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
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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
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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 between several pegmatite fields. Garnets are local sources of information to better understand the partial crystallization trends of different granitic
pegmatite systems found in a pegmatite field. This is due to the major element fractionation that occur in garnets during fractional crystallization of pegmatite melts. It will be interesting to see the fractionation correlation between garnet and columbite-tantalite minerals, because
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they form in the same granite pegmatite systems and they both have fractionation paths related to their major element chemistry. Detailed mapping of a well-evolved pegmatite at Solås was performed to provide information of in-situ mineral assemblages, and to better understand columbite-tantalite and garnet genesis. Substitution schemes of high-field strength elements and lanthanoids can provide information regarding development of these minerals in the Evje-Iveland pegmatite field.
1.1 What is a pegmatite?
Figure 2: A cut granite slab hosting a pegmatite vein located at the University of Oslo.
Pegmatites are coarse-grained holocrystalline igneous rocks with mineral grain sizes over 2.5 cm forming during the last stage of a crystallizing magma (figure 2). These rocks are known to carry high concentrations of rare-elements, industrial minerals and gemstones (London, 2008). The pegmatites variable mineralogy depending on their mode of origin, and can have a sub-, met-, peraluminous or peralkaline compositions (London, 2008). The formation of a pegmatite is attributed to two modes of origin. Firstly, a pegmatite can form by hydrothermal fluid solution by differentiating from a parental magma during the last stages of
crystallization. Secondly, a pegmatite may also form directly as a product of partial melting
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(anataxis) of crustal material (London, 2008). Both of these origins can carry very different chemical signatures due to the available and assimilated elements.
Classification of pegmatites is based on geological and geochemical characteristics that are applied to a specific set of classes, subclasses, types and subtypes. The most used chart today is the revised pegmatite classification chart by Cerný & Ercit, (2005) based on the original from Ginsburg & Rodionov, (1960). The rare-element class (REL) is the most important class in this chart. Pegmatites are also separated into a set of geochemical families (Cerný, 1991a; Cerný & Ercit, 2005). The niobium-yttrium-fluorine family contain abundant Nb, Y, rare-earth elements (REE), Sc, Ti and U, while the lithium-cesium-tantalum family contain Li, Be, Sn, Rb, Cs and Ta. The mixed NYF+LCT family consist of primary NYF-type mineralogy contaminated by LCT-characteristic mineral assemblages (Cerný, 1991a, 1991b;
Cerný & Ercit, 2005). Typically, differentiated pegmatite magma assimilate some
characteristics from active partial melting of a host rock, such as can be seen in sedimentary- derived granites (S-type) that host primary LCT-mineralogy (Chapell & White, 2001;
London, 2008). Pegmatites of anorogenic (A-type) or igneous-derived (I-type) origins formed directly from partial melting of a host rock usually have a more primitive niobium- yttrium-fluorine (NYF) signature, which may be contaminated by LCT-characteristic mineralogy (Whalen et al, 1987; Cerny et al, 1991a; Chapell & White, 2001; Cerný & Ercit, 2005). These types of pegmatites can be studied and classified by using regional geology, mineralogy and geochemical analysis to determine how they formed (Cerný & Ercit, 2005).
Rare-element pegmatites are separated into two different classes: The muscovite rare- element (MSREL) and rare-element pegmatites. These types form in anorogenic
environments related to NYF-type magmatism in extensional orogenic settings (Martin & De Vito, 2005; London, 2008; Thomas et al, 2012). MS-REL is a pegmatite class that combine economic amounts of mica with rare-element enrichments. REL-class pegmatites are
enriched in rare-elements, which can be further divided into a set of subclasses depending on the geochemistry of the pegmatite melt (Cerný & Ercit, 2005). Rare-element pegmatites are related to both modes of origin, but the content of these pegmatites may differ due to emplacement settings. The rare-element class pegmatites are some of the most well-known and extensively studied rock types in igneous petrology because of their economic
importance (Cerný, 1991a; Cerný & Ercit, 2005).
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Pegmatites can be either unzoned or zoned depending on their origins (London, 2008). The unzoned pegmatites are more or less mineralogical homogenous and it may include oriented mineral textures. They are usually found in high-grade metamorphic suites (London, 2008).
The zoned pegmatites however are quite distinct in how they crystallized, as each zone contains certain textures and minerals that may or may not be found in the other zones. A zoned pegmatite can contain a border, wall, intermediate and core zones as defined
originally by Cameron et al, (1949) (London, 2008). The border zone is the outermost shell against the host rock. It is a thin zone of granitic intergrowth with crystal sizes around 2-5 mm, but no special mineralization of note. This border zone ends abruptly after a few cm where the grain sizes gets larger, and marks the transition to the wall zone (London, 2008).
The wall zone is one of the larger zones in a pegmatite and can be distinguished by the graphic granite and skeletal growth of feldspar/quartz textures. The structure of the zone is like the border zone only with larger grain sizes, and the addition of minor accessory minerals. It is accompanied by minerals like tourmaline, micas and beryl that may have an orientation towards the core of the pegmatite (London, 2008). Pegmatites can have several intermediate zones. These zones are dependent on a mineral phase that is very prevalent, and the grain sizes of the minerals in these zones can up to meter-scale. Zonation like this can be variable in the sense that it may contain lenses and small irregular zones with specific
mineralization, which in turn are a part of a major zone in the pegmatite. The core consists of megacrystic quartz and feldspar that can reach several meters in size, but some pegmatites might have other mineral species that reflect pegmatite affinity (London, 2008).
1.2 Regional geology
The geology of southwestern Norway (figure 3) is a result of large scale tectonic phases that occurred during the Mesoproterozoic era (1600-1000 Ma). These phases are related to the orogenic processes of the Gothian (1750 – 1500 Ma) and Sveconorwegian (1140 – 900 Ma) orogenies that occurred in the latter part of the era (Gaál & Gorbatschev, 1987; Bingen et al, 2008a). The Sveconorwegian orogeny is the most recent orogenic event in the Southwestern Scandinavian Domain (SSD) and is the most influential. The orogeny is characterized by
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extensive metamorphism, magmatism and emplacement of small amounts of crust in the southwestern part of the Fennoscandian shield (Andersen, 2005; Bingen et al, 2008a).
