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

SD9800025

PHYSICS DEPARTMENTFACULTY OF SCIENCE

UNIVERSITY OF KHARTOUM

SEPTEMBER 1996

We regret thatsome of the pagesin this report may

not be up to theproper legibilitystandards, eventhough the best

possible copy wasused for scanning

ABSTRACT

X-RA Y DIFFRACTION STUDY OF M1NERAL0GICALCOMPOSITION OF MUDSTONES FROM EASTERN GADAREF

AREA, SUDANM.Sc. by YASSIN AHMED ABDELGADIR KARIM ELDIN 1996

This study reviews the theoretical and experimental aspects of Xraydiffraction (XRD) technique. Moreover, the mineralogical composition ofsome mudstones from Gadaref region has been investigated usingDIFFRAC-AT software package, by means of searching and matchingprocedure in the standard XRD patterns edited by the International Centerfor Diffraction Data (ICDD).

The X-ray diffraction analysis of the Gadaref mudstones revealedthat quartz, kablinite and tridymite are the major mineral constituents ofthese 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 contentbetween 71-100 % This most probably indicates that these rocks weresubjected to intense weathering and leaching under warm humid climate.These conditions seem to be less favourable for the formation of clayminerals chlorite, illite and smectite. Generally, the clay mineral types,abundances and distribution appear to be influenced mainly by source rockgeology, the local environment and climate. Moreover, the high silicacontent of the mudstones reflects the influence of both hydrothermal andweathering processes.

The high kaolinite content of these mudstone might suggest a goodpotential 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 furtheradditions to the refinement procedures and the purchasing of newcomputer's facilities.

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VsJ'

M-Jai . i j ^ J ' l ^N 1 J _ ^ ^yUill JSLiJl LL^ j l ^ J i ^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) C J I L ~ 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 (J i jc 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 O L . ^ - OI

IJL*

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Several individuals have helped in one way or another during thepreparation of this study. If I decide to enumerate, the listing willdefinitely be lengthy. However, 1 must mention certain people whosehelp was certainly invaluable.

| Firstly, my Supervisor, Dr O.man Mahmoud Abdullatif who takesi 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.ShaddadI 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 forI providing Laser Jet III printer which matches the DIFFRAC-AT package,* for making this study possible by giving me access to the Department'sI resources. Also my great thanks are extended to Mr. Hosham, Miss. MonaH and Miss. Hyfa working for Gortas Computer Service for rearrangementsI 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, theInternational Program in Physical Sciences(IPPS) for their generaous gift,the DIFFRAC-AT software.

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

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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 iACKNOWLEDGEMENTS iiiDEDICATION iv

CHAPTER 1 1

INTRODUCTION 1

1-0 Introduction 11-1 Objectives 2

1-2 Methods 2

CHAPTER II 4

THEORETICAL BACKGROUND 4

II-O Introduction 4II-1 The Crystalline Solid 411-2 The Unit Cell 411-3 The Crystal Lattice 511-4 Crystallographic Notation "Miller Indices" 8II-5 The Reciprocal Lattice 1011-6 X-Ray Diffraction 1111-7 Detennination of d-spacing and Intensities 14H-8 The Intensity of Diffraction 15II-8.a. Scattering by an Electrons 15II-8.b. Scattering by an Atom 16II-8.C. Scattering by a Unit Cell 19II-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 22III-l Production of X-Rays 22III-2 The X-Ray Generator 26III-3 The Cooling System 26III-4 The Goniometer 28III-5 The Detector 28III-6 TheDACO-MP 28III-7 Mode of Operation of The Diffractometer 30III-8 Data Processing with the DACO-MP 32III-8 a. The Peak Search 32III-8.b. The Extended Operations 33II[-9 Data Processing with DIFFRAC-AT V3.1 34111-10 Samples Separation and Preparation 36III-11 Data Collection of Mineral Samples 36

Using D500 Measuring Routine

CHAPTER IV 37

GEOLOGICAL LITERATURE REVIEW 37

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

IV-3 Regional Geology 41

CHAPTER V 43

RESULTS, INTERPRETATION AND DISCUSSIONS 43

CHAPTER VI 70

CONCLUSIONS AND RECOMMENDATIONS 70REFERENCES 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 occurmostly in sedimentary rocks such as sai ones, mudstones, claystones andlimestones (Tucker, 1988, 1991).

From a geological point of view the knowledge of mineralogy is highlyimportant for rock classification and the determination of origin anddepositional environments of rocks. Moreover, the mineralogy is helpfull ingeological prospecting, exploration and evaluation of the economic potential

: of mineral deposits. This depends primarily on accurate identification of theI minerals, knowledge of the composition and association in which they occurj. in nature. Therefore, it is important to study the characteristic of the depositsf 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 upjj 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 tothree origins: (i) inheritance, (ii) neoformation and (iii) transformation

', (Tucker, 1991).

