Contents

DECLARATION

ABSTRACT

ACKNOWLEDGEMENTS

GLOSSARY

CONTENTS

Chapter 1 Introduction

Section 1.1 Philosophy of Study

Section 1.2 São Luiz alluvial diamond deposit

Section 1.3 The diamond deposits of Guinea

Section 1.4 Diamond from a social perspective

Section 1.4.1 Historical interest in diamond

Section 1.4.2 General diamond characteristics

Section 1.5 Diamond studies

Section 1.5.1 Physical characteristics

Section 1.5.2 Compositional characteristics

Section 1.5.2.1 Carbon isotopic content of diamond

Section 1.5.2.2 Nitrogen in diamond

Section 1.5.2.2.1 Aggregation of N in diamond and Infra Red absorption characteristics

Section 1.5.2.2.2 Nitrogen Isotopic content of diamond

Section 1.5.2.3 Additional Impurities

Section 1.5.3 Interrelation of compositional and physical characteristics

Section 1.5.4 Formation of diamond

Section 1.6 Inclusions in diamond

Section 1.6.1 Peridotitic parageneses

Section 1.6.2 Eclogitic paragenesis

Section 1.6.3 Sulphide inclusions

Section 1.6.4 Occurrence and significance of inclusion type

Chapter 2 Inclusion Chemistry

Section 2.1 Inclusion break-out

Section 2.2 Major and minor element analyses of São Luiz and Guinean inclusions determined by electron microprobe

Section 2.2.1 Inclusion type analysis

Section 2.2.1.1 Inclusions of olivine composition

Section 2.2.1.2 Silica inclusions

Section 2.2.1.3 Inclusions with garnet-like compositions

Section 2.2.1.3.1 Grosspaldite garnets

Section 2.2.1.3.2 Majoritic garnets

Section 2.2.1.3.3 TAPP grains

Section 2.2.1.4 fPer inclusions

Section 2.2.1.5 Inclusions with pyroxene-like compositions

Section 2.2.1.6 CaSiO3 composition inclusions (CaSi-Pvk)

Section 2.2.1.7 Alumina inclusions

Section 2.2.1.8 ‘Inclusions’ of native iron

Section 2.2.1.9 Additional phases

Section 2.2.2 Compositional studies of composite grains

Section 2.2.2.1 EPMA mapping of composite grains

Section 2.2.2.2 EPMA transects across composite grains

Section 2.3 Coexisting phases and mineral associations

Section 2.4 Trace element analyses of São Luiz inclusions by ion microprobe

Section 2.4.1 Trace element characteristics of olivine inclusions

Section 2.4.2 Trace element characteristics of Alumina inclusions

Section 2.4.3 Trace element analyses of inclusions of broadly garnet composition

Section 2.4.3.1 Trace element characteristics of majoritic garnets

Section 2.4.3.2 Trace element characteristics of inclusions with TAPP composition

Section 2.4.4 Trace element characteristics of fPer inclusions

Section 2.4.5 Trace element analyses of inclusions of pyroxene composition

Section 2.4.5.1 Trace element characteristics of upper mantle pyroxene

Section 2.4.5.2 Trace element characteristics of Type I, Type II and Type III pyroxenes

Section 2.4.6 Trace element characteristics of CaSiO3 composition inclusions (CaSi-Pvk)

Section 2.4.7 Discussion of trace element characteristics of inclusions from São Luiz

Section 2.5 Mössbauer Study of inclusions

Section 2.5.1 Mössbauer study of garnet composition inclusions

Section 2.5.1.1 Mössbauer study of majoritic garnet

Section 2.5.1.2 Mössbauer analyses of TAPP

Section 2.5.2 Mössbauer analyses of fPer inclusions

Section 2.5.3 Mössbauer analyses of pyroxene inclusions

Section 2.5.4 Summary of Mössbauer data

Section 2.6 SEM and TEM analyses of fPer inclusions

Section 2.6.1 Observation of ‘blebs’ in fPer inclusions

Section 2.6.2 Additional visual characteristics of fPer inclusions

Section 2.6.3 Genesis of high BS-intensity features in fPer inclusions

Chapter 3 Structural features of inclusions from São Luiz and Guinean diamonds

Section 3.1 Techniques adopted for structural analyses

Section 3.2 Subjects of structural analysis

Section 3.3 Results of structural analysis

Section 3.3.1 Investigation of the structure of the tetragonal-pyrope almandine phase (TAPP)