Figure 3: A map of the Southern Scandinavian Domain (SSD). a) The regional scale blocks of south Norway: H-R – Hardangervidda-Rogaland, T – Telemark, B-L – Bamble-Lillesand, K-M – Kongsberg-Marstrand and R-L – Randsfjord-Lygnern. Other: O – Oslo Rift, SNF – Sveconorwegian Front, TIB – Transscandinavian Igneous Belt, MUL – Mandal-Ustaoset Lineament and KBSZ Kristiandsand-Bagn Shear Zone (Taken from Pedersen et al, 2009)
The proterozoic basement in southwestern Norway consist of metamorphosed late paleoproterozoic to early mesoproterozoic and late mesoproterozoic rocks with small
additions of material from the Sveconorwegian orogen (Andersen, 2005; Bingen et al, 2005).
The Southwestern Scandinavian Domain consist of several large lithotectonic blocks, which constrain Sveconorwegian events by exposed regional faults and lineaments. The Telemark block is limited by the Mandal-Ustaoset Lineament to the west and the Porsgrunn-
Kristiansand Fault Zone to the east (figure 3).
The Sveconorwegian orogen (SNO) started around 1220 Ma with the closing of an oceanic basin by eastwards subduction between the continent of Laurentia and Fennoscandia (Bingen et al, 2008a). This started a sequence of four distinct phases that encompass the main events
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of the SNO. Initially, the Arendal phase (1140-1080 Ma) marked an early continent- continent collision between Laurentia and Fennoscandia. The Agder phase (1050-980 Ma) recorded the main Sveconorwegian event that were caused as an oblique collision event between Laurentia/Fennoscandia and an exotic continental fragment. The Falkenberg (980 – 970 Ma) and Dalane phases (970 – 900 Ma) culminated the peak collision and subsequent gravitational relaxation of the orogeny (Bingen et al, 2008a).
1.2.1 The Setesdal Region and the Evje-Iveland pegmatite field
Figure 4: Geological map over pegmatite occurrences in South Norway. Evje-Iveland pegmatites are found to the west of the Porsgrunn-Kristiansand Fault Zone that separates the Telemark and Bamble-Lillesand blocks (Taken from Müller et al, 2015)
The basement rocks in Setesdal have been overlain by supracrustal metavolcanics and metasediments, underwent regional metamorphism and finally were intruded by anorogenic
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mafic and felsic igneous rocks and pegmatites (Pedersen & Konnerup-Madsen, 2000;
Pedersen et al, 2009). The basement rocks consist of mostly mafic banded gneisses in upper amphibolite-lower granulite facies. These basement gneisses make up the Iveland-
Gautedstad Metagabbro Complex (IGMC), which host many of the rare-metal REE-bearing pegmatites of Evje-Iveland (figure 4) (Pedersen, 1981; Pedersen & Konnerup-Madsen, 2000;
Larsen, 2002).
Magmatism in the Setesdal region occurred in two major pulses. The first one created the protolith for the Fennefoss augen gneiss, Evje-amphibolite and Flåt ”ore”-diorite (Barth, 1947; Pedersen & Konnerup-Madsen, 2000). The latter pulse were responsible for several stages of granitoid intrusions in which the Høvringsvatnet complex were a major part of (figure 4). The magmatism was caused by post-orogenic gravitational stresses during the last part of the Dalane phase (Bingen et al, 2006; Bingen et al, 2008a). The Høvringsvatnet granite (980 +/- 4 Ma) host many pegmatite dikes (910 +/- 14 Ma) in northern Iveland, but it cannot be the parental pluton for the main IGMC-hosted pegmatites since the pegmatites are approx 70 Ma younger (Pedersen & Konnerup-Madsen, 2000; Scherer et al, 2001; Snook, 2014). It is more likely that the pegmatites are related to crustal underplating and partial melting of the dense mafic rocks that make up the IGMC (Snook, 2014)
The Evje-Iveland pegmatite field
The Evje-Iveland pegmatite field is a large area in southern Norway covering roughly 10 km E-W and 30 km N-S in Setesdal, Telemark domain (figure 4) (Pedersen & Konnerup-
Madsen, 2000; Müller et al, 2015). The pegmatites hosted in banded gneisses and IGMC- amphibolite are found as flow structures in the rock, which were formed in the last stages of the Dalane phase at the end of the SNO (Larsen et al, 2004; Bingen et al, 2008a). The region was experiencing extensional stresses related to upwelling of hot mantle magma in the Rogaland – Vest-Agder region (930-920 +/- 3 Ma) (Schärer et al, 1996; Bingen & van Breemen, 1998; Bingen & Stein, 2003; Andersen, 2005; Bingen et al, 2006). Bingen et al, (2008a) refer to the gravitational collapse of the Sveconorwegian orogeny in the Dalane phase as related to extensional tectonics. It is assumed that this mantle thinning of the crust
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is one of the main heat sources for partial melting of the IGMC to produce the pegmatites found in Setesdal (figure 5).
Figure 5: A schematic of late magmatism and potential underplating in Evje-Iveland and Froland near the Porsgrunn-Kristiansand Fault Zone. The Iveland pegmatites are not related to the Høvringsvatnet granite (Taken from Müller et al, 2015)
There are 400 - 600 known pegmatite dikes, mines and quarries in Setesdal (Müller et al, 2012, 2015). A feldspar and quartz-mining industry thrived in this area over many years, but now most of the old mines are overgrown, neglected and submerged in water. The
pegmatites generally strike towards NNE-SSW, and they are hosted as leucosome dikes in the dark grey colored IGMC-amphibolite (Bjørlykke, 1935, 1937; Larsen et al, 2004;
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Pedersen et al, 2009; Snook, 2014). They are classified as mainly MSREL-REE and REL- REE pegmatites due to their extensive rare-element mineral assemblage (Cerný & Ercit, 2005; Snook; 2014; Müller et al, 2015). They are further separated into subclasses and types appropriate of the local mineral assemblage, where most fall under either the euxenite or gadolinite-subtype (with minor amounts of the allanite-monazite subtype). The original pegmatite magma affinity in Evje-Iveland was of the NYF-type with almost negligible amounts of F in the system. Furthermore, the Evje-Iveland pegmatite signature is that of mixed NYF+LCT origins due to local LCT-contamination by assimilation of the surrounding supracrustal rocks. The pegmatites follow the zonation scheme described by London, (2008), which have developed border, wall, intermediate and core zones, and some of them also carry late-stage cleavelandite pods indicative of well-fractionated systems (Bjørlykke, 1935;
Frigstad, 1984; London, 2008).
