from the electron is given by :

4 \ 2 / =/. sin a \m c R J

Where Io is the intensity of the incident beam, e and m are the charge and mass of the electron, c is the speed of light and a is the angle of scattering.

Fig.II-5 represents an electron at O that scatters an incident beam along a diffraction direction OD with an angle 20, the y- component of the beam accelerates the electron in the direction OE at an angle ay=90° to the direction of scattering, the z-component accelerates the electron in the ON direction with an angle az =(90-2G)°

The intensity in the direction OD is the sum of the intensity components I^and fcz i.e.

- l z — — l0 ey •-j-V'Y I sin 90 + - 2 4 2 sin (90-20) km c R

1+cos 20 (11-14) 2 4 2

(15) I 1 Tliis quantity o$. is known as the polarization factor.

II-8.b. Scattering by an Atom :

The waves scattered by all the electrons in an atom have the same path length for the incident beam direction and are therefore in phase (fig. II-6). Hence the amplitude of the wave from the whole atom is proportional to the number of electrons in the atom for this direction. The efficiency of scattering by an atom in a particular direction is known as its atomic scattering factor, f0, and is expressed by the ratio

fo^AA/A, (11-15)

Where AA is the amplitude of the wave from the whole atom and A« is the amplitude of the wave from a free electron. The intensit)'of scattering is proportional to the square of the amplitude i.e.

where IA, Ie are the intensities of the beam from the whole atom and the electron respectively (Nuffield, 1966). Tig. \[-5 Polarization of radiation scatter by an electron. l'ijj.ll-6 ScttUcrint; by sui atom.

path difference \

x 1I-8.C. Scattering bv a Unit Cell:

Where the scattering from an atom depends on the distribution of its electrons, the scattering from a unit cell depends on the atomic arrangements. In the study of the scattering by a unit cell, the most important factor, is the structure factor, F(hkl), so that F(hkl) is known as the structure amplitude and is defined as the ratio of the amplitude of the wave scattered by all atoms in the cell to the amplitude and the wave by one electron i.e. from fig. (II-7)

tF(hkl)| = [A2+B2]l/2

= [(Fcosa)2 +(Fsina)2]l/2 (11-17)

Where (hkl) is the phase angle of the composition wave due to all kinds of atoms (Nuffield, 1966).

II-8.d. The Temperature Factor :

Debye deduced that the scattering factor of an atom at ordinary temperatures, f, is related to its scattering factor at rest, f0, by ihe expression

2 2 f = f0 exp {-B(sin e/X )} (11-18)

where B is the temperature factor which incorporates the mean displacement of the atom from its mean position. B depends on the kind of atom, and also on the orientation of the reflecting planes in the crystal, X is the wavelength and 0 is the Bragg angle (Nuffield, 1966). I'ijj.II-7 Vector reresentation of waves with different

amplitude and phases.

(20) II-8.e. The Absorption Factor :

The incident and reflected beams are partially absorbed when passing through a crystal, and consequently the intensity of reflection is less than that from a perfectly non absorping substance. The absorption effect evidently depends not only on the absorption coefficient of the crystal but also on its cross-section. In the case of a powdered specimen, the absorption depends on the density of the packing of the particles. The result of this is that the intensities of reflection vary with the Bragg angle . As 0 increases, the volume of the specimen contributing to the reflection also increases. Hence the absorption factor decreases with increasing Bragg angle and has the opposite effect of the temperature factor (Nuffield, 1966).

(21) Ii* ' ' j M.)l.JES AND DATA PROCESSING:

III-O Introduction :

The aim of this chapter is to explain the various techniques which have been used to study ihe mudstone samples. It deals also with the method of X- ray generation with its accompanying cooling system, the X-rays diffractometer together with the method of samples preparation. Moreover, data collection and computer techniques for data analysis with the DIFFRAC- AT software will also be discussed.

IH-1 Production of X-rays :

X-rays are part of the electromagnetic radiation with very short wavelength in range (0.5-2.5 A0) and are produced when a beam of highly accelerated electrons strike a target (metal .mode) fig.Ill-1. These electrons are produced by heating a filament, and they are accelerated by a potential difference of the order of tens of Kilovolts, applied between the filament and the target. Both the filament and target are situated in an evacuated tube. X- rays which are produced pass out of the tube through a window made of low absorbing material (Cullity, 1978).

When the electrons strike the target, some are stopped in one impact and give all their energy. While others are deviated by the atoms of the target lo sing fractions of their total kinetic energy. Due to the energy of the impining electrons, die K inner shells of the electrons of the target atom are being ejected, the outer L, M shells electrons drop down to fill the inner empty levels and thus emit characterise X-ray \ine$ Ka and Kp with well- defined energy (fig.III-2).