The samples investigated are collected from several outcrops fromeastern Gadaref area. These samples are mainly mudstones and siltstonesrocks belonging to what is known in Sudan as the "Nubian SandstoneFormation . 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 andexperimental aspects of XRD technique and, second, to characterize anddetermine the mirteralogical composition of some mudstones and to assesstheir potential in kaolin industry.

1-2 Methods:

The nmdstone samples were prepared by crushing, disaggregation andsieving. Then, the XRD analyses were carried out on whole powderedsamples. 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 willbe discussed in chapter II.In chapter III the experimental set up, dataprocessing with DIFFRAC-AT software, samples preparation and collectionare given .The geological literature review are given in chapter IV. Chapter Vdeals with the data analysis and the results obtained using DIFFRAC-ATroutine facilities, and finally the conclusions and recommendations are givenin chapter VI.

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

V

{.

\

*

1

Theoretical

Unit cell

Introduction

Samples Analysis

Preparation

XRD

IntroductionOf

Diffraction

Separation

XRD analysis

Experimental

Production

OfX - rays

DIFFRAC-AT

Conclusionsand

Recommendations

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^ Tertiary tor'+ Quaternary!.

VCretaceous!

Upper I?roterozoicL

Gedarefv \/

V V V »

• ,AV V

• - ' . • ' . ' s v v . v

L;

\.- .-.'ILake Atba.-a

"iAlluviums, wadi fil ls, terracesdelta and swamp depositsUmm Rawaba Formation(

. •„;. •••; Umm Rawaba FormationI-.- — -.;(unconsolidated sands with *'gravels, clays and shales

Mesozoic i [ ^ V j Basic volcanics. mainly bass

toTertiaryi r ^Acidic and intermediate vole' I X 'mainly rhyolites and tracny:

...-•jGedaref Formation (conglom_i_Jsandstones,siltstones and muc

^^ ^ Proterozoic

Shist group, undifferentiatec

C*l*ZvtjGranites, undifferent iated .

intrusives, mainly gatv

Ultrabasic rocks and serper

Gneiss Group, undifferentiat

study-area

faultjand fracture.

Internationalboundary

Railway

Main road50 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 brieflyreviewed, namely : the crystalline solid, the unit cell, the crystal lattice, Millerindices, the reciprocal lattice, Bragg law, the intensity of diffraction as well asthe factors affecting it. The theoretical aspects have been revealed extensivelyin the literatures (Animalu, 1978; Nuffield, 1966;). Practical application of X -ray diffraction and method:; of minerals identification and estimation ha rebeen provided by Tucker, (1988); Carol, (1970); Thorez, (1976) andZussman, (1977).

H-I The crystalline solid :

A crystal may be defined as a solid composed of atoms arranged in apattern periodic in three dimensions. As such, crystals differ in a fundamentalway from gases and liquids because the atomic arrangement in the latter donot possess the essential requirement of periodicity.

H-2 The Unit Cell:

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

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

Since all the cells of the lattice are identical, the size of the unit cellcan in turn be described by the three vectors a, b, and c drawn from one

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corner of the cell taken as origin (fig.II-1). These vectors define the cell andare called the crystallographic axes of the cell.

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

The vectors a, b, c define, not only the unit cell, but also the wholepoint 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 aninfinite 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). Ifthere is only one species of atoms, it may be possible to place these on thelattice sites so that lattice vectors correspond to the positions of atoms, this isnamed the Bravais lattice( figJ-2a). More frequently, however, there may begroup of atoms in a crystal, a lattice site may be associated not only with oneatom but with a set of atoms, the lattice is said to have a basis ( fig. II-2b)(Animalu, 1978).

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rig. 11-1 A Unit Cell.

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Fig.II-2 Two dimensional lattice,

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

(a)

o

O Xo 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) onthe a,, a.7 and a3 axes respectively, so that the equation of the plane may bewritten as

or

P

l z= l (H-3)

It follows that the direction cosines of the normal to the planes {hkl) areproportional to h, k, 1 respectively. A direction normal to a plane with Millerindices {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 thenegative intercept (Animalu, 1978).

POOR QUALITYORIGINAL

(B)

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

i

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H-5 The Reciprocal Lattice :

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

Geometrically, the analytical equation (II-3) has two interpretationswith the (hkf) so considered fixed (x,y,z) variable. With (hkf) fixed, theequation 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 ofplanes (hkf) passing through a fixed point.

Thus, a plane with a set of points on it and a point with set of planespassing 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 (thereciprocal lattice space, also called k-space). The points, g, labeling thelattice planes are called reciprocal lattice points and may be defined by themathematical relation (Animalu, 1976).

g.I = N (II-4)

orexp. (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 :

andh:k:l» g:<:gy:gz

or

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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 reciprocallattice 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{a2 xa})

a,-a2

b2 =

* , = •

a. a,

(a, xa2)

xo3

-• The common denominator in each case is

:"'t. -a, a.