1.2.2 The Solås pegmatite
Solås is a small hill located roughly 4km north of Iveland church (figure 4). It is home to a 200 m long, and 5 m thick tabular MSREL-REE, allanite-monazite subtype pegmatite dike that strike roughly N-S at the eastern part of the hill Meråsen, and it dips roughly 20° NW (Frigstad, 1984; Snook, 2014). A secondary conformable pegmatite lies approximately 10m above the Solås pegmatite (Snook, 2014). The pegmatite is fairly well exposed, especially where the main mine (Solås) has been excavated, and it is hosted in amphibolite
(metagabbro) in the IGMC-field. The contact in the border is sharp. The southern part of the pegmatite ends just before a decline into a large swamp, and the northern part thins out towards the north end of the hill as granitic veins. The exposed parts of the pegmatite vary from aplitic to coarse granitic veins and veinlets, graphic granite and large pieces of pink feldspar shown as a contrast to the grey-black amphibolite. It is a pegmatite with well- developed zonation. Rare-element mineralization at Solås is mainly restricted to Y, Nb and REE-oxides with some to no Be, U, Ti and F-minerals, except for the cleavelandite zone.
The cleavelandite zone contain Ta, F, Mn, Na-minerals, with little to no Nb or REE present.
This places the Solås pegmatite in the mixed NYF+LCT family (Snook, 2014; Müller et al, 2012, 2015).
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2. Methods
Fieldwork
The Evje-Iveland pegmatite field hosts many old feldspar quarries and mines that are suitable to get sample material from, and several of these were picked out as relevant due to accessibility and ease of sampling. Most of the rare minerals needed for analysis are hard to come by in the field, so many of the samples used were material provided from the Natural History Museum in Oslo. Major minerals and rock samples were collected in the field from the pegmatite Solås and several other relatively accessible pegmatites in the area with local help. Samples were collected from different pegmatite zones and if inaccessible the mine tailings were used as a substitute.
Sample preparation
Samples were prepared as thin sections and epoxy at the Department of Geoscience and the Natural History Museum (NHM), University of Oslo. Material for thin section analysis were picked out, sawed and sent to preparation in the thin section lab at the Department of
Geosciences, UiO. The epoxy mounts were made at NHM with EpoFix standard resin &
hardener in molds, which were subsequently polished at the Department of Geoscience, UiO.
Sample descriptions are presented in appendix 1.
Scanning electron microscope (SEM)
The SEM is a Hitachi 3600-N Scanning Electron Microscope with an EDS (energy
dispersive spectrometer) used at NHM. The beam voltage was 15 kV, and the pressure in the low-vacuum chamber was 20 Pa during analysis.
The SEM were used to gather semi-quantifiable data for minerals not covered by microprobe analyses and to document textures and mineral paragenesis.
11 Electron microprobe (EMP)
The CAMECA SX-100 electron microprobe instrument at the Department of Geosciences, UiO is coupled with five wavelength-dispersive spectrometers (WDS). Partial WDS-
analyses on selected samples were done to ensure that all relevant elements in the columbite- tantalite mineral group were covered. Backgrounds where set for all elements with due to the nature of the minerals being oxides and not silicates, so standard silicate programs could not be used. Garnet analyses were done with a standard major element program for silicate analysis.
For columbite-tantalite analysis the accelerating voltage was 20kV, beam current 20 nA, peak count time 10s, and a focused electron beam. 142 spot analyses where made on 9 epoxy samples with 1-3 columbite-tantalite crystals in each. The results presented from the
microprobe were above the limit of detection for the instrument. The standards used for analysis were: Wollastonite (Ca Kα), pyrophanite (Mn Kα, Ti Kα), Si-Al glass with 15 Wt%
UO2 (U Mα) and 15 Wt% ThO2 (Th Mα), synthetic orthophosphates of Y (Y Lα), Yb (Yb Lα), Sc (Kα) (from the Smithsonian Institute - Jarosewich and Boatner, 1980), and metallic Fe (Fe Kα), Nb (Nb Lα), Ta (Ta Lα). All data were corrected with the matrix correction PAP procedure of Pouchou & Pichoir, (1985). The first two analyses on sample 17012 Rosås used the Ta Mα-line, but the amount of Ta measured was to low so only the Ta Lα-line was used.
The Y Lα caused trouble with Nb Lα and Ta Lα for the first 15 analyses (Point 1-15: 17012 Rosås, 17161 Thortveittunnelen and 17180 Mølland), which were corrected by using estimated counts per second from other Y-analyses. All data presented have been corrected for the limit of detection (LOD) during data processing post-analysis.
For garnet analysis the accelerating voltage was set to 15kV, beam current to 20nA, peak count time 10s and with a focused electron beam. All analyses were above the limit of detection. Standards used for analysis were: Wollastonite (Ca Kα, Si Kα), pyrophanite (Mn Kα, Ti Kα), metallic iron (Fe Kα), synthetic MgO (Mg Kα), synthetic Al2O3 (Al Kα), albite (Na Kα) and orthoclase (K Kα). All data were corrected with the matrix correction PAP procedure of Pouchou & Pichoir, (1985), and data below the limit of detection were corrected during data processing.