(22) These characteristic lines have different wavelengths, their intensity depend on the tube voltage. The X-rays energy, E(KeV) of these characteristic lines )$• related to their wavelengths by the following relation (Cullity, 1978):

X (A0) = 12.4 (III-l) E(Kev)

For X-ray diffraction, we require X-ray energies in the range (10-50) KeV.

(25) Fig.lII-1 A section of a Uontgen X-ray tube.

out Water cooled

Beryllium window

X-ray beam Tnrcjol "Electrons " Filament

?0-G0kV

"»£l£gcu§ted glass tube - Shielding

5-35 mA 12 V

(24) he generation of .\•••--y ,f c er due to the transfer of rv"' u'K shell.

KlK "i

X-ray inlnnsity

Characteristic line spectrum from Cu

Continuous spectrum

1 Wavelength X (A) 2 Mnxiinum electron energy Kp 1.3922 ! K«, 1.5405 i-

KCY3 1,5408 I ons

I POOR QUALITY ORIGINAL

(25) ITI-2 The X-ray Generator :

The X-ray generator used is a KRISTALLOFLX K710. It is a powerful device for supplying highly stable HT voltage to X-ray tubes with earthed cathode like film cameras, diffractometres, and X-ray spectrometers. The generator supplies the X-ray tube with a negative polarity high voltage from 20 KV to 50 KV and a current of 5 mA to 40 mA. It can function with any X-ray tube requiring a negative high voltage and with a nominally rated i filament between 5 volts and 12 volts. The generator is supplied with a power cord for connection to 2088/220/240 power line. This line must be protected with 25 A fuse. In addition to the electrical distribution ground another chassis ground should be installed. Water supply should be able to provide a 4 liter/min. pressure. This pressure may increase or decrease depending on restrictions in the X-ray tube. A closed-loop recirculating cooling system is highly recommended (Technical Description, X-ray high voltage generator manual).

II1-3 The Cooling System :

The cooling unit which is a Kulver one is delivered with all components of the cooling circuit such as circulating pump, vaporizing cooler, temperature controller, temperature monitor, antifreeze protection, screwed connection, flow monitor, storage tank, safety value for maximum pressure limiting and connecting leads readily installed is used in this work (Description and operating instructions manual). Fig.III-3 shows the cooling system and its components connected to the generator.

(26) Rücklauf out 1 et 1/0,/oaA ft; 4 Kompressor Kondensotor

Strömungs- wächter Compressor flow controller

Sammler reserve)! r in Sicherheifs- ifiermosTQt i" f 'i safety temperature Trockner "S cont roljer • drier © ^** temperature it'—j regulator - ^ H ,.-' I Tsmperctur- Schauolcs inspect ".on ! glass expansions - 2 .yeniil I*pansion valve V) Srh Filter Pumpt HI-4 The Goniometer : ^ |p thfb

The D500 Siemens goniometer/with its attachments for the meaurements, is mounted in a radiation protection housing with the Lead-glass window. (Siemens D500/D501 diffractometer operating instruction manual).

The diffractometer has the advantage that it can be used for almost all applications of X-ray diffraction techniques, such as structural analysis and phase analysis. In its basic design it is used to collect the data that are needed to identify the minerals existing in the samples. The sample holder is supported on the axis of the goniometer which is fully automatic and is controlled by a DACO-MP (described later)or a Quad (80486 version) computer (Siemens D500/D501 diffractometer operating instruction manual).

The data from powder samples can be recorded and tabulated as angle position versus intensity of diffraction by means of a printer.

HI-5 The Detector:

The detector used is a Nal (TI) scintillator crystal counter. It can be used to measure X-radiation in the wavelength range from 0.05 nm to 0.27 nm. It has a diameter of 25 mm with a 0.2 mm Beryllium inlet radiation window, 10'^ sec. dead time and 1200V-1300 V operating voltage. A monochromator is usually mounted in front of the detector. This monochromator allows only the Ka radiation ofthe X-ray tube to reach to the detector. The Kp and continuous radiation ofthe X-ray tube as well as the fluorescence radiation ofthe specimen are suppressed (Siemens D500/D501 diffractometer operating instruction manual).

III-6 The DACO-MP;

The DACO-MP is a micro-computer based controller, with 32 kBytes of ROM and 28 kBytes of RAM for version 2. The DACO-MP normally controls one or two circles diffractometer with one X-ray detector.