(II-8-a)

(II-8-b)

(II-8-c)

(H-9)

- 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 crystalf-*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 presentationthe X-ray diffracted beams are found only v n th< reflections are from theparallel planes. Bragg planes are a set of a' s o f the crystal wtere the raysinterfere constructively (fig.II-4). The scattering is elastic, so that thewavelength of the diffracted photon does not change on reflection.

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

so that

let

then

or

sin 0=xd

(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 inivrofk.

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'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 byapplying Bragg's law, the d-spacing are obtained from 29-d tabulations forthat particular wavelength. V is worthwhile to consider briefly the question,what are the d-spacing because of the confusion which sometimes existsregarding 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 latticespacing gives an integral series of d/n of these d-spacing. It is customary toinclude the order of reflection, n, in the indices of reflection so that, forexample, 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

(11-12)</(00i) = (%')sin 0(001)

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

In the first place, 29 or sin9 depends on the wavelength, A., used andthere is no unique A. for a given substance. Secondly, the use of the d-spacingand the associated intensities for the X-rays identification of crystallinematerials are the cnes used by the Joint Committee of Powder DiffractionStandards (JCPDS).

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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 thescattered beam depends on the angle of scattering.

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

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

/ =/.4 \

\m c R J

2

sin a

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

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

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

- ley

z — — l0 •-j-V'Y I sin 90 + -km c R

2 4 2sin ( 9 0 - 2 0 )

2 4 2

1+cos 20 (11-14)

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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 pathlength 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 thenumber of electrons in the atom for this direction. The efficiency of scatteringby 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« isthe amplitude of the wave from a free electron. The intensit)'of scattering isproportional to the square of the amplitude i.e.

where IA, Ie are the intensities of the beam from the whole atom and theelectron 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 itselectrons, 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 thestructure factor, F(hkl), so that F(hkl) is known as the structure amplitude andis defined as the ratio of the amplitude of the wave scattered by all atoms inthe 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 allkinds of atoms (Nuffield, 1966).

II-8.d. The Temperature Factor :

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

f = f0 exp {-B(sin2e/X2)} (11-18)

where B is the temperature factor which incorporates the meandisplacement of the atom from its mean position. B depends on the kind ofatom, and also on the orientation of the reflecting planes in the crystal, X isthe wavelength and 0 is the Bragg angle (Nuffield, 1966).

I'ijj.II-7 Vector reresentation of waves with different

amplitude and phases.

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II-8.e. The Absorption Factor :

The incident and reflected beams are partially absorbed when passingthrough a crystal, and consequently the intensity of reflection is less than thatfrom a perfectly non absorping substance. The absorption effect evidentlydepends not only on the absorption coefficient of the crystal but also on itscross-section. In the case of a powdered specimen, the absorption dependson the density of the packing of the particles. The result of this is that theintensities of reflection vary with the Bragg angle . As 0 increases, thevolume of the specimen contributing to the reflection also increases. Hencethe absorption factor decreases with increasing Bragg angle and has theopposite effect of the temperature factor (Nuffield, 1966).

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

III-O Introduction :

The aim of this chapter is to explain the various techniques which havebeen used to study ihe mudstone samples. It deals also with the method of X-ray generation with its accompanying cooling system, the X-raysdiffractometer 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 shortwavelength 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 electronsare produced by heating a filament, and they are accelerated by a potentialdifference of the order of tens of Kilovolts, applied between the filament andthe 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 lowabsorbing material (Cullity, 1978).

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

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

X (A0) = 12.4E(Kev)

(III-l)

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

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

out

Tnrcjol

?0-G0kV

Water cooled

Berylliumwindow

X-ray beam

"Electrons

" Filament

"»£l£gcu§ted glass tube

- Shielding

5-35 mA12 V

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h e g e n e r a t i o n o f .\•••--y

transfer of rv"', f c er due to the

u'K shell.

X-rayinlnnsity

Mnxiinum electron energy

ons

KlK "i

Characteristic line spectrumfrom Cu

Continuous spectrum

1 Wavelength X (A) 2

Kp 1.3922 !

K«, 1.5405 i-KCY3 1,5408 I

I POOR QUALITYORIGINAL

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ITI-2 The X-ray Generator :

The X-ray generator used is a KRISTALLOFLX K710. It is apowerful device for supplying highly stable HT voltage to X-ray tubes withearthed cathode like film cameras, diffractometres, and X-ray spectrometers.The generator supplies the X-ray tube with a negative polarity high voltagefrom 20 KV to 50 KV and a current of 5 mA to 40 mA. It can function withany 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 apower cord for connection to 2088/220/240 power line. This line must beprotected with 25 A fuse. In addition to the electrical distribution groundanother chassis ground should be installed. Water supply should be able toprovide a 4 liter/min. pressure. This pressure may increase or decreasedepending on restrictions in the X-ray tube. A closed-loop recirculatingcooling system is highly recommended (Technical Description, X-ray highvoltage generator manual).

