Petrography, geochemistry and stable isotope characteristics of the Navachab gold deposit, Namibia [Elektronische Ressource] / vorgelegt von Katharina Wulff

Kwulff

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2008
• Nombre de lectures: 54
• Langue: English
• Poids de l'ouvrage: 26 Mo

Extrait

Petrography, geochemistry and stable isotope characteristics of
the Navachab gold deposit, Namibia


Von der Fakultät für Georessourcen und Materialtechnik der
Rheinisch -Westfälischen Technischen Hochschule Aachen

zur Erlangung des akademischen Grades einer


Doktorin der Naturwissenschaften
genehmigte Dissertation

vorgelegt von Diplom-Geologin

Katharina Wulff
aus Hamburg


Berichter: Univ.-Prof. Dr. rer. nat. Franz Michael Meyer
Univ.-Prof. Dr. rer. nat. Ulrich Kramm

Tag der mündlichen Prüfung: 19. Juni 2008



Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar




Foreword


This project was initiated at the Institute of Mineralogy and Economic Geology at RWTH Aachen
University in co-operation with Prof. A. Kisters, Stellenbosch University and Navachab Gold Mine. It was
granted by the DFG (Deutsche Forschungsgemeinschaft; grant ME1425/13-1) and by RWTH Aachen
University. Sample shipment and accommodation during field work were provided by Navachab Gold
Mine.

I want to thank Prof. F.M. Meyer for the placing and supervision of this interesting project and for his
worthy contributions and comments. Dr. Annika Dziggel and Dr. Jochen Kolb I thank for their patient
guidance and supervision and for many helpful discussions. In case of need, I always found in you
committed persons to turn to.

I wish to thank the people at Navachab Gold Mine (AngloGoldAshanti), especially Frik Badenhorst,
Juanita Badenhorst and Herbert Roesener, for their support in all matters of need during field work and
for accommodation and hospitality. I also thank Nick Steven (Rockwater Consulting) for his support and
advice in many occasions and for useful discussions and comments. The commitment of you all
contributed decisively to field work becoming a success.

Prof. Torsten Vennemann from the Institute of Mineralogy and Geochemistry at the University of
Lausanne is thanked for the co-operation during stable isotope analysis and for many worthy and
encouraging comments on stable isotope geochemistry. I thank Dr. Benita Putlitz for introducing me into
the use of the laser line and for help and advice during stable isotope analyses.
Dr. Michael Böttcher from the Max Planck Institute for Marine Microbiology, Bremen, carried out the
sulphur isotope analyses.

Thanks to the technical staff at the Institute of Mineralogy and Economic Geology at RWTH Aachen
University: Thomas Derichs (preparation of the thin sections and polished sections), Dr. Sven Sindern
(XRF analyses), Roman Klinghardt (Electron Microprobe), Mario Kittel and Mona Schmidt (Student
Assistants), Monika Wiechert (Photography Laboratory).

Finally I want to thank my mates at the IML, especially Alexander Otto, Markus Lögering, Laila Sharif and
André Hellmann for many helpful discussions and for their company during all the time.














Contents


Abstract V
Zusammenfassung IX

1. Introduction………………………………………………………………………….. 1
1.1 Gold deposits in orogenic belts…………………………………………………... 1
1.2 The Navachab gold deposit………………………………………………………. 1
1.3 Objectives………………………………………………………………………….... 2
1.4 Methods……………………………………………………………………….……... 2


2. Regional Geology…………………………………………………………………... 5
2.1 The Damara Orogen……………………………………………………………….. 5
2.2 The Central Zone of the Damara Orogen…………………………………….….. 6
2.3 Geology of the Navachab gold deposit…………………………………………... 9
2.4 Genetic models of the Navachab gold deposit………………………………….. 13


3. Structural Geology…………………………………………………………………. 15
3.1 Host rocks………………………………………………………………………….... 15
3.2 Intrusive rocks………………………………………………………………………. 16
3.3 Structural geology of the gold mineralisation…………………………………..... 16
3.3.1 Massive sulphide lenses……………………………………………………….... 16
3.3.2 Qtz sulphide veins………………………………………………………………... 19
3.4 Contacts between major rock units…………………………………………….. 22
3.5 Later faults…………………………………………………………………………... 22