(28) The DACO-MP is a controller for the Siemens difrractometers D500, D500TT and D501. Its companion product is an alphanumeric teleprinter, allowing dialogue and graphic output of the diffractometer. Used as a stand - alone controller for a D500 or other diffractometer, the DACO-MP may control any measurement process and also perform complex computation on the results when a large pmount of data is not required (DACO-MP user's reference manual V2.1 or V2.2, 1985).

The DACO-MP V2 firmware is logically made up of seven tasks that may potentially run in parallel. By ascending priority, one finds: •4 0) The sequence for analytical programs stored in memory. (ii) The completion of time-consuming commands. (iii) The initialization routines for commands from the computer. (iv) The computer input processor task. -j (v) The error message output task. ;i (vi) The display update task. (vii) The local terminal input processor and command initialization task.

Only tasks (i), (iii), (iv) and (vii) need to be considered to understand the posibilities and restrictions of the system, the other tasks are listed for information only (DACO-MP user's reference manual V2.1 or V2.2, 1985).

The DACO-MP user RAM is divided into four buffers, instruction buffer (I-buffer), data buffer (D-buffer), register buffer (Regs) and secondary j memory area (Matrix). The D-buffer value may change slightly with firmeware. The sum of the 4-buffer values gives the total available user RAM i memory which is more than 23 kB (DACO-MP user's reference manual V2.1 I orV2.2, 1985). I The DACO-MP provides writing and executing programs using its acceptable commands for many treatments associated with the data needed for the analytical purposes. The results obtained by the executable programs of the DACO-MP are printed out in the form of the graphics (charts), including peaks (intensity heights), 2G position and the corresponding d- spacing values (Getting started with the DACO-MP V2.1 or V2.2, 1985). III-7 Mode of Operation of the diffractomter ;

The radiation emanating from the line focus B of the X-ray tube is diffracted at the specimen P and recorded by the detector D. The specimen is rotated at a constant angular speed, whereas the detector moves about the specimen. The diffraction angle (20) is always equal to double the glancing angle(8) (Siemens D5OO/TJ5O1 diffractometer operating instniction manual). The beam path of the diffractometer is shown in fig. (III-4).

Whenever the Bragg condition is fulfilled, the primary beam is reflected from the specimen to the detector. The intensity of the reflected radiation is measured by means of the detector and then transferred to the measuring electronic systems, the DACO-MP and the printer. The anj^ular position of the reflection is indicated on the goniometer (Siemens D500/D501 diffractometer operating instniction manual).

The focus, specimen and the detector diaphragm are located on the focusing circle F, while the focus and the detector diaphragm are located on the measuring circle M. The entire effective surface of the specimen would have to be located on the focusing circle so that the diffracted radiation is focused before it reaches the detector. In practical designs the surface of the plane specimen is merely placed tangentially to the focusing circle (Siemens D5OO/D5O1 diffractometer operating instniction manual).

(30) Fig. IH-^i Focusing Geometry of the diffractometer in case of 20/0 operation.

B Focus of the x-ray tube ,9 Glancing angle M: BI.I.II,111 Aperture diaphragms 2,9 Diffraction angle Bi.rv Detector diaphragm 9 Aperture angle D Detector M Measuring circle Yip filter F Focusing circle 1 P Specimen

(31) III.8 Data Processing with the DACOP-MP:

§• HI*8.a. The Peak Search ;

Because of the statistical character of the experimental data, the observed intensities, when plotted, do not fall along a theoretical smooth .curve, but deviate more or less from it This produces a rather chaotic ^diagram1 and gives rise tc artificial peaks. The DACO-MP, detects a peaks ^talttd'th^iQlost important parameter of the DACO-MP's peak search algorithm I is*; called the peak "width (pkw). This peak width is defined as the length of ^-"^—^il 'placed symmetrically around each point in order to compute its polynomial. In other words around each measurement point an 'of prescribed length is placed symmetrically and then the least square ' fitting *t0f the polynomial is performed. The best value of pkw greatly depends 'on the given raw data. The pkw value is given in degrees (Getting started ".with the DACO-MP V2.1 or V2.2, 1985).

Experience showed that for peaks to be recognized they should match »the following conditions

1/2 FWHM < pkw < 2FWHM

r i Where FWHM is the chord of the peak at the relative intercept level (0 5)

The number of points placed symmetrically around each data point is V the integer closest to (pkw/step size). This integer is bound to lie between 1 ^and"l5.