II1-3 The Cooling System :

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

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in

"S©

H

2

Rücklauf out 1 et

Strömungs-wächter

f l o w c o n t r o l l e r

1/0,/oaA ft;4 Kompressor Kondensotor

Sicherheifs-ifiermosTQt i" fsafety temperaturecont roljer

^** temperatureit'—j regulator

,.-' I Tsmperctur-

SrhF i l t e r

V)

Pumpt

' i

Compressor

expansions -.yeniilI * p a n s i o n v a l v e

Sammlerreserve)! r

• Trocknerdrier

- ^

Schauolcsinspect ".on

! glass

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 operatinginstruction manual).

The diffractometer has the advantage that it can be used for almost allapplications of X-ray diffraction techniques, such as structural analysis andphase analysis. In its basic design it is used to collect the data that are neededto identify the minerals existing in the samples. The sample holder issupported on the axis of the goniometer which is fully automatic and iscontrolled 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 angleposition 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 beused to measure X-radiation in the wavelength range from 0.05 nm to 0.27nm. It has a diameter of 25 mm with a 0.2 mm Beryllium inlet radiationwindow, 10'^ sec. dead time and 1200V-1300 V operating voltage. Amonochromator is usually mounted in front of the detector. Thismonochromator allows only the Ka radiation ofthe X-ray tube to reach to thedetector. The Kp and continuous radiation ofthe X-ray tube as well as thefluorescence radiation ofthe specimen are suppressed (Siemens D500/D501diffractometer operating instruction manual).

III-6 The DACO-MP;

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

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The DACO-MP is a controller for the Siemens difrractometers D500,D500TT and D501. I t s 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 maycontrol any measurement process and also perform complex computation onthe results when a large pmount of data is not required (DACO-MP user'sreference manual V2.1 or V2.2, 1985).

The DACO-MP V2 firmware is logically made up of seven tasks thatmay 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 understandthe posibilities and restrictions of the system, the other tasks are listed forinformation 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 withfirmeware. 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 V2.1I orV2.2, 1985).

IThe DACO-MP provides writing and executing programs using its

acceptable commands for many treatments associated with the data neededfor the analytical purposes. The results obtained by the executable programsof 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 isdiffracted at the specimen P and recorded by the detector D. The specimen isrotated at a constant angular speed, whereas the detector moves about thespecimen. The diffraction angle (20) is always equal to double the glancingangle(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 reflectedfrom the specimen to the detector. The intensity of the reflected radiation ismeasured by means of the detector and then transferred to the measuringelectronic systems, the DACO-MP and the printer. The anj^ular position ofthe reflection is indicated on the goniometer (Siemens D500/D501diffractometer operating instniction manual).

The focus, specimen and the detector diaphragm are located on thefocusing circle F, while the focus and the detector diaphragm are located onthe measuring circle M. The entire effective surface of the specimen wouldhave to be located on the focusing circle so that the diffracted radiation isfocused before it reaches the detector. In practical designs the surface of theplane specimen is merely placed tangentially to the focusing circle (SiemensD5OO/D5O1 diffractometer operating instniction manual).

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Fig. IH-^i Focusing Geometry of the diffractometer in case of20/0 operation.

M

M:

1

BBI.I.IIBi.rvD

P

Focus of the x-ray tube,111 Aperture diaphragms

Detector diaphragmDetectorYip filterSpecimen

,92,9

9MF

Glancing angleDiffraction angleAperture angleMeasuring circleFocusing circle

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III.8 Data Processing with the DACOP-MP:

§• HI*8.a. The Peak Search ;

Because of the statistical character of the experimental data, theobserved 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^ - " ^ — ^ i l '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' o n 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 isV 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 thresholdand 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 themanual V2 1, V2.2, 1985)

ni l

111-8.1). The Extended One ration :

In order to get good results agreeing with or matching the criteriarecorded in the (JCPDS^ files, the DACO-MP provides computationaloperations 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 thissmoothing depends on a coefficient called smoothing (Smol) which is aninterval taken for the curve smoothing. The number of points placedsymetrically 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 diffractogramis 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 backgroundsubtraction algorithm. Let Y(20) be the equation of the convex envelope ofthe 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 controlKa2 stripping. This algorithm works on a third degree least squareapproximation polynomial computed on a fraction of the diffractogram. Thelength of this fraction is derived from (Smo2) as with (pkw) and (smol) forthe 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).