4. Petrography………………………………………………………………………….. 23
4.1 Host rocks…………………………………………………………………………… 23
4.1.1 Spes Bona Formation……………………………………………………………. 23
4.1.2 Okawayo Formation……………………………………………………………… 24
4.1.3 Oberwasser Formation…………………………………………………………... 27
4.2 Intrusive rocks………………………………………………………………………. 28
4.2.1 Metalamprophyre…………………………………………………………….…… 28
4.2.2 Pegmatite dykes………………………………………………………………….. 28
4.2.3 Aplite dykes……………………………………………………………………….. 29
4.3 Gold mineralisation and alteration……………………………………………….. 29
4.3.1 Qtz sulphide veins………………………………………………………………... 29
4.3.2 Alteration around veins…………………………………………………………... 33
I
4.3.3 Massive sulphide lenses…………………………………………………………. 42
4.3.4 Alteration around massive sulphide lenses……………………………………. 47
4.3.5 Ore petrography…………………………………………………………………... 51
4.4 Retrogression……………………………………………………………………….. 54
4.5 Thermobarometry…………………………………………………………………... 54
4.5.1 Temperature conditions during mineralisation……………………………….... 55
4.6 Summary…………………………………………………………………………….. 55


5. Fluid Inclusions……………………………………………………………………... 59
5.1 Petrography…………………………………………………………………………. 59
5.2 Microthermometry…………………………………………………………………... 61
5.3 Interpretation…………………………………………………………………........... 62
5.4 Summary………………………………………………………………………......... 63


6. Geochemistry………………………………………………………………………... 65
6.1 Host rocks…………………………………………………………………………… 65
6.1.1 Bt-schists…………………………………..……………………………………… 65
6.1.2 MC unit…………………………………………………………………………….. 67
6.1.3 Grey Banded Marble……………………………………………………….......... 68
6.1.4 Breccia Marble……………………………………………………………………. 69
6.2 Intrusive rocks………………………………………………………………………. 70
6.2.1 Pegmatite and Aplite dykes……………………………………………………… 70
6.2.2 Metalamprophyre…………………………………………………………………. 72
6.3 Alteration and gold mineralisation……………………………………………...… 72
6.3.1 Bt-schists………………………………………………………………………….. 72
6.3.2 Grey Banded Marble……………………………………………………………... 74
6.3.3 Breccia Marble……………………………………………………………………. 75
6.3.4 MC unit…………………………………………………………………………….. 76
6.3.5 Qtz sulphide veins……………………………………………………………..…. 80
6.3.6 Correlations between gold and other elements……………………………..… 81
6.4 Mass balance calculations……………………………………………………….... 82
6.4.1 The Gresens approach…………………………………………………………... 82
6.4.2 Immobile elements……………………………………………………………….. 84
6.4.3 Results…………………………………………………………………………….. 84
6.5 Summary…………………………………………………………………………….. 85


7. Stable Isotopes…………………………………………………………………….... 91
7.1 O-, C- and H-isotopes…………………………………………………………….... 91
7.1.1 Host rocks………………………………………………………………………..... 91
II

7.1.2 Magmatic rocks………………………………………………………………….... 93
7.1.3 Mineralisation and alteration…………………………………………………….. 94
7.1.4 Modelling isotopic variations in the carbonates……………………………….. 98
7.1.5 Ore fluid composition…………………………………………………………...... 102
7.2 S-isotopes……………………………………………………………………..…….. 106
7.3 Summary…………………………………………………………………………….. 107


8. Discussion…………………………………………………………………………… 109
8.1 Pre-metamorphic evolution………………………………………………………... 109
8.2 Damaran Orogeny………………………………………………………………...... 109
8.3 Gold mineralisation………………………………………………………………..... 110
8.3.1 Formation of the massive sulphide lenses………………………………...…... 110
8.3.2 Formation of the Qtz sulphide veins……………………………………………. 111
8.3.3 Fluid composition……………………………………………………………….... 113
8.3.4 Fluid origin………………………………………………………………………… 113
8.3.5 Transport and precipitation……………………………………………...…….… 116
8.3.6 Alteration……………………………………………………………………….….. 117
8.4 Suggested genetic model for the Navachab gold deposit…………………….... 119


9. References…………………………………………………………………………… 121


10. Appendices…………………………………………………………………………. 129
10.1 Mineral abbreviations……………………………………………………………... 129
10.2 Samples and sections…………………………………………………………….. 129
10.3 Structural measurements………………………………………………………… 132
10.4 Mineral chemistry………………………………………………………………….. 137
10.4.1 Mineral chemistry of the Bt-schists of the Oberwasser and Spes Bona
Formations………………………………………………………….................... 137
10.4.2 Mineral chemistry of the calcsilicate rocks of the MC unit………………...... 143
10.4.3 Mineral chemistry of the Grey Banded Marble……………………………..... 153
10.4.4 Mineral chemistry of the Breccia Marble……………………………………… 161
10.4.5 Mineral chemistry of the Qtz sulphide veins (silicate minerals)……………. 162
10.4.6 Ore mineral chemistry………………………………………………………….. 163
10.4.7Mineral chemistry of the Metalamprophyre…………………………………… 166
10.5 Fluid inclusions…………………………………………………………………….. 169
10.6 Geochemistry…………………………