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Quadropole laser ablation – inductively coupled plasma mass spectrometer (LA-ICP- MS)
Garnet and columbite-tantalite trace element analysis were carried out on a Bruker Aurora Elite Quadropole LA-ICP-MS instrument at the Department of Geosciences, UiO.
The laser beam ablation width was 50 µm. The energy of the laser (CETAL 213 nm laser microprobe) was set at 40% for analyzing garnets, but increased to 60-65% during ablation of standards for monitoring instrumental drift. Error margins may vary between 5-10% due to ablation of potential mineral inclusions and/or epoxy. 10-11 analysis spots were chosen on each sample preferably in the rim and core in a whole crystal. Crystal fragments with no discernible orientation only got 3-5 analysis spots. Helium was used as a carrier gas. The standard glass NIST SRM 610 was used to normalize the data acquired after 10-12 spots. All ICP-MS data presented in this thesis have been corrected for limits of detection and dead time overload. The trace elements analyzed for garnets were: 27Al, 29Si, 45Sc, 51V, 53Cr, 66Zn,
89Y, 139La, 140Ce, 141Pr, 143Nd, 147Sm, 151Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 173Yb and 175Lu. The 29Si has been used as an internal standard, with Si from microprobe data used as external standard. Data correction was done in the Glitter 4.2.2 program by Griffin et al, (2008).
For columbite-tantalite analysis the glass NIST SRM 610 were used as an external standard.
The glass BHVO were analyzed together with NIST SRM 610 to monitor drift and
compatibility of Ti. The laser ablation width was 50 µm during analysis, and the laser energy were set to 50%. For ablation of NIST SRM 610 40 µm beam width and 65% laser energy were used. Lastly on the BHVO standard were used a 50 µm beam width and 75% laser energy. La, U and Pb sensitivities had to be adjusted midway in session due to dead time on the sensor. Trace elements analyzed for columbite-tantalite were: 25Mg, 29Si, 45Sc, 49Ti, 89Y,
118Sn, 139La, 140Ce, 141Pr, 143Nd, 147Sm, 151Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 173Yb,
175Lu, 182W, 206, 207, 208Pb, 209Bi, 232Th and 238U. 49Ti were used as an internal standard because the Ti-values do not vary as much as the other major elements. Ti measured from microprobe data were used as an external standard.
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3. Results
3.1 Field observations in the Solås pegmatite
A study of the Solås pegmatite dike was performed to better understand the formation of columbite-tantalite and garnet mineralization in-situ. Detailed mapping of the pegmatite was done to better understand the extent of it (figure 6). The pegmatites of Evje-Iveland differ in their degree of fractionation and Solås represents one of the most well-exposed and
fractionated pegmatites available (Müller et al, 2012, 2015).
Table 1: Mineral assemblage occurring at the Solås pegmatite
Quartz, albite, microcline, muscovite, magnetite, biotite, beryl, garnet, allanite-(Ce), topaz, amazonite, fluorite, microlite, columbite1, tantalite,
ilmenite, aeschynite-(Y)1, tourmaline, cleavelandite, fergusonite-(Y)1, polycrase-(Y)1, monazite-(Ce), xenotime-(Y), zircon1, galenam, rutile2,
samarskite-(Y)2, chlorite2, hematite2, bästnasite2, calcite3 1) Snook, (2013), 2) Frigstad, (1984), 3) From Neumann, (1960) referenced in Frigstad, (1984), m) observed in a microscope.
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Figure 6: Local geology at the Solås hill. The contour map was taken and modified from NGU maps (NGU map-data: http://geo.ngu.no/kart/berggrunn/).
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Figure 7: A vertical sketch of the pegmatite zones at the Solås mine. The background of the sketch is the open pegmatite quarry seen in figure 6. The granitic border zone is not
exposed in the profile at this portion of the pegmatite. The most diverse mineralization occurs in the bottom of the pegmatite.
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Figure 8: Mineral paragenesis chart for the Solås pegmatite. The cleavelandite zone at Solås is located just before the core zone.
Granitic border zone
The exposed interior at the Solås pegmatite reveals a zoned granitic pegmatite hosted in metagabbroic amphibolite (figure 7). The mineral paragenesis for reference is shown in table 1 and figure 8. The border zone has a granitic composition and is up to 5-7 cm thick when it is exposed towards the amphibolite (figure 9a). The crystals of microcline, albite and quartz are not equigranular, as the albite and/or lesser microcline tend to be slightly larger in size (5 mm – 3 cm) than the quartz (1-3 mm). Albite crystals are observed to be slightly rounded – light blocky texturally with well-developed polysynthetic twinning. Other minerals found in the border zone are small flakes of black biotite and anhedral grains of magnetite no larger
17
than 1-2 millimeters. Green muscovite flakes (< 1mm) are found as overgrowth on biotite >
5cm from the contact.
The amphibolite contains biotite, plagioclase and magnetite, while further away from the border amphiboles reappear in the rock. There seems to have been some chemical exchange in the contact where amphiboles are replaced by biotite (figure 9a). Magnetite crystal clusters can be observed in the amphibolite within 5 cm of the contact to the granitic border zone of the pegmatite. The border zone represents a relatively thin chilled margin due to the small grain sizes present and observed border metasomatism (Joliff et al., 1992; London, 2008).
18
Figure 9: a) Exposed border between the pegmatite and host amphibolite show
concentrations of biotite in the granite and magnetite concentrations in the amphibolite
19
section. b) The thin section 2M from the border zone at Solås. Mark “a” show biotite formation in the pegmatite, while “b” shows abundant magnetite in the amphibolite.
Wall zone
Figure 10: Various wall zone textures. a) A thin sheet of biotite and skeletal quartz/graphic granite textures in white albite. b) A sharp contact between the wall zone and intermediate zone. Note the coloring of amazonite in the white-pink microcline. c) Cluster of allanite
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needles and garnet found in the bottom of the pegmatite. Some garnets are intersected by allanite needles. Allanite decomposition form secondary minerals (brown-orange). d) Magnetite replacement at the end of the wall zone/intermediate zone. A muscovite+garnet corona texture is present by replacing the magnetite.