7 The second parameter of the peak search computation is the threshold and is a multiple of the standard deviation. The default memory value of the (thr) is 1 and this practically fits in all cases (Getting started with the manual V2 1, V2.2, 1985)

nil 111-8.1). The Extended One ration :

In order to get good results agreeing with or matching the criteria recorded in the (JCPDS^ files, the DACO-MP provides computational operations for the raw data detected experimentally. These operations are : (i) Curve Smoothing r For the experimental data (intensities) to match the theoretical curve, the extended operation curve smoothing is usually done. The algorithm of this smoothing depends on a coefficient called smoothing (Smol) which is an interval taken for the curve smoothing. The number of points placed symetrically around each data point is the integer closest to (Smol/step size). This integer is bound to lie between 1 and 15.

For each data point, a third degree approximation of the diffractogram is derived frorri these points, and the central point (point under consideration) is replaced by a coefficient of power zero of the computed polynomial. (Getting started with the DACO-MP manual V2.1, V2.2, 1985).

(ii) Continuous background subtraction: The coefficient background (bkg2) is used to adjust the background subtraction algorithm. Let Y(20) be the equation of the convex envelope of the diffractogram, the continuous background 13(20) is then estimated (DACO-MP user's reference manual V2.1, V2.2, 1985 ) to be :

B(20) = Y(20) -bkg2.{Y(20)}'/2

(iii) K alpha2 stripping : The argument called smoothing (Smo2) is an interval used to control Ka2 stripping. This algorithm works on a third degree least square approximation polynomial computed on a fraction of the diffractogram. The length of this fraction is derived from (Smo2) as with (pkw) and (smol) for the peak search and the curve smooting .

The Ka2 stripping algorithm is derived from the Rachinger method (Getting started with the DACO-MP manual V2.1, V2.2, 1985).

(33) HI-9 Data Processing with DIFFRAC-AT V3.1 : DIFFRAC-AT is an integrated software package for the powder X-ray diffraction. It has been developed for Siemens X-ray diffractometers and provides the measuring routines for Siemens D5000 and D500 diffractometers (DIFFRAC-AT V3.1 Start up manual, 1992). It consists of the following major programs: graphic evaluation package (EVA). b)The plot utilities (PLOMN). j c)The DIFFRAC-AT integrator (DMENU).

cDThe quantitative routines (EDQand XQUANT). <2)The data exchange program (XCH). f )The powder diffraction data base maintenance program (MAINT). g) The D500 measuring routines. The DTFFRAC-AT package was installed using an installation program D5 INSTAL following the hints in the manual of the software. The software had been designed to run on 100 % compatible IBM ps/2 computer or other related ones. The DIFFRAC-AT is compatible with DOS 3.x to DOS 5.x and MS WINDOW can be used to call DIFFRAC-AT as a non-WINDOW application. The recommended system printer for DIFFRAC-AT is HP-PATNJET since it produces good quality colour pictures. The HP LASER JET II and III are supported for high quality black and white documents, also the HP plotter model 7475A and 7550-PLUS are supported for graphics. Fig.III-5 shows a block diagram of the system in the DACO-MP mode .

I For a detailed description for the different files and sub-files, of the DIFFRAC-AT, the reader is referred to Caussin et al., 1988, 1989, Chaung 1974, 1975. A comperhensive review of the DIFFRAC-AT is given by (Idris, 1994).

(34) Fig.III-5 Block diagram of the system in DACO-MP mode.

I 2 •—I Termini! Jinrl DACO- MP COMPUTER

SYSTEM PRINTER KEYBOARD MOUSE LJ

(35) • The collected mudstonerock samples from eastern Gadaref were first crushed and disaggregted manually in a procelain morter. Then the samples were sieved using sieve sizes between 1.000 mm-0.032 mm. The X-ray powder diffraction measurements were performed on samples having sizes less than 0.025 mm. Finally, the resulting fine crystalline powdered samples were placed in a sample holder, ready for the measurements.

IH-11 Data Collection of Mineral Samples Using D500 Measuring Routine :

The measurements of samples were performed with the measuring conditions adjusted when editing the measurements. The standard patterns stored in DIFFR.AC-AT package by means of EVA program using search/match window.

The samples were scanned with the parameters adjusted as follows:

(i) X-scale 2° per cm ( Deg / cm).

(ii) Start angle 5° ( 2TH).

(iii) End angle 50" ( 2TH).

(iv) Step size 0.05° ( Deg).

(v) Counting time 2 sec ( per step ).

(vi) Peak width 0.14°.

(vii) Y-scale 100 cps per cm (pulses / s / cm ).

(36) CHAPTER IV

IV-0 Introduction;

This chapter reviews the sedimentology of mudrocks particularly their mineralogical composition, origin and depositional environments. These aspects have been dealt with extensively in the literatures (Tucker, 1991; Chamley, 1989; Weaver, 1989). Moreover, it also deals with the regional geology of the study area specially the Nubian Sandstone Formation.