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HI-9 Data Processing with DIFFRAC-AT V3.1 :

DIFFRAC-AT is an integrated software package for the powder X-raydiffraction. It has been developed for Siemens X-ray diffractometers andprovides the measuring routines for Siemens D5000 and D500diffractometers (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 programD5 INSTAL following the hints in the manual of the software. The softwarehad been designed to run on 100 % compatible IBM ps/2 computer or otherrelated ones.

The DIFFRAC-AT is compatible with DOS 3.x to DOS 5.x and MSWINDOW can be used to call DIFFRAC-AT as a non-WINDOWapplication.

The recommended system printer for DIFFRAC-AT is HP-PATNJETsince it produces good quality colour pictures. The HP LASER JET II and IIIare supported for high quality black and white documents, also the HP plottermodel 7475A and 7550-PLUS are supported for graphics. Fig.III-5 shows ablock diagram of the system in the DACO-MP mode .

I For a detailed description for the different files and sub-files, of theDIFFRAC-AT, the reader is referred to Caussin et al., 1988, 1989, Chaung1974, 1975. A comperhensive review of the DIFFRAC-AT is given by (Idris,1994).

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!

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

I 2

COMPUTER

KEYBOARD

•—I Termini! Jinrl

DACO- MP

MOUSE

LJSYSTEM PRINTER

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The collected mudstonerock samples from eastern Gadaref were firstcrushed and disaggregted manually in a procelain morter. Then the sampleswere sieved using sieve sizes between 1.000 mm-0.032 mm. The X-raypowder diffraction measurements were performed on samples having sizesless than 0.025 mm. Finally, the resulting fine crystalline powdered sampleswere placed in a sample holder, ready for the measurements.

IH-11 Data Collection of Mineral Samples Using D500 MeasuringRoutine :

The measurements of samples were performed with the measuringconditions adjusted when editing the measurements. The standard patternsstored in DIFFR.AC-AT package by means of EVA program usingsearch/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 ).

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CHAPTER IV

</:r*. , 'w-" •"' ' ' ' n : : " A T r " i ' REVIEW:

IV-0 Introduction;

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

IV-1 Mineralogical Composition:

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

IV-2 Clay minerals:

Clay minerals are hydrous aluminosilicates with a sheet or layeredstructure; they are phyllosilicates, like the micas. The sheets of a clay mineralare of two basic types. One is a layer of silicon-oxygen tetraheHra with threeof the oxygen atoms in each tetrahedra and linked together to form ahexagonal network (Fig.IV-1). The basic unit is S12O5 but within these silicalayers aluminium may replace up to half the silicon atoms. The second type oflayer consists of aluminium in octahedral coordination with O2' and OH' ionsso 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 beoccupied, 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 mineralgibbsite (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 sheetsof silica tetrahedra and aluminium or magnesium octahedra linked together byoxygen atoms common to both (Tucker, 1991).

The stacking arrangement of the sheets determines the clay mineraltype, as does the replacement of Si and Al ions by other elements.Structurally, the two basic groups of clay minerals are the kandite group andsmectite group (Tucker, 1991).

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

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

Illite, the most common of the clay minerals in sediments, is related tothe mica muscovite. It has a three-layered structure, like the smectites butAl3+ substitution for Si4 ' in the tetrahedral layer results in a deficit of chargewhich is balanced by Potassium ions in interlayer positions (Fig.IV-1). Somehydroxyl (OH"), Fe2+ and Mg2* ions also occur in illite. The basal spacing isabout 10 A0 (Tucker, 1991).

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

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During weathering and diagenesis, interlayer cations can be leached outof the clay minerals by percolating waters. Because of their fine crystal sizeand the presence of unsatisfied bonds, clay minerals are important in theprocess of ion exchange. Ions in aqueous solutions can be adsorbed on to anddesorbed from clays, with the water chemistry controlling the exchangeprocess. Some elements, such as iron can be transported by adsorption onclays.

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

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£

c

Vj3

Si

silicon-oxygentetrahedralunit

Basic Units

aluminaoctahedra l^ v

unit ~

O and '•.' " Oxygen atoms o and • ~ Silicon atoms C and Oand O = Hydroxyls O Aluminum, maonesiuetc

: kandite eg kaolinite AI2O3.2Si02.2H2O

A\ /\/k A\ / \ / ' ^ Aalumina (gibbsite) layersilica layer

basal spacing 7A

e.g. montrru

/H

/

H

/ vr~~:

20/ \.

7°

H,0

'VV'

H20

'VV

A, /<-"\/N.H20

\?"«i/VA /IS. .A.