The wall zone coarsens into larger crystals (5-10 cm) with a porphyritic granite texture (crystals larger than 2.5 cm) that define the graphic wall zone. Quartz and feldspars create graphic granite and skeletal intergrowth textures that is dominating this zone (figure 10a).
The graphic and skeletal quartz is concentrated here compared to the intermediate zone, and microcline abundances is gradually increasing while the amount of albite decrease towards the core of the pegmatite. In the bottom of the wall zone (bottom of the pegmatite) a
concentration of blue graphic granite and skeletal textures can be observed. The blue color is more intense closer to the intermediate/cleavelandite and core zones (figure 10b). Close to the cleavelandite zone the graphic feldspar transition gradually into a more bladed habit and the blue color diminish slightly. Orange altered allanite-(Ce) needles and euhedral red garnets are found in the bottom of the pegmatite growing up towards the core (figure 10c).
The thin needles are diverging from a central point radiating outwards and partly intersecting garnets that grow around them. Observed major mineralogy is quartz, plagioclase and
microcline.
The wall zone has accessory mineralogy consisting mostly of light greenish muscovite, allanite-(Ce), garnet, ilmenite, beryl, magnetite, monazite-(Ce), polycrase-(Y)-euxenite-(Y) and large thin slivers of biotite. Magnetite crystal size reach 3-5 cm in diameter and is mostly anhedral due to reaction/replacement textures (e.g biotite). A corona of muscovite and minor garnet is partly replacing the magnetite crystals in a feldspar matrix (Figure 10d).
Biotite is observed as slivers of long thin black sheets up to 30 cm long. Beryl crystals are yellow-green subhedral-euhedral embedded in the bottom of the pegmatite, but they are sparsely distributed. The crystals are yellow-green in the wall zone matrix, but quite yellow when hosted in the bluer graphic granite/skeletal texture. Even so, yellow beryl in the blue wall close to the cleavelandite zone shows dissolution (embayment) by some kind of
reaction with sugar albite. Ilmenite and monazite-(Ce) was found in feldspars from the waste rock pile, and was interpreted to be from the wall zone close to the intermediate zone due to
21
the presence of biotite and the size of the feldspar crystal. Ilmenite crystals are dark grey with a tabular habit ca. 2 mm thick, while the monazite crystal embedded in feldspar are 1-2 mm thick. Red garnet occurs close to the allanite needles as mainly euhedral clusters of 5 – 10 mm thick crystals hosted in blueish albite and grey quartz. The core of intersected garnets by allanite needles look corroded in backscatter imaging, and muscovite grows around these grains. REE-oxides like polycrase-(Y) are found as small black 1 mm thick euhedral crystals embedded as clusters randomly in the wall zone. The polycrase crystals are well terminated in many of the exposed samples.
The wall zone ends gradually as biotite and magnetite disappears from the wall zone matrix, quartz graphic intergrowth in feldspars lessen in concentration, and the grain size of major minerals sharply increases.
22 Intermediate zone
Figure 11: Sample images from the intermediate zone at Solås. a) Contact relationship between the intermediate and core zone. A quartz-muscovite symplectite formed above the core quartz, and blue amazonite is observed in contact with the core. b) A graded texture where microcline-quartz quickly grow very large over a small area close to the core. c) Contact relationship between amazonite and cleavelandite by the core. Cleavelandite blades grow out of replaced amazonite.
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The pegmatite has an intermediate zone that primarily consists of pink microcline feldspar, white albite and quartz with accessory garnet, tourmaline, amazonite, muscovite, beryl and areas with rare minerals like polycrase-(Y), euxenite-(Y) and fergusonite-(Y). The wall zone has both skeletal and graphic intergrowths of quartz and feldspar, but in the intermediate zone the graphic intergrowth is dominant. A blue amazonite color can be observed in the microcline closest to the core quartz and it is slightly bleached further away from the core (figure 11a). The microcline (and minor amounts of albite) crystals increase in size, while attaining a blockier habit and can be up to a few meters (1-2 m wide), while quartz slowly grade from graphic textures to non-graphic single crystalline phases (figure 11b). Step-tiered textures in feldspar and quartz are well exposed in this zone due to exposure. The large crystals of microcline (and some albite) also host a symplectic texture of muscovite/quartz intergrowth (simultaneous growth of two crystals; Winter, 2010). This texture originates as a radial pattern, but becomes more complex in shape throughout the zone. A symplectite like this is also found just above smoky quartz in the middle right of the pegmatite bordering the core quartz (figure 11a). Black tourmaline is enclosed by quartz and muscovite in small clusters with crystalline needles up to a 2-3 mm wide and 1-5 cm long. The tourmaline is located a meter above the symplectite close to the core. Grey-green muscovite is found as flat oriented layers with quartz in between, and more accessory minerals can be found in small amounts in this texture. Between the quartz and muscovite some garnet mineralization and a few black crystals of REE-oxides were observed.
The intermediate zone borders the core and cleavelandite zone in the bottom right of the pegmatite. The transition to the core is sharp, but the cleavelandite zone transition is more gradual as white-pink blocky feldspars are resorbed and replaced with sugary albite and bladed blue-white cleavelandite (figure 11c).
Core zone
The core zone consists of mega-crystalline smoky quartz up to several meters (Snook, 2014).
Quartz crystallized between euhedral cleavelandite plates in the lower part of the core, and in the upper part close to a muscovite-quartz symplectite (figure 11a). A euhedral green beryl crystal is imbedded in the quartz core in the lower part of the zone, and amazonite
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microcline can be found bordering the core quartz from the intermediate zone on the right side.
Cleavelandite zone
In the lower part of the pegmatite close to the core a cleavelandite-rich phase appears as a distinctive zone. The cleavelandite zone consists of white-blue tabular and bladed albite (cleavelandite), quartz, muscovite, garnet, topaz, fluorite, microlite, and tantalite-(Mn).
Figure 12: Parts of the exposed cleavelandite pod at Solås. a) Contact between the cleavelandite, wall, intermediate, and core zone with a euhedral topaz embedded in between. b) Cleavelandite blades bordering blue saccharoidal albite of the wall zone.