IV-1 Mineralogical Composition:

The main constituents of mudrocks are clay minerals and silt grade quartz. Since mudrocks are largely detrital, the clay mineralogy to a large extent reflects the climate and geology of the source area (Tuker, 1991).

IV-2 Clay minerals:

Clay minerals are hydrous aluminosilicates with a sheet or layered structure; they are phyllosilicates, like the micas. The sheets of a clay mineral are of two basic types. One is a layer of silicon-oxygen tetraheHra with three of the oxygen atoms in each tetrahedra and linked together to form a hexagonal network (Fig.IV-1). The basic unit is S12O5 but within these silica layers aluminium may replace up to half the silicon atoms. The second type of layer consists of aluminium in octahedral coordination with O2' and OH' ions so that in effect the Al?+ions are located between two sheets of O/OH ions (Fig.IV-1). In this type of layer, not all the Al (octahedral) positions may be occupied, or Mg2*", Fe or other ions may substitute for the Al3+. Layers of Al- O/OH in a clay mineral are referred to as gibbsite layers since the mineral gibbsite (Al(OH).?) consists entirely of such layers. Similarly, layers of Mg- O/OH are referred to as bnicite layers after the mineral brucite (Mg(OH)2) composed solely of this structural unit. Clay minerals, then, consist of sheets of silica tetrahedra and aluminium or magnesium octahedra linked together by oxygen atoms common to both (Tucker, 1991). The stacking arrangement of the sheets determines the clay mineral type, as does the replacement of Si and Al ions by other elements. Structurally, the two basic groups of clay minerals are the kandite group and smectite group (Tucker, 1991).

Members of the kandite group have a two-layered structure consisting of a silica tetrahedral sheet linked to an alumina octahedral (gibbsite) sheet by common O/OH ions (Fig. IV-1). Replacment of AJ and Si does not occur so that the structural formula is (OH)4Al2Si2O5. Members of the kandite group are kaolinite, by far the most important, the rare dickite and nacrite, which have a different lattice structure, and halloysite which consists of kaolinite layers separated by sheet of water. Related structurally to kaolinite are the alumino-ferrous silicate chamosite and berthierine and the ferrous silicate greenalite (Tucker, 1991). Kaolinite has a basal spacing, i.e.distance between one silica layer and the next, of 7A0.

Members of the smectite group have a three-layered structure in which an alumina octahedral layer is sandwiched between two layers of silica tetrahedral (Fig.IV-1). The typical basal spacing is 14 A0 but smectites have the ability to absorb water molecules and this changes the basal spacing, it may vary from 9.6 A0 (with no adsorbed water) to 21.4 A0. This feature of Smectites as a result of which they are often called (expandable clay), is utilised in their X-ray identification. The common Smectite is montmorillonite, it approximates to AL^SuOioMOH^.nHjO but substitution of the Al3"1" by Fe2+, Mg2"1" and Zn2+ can take place. Nontronite, saponite and stevensite are other smectites occasionally found in sediments.

Illite, the most common of the clay minerals in sediments, is related to the mica muscovite. It has a three-layered structure, like the smectites but Al3+ substitution for Si4'in the tetrahedral layer results in a deficit of charge which is balanced by Potassium ions in interlayer positions (Fig.IV-1). Some hydroxyl (OH"), Fe2+ and Mg2* ions also occur in illite. The basal spacing is about 10 A0 (Tucker, 1991).

In addition to the four common clay minerals, illite, kaolinite, montmorillonite and chlorite, mixed-layer clay are also common. In particular illite-montmorillonite and chlorite-montmorillonite. Specific names have been applied where there is a regular mixed-layering, corrensite for a chlorite- montmorillonite mixed-layer clay for example.

(38) During weathering and diagenesis, interlayer cations can be leached out of the clay minerals by percolating waters. Because of their fine crystal size and the presence of unsatisfied bonds, clay minerals are important in the process of ion exchange. Ions in aqueous solutions can be adsorbed on to and desorbed from clays, with the water chemistry controlling the exchange process. Some elements, such as iron can be transported by adsorption on clays.

Quartz in mudrocks is chiefly of silt-grade size. Feldspars are generally present in low concentrations and this because of their low chemical stability. Other minor constituents include muscovite, biotite, calcite and dolomite (Tucker, 1991).

