An experimental study on the behaviour of copper and other trace elements in magmatic systems [Elektronische Ressource] / vorgelegt von Patrick Were

Were

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2007
• Nombre de lectures: 9
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

An experimental study on the behaviour of
copper and other trace elements in
magmatic systems




Dissertatation
zur Erlangung des Grades eines Doktors der Naturwissenschaften






der Geowissenschaftlichen Fakultät
der Eberhard-Karls-Universität Tübingen















vorgelegt von
Patrick Were
aus Jinja (Uganda)


2007



2
Thesis jury









































Tag der mündlichen Prüfung: 14. Mai 2007

Dekan: Prof. Dr. Peter Grathwohl

1. Berichterstatter: Prof. Dr. Hans Keppler

2. Berichterstatter: Prof. Dr. Dr.h.c. Muharrem Satir

3


Acknowledgements

I would like to thank my in-laws, Mr. and Mrs. Higwira for keeping my family during
the period I have been abroad. I am indeed grateful for their support, patience and
understanding.
Funding of this research was provided by DFG grant Gottfried Wilhelm Leibniz-Preis
2001 to Professor Dr. Hans Keppler. I am very grateful to him for having given me
the chance to do my Ph.D research work, benefiting from his grant. As my
supervisor, he carefully read through the entire dissertation and made many
suggestions for its improvement, in matters of substance as well as style. I am
grateful for his generous effort on his part, but any remaining errors are of course
mine.
Professor Dr. Muharrem Satir opened my eyes as regards to the use of stable and
radioactive isotopes in geochemistry. I would also like to thank him for the moral
support and advice he often offered me whenever I had difficulties of any kind.
I should like to extend my thanks to the entire academic staff of the Institute of
Mineralogy at the University of Tübingen for their endeavours in teaching me the
theory and practical aspects necessary for safe use of experimental and analytical
equipment. Dr. Thomas Wenzel, the chief of the Microprobe laboratory, helped me a
great deal with the chemical analysis of samples using the Electron microprobe.
Andreas Audetat, then a post-graduate and head of our research team, helped me a
great deal with the calculations necessary for the preparation of the starting glasses
and mixtures for my experiments.
The technical team at the Bayerisches Geoinstitut, particularly Mr. Detlef and Anke,
also deserve many thanks. They helped me to get some analytical results of my
problematic samples using Electron microprobe.
I would also like to thank the workshop staff, particularly the Meister, Mr. Walker, and
Barbara, for the care and maintenance of the experimental and analytical equipment,
and Mrs. Gill-Kopp, for fine polishing of my samples.
Finally I would like to thank my family for all their love and prayers. i
Table of Contents

Abstract (1)

Zusammenfassung (5)