Dissolution textures are observed in the yellow beryl crystals embedded here. REE-oxides (polycrase-(Y)/euxenite-(Y)) show orange pleochroic halos.
Crystals of cleavelandite are observed closest to the core of the pegmatite as flat white-blue tabular crystals that are radiating out from central points in a fan-like pattern. The crystals size grades from small transitional indiscernible grains 20 cm away from the core, to 2-3 mm thick and 5 cm long tabular crystals closest to the core and intermediate zone borders. Figure
25
12a show how cleavelandite crystals border the other main zones of Solås. Cleavelandite crystals are observed growing out of replaced feldspars in the intermediate and wall zone (figure 12b). Sample (MS3-6) (figure 13) from the cleavelandite zone in the Solås mine is provided by Kjell Gunnulfsen. The sample contain minerals not regularly found at the locality today. This specimen has a platy cleavelandite texture that progresses from blue- white saccharoidal albite-cleavelandite graphic granite/skeletal quartz to coarse blue-white euhedral cleavelandite-plates surrounding the accessory minerals of fluorite, beryl, microlite, tantalite, muscovite, and garnet. The cleavelandite plates are just a few mm thick and
saccharoidal in this sample indicating an origin some distance from the core zone.
Cleavelandite zone mineralogy is diverse and remarkably different from the rest of the pegmatite. It appears that the sugary albite found right below the cleavelandite zone has been extensively altered by flux-rich fluids. The sugary albite grades into cleavelandite blades, and the microcline have notches and pocks of resorbed material by these fluids. The resorbed K and Al from microcline may have supported muscovite, garnet and topaz formation in this zone.
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Figure 13: Cleavelandite pod sample MS3-6 aquired from Kjell Gunnulfsen. This specimen covers the transition from sugar albite to well-formed cleavelandite plates. The sample contain most of the minerals described from the cleavelandite zone.
Topaz occurs as up to 5-10 cm subhedral-euhedral crystals between quartz and cleavelandite plates close to the core of the pegmatite. The topaz is heavily fractured but otherwise
translucent with a faint yellowish hue. Fluorite is observed in small clusters between cleavelandite plates as green and purple subhedral 1-3 mm large crystals. Green is the dominant fluorite color, but minor amounts of purple fluorite can occur close to the green type. Microlite crystals are small brown anhedral grains usually 1-2 mm in size. It is found between well-developed cleavelandite plates, but none have been located close to the core of
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the pegmatite. Orange spessartine garnet occur as small irregular masses no more than 1 mm in size in fine grained cleavelandite much like that of the rock sample supplied by Kjell Gunnulfsen. Several small 1-2 mm reddish black euhedral garnet grains occur close to the muscovite books in the same supplied sample, but has not been found in the pegmatite mine.
Muscovite clusters have a more greyish hue than muscovite from the main pegmatite zones.
In some places, the cleavelandite plates are euhedral with muscovite being formed as overgrowth on the outer parts of the crystals. It seems that some minerals occur in higher concentrations around these muscovite books like red-black garnet, microlite, fluorite and tantalite-(Mn). Most of these minerals occur in the main cleavelandite-matrix although the crystals are usually larger and better developed close to the muscovite. The tantalite in the cleavelandite zone are small 0.5 - 2 mm thick subhedral-euhedral tabular crystals with a black color. The crystals are embedded in cleavelandite as single grains sparsely distributed throughout the sample, but it is not present close to the core quartz in the Solås mine wall.
3.2 Descriptions of individual minerals from Solås
Quartz (SiO2)
The Solås pegmatite is dominated by the smoky grey variant of quartz. The crystals are measured to be 1-3 mm in the border zone grading to meter-scale further into the core of the pegmatite. The crystals are mainly anhedral, but can show developed crystal faces in some samples. Wall zone quartz crystallized together with feldspars that create step-tiered cylindrical crystals in graphic textures. Quartz is often seen as small inclusions in other minerals suggesting these other minerals formed later than quartz. Black-red garnet and greenish muscovite is often intergrown with quartz masses.
Microcline (KAlSi3O8) – Amazonite (KAlSi3O8)
Microcline occurs as white-pink to pinkish-red blocky crystals. The crystals are subhedral 3- 10 mm big in the border zone of the pegmatite, and becomes up to 1-2 m in size further in towards the core. Most of the euhedral crystals are concentrated in the intermediate zone, but
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lesser amounts can be found in the wall zone as well. The amazonite variety is found closest to the core of the pegmatite on the eastern side bordering a sugary albite-phase and
cleavelandite. The color is light blue strongest towards the core and cleavelandite zone, but fades quickly a few meters away. Microcline perthite lamellae is not easy to discern as it is very faded. Anhedral microcline are often observed as small inclusions in other minerals.
Albite (NaAlSi3O8)
As with K-feldspar and quartz, albite can be found throughout the whole pegmatite. Albite crystals range from 5-30 mm in the border zone of the pegmatite and consistently increase in size towards the core of the pegmatite. Crystals in the intermediate zone reach 0.5-1 m. The color is usually white-grey to white-pinkish with weak to well-formed polysynthetic
twinning. Crystals of albite close to the core are only a minor component of the intermediate zone with mainly large K-feldspar crystals taking the space. Two more types of albite exist in this pegmatite:
The sugary albite form consists of white-blue feldspar crystals that have been recrystallized close to the cleavelandite zone. The crystals are anhedral, and the shape of the crystals is indiscernible. It looks like the crystals get a fan-shape closer to the core, which may relate to the other form of albite namely cleavelandite. The cleavelandite crystals are a variant of albite that occur as brittle fan-like tabular plates within the secondary metasomatic zone in Solås close to the sugary albite and the core zone. The crystals range from small (<1 mm) anhedral plates in the altered wall zone/intermediate zone to euhedral well-developed plates (4-5 cm large) closest to the core. The hue of the crystals ranges from slightly white to more intense blue.