Ca/Na

2A:2O3.8SiO;,.2H2O nH2OMg. Ca)O.AI2O3.5SiO2 nH2O

much substitution ofAl by Mg and Fe

mterlayer H2O. and Ca and Na

I basal spacing 14 Ai but expandable fromj 9.6 to 2V4 A

H2O Ca/Na H2O

illite K.Al2(OH)2.fAISi3(O. OHl,0l

substitution of Si bA l m s ' l l C 8 '«yers

OH"m ' .er lsver K • togetherw l h i o m «=OH

K" K" Ty VVVV i basal spacing 1 0 ^

K" Fe/Mg

chlorite Mg6(AI.Fe)(OH8)(AISi)4O,0

substitution 0 , A l b F e

b r u c i t e '*ye'L IMg-OH)between Al-S. sheets

II

j b a s a l spat ing 14 A

\^/\?'

A A

- g,- - ^ \ ^ - \~^ \t^

•V \ ^ ^ \ / SSJb% / - \ /h. y<?v / \

The identification of clay minerals in mudrocks is normally undertakerthrough 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 etal., 1980; Chamley, 1989 and Weaver, 1989).

Mudrocks can be deposited in different environments such as riverfloodplain, lakes, deltas, continental shelves and deep-sea. Mudrocks in thegeological 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 highEthiopian plateau and the Sudanese plateau. The sedimentary rockscomposed of what is known as the Nubian Sandstone Formation whichmainly consists of sandstone, siltstone and mudstone. These rocks oftencovered by black cotton soil and intruded by basaltic lavas. The sedimentaryplateau is dissected in its eastern part by the rivers Mtbara and Setit.

The mudstone of the study area represent deposits formed by processesof erosion, transportaion and deposition within floodplains and overbanksareas of Cretaceous braided river system which deposited the NuoianSandstone Formation (Omer, 1983).

The oldest geological unit is a highly weathered unfoliated porphyriticgranite outcrops belonging to the Early Cambrian Basement complex of theSudan. These basement rocks are overlain by series of Mesozoic clasticsediments, generally known as Nubian Sandstone Formation and consideredto be of Cretaceous age in the region of Gadaref-Showak (Omer, 1983). Inthe area studied, the Nubian is represented by fine-grained moderately sortedyellowish to pinkish sandstone and mudstone. Locally they are intruded bybasaltic rocks of Tertiary age occurring as sills, dykes and flows covering

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them. They are covered by cracking dark clays, essentially composed ofmontmorillonites 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 Gadarefto the upper Cretaceous on the basis of wood fragments. The heavy mineralsuite is poor : consisting of zircon, tourmaline, pyroxene,rutile and kaynite,and indicates a source area mainly composed of igneous rock with minorinput from metamorphics (Omer, 1983).

The zircon show up in two form : one fresh with its original crystalshape, the other very worn with rounded outlines this double form leads tothink that in this region, the Nubian sandstone has been fed from two differentsources, one coming from direct erosion of Basement, the other possiblycoming 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 theassemblage along with an increase in the mixed-layer clays (Omer, 1983).

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

At Gadaref, according to the geological history the paleotopographyshows features characteristic of a subarial environment such as kaolinite,geothite and brightly coloured sandstone. Kaolinite shales and common roottraces, as well as the surface morphology of the quartz grains indicate intenseweathering in a Sudan- type climate but there are also signs of marinedepositional environment which is confirmed by grain size study (Omer,1983). The clay minerals distribution in the Sediments of Gadaref areaappears to be influenced by source rock geology, climate and the localenvironment.

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CHAPTER V

RESULTS AND DISCUSSIONS:

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

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

From XRD analysis quartz, kaolinite and tndymite are the majormineral constituents of these rocks, whereas alunite, coalingate, cristabolite,gutsvechite, hematite, meta-alungen, minamite, monteponite and samarskiteoccur as minor constituents. Except two samples, kaolinite in 18 samples

ranged between 71-100 %. Ten o r these samples Have ivavihnitrctmitmi' n''100 % each. Other clay minerals like chlorite, illite and smectite occur inminor amounts. High kaolinite content in these mudstones, most probablyindicates intense chemical weathering under warm humid climate in the past.Other geological evidence from Gadaref area tends to support suchconclusion (Omer, 1983).

The Sedimentological evidence suggests that the kaolinite is of detritaiorigin mainly inherited from source rocks which subjected to intense chemicalweathering and leaching under humid warm climate. The limited occurrencesof smectite, chlorite and illite may indicate the interruption by short dryperiods which favour limited weathering and leaching under rather alkalineconfined environment. Therefore, smectite, chlorite and illite origin may beattributed to neoformation (Chamley, 1989).

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From these samples, five samples show reddish colour indicating thepresence of geothite, however, in the fitting the geothite does not appear.Also from the fitting tridymite appeared instead of cristabolite which appearsin 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 riverenvironment. The kaolins have been affected by secondary silicification andalunitization processes. These processes are attributed to hydrothermal andweathering activities affecting the kaolins in the area (Wipki et al., 1993). Themineralogical composition revealed in this study support the abovesuggestions.