(39) Basic Units £ alumina silicon-oxygen octahedral^ v tetrahedral unit ~ unit

O and '•.' " Oxygen atoms o and • ~ Silicon atoms C andd OO = Hydroxyls O Aluminum, maonesiu etc

: kandite eg kaolinite AI2O3.2Si02.2H2O illite K.Al2(OH)2.fAISi3(O. OHl,0l

alumina (gibbsite) layer A\ /\/k A\ /\/'^ A silica layer substitution of Si b Al m s'llC8 '«yers OH" m'.erlsver K • together wlhiom basal spacing 7A «=OH K" K" T

c y VVVV i basal spacing 10 ^

2A:2O3.8SiO;,.2H2O nH2O K" Fe/Mg

Vj e.g. montrru Mg. Ca)O.AI2O3.5SiO2 nH2O 3 chlorite Mg6(AI.Fe)(OH8)(AISi)4O,0 -^g,- -^ \^- \~^ \t^ / v much substitution of substitution 0, Al b Fe / r : A, /<-"\/N. Al by Mg and Fe ~~ brucite Si H 20 H,0 H20 '*ye'L IMg-OH) / \.'VV' \?"«i/V mterlayer H2O. and Ca and Na \^/\?' •V \^ ^ \/ SS between Al-S. sheets / A /IS. .A. A AJb% /-\ /h.^ y

H2O Ca/Na H2O The identification of clay minerals in mudrocks is normally undertaker through X-ray diffraction of the less than 2 micron fraction of the sediments. Clay minerals and 'heir structure are dealt with extensively in the literature (Grim, 1968; Millot, 1970; Weaver and Pollard, 1973; Velde, 1977; Potter et al., 1980; Chamley, 1989 and Weaver, 1989).

Mudrocks can be deposited in different environments such as river floodplain, lakes, deltas, continental shelves and deep-sea. Mudrocks in the geological record are produced by the following processes (Tucker, 1991): 1. Processes of weathering and soil formation upon pre-existing rocks and sediments. i 2. By normal processes of erosion, transportation and deposition.

3. By in situ weathering and/or later alteration of volcaniclastic deposits.

IV-3 Regional Geology:

The study area is located at eastern Gadaref in eastern Sudan. Geologically, the Sedimentary plateau there is located between the high Ethiopian plateau and the Sudanese plateau. The sedimentary rocks composed of what is known as the Nubian Sandstone Formation which mainly consists of sandstone, siltstone and mudstone. These rocks often covered by black cotton soil and intruded by basaltic lavas. The sedimentary plateau is dissected in its eastern part by the rivers Mtbara and Setit.

The mudstone of the study area represent deposits formed by processes of erosion, transportaion and deposition within floodplains and overbanks areas of Cretaceous braided river system which deposited the Nuoian Sandstone Formation (Omer, 1983).

The oldest geological unit is a highly weathered unfoliated porphyritic granite outcrops belonging to the Early Cambrian Basement complex of the Sudan. These basement rocks are overlain by series of Mesozoic clastic sediments, generally known as Nubian Sandstone Formation and considered to be of Cretaceous age in the region of Gadaref-Showak (Omer, 1983). In the area studied, the Nubian is represented by fine-grained moderately sorted yellowish to pinkish sandstone and mudstone. Locally they are intruded by basaltic rocks of Tertiary age occurring as sills, dykes and flows covering

(41) them. They are covered by cracking dark clays, essentially composed of montmorillonites and known as "black cotton soil" of Quaternary age (Hussein et al, 1989).

The various age determination made on the fossil wood fragments, (Chialvo, 1975), attributed the Nubian sandstone in eastern Sudan at Gadaref to the upper Cretaceous on the basis of wood fragments. The heavy mineral suite is poor : consisting of zircon, tourmaline, pyroxene,rutile and kaynite, and indicates a source area mainly composed of igneous rock with minor input from metamorphics (Omer, 1983).

The zircon show up in two form : one fresh with its original crystal shape, the other very worn with rounded outlines this double form leads to think that in this region, the Nubian sandstone has been fed from two different sources, one coming from direct erosion of Basement, the other possibly coming from reworking of preexisting sediments (Omer, 1983).

The Gadaref clay minerals suite is dominated by kaolinite, montomorillonite and chlorite also make up an important part of the assemblage along with an increase in the mixed-layer clays (Omer, 1983).

The montomorillonite and the mixed clays are either the result of an incomplete alteration or a neogenesis in an alkaline confined environment. This last hypothesis seems the best in the present case, for we know that the sandstone in this area, which are grey or white and lack red iron pigementation, were not deposited in aco^inental environment but in a marine basin (Omer,1983). There ,we see the reverse phenomenon of hydrolysis : the agradation, which can lead the transformation clay minerals up to the neoformation of chlorite and montomorillonite (Millot, 1964).