Muscovite KAl2(AlSi3O10)(F,OH)2
Anhedral-subhedral muscovite clusters and “books” can be observed throughout the outer wall zone into the intermediate zone towards the core of the pegmatite. The crystals found have a slight greenish-gray color and are usually intergrown with quartz in a symplectic
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texture. These clusters of muscovite get progressively larger towards the core. Symplectic crystals are usually homogenous in size (ca 1-2 cm), but the crystal books by the core can be as large as 10 cm. Muscovite in the cleavelandite zone is usually pale grey with a subtle greenish hue, 1-2 cm, and encompasses euhedral cleavelandite plates.
Biotite K(Mg,Fe)3(AlSi3O10)(F,OH)2
Biotite is not an abundant mica in this pegmatite. Most of the biotite is found as small black anhedral books 1-2 mm wide in to the granitic border zone towards the amphibolite, or as long thin sheets (20-40 cm) in the wall zone. The slivers of biotite sheets seem to orient towards the core of the pegmatite.
Beryl (Be3Al2Si6O18)
Beryl is observed as green-yellow euhedral-subhedral crystals in the wall – intermediate zone and the sugar albite/cleavelandite zone of the pegmatite. The crystals usually have well- formed crystal faces, except in the sugary albite zone where it seems to be slightly dissolved.
Beryl in Solås is normally 2-5 cm wide and 10-15 cm long. No other beryllium minerals were found, although other Be-minerals or (Be-carrying) have been described from this locality (hellandite-(Y), gadolinite-(Y) and bertrandite (mindat with references therein:
http://www.mindat.org/loc-32623.html, visited: 20.12.2015)
Magnetite (Fe3O4)
The magnetite crystals in this pegmatite can be found in the granitic border zone and in the outer wall zone embedded in graphic granite. The mineral is quite common in the granitic border zone as 2-3 mm dark metal grey crystals. It is also found a few cm into the
amphibolite. Progressively larger crystals can be found further into the wall zone embedded in graphic granite. On the edge between the graphic granite and the intermediate zone of massive feldspar the magnetite can get as large as 5 cm in diameter. The crystals are
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subhedral-anhedral due to extensive replacement of the mineral with either biotite or muscovite/garnet.
Ilmenite (FeTiO3)
Ilmenite is found as small plates embedded in feldspar taken from the tailings at Solås. The crystals are flat, subhedral-euhedral, tabular crystals 3-5mm thick and 5 cm long. The colour is black-grey with a light fatty texture to it. It is associated with a close-lying xenotime-(Y), polycrase-(Y) and albite.
Topaz (Al2SiO4(F,OH)2)
Topaz occurs as large euhedral colorless semi-transparent crystals in sizes up to 10 cm wide.
The topaz crystals can only be found in the Na-rich cleavelandite zone below the core, and the crystals found is always very heavily fractured. The fracturing might have formed from blasting of the pegmatite.
Garnet (Almandine (Fe3Al2Si3O12) – Spessartine (Mn3Al2Si3O12))
Garnet is found throughout most of the zones of this pegmatite except the border and core zones. Garnets are usually found as the deep-red orange almandine-spessartine variant in the wall and intermediate zone of the pegmatite. Crystal habit is quite varied as the mineral can form as small clusters 2-3 mm wide together with quartz and muscovite, but closer to the core the crystals get bigger (4-5 cm), more euhedral in form and attain a slight orange tint at the edges. The pure orange spessartine variant can only be found in the cleavelandite zone together with cleavelandite, muscovite, fluorite and more. These spessartines are found as small aggregates of anhedral crystals <1-2 mm in size. Some small amounts of 1 mm black- red euhedral garnet are found close to muscovite clusters.
31 Tourmaline (Na(Fe32+)Al6(BO3)3(Si6O18)(OH)4)
Tourmaline was observed in one place in the exposed upper part of the intermediate zone over the core. The crystals are found as black needles growing closely together in a mix of quartz and muscovite. The crystals are subhedral-euhedral 2-3 cm long needles.
Allanite-(Ce) (Ce,Ca,Y,La)2(Al,Fe3+)3(SiO4)3(OH)
Allanite in the Solås pegmatite occurs as small thin radiating needles in the lower part of the pegmatite. The color is black with a crust of rusty yellow-brown secondary minerals. The crystal length varies from a few cm up to 20 cm, and its width usually 1-2 mm. It also occurs in smaller radiating needles in the lower western end of the exposed pegmatite mine.
Euhedral garnet crystals cluster around these needles, and are sometimes bisected by them.
Polycrase-(Y) (Y(Ti,Nb)2O6) - Euxenite-(Y) (Y(Nb,Ti)2O6)
Polycrase-(Y) is found as 1-5 mm thin tabular/prismatic euhedral crystals embedded in albite, microcline and magnetite grains. They are brownish-black in color, metamict, and occur in small clusters of 5-10 crystals together. The crystals are found mainly in the wall zone and occur in single crystals slightly into the intermediate zone of the pegmatite.
Results from semi-quantitative SEM-analysis on selected grains of black minerals show that some of these grains have Nb > Ti, so that they are euxenite-(Y). These crystals occur further into the wall zone/intermediate zone than polycrase-(Y).
Fergusonite-(Y) (YNbO4)
Fergusonite-(Y) occur as very small (1 mm) euhedral black grains in the wall zone of the pegmatite. Only one small grain was found.
32 Columbite-Tantalite ((Fe,Mn)(Nb,Ta)2O6)
Columbite and tantalite is mineralized in different zones in the pegmatite. Columbite was unfortunately not found in any of the samples collected. Columbite has been reported by Snook, (2013) and Frigstad, (1968). Other samples that were suspected to be columbite were magnetite with abundant polycrase-(Y) or just solitary REE-oxides (polycrase-(Y) or
euxenite-(Y)).
Tantalite occurs only in the sugary albite/cleavelandite zone. The tantalite crystals are quite small (2-3 mm) euhedral tabular minerals with a black color. The crystals are scattered throughout the zone with no inherent mineral associations. Tantalite is not present in the cleavelandite zone when the cleavelandite minerals change from sugary albite to large (4-5 cm) fan-shaped blades.