Kaolin has many industrial uses, such as : paper industry, ceramics,refractory industry, paint industry, polymers and plastic industry, medicineindustry, etc. Some of the kaolinite deposits are currently used in small scaleactivities such as white wash, paint and for other building purposes. Thekaolinite deposits are considered also feasible for production of wall-andfloor-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 befeasible.

However, from economic point of view several factors have to beconsidered concerning the economic potential of kaolinite deposits inSudan:

1. Quality or mineralogical composition of the Kaolinite, thicknesses, lateralI extensions and the reserve.i

!

} 2. Development of adequate infrastructures and favourable geographicalI position.I

3. Open pit mining seems highly favourable for most of the Kaolinite depositsin Sudan, since the geological conditions are optimum.

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

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conducted such as determination of firing colour, sinter- and klinker-pointand 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 andbdullatif, 1993).

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

Sample Name

7C1

A6

A7

A13

A14

B6

B7

B8

Chemical FormulaSiO2

Al22SiO2O5(OH)4SiO2

SiO2

Al22SiO2O5(OH)4

SiO2

SiO2

Al22SiO2O5(OH)4

SiO2

Al22SiO2O5(OH)4

SiO2

Al22SiO2O5(OH)4

CdO(Al,Fe)3(PO4,VO4)2

(OH)3.8H2OSiO2

Al22SiO2O5(OH)4

Fe2O3

Mg10Fe2(OH)24(CO3).2H2O

SiO2

Al22SiO2O5(OH)4SiO2

SiO2

Na-Al-SO4-OH

Mineral NameQuartz

KaoliniteTridymite

QuartzKaolinite

TridymiteQuartz

Kaolinite

QuartzKaolinite

QuartzKaolinite

MonteponiteGutsvechite

QuartzKaoliniteHematite

Coalingate

QuartzKaolinite

TridymiteTridymite

Alunite

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Sample Name

B13

B14

C7

C8

C14

D10

MHA

RC2

S6

SWV1

Chemical Formula

Al22SiO2O5(OH)4

SiO2

A]22SiO2O5(OH)4SiO2

SiO2

Al22SiO2O5(OH)4SiO2

SiO2

Al22SiO2O5(OH)4

SiO2

SiO2

Al22SiO2O5(OH)4SiO2

SiO2

Al22SiO2O5(OH)4

SiO2

Al22SiO2O5(OH)4SiO2

SiO2

Al22SiO2O5(OH)4

SiO2

Al22SiO2O5(OH)4A12(SO4)3.14H2O

SiO2

Al22SiO2O5(OH)4

Mineral NameQuartz

Kaolinite

QuartzKaolinite

TridymiteQuartz

KaoliniteTridymite

QuartzKaolinite

CristaboliteQuartz

KaoliniteTridymite

QuartzKaolinite

QuartzKaolinite

TridymiteQuartz

Kaolinite

QuartzKaoliniteMeta-AlunogenQuartz

Kaolinite

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Sample Name

SWV2

TLC

Chemical FormulaSiO2

Al22SiO2O5(OH)4

SiO2

YNb206SiO2

Al22SiO2O5(OH)4

SiO2

(Na.Ca)l-xA13(SO4)2(OH)6

Mineral NameQuartz

KaoliniteCristaboliteSamarskite

QuartzKaolinite

TridymiteMinamite

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

SampleKaoliniteSmectite

IlliteChlorite

Normal7

12-141014

Glycolated7171014

Heated(550°C)—101014

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

Sample7C1A6A7A13A14B6B7B8

B13B14ClC8

C14D10NHARC2S6

SWV1SWV2TLC

Kaolinite %601008774100100772588100100638110010098100717975

Smectite %17—13————————37——————2115

Illite %23—————237512———19——

2—29—10

Smeciite/Chlorite %———26—————————————

——

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CHAPTER VI

CONCLUSIONS AND RECOMMENDATIONS;

The XRD analysis of mudstone samples from east of Gadaref regionreveals that quartz, kaolinite and tridymite are the major mineral constituentsof these rocks, whereas alunite, coalingate, cristabolite, gutsvechite ,hematite, meta-alungen, minamite, monteponite, samarskite, smectite, illiteand chlorite are minor constituents. In most samples kaolinite ranges between71-100%.

The high kaolinite contents of these rocks indicate that the source rocksmight have been subjected to intense chemical weathering and leaching underacidic unconfined environment and the prevalence of warm humid climate.The occurrence of minor abundances of illite, smectite and chlorite maytestity to dryer climatic periods, where limited weathering and leachingprevailed and allowed their neoformation within an alkaline confinedenvironment. The high silica contents in these mudstone most probablyindicates the influence of both hydrothermal and weathering processes.