Section 3.3.1.1 Gandolfi camera X-Ray diffraction of TAPP

Section 3.3.1.2 ESPRC X-Ray Diffraction of TAPP, BZ244B

Section 3.3.1.3 Micro-X-Ray diffraction of TAPP, BZ265A at Brookhaven

Section 3.3.1.4 TAPP as a unique phase

Section 3.3.2 Investigation of the structure of alumina inclusion BZ227A

Section 3.3.2.1 ESPRC X-Ray diffraction of alumina, BZ227A

Section 3.3.3 Investigation of the structure of fPer inclusions

Section 3.3.3.1 Gandolfi camera X-Ray diffraction of fPer grains

Section 3.3.3.2 Micro-X-Ray diffraction of fPer at Brookhaven

Section 3.3.3.3 X-Ray diffraction of fPer, BZ257A1 at Edinburgh

Section 3.3.4 ESPRC X-Ray diffraction of olivine inclusion, BZ243C

Section 3.3.5 Structural investigation of pyroxene composition phases

Section 3.3.5.1 X-Ray diffraction of pyroxenes at UCL

Section 3.3.5.2 ESPRC X-Ray diffraction of pyroxenes, BZ241B2 and BZ242B

Section 3.3.5.3 Micro-X-Ray diffraction of pyroxenes at Brookhaven

Section 3.3.6 Additional observations on structural investigations

Section 3.4 Summary of structural determinations

Chapter 4 The nature of mantle regions as seen through study of São Luiz and Guinean inclusions

Section 4.1 Bulk compositions of the mantle

Section 4.2 Mantle Geotherms

Section 4.3 Mantle convection

Section 4.4 Phase relations in mantle systems and the source of São Luiz and Guinean diamonds

Section 4.4.1 Phase relations in the earth’s transition zone and lower mantle

Section 4.4.1.1 The system MgO - FeO - SiO2

Section 4.4.1.2 The role of Al and Ca on mantle phase relations

Section 4.4.1.3 The role of Na on mantle phase relations

Section 4.4.1.4 Additional components

Section 4.4.1.5 The role of fluid

Section 4.4.1.6 Phase relations involving complex systems

Section 4.4.1.7 Melting relations

Section 4.4.2 The source of São Luiz and Guinean diamonds

Section 4.4.2.1 The UM association

Section 4.4.2.2 Source of majoritic garnet association inclusions (TZ association)

Section 4.4.2.3 Source of the UM/LM association; BZ243

Section 4.4.2.4 The LM I association

Section 4.4.2.5 Source of the LM II association

Section 4.4.2.6 Source of the LM III association

Section 4.4.2.7 Deep mantle inclusions; phase relations over the upper mantle / lower mantle boundary and mantle convection

Section 4.5 Equilibration of São Luiz and FEG inclusions and element partitioning

Section 4.5.1 Partitioning studies

Section 4.5.1.1 Fe / Mg partitioning between fPer and olivine composition

Section 4.5.1.2 fPer - MgSi-Pvk partitioning and thermal state of the upper mantle / lower mantle boundary

Section 4.5.1.3 Deep mantle phases / Liquid

Section 4.5.1.4 Trace element partitioning

Section 4.5.2 Equilibration in composite inclusions

Section 4.6 Liquids in equilibrium with São Luiz associations

Section 4.7 Mantle oxidation through studies of São Luiz inclusions

Chapter 5 Diamond characteristics

Section 5.1 Morphology

Section 5.2 Colour

Section 5.3 Deformation features

Section 5.3.1 Observations of brittle deformation in diamond

5.3.1.1 Visual observation of fracture systems

Section 5.3.1.2 Observation of diamond fracture systems at high resolution

Section 5.3.2 Plastic deformation

Section 5.4 Chemistry of diamond fragments and unbroken stones

Section 5.4.1 Bulk d 13C detemination of broken stones

Section 5.4.2 Nitrogen characteristics of broken and bulk stones

Section 5.4.2.1 FTIR analysis of broken and bulk stones

Section 5.4.2.2 Nitrogen composition by bulk analysis

Section 5.4.3 Additional atomic species within São Luiz diamonds

Section 5.5 Chemistry of polished diamond ‘flats’