Monazite/Xenotime (CePO4/YPO4)
These two phosphates are found as small 1-2 cm crystals in the wall zone of the pegmatite.
They are light yellow-brown in color and subhedral tabular in shape. These minerals are found embedded in albite.
Galena (PbS)
Galena is the only sulphide found in samples from this pegmatite. It is found as inclusions in columbite-tantalite and other REE-oxides as euhedral crystals (< 1mm). A few inclusions were also found in albite and microcline.
Fluorite (CaF2)
Fluorite is observed as small (3-5 mm) subhedral crystals in the cleavelandite zone of the pegmatite. The crystals are both green and purple. The purple fluorite is found as anhedral- subhedral masses with crystals sizes up to 1 mm, while green fluorite more widespread and
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dominant in the samples. Fluorite is embedded in between cleavelandite blades as small solitary clusters with no apparent relation to other minerals.
Microlite (Na,Ca)2Ta2(O,OH,F)
Microlite is only found in the cleavelandite replacement zone as small (1-2 mm) crystal masses associated with fluorite, muscovite and tantalite-(Mn). The crystals are embedded in between cleavelandite plates anhedral-subhedral in shape and brown in colour. Microlite is found as inclusions and vein fillings in columbites and tantalites.
3.3 Columbite-tantalite mineral chemistry
Most of the samples analyzed by EMP/LA-ICP-MS came from the collection of the Natural History Museum in Oslo. These samples come from large, well known pegmatite mines, while a minority is supplied from lesser known mines and prospects in the same area. Most of the columbite-tantalite samples from the collection do not carry matrix minerals, which makes it harder to determine the in-situ development in the pegmatites. Distribution of these minerals is plotted in this map (figure 14) over the Evje-Iveland pegmatite field. Most samples are from mines in the central IGMC, while others are from granites and gneisses at the edges of the Evje-Iveland pegmatite field.
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Figure 14: Columbite-tantalite sample map from Evje-Iveland. Most samples are located in amphibolite, and other in surrounding gneisses.
Individual sample points are used to illustrate fractionation trends in the columbite-tantalite group minerals. The compositions are shown in figure 15 and individual sample data is presented in appendix 2. A general overview of average columbite-tantalite compositions per pegmatite is presented in table 2.
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Table 2: Representative average compositions of columbite-tantalite minerals from the Evje- Iveland pegmatite field, South Norway. EMP and LA-ICP-MS data.
Sample 1 2 3 4 5 6 7 8 9
n 4 5 5 5 4 5 3 4 6
Nb2O5 wt% 50.3(7) 24(5) 65.1(8) 60(3).93 58.8(6) 29(1) 58.6(6) 61.3(1) 64(3) Ta2O5 28(1) 57(6) 8.5(9) 18(4) 15.7(2) 53.1(9) 20.2(3) 14.54(3) 12(2) FeO 12.8(5) 1(1) 9.4(3) 13.8(3) 11.7(2) 1.4(1) 5(1) 7.8(1) 9(2) Fe2O3** 1.9(5) 3(1) 3.0(6) 1.6(3) 1.7(4) 0.6(2) 1.5(2) 2.5(1) 2(1) MnO 4.37(2) 11(9) 7.4(2) 4.5(3) 4.85(6) 14.5(2) 12(1) 9.17(8) 8(2) TiO2 1.50(6) 1(1) 3.6(2) 1.2(2) 4.1(2) 1.2(1) 1.4(3) 3.4(2) 2(1)
UO2 - - 0.12(5) - <0.01 0.1(1) 0.09(4) 0.30(7) <0.01
ThO2 - - <0.01 <0.01 <0.01 <0.01 - - -
CaO - <0.01 0.01(1) <0.01 0.02(1) 0.03(2) <0.01 0.01(1) <0.01 Sc2O3 0.07(1) 0.13(8) 0.35(9) 0.08(1) 1.71(4) <0.01 0.01(1) 0.30(1) <0.01 Y2O3 0.30(2) <0.01 0.6(1) 0.33(6) 0.46(9) 0.10(5) 0.27(1) 0.52(6) 0.41(4) REE2O3*** <0.01 0.18 0.5 0.05 0.21 0.2 0.04 <0.01 <0.01
MgO* <0.01 <0.01 0.4 0.14 0.31 <0.01 0.07 0.2 0.3
SiO2* - <0.01 <0.01 - - <0.01 <0.01 <0.01 -
SnO2* 0.08 0.3 0.05 0.05 0.09 0.02 0.01 0.10 0.02
WO3* 1 0.2 1.6 0.6 1.6 0.20 0.37 0.25 0.4
PbO* 0.01 0.01 <0.01 <0.01 <0.01 0.03 0.02 0.06 0.01 Bi2O5* <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
Total 101.3 101.0 101.0 101.8 101.6 101.4 101.1 101.5 101.1
W apfu 0.01 0.00 0.02 0.01 0.02 0.00 0.00 0.00 0.00
Bi 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Nb 1.42 0.78 1.67 1.63 1.54 0.92 1.59 1.61 1.69
Ta 0.49 1.10 0.13 0.29 0.25 1.01 0.33 0.23 0.20
Si 0.00 0.03 0.01 0.00 0.00 0.01 0.00 0.01 0.00
Sn 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ti 0.07 0.08 0.16 0.05 0.18 0.06 0.07 0.15 0.09
U 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Th 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Σ B 1.99 2.00 1.99 1.99 1.99 2.00 2.00 2.00 1.99
Fe2+ 0.67 0.09 0.45 0.69 0.57 0.09 0.29 0.38 0.48
Fe3+ 0.09 0.05 0.13 0.08 0.08 0.04 0.07 0.11 0.09
Ti 0.00 0.02 0.00 0.00 0.00 0.01 0.00 0.00 0.00
Sc 0.00 0.01 0.02 0.00 0.09 0.00 0.00 0.02 0.01
Mn 0.23 0.82 0.36 0.23 0.24 0.86 0.63 0.45 0.39
Ca 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00