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

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

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

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REFERENCES

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2.Animalu, O.E. (1978). Interdmediate Quantum Theory of CrystallineSolids. Prentice Hall of India Private Limited, New Delhi.

3. Carol, D. (1970). Clay minerals : A guide to their X-ray identification.Geological Society of America, special paper 126.

4.Caussin, P.J. Nusinoici and Berad, D.W. (1988). Advances in X-rayanalysis, vol.31, page 423-430.

5.Caussin, P.J. Nusinoici and Berad, D.W. (1989). Advances in X-rayanalysis, vol.32, page 531-538.

6.Chamley, H. (1989). Clay sedimentology. Springer-Verlag.

7. Chialvo, J. (1975). Contribution a la geologie du confluent Atbra-Setit.Etude des sites de barrage de Rumela et Burdana, Soudan. Doctorart 3Cycle Thesis, Univ. Grenobe, France, 203 pp.

8. Chung, F.H. (1974). J.Appl. Cryst.vol.7; page 519-525.

9. Chung, F.H. (1975). J.Appl.Cryst.vol.8; page 17-19.

lO.Cullity, B.D. (1978). Elements of X-ray diffraction, 2nd edition.Addison- Wesley publishing company, INC., London.

11 .DACO-MP user's reference manual V2.1, V? ? (1985).

12.DIFFRAC-AT V3.1 EVA user's guide manual, (1992). Progress inAutomation Siemens.

13.DIFFRAC-AT V3 search tutorial manual, (1992). Progress inAutomation Siemens.

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14.DIFFRAC-AT 3.1 start up manual, (1992). Progress in AutomationSiemens.

15.Getting started with the DACO - MP manual V2.1, V2.2, (1985).

16.Grim, RE. (1968). Clay Mineralogy, pp.596. Me Graw-Hill, NewYork.

17.Hussein, T., Mula, A.G. and Schneider, H. (1989). Geological andSeismic investigations with regard to shallow ground water exploration inEastern Sudan Republic. JAES, vol.8, No.l, pp 75-78.

18. Ibrahim, Tand Abdullatif, f(1993). A geological report on some industrialmineral deposits in the Sudan.

19.1dris, H. (1994). X-ray diffraction study of clays and minerals. M.Sc.thesis, Department of Physics, U of K.

2O.Kittel, C. (1965). Introduction to Solid State Physics. Berkeley,California.

21.Martin, T.L. and William, F.L. (1970). Electrons and Crystal.Brook/Cole Publishing Company Belmont, California.

22.Millot, G. (1970). Geology of clays, pp.429. Springer-Verlag, NewYork.

23Nuffield, E.W. (1966). X-ray diffraction methods. John Wiley andSons, INC. New York.

24.Omer, f (1983). The geology of the Nubian Sandstone Formtion inSudan. Geological and mineral resourses department. The ministry ofEnergy and Mining, Sudan.

25.Potter, P.E., Maynard, J.B. and Pryor, W.A. (1980). Sedimentology ofshale, pp.270. Springer-Verlag, Berlin.

26.Siemens D500/D501 Diffractometer Operating Instruction Manual.Mode No.C79000-B3400-C042-10.

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26.Siemens D500/D501 Diffractometer Operating Instruction Manual.Mode No.C79000-B3400-C042-10.

27.Siemens Technical Description, X-ray high voltage Generator.KRISTALLOFLEX 710/710H; 7KP5000-8AA to -8AD. Mode No.C79000-B3476-C081-06.

28.Thorez, J. (1975). Practical identification of clay minerals. Edition G.Leotte, Dison Belgium.

29.Tucker, M. (1988). Techniques in Sedimentology. Blackwell ScientificPublications. Oxford 0X2 OEL 8 John Street.

3O.Tucker, M. (1991). Sedimentary Petrology: An introduction to theorigin of Sedimentary rocks. Blackwell Scientific Publications. OxfordOX2 OEL 8 John Street.

31. Velde, B. (1977). Clays and clay minerlas in naturals and syntheticsystems, pp.218. Elsevier, Amesterdam.

32. Weaver, C.E. and Pollard, L.D. (1973). The Chemistry of clay minerals,pp.213. Elsevier, Amesterdam.

33.Weaver, C.E. (1988). Clays, muds and shales. Developments insedimentology 44, p. 819.

34.Wipki, M., Germann, K. and Schwartz, T. (1993). Alunitic kaolins ofGedaref region (NE Sudan). In Geoscientfic Research in Northeast Africa,Thorweihe and Schandelmeier (eds). P.509-514. Balkema, Rotterdam.

35.Zussman, J. (ed). (1977). Physical methods in determinativemineralogy (second edition). Academic press.

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