At Gadaref, according to the geological history the paleotopography shows features characteristic of a subarial environment such as kaolinite, geothite and brightly coloured sandstone. Kaolinite shales and common root traces, as well as the surface morphology of the quartz grains indicate intense weathering in a Sudan- type climate but there are also signs of marine depositional environment which is confirmed by grain size study (Omer, 1983). The clay minerals distribution in the Sediments of Gadaref area appears to be influenced by source rock geology, climate and the local environment.

(42) CHAPTER V

RESULTS AND DISCUSSIONS:

The results were obtained using EVA program . For each sample diffractogram (.RAW file appeared in EVA window )the background was subtracted using (subtract and replace window).The data were then smoothed by adjusting the peak width,pkw, (which ranged from 4 times to 60 rimes the step size ) to give the best smoothed diffractogram. Then by using [SEARCH / MATCH] window, the search process was done by matching the standard pattern with the unknown pattern in the mineral subfile by a selection of the appropriate criterion(one or three) and penalty values (8). These values give the mineral name, chemical formula, quality mark and crystal structure for each sample constituents.

Figs. V-(l»20) show the diffractogram results, while table V-l shows the mineral types identified in samples. Table V-2 shows the d-spacing of the clay minerals under normal, glycolation and heating Conditions. lM*(taS shows the percentages of the clay minerals in the samples studied.

From XRD analysis quartz, kaolinite and tndymite are the major mineral constituents of these rocks, whereas alunite, coalingate, cristabolite, gutsvechite, hematite, meta-alungen, minamite, monteponite and samarskite occur as minor constituents. Except two samples, kaolinite in 18 samples ranged between 71-100 %. Ten or these samples Have ivavihnitrctmitmi'^n'' 100 % each. Other clay minerals like chlorite, illite and smectite occur in minor amounts. High kaolinite content in these mudstones, most probably indicates intense chemical weathering under warm humid climate in the past. Other geological evidence from Gadaref area tends to support such conclusion (Omer, 1983).

The Sedimentological evidence suggests that the kaolinite is of detritai origin mainly inherited from source rocks which subjected to intense chemical weathering and leaching under humid warm climate. The limited occurrences of smectite, chlorite and illite may indicate the interruption by short dry periods which favour limited weathering and leaching under rather alkaline confined environment. Therefore, smectite, chlorite and illite origin may be attributed to neoformation (Chamley, 1989).

(43). From these samples, five samples show reddish colour indicating the presence of geothite, however, in the fitting the geothite does not appear. Also from the fitting tridymite appeared instead of cristabolite which appears in two samples only in the fitting.

On the basis of sedimentological evidence, Wipki et al., (1993) concluded that Gadaref kaolin is transported and deposited in braided river environment. The kaolins have been affected by secondary silicification and alunitization processes. These processes are attributed to hydrothermal and weathering activities affecting the kaolins in the area (Wipki et al., 1993). The mineralogical composition revealed in this study support the above suggestions.

Kaolin has many industrial uses, such as : paper industry, ceramics, refractory industry, paint industry, polymers and plastic industry, medicine industry, etc. Some of the kaolinite deposits are currently used in small scale activities such as white wash, paint and for other building purposes. The kaolinite deposits are considered also feasible for production of wall-and floor-tiles, drainage pipes and raw material for ceramic afterwet processing (Ibrahim and Abdullatif, 1993). The high kaolinite contents of these rocks, indicate that the economic exploration of these kaolin deposits might be feasible.

However, from economic point of view several factors have to be considered concerning the economic potential of kaolinite deposits in Sudan:

1. Quality or mineralogical composition of the Kaolinite, thicknesses, lateral I extensions and the reserve. i ! } 2. Development of adequate infrastructures and favourable geographical I position. I 3. Open pit mining seems highly favourable for most of the Kaolinite deposits in Sudan, since the geological conditions are optimum.

4. Finally, more work is needed so as to assess the economic potential including chemical and preliminary technological tests which have to be

(44) conducted such as determination of firing colour, sinter- and klinker-point and water absorption capacity of the fired material.

Therefore, for sound evaluation of these deposits for industrial ^plications, both field and laboratory tests are needed (Ibrahim and bdullatif, 1993).

