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Master Thesis, Natural History Museum Columbite-tantalite and garnet geochemistry in Evje-Iveland, South Norway Mats Lund Columbite-tantalite and garnet geochemistry in Evje-Iveland, South Norway Mats Lund Master Thesis in Geosciences Discipline: Geology and mineralogy Department of Geosciences and Natural History Museum Faculty of Mathematics and Natural Sciences University of Oslo 1 February 2016 © Mats Lund, 2016 Supervisors: Associate prof. Rune Snæring Selbekk, Henrik Friis and prof. Tom Andersen Cover image: A road cut at Iveland showing white pegmatite lenses hosted in dark grey amphibolite. This work is published digitally through DUO – Digitale Utgivelser ved UiO http://www.duo.uio.no It is also catalogued in BIBSYS (http://www.bibsys.no/english) All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Acknowledgements It still feels somewhat weird to have finished five years of geoscience-related studies at the University of Oslo. It has been a blast! I want to thank my main supervisor Rune Selbekk for allowing me to be his student during these two years. I especially loved our trips to Asylet together with other personnel from the museum to drink beer and talk crap. A sincere thank you goes to my co-supervisors Henrik Friis and Tom Andersen. Both Henrik and Tom’s positive attitude for helping me along with understanding both physical and chemical data will be remembered. I still do not understand how I managed to transcribe Tom’s handwriting, but I understood the context nevertheless. Your intense analysis of what I had written and what I had to fix is extraordinary, and it made me rewrite whole paragraphs and chapters. I am so glad for it, because it helped a ton! Many hours have been spent waiting for thin sections and epoxy mounts produced by Salahalldin Akhavan, which have been used extensively throughout the study. It has been really helpful, and I appreciate the time used to make them. I want to thank Siri Simonsen and Muriel Erambert for their help with both data acquisition and interpretation. It is hard to do this kind of analytical studies for the first time without having some kind of help as you go along. Honorable mentions must go to the local enthusiasts in the Iveland municipality. Kjell Gunnulfsen, Andreas Corneliussen and Arild Omstad for help with sampling, accessing the localities, and general banter on our time off during the field excursions. I also want to direct my thanks to all the support from people at the museum and at the study room floor in the ZEB building. Last but not least, I want to thank my family and friends for moral and material support during this period. Kjetil Stokkeland has been my partner in crime for the last two years. We’ve shared office space for at least a year together, and I have now proof that he is extremely weird. Then again, it takes one to know one. Thank you, mom and dad for allowing me to eat all your food, drink your beer and to give me some time off from the writing process. My brother, for general banter and support during downtime. My friends near and far, Norwegians and internationals, I want to thank you for the good times and the brotherhood we had. Now I can go back to become a social being again. Abstract A mixed NYF+LCT pegmatite field is located in Evje-Iveland, South Norway. The pegmatites are hosted in amphibolites and gneisses formed during the Sveconorwegian Orogeny. They vary in fractionation from low to well-fractionated systems, and they identify as rare- element REE and muscovite rare-element REE classes. Little is understood of how columbite-tantalite minerals form in this particular pegmatite field, as most work done have been on garnet and high-purity quartz. A study of a well-fractionated muscovite rare- element REE, mixed NYF+LCT pegmatite at Solås were done to better understand the development of the dike and distribution of minerals present. The pegmatite was also intended to be used as a staging point to understand columbite-tantalite paragenesis, as Solås is one of the best fractionated systems present in Evje-Iveland. Sadly, no columbite were recovered and only tantalite-(Mn) from a cleavelandite pod were found. Columbites from all over Evje-Iveland were studied collectively, and were found to follow a fluorine- poor trend. Columbite-tantalite from cleavelandite zones follow a fluorine-rich trend, even if no fluorine minerals have been reported. Fluorine influence the solubility and transportation of high-field strength elements as a flux, but not as a transporting agent. Columbite-(Fe) and columbite-(Mn) minerals form in the wall zone towards the intermediate zone, while Ta-rich columbite-(Mn) occur together with tantalite-(Mn) in cleavelandite zones. Older studies and a few field observations show that columbite-(Fe) may form with REE-oxides like polycrase-(Y) and euxenite-(Y), but after the oxides have crystallized. This is dependent on the amount of REE and Y present in the pegmatite magma and may vary from pegmatite to pegmatite. More fractionated columbite-(Mn) may form solitary crystals in the intermediate zone with no other minerals forming around it, as is the case at the Hovåsen pegmatite. Garnet data were used as a fractionation trend tool together with columbite-tantalite data to better understand how the pegmatite systems in Evje-Iveland formed. The almandine-spessartine variant of garnet contains up to 2 wt% Y2O3 in some pegmatites, while spessartines formed in the cleavelandite zone are Mn-rich, but almost no Y or REE are present. A slight increase in Na are observed with high-Y content, but no good correlation could be made for the substitution of these elements into the garnet structure. Table of contents 1. INTRODUCTION ..................................................................................................................... 1 1.1 WHAT IS A PEGMATITE? .......................................................................................................... 2 1.2 REGIONAL GEOLOGY ............................................................................................................... 4 1.2.1 The Setesdal Region and the Evje-Iveland pegmatite field .......................... 6 1.2.2 The Solås pegmatite ............................................................................................... 9 2. METHODS ............................................................................................................................... 10 3. RESULTS ................................................................................................................................. 13 3.1 FIELD OBSERVATIONS IN THE SOLÅS PEGMATITE .................................................................. 13 3.2 DESCRIPTIONS OF INDIVIDUAL MINERALS FROM SOLÅS ........................................................ 27 3.3 COLUMBITE-TANTALITE MINERAL CHEMISTRY...................................................................... 33 3.4 GARNET MINERAL CHEMISTRY .............................................................................................. 49 4. DISCUSSION ........................................................................................................................... 67 4.1 SOLÅS PEGMATITE EVOLUTION ............................................................................................. 67 4.2 COLUMBITE-TANTALITE PARAGENESIS IN EVJE-IVELAND ..................................................... 71 4.3 GARNET CHEMISTRY ............................................................................................................. 80 5. CONCLUSION ........................................................................................................................ 91 6. FUTURE WORK ..................................................................................................................... 93 7. REFERENCES ........................................................................................................................ 94 8. APPENDIX............................................................................................................................. 102 8.1 APPENDIX 1: SAMPLE DESCRIPTION ..................................................................................... 102 8.2 APPENDIX 2: COLUMBITE-TANTALITE DATA ....................................................................... 104 8.3 APPENDIX 3: EUXENITE-(Y) DATA ...................................................................................... 121 8.4 APPENDIX 4: GARNET DATA ................................................................................................ 122 1. Introduction Figure 1: A map of South Norway. Evje-Iveland is located in the Aust-Agder county 40 km north of Kristiandsand. There have been few studies on the mineralogy of the Evje-Iveland pegmatites in modern times except for garnet and high-purity quartz (figure 1) (Larsen et al, 2000; Müller et al, 2009, 2012, 2015; Snook, 2014). The aim is to determine the paragenesis of the columbite- tantalite mineral group in the Evje-Iveland pegmatite field. The paragenesis can provide insight to how high-field strength elements behave in granitic pegmatite melts made from hydrous fractional crystallization. It will be interesting to see how columbite-tantalite minerals form in the whole field, as it has not been thoroughly studied before in Evje- Iveland. Correlation of data with other studies can provide information about physical and chemical differences

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