1. MAGMATIC-HYDROTHERMAL DEPOSITS (9)

1.1. Basic concepts (9)

1.2. Sources of metals in magmas (10)

1.3. Sources of a magmatic aqueous phase (12)

1.4. Composition and characteristics of magmatic-hydrothermal solutions (18)

1.5. Pegmatites and their significance to granite-related ore-forming processes (22)

1.6. Fluid-melt trace element partitioning (23)

1.7. Water content and depth of emplacement of granites and their
relationships to ore-forming processes (29)

1.8. Models for the formation of porphyry-type Cu, Mo and W deposits (31)

1.8.1. The origin of porphyry Cu-(Mo) and porphyry Mo-(Cu) type deposits (31)

1.8.2. The origin of porphyry W-type deposits (33)

1.9. Fluid flow in and around the granite plutons (34)

1.10. Skarn deposits (36)

1.11. Near-surface magmatic-hydrothermal processes, the “epithermal”
family of Au-Ag-(Cu) deposits (40)

1.12. Conclusion (42)

2. DISTRIBUTION OF TRACE ELEMENTS BETWEEN BIOTITE
AND HYDROUS GRANITIC MELT (44)

2.1. Aims (44)

2.2. Experimental methods (46)
ii
2.2.1. High-pressure equipment (47)

2.2.2. Starting materials and preparation of capsules (52)

2.2.2.1. Starting materials (52)

2.2.2.2. Charge preparation (57)

2.2.3. Investigation of run products (58)

2.2.3.1. Phase identification (58)

2.2.3.2. Reflected light microscopy (58)
2.2.3.3. X-ray powder diffractometry (59)

2.2.3.4. Electron microprobe analysis (EMPA) (61)

2.2.3.5. Raman spectroscopy (62)

2.3. Experimental results (63)

2.3.1. Phase assemblages (63)
2.3.1.1. Biotite (63)

2.3.1.2. Allanite (66)

2.3.1.3. Amphibole (67)

2.3.1.4. Pyroxene (68)

2.3.1.5. Feldspars (69)
2.3.1.6. Magnetite (70)

2.3.2. Trace elements partitioning between biotite and melt (76)

2.3.2.1. Transition metals, alkali & alkaline earth elements (83)
2.3.2.2. Rare earth elements in biotite (86)

2.3.2.3. Discussion of Brice model (lattice strain theory) (91)

2.3.3. Trace elements partitioning between Allanite and melt (93)

2.3.3.1. Alkali earth elements in allanite (95)

2.3.3.2. Rare earth elements in allanite (96)

2.4. Geological implications of the partitioning data (97) iii

2.4.1. Crystallisation and fractionation as an ore-forming process (97)
2.4.1.1. Batch crystallisation of biotite (97)

2.4.1.2. Enrichment/depletion of ore-metals in the residual melts (97)
2.4.1.3. Enrichment/depletion of REEs in the residual melts (98)
2.4.1.4. Batch crystallisation of allanite (99)
2.4.1.5. Fractional crystallisation of biotite (101)
2.4.1.6. Enrichment/depletion of ore-metals in the residual melts (101)
2.4.1.7. Enrichment/depletion of REEs in the residual melts (102)
2.4.1.8. Fractional crystallisation of allanite (103)

3. SPECIATION AND OXIDATION STATE OF COPPER IN SILICATE
MELTS (105)

3.1. Aims (105)

3.2. Experimental methods (107)

3.2.1. Sample synthesis (107)

3.2.1.1. Starting materials and preparation of glass samples (107)

3.2.1.2. Chemical composition of samples (108)

3.2.1.3. Determination of density of silicate melts (109)

2+3.2.1.4. Preparation of standards for Cu in glasses (112)

3.2.1.5. Gas mixing furnaces (114)

3.2.1.6. The technique (114)

3.2.1.7. Measures to avoid explosion hazards (118)

3.2.2. Optical spectrometry (119)

3.2.2.1. Spectrometer

3.2.2.2. Optical absorption measurements (120)

3.3. Results and Discussion (122)
iv
2+3.3.1. ε, the extinction coefficient, ε, of Cu (127)

3.3.2. Oxidation state of copper in silicate melts (128)

3.4. Thermodynamic data analysis (139)

3.5. Geological implications (142)

2+ 1+ 3.5.1. Cu /Cu ratio in granite and diorite melts (142)

2+ 1+ 3.5.2. Cu /Cu ratio in basaltic (tholeiite & alkalibasalt) melts (143)

2+ 1+ 3.5.3. Implications of Cu /Cu ratio for mineral-melt partitioning (145)

4. SOLUBILITY OF COPPER IN ROCK-FORMING MINERALS (146)

4.1. Aims (146)

4.2. Sample synthesis (148)

4.2.1. Starting materials and sample preparation (148)

4.2.2. Charge preparation (151)

4.2.3. Experimental techniques (151)

4.2.4. Investigation of run products (152)

4.3. Results and Discussion (153)

4.3.1. Copper solubility in orthoclase (153)

4.3.2. solubility in albite (157)

4.3.3. Copper solubility in muscovite (159)

4.3.4. solubility in phlogopite (161)

4.3.5. Copper solubility in silica (Qtz) (162)

4.4. Outlook (165)
5. REFERENCES (166)
6. Appendices (175)
1. Calculation of NBO (175)
2. Oxygen pressure in standard capsules (177)
3. EMPA in biotite and residual melt at 800°C and 2 kbar (178)

Erklärung (192)
v
LIST OF FIGURES

Fig. 1.1. Magma genesis (divergent- and convergent-margin settings (1