(45) Table V-l. The mineral types identifled in the samples

Sample Name Chemical Formula Mineral Name

SiO2 Quartz 7C1 Al22SiO2O5(OH)4 Kaolinite SiO2 Tridymite SiO2 Quartz A6 Al22SiO2O5(OH)4 Kaolinite SiO2 Tridymite

SiO2 Quartz A7 Al22SiO2O5(OH)4 Kaolinite

SiO2 Quartz A13 Al22SiO2O5(OH)4 Kaolinite

SiO2 Quartz Al22SiO2O5(OH)4 Kaolinite A14 CdO Monteponite (Al,Fe)3(PO4,VO4)2 Gutsvechite (OH)3.8H2O SiO2 Quartz Al22SiO2O5(OH)4 Kaolinite B6 Fe2O3 Hematite Mg10Fe2(OH)24(CO3).2 Coalingate H2O

SiO2 Quartz B7 Al22SiO2O5(OH)4 Kaolinite SiO2 Tridymite SiO2 Tridymite B8 Na-Al-SO4-OH Alunite

(46) Sample Name Chemical Formula Mineral Name Quartz

B13 Al22SiO2O5(OH)4 Kaolinite

SiO2 Quartz B14 A]22SiO2O5(OH)4 Kaolinite SiO2 Tridymite

SiO2 Quartz C7 Al22SiO2O5(OH)4 Kaolinite SiO2 Tridymite SiO2 Quartz C8 Al22SiO2O5(OH)4 Kaolinite SiO2 Cristabolite SiO2 Quartz C14 Al22SiO2O5(OH)4 Kaolinite SiO2 Tridymite SiO2 Quartz D10 Al22SiO2O5(OH)4 Kaolinite

SiO2 Quartz MHA Al22SiO2O5(OH)4 Kaolinite SiO2 Tridymite

SiO2 Quartz RC2 Al22SiO2O5(OH)4 Kaolinite

SiO2 Quartz S6 Al22SiO2O5(OH)4 Kaolinite A12(SO4)3.14H2O Meta-Alunogen SiO2 Quartz SWV1 Al22SiO2O5(OH)4 Kaolinite

(47) Sample Name Chemical Formula Mineral Name

SiO2 Quartz SWV2 Al22SiO2O5(OH)4 Kaolinite SiO2 Cristabolite YNb206 Samarskite

SiO2 Quartz Al22SiO2O5(OH)4 Kaolinite TLC SiO2 Tridymite (Na.Ca)l- Minamite xA13(SO4)2(OH)6

Table V-2.The d-spacing of the clay minerals under the normal, glycolation and heating.

Sample Normal Glycolated Heated(550°C) Kaolinite 7 7 — Smectite 12-14 17 10 Illite 10 10 10 Chlorite 14 14 14

(48) Table V-3. The persentages of the clay minerals in the samples

Sample Kaolinite % Smectite % Illite % Smeciite/Chlorite % 7C1 60 17 23 — A6 100 — — — A7 87 13 — — A13 74 — — 26 A14 100 — — — B6 100 — — — B7 77 — 23 — B8 25 — 75 — B13 88 — 12 — B14 100 — — — Cl 100 — — — C8 63 37 — — C14 81 — 19 — D10 100 — — — NHA 100 — — — RC2 98 — 2 — S6 100 — — — SWV1 71 — 29 SWV2 79 21 — — TLC 75 15 10 —

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-r r 10 15 20 25 30 35 :• TLC .PP TLC (CT: 2.G SS:0.050dg, WL: 1.5406Ao) 40 CHAPTER VI

CONCLUSIONS AND RECOMMENDATIONS;

The XRD analysis of mudstone samples from east of Gadaref region reveals that quartz, kaolinite and tridymite are the major mineral constituents of these rocks, whereas alunite, coalingate, cristabolite, gutsvechite , hematite, meta-alungen, minamite, monteponite, samarskite, smectite, illite and chlorite are minor constituents. In most samples kaolinite ranges between 71-100%.

The high kaolinite contents of these rocks indicate that the source rocks might have been subjected to intense chemical weathering and leaching under acidic unconfined environment and the prevalence of warm humid climate. The occurrence of minor abundances of illite, smectite and chlorite may testity to dryer climatic periods, where limited weathering and leaching prevailed and allowed their neoformation within an alkaline confined environment. The high silica contents in these mudstone most probably indicates the influence of both hydrothermal and weathering processes.

Moreover, the high kaolinite contents of these rocks suggest a good potential for economic exploitation. Further studies, however, might be needed to study other chemical and technical properties.

It is suggested that, for further XRD studies more facilities should be made available. These includes: The profile fitting program for determining the crystal structure of fabricated compounds and the PDF(JCPDS) file containing the reference intesity (Ki) values for the quantification purposes.

Moreover, it is highly recomflier*H for better display, that an HP Laser jet III interfaced to the system. It would be Rvalue for the material science research group to have the ceramic and superconductor sub-file.

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