Section 5.5.1 Determination of d13C

Section 5.5.2 Nitrogen analyses of polished plates

Section 5.5.2.1 FTIR analysis for Nitrogen in polished plates

Section 5.5.2.2 Determination of nitrogen content by ion microprobe

Section 5.6 Cathodoluminescence

Section 5.6.1 Cathodoluminescence characteristics of São Luiz diamonds

Section 5.6.2 Interpretation of cathodoluminescence characteristics of São Luiz diamonds

Section 5.7 Summary of diamond characteristics

Chapter 6 The nature of mantle regions as seen through study of São Luiz diamonds

Section 6.1 Mechanisms of diamond formation

Section 6.1.1 Diamond Stability in terms of fluid species

Section 6.1.2 The atomistic growth of diamond and the presence of N and H in São Luiz diamonds

Section 6.2 Formation reactions of deep mantle diamonds and mantle carbon and nitrogen content: inferences from São Luiz stones and deep mantle diamonds from other localities

Section 6.3 Formation environment of São Luiz diamonds

Section 6.3.1 Processes affecting nitrogen content and stable isotope ratios

Section 6.3.2 Formation environment of São Luiz diamonds

Section 6.3.3 Interpretation of additional features of São Luiz diamonds

Chapter 7 Exhumation

Section 7.1 Internal pressure

Section 7.1.1 Thermoelastic poperties of minerals

Section 7.1.2 Calculation of elevated internal pressures

Section 7.1.3 Previous indications of elevated internal pressures of diamond inclusions

Section 7.1.4 Internal pressures imposed on fPer inclusions

Section 7.2 Integrity of diamond system through exhumation

Section 7.3 Processes of exhumation

Section 7.3.1 Mantle Plumes and plume-instigated kimberlite magmatism

Section 7.3.2 Entrainment into mantle convection and kimberlite magmatism

Section 7.3.3 Superkimberlites

Section 7.3.4 Rate of exhumation

Chapter 8 Summary and Conclusions

 

Chapter 9 Suggestions for further work

 

References

Appendices

Appendix 1 Inclusion breakout

Appendix 1.1 Apparatus and Methodology

Appendix 1.2 Summary of visual observations on diamonds BZ215 - BZ272, JH7 - JH17 and GU4 with details of breakage where applicable

Appendix 2 Summary of EPMA study and inclusion release from São Luiz diamonds for the present study including Guinean inclusions and unbroken stones assigned BZ- numbers

Appendix 3 Major and minor element compositions of inclusions

Appendix 3.1 Single point electron microprobe analyses

Appendix 3.2 Averaged electron microprobe analyses including cation concentrations

Appendix 4 Trace element compositions of inclusions

Appendix 4.1 Ion Microprobe analyses

Appendix 4.2 Averaged Chondrite Normalised Ion Microprobe Analyses

Appendix 5 Ion Microprobe analyses of d 13C and nitrogen content of polished slabs, BZ251, BZ252, BZ254 and BZ255

Appendix 6 Fourier Transform Infra Red (FTIR) analyses of São Luiz and Guinean diamond

Appendix 6.1 One phonon region of FTIR spectra

Appendix 6.2 Tabulation of results of deconvolution of FTIR spectra

Appendix 7 Compositional analyses of bulk diamond

Appendix 8 Electron probe principles and calculations

Appendix 9 Ion microprobe operating conditions and calculations

Appendix 9.1 Analysis of diamond inclusions for trace elements

Appendix 9.2 Analysis of diamond flats for d 13C and N

Appendix 10 X-Ray theory and operating conditions employed

Appendix 11 Gas extraction and the determination of bulk d 13C and d 15N composition of diamond

Appendix 12 Database of experiments aimed at elucidating the state of the deep mantle

Appendix 13 Thermoelastic properties of mantle mineral phases

Appendix 14 Seismologically based models of the mantle and PREM

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