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MASTER'S THESIS

Mineral of Gangue in the Kiirunavaara

Joakim Nordstrand

Master of Science (120 credits) Exploration and Environmental Geosciences

Luleå University of Technology Department of Civil, Environmental and Natural resources engineering Fall 08

Till T.

Abstract The iron-ore of Kiirunavaara is one of the largest magnetite-apatite mineralisation in the world. It is well known for its purity and size and its origin has been the subject of an intense debate for over a century. The composition of the most important minerals from an economic point of view, magnetite and apatite, has been well studied but little is known about the composition and role of the minerals. Nowadays, even the have been targeted for investigations, both in Kiirunavaara and in similar deposits elsewhere, e.g., Sierra la Banderra, Chile. The growing interest derives mainly from the importance of the gangue minerals in ore processing but also because they might hold the key to the origin of the . In this study, a large scale microprobe investigation of over 250 analyses has been carried out mainly focussing on silicates within the ore body but also to some extent on sulphates, phosphates and carbonates. Most of the analysed grains belonged to either the group or the group. and are by far the most abundant silicates within the ore body. Through (EMPA) analysis of 198 separate grains, this investigation led to the broadest and most updated characterisation of silicates within the Kiirunavaara ore body. It also briefly looks at setting and chemistry of sulphates, phosphates, and carbonates. This study indicates that silicates may have been formed during shifting periods of crystallization and chemical environments, and that the mineral assemblage and composition do not oppose a magmatic origin.

Aknowledgements I would like to thank the mine planning department at LKAB and my manager, Carlos Quinteiro for providing the resources needed to carry out this study.

I would also like to thank Lassi Pakkanen and Bo Johansson for their help and hospitality during my visit at GTK, Espoo. I also want to send a special thanks to Nils Jansson and Therese Bejgarn at LTU for guiding me through some difficult hours of petrography.

Thanks also to my supervisor at LTU, Olof Martinsson for planning and aiding during petrographic sessions, as well as my opponent, Ivar van der Stijl for his thorough work when inspecting this thesis.

Sincere thanks also goes to Fredrik Johansson for a professional help regarding lay-out of pictures and diagrams. And to Jaqueline Nason for an indispensable help in language correction.

I would also like to extend my sincere appreciation to my family, especially Lucile, for coping with my late nights at the office and my extra days of work during our vacations.

Last but not least, my deepest gratitude to my supervisor at LKAB, Ulf B. Andersson, for hours of reading, editing, calculating and guiding me in the right direction. It has been tough at times but a learning experience.

Contents

Chapter 1: Introduction ...... 1 Regional geology ...... 2 Local Geology ...... 4 Ore body description ...... 4 type ore ...... 5 Methodology ...... 7 Sampling ...... 7 Analysis ...... 7 Data processing ...... 8 Results ...... 9 Silicates ...... 9 Amphibole ...... 9 Mica ...... 12 Chlorite ...... 15 and -minerals ...... 17 ...... 19 Allanite ...... 19 ...... 21 and ...... 21 and ...... 21 Carbonates ...... 22 Sulphates and phosphates ...... 23 Oxides ...... 24 Discussion ...... 25 Silicates ...... 25 Amphibole ...... 25 Mica and chlorite ...... 27 Talc and clay-minerals ...... 29 Titanite ...... 30 Allanite ...... 32 Zircon and thorite...... 32 Carbonates ...... 33 Conclusions ...... 35 Amphibole ...... 35 Mica ...... 35

Chlorite ...... 36 Talc ...... 36 Titanite ...... 36 Zircon and thorite ...... 36 Carbonates ...... 36 Sulphates and phospates ...... 37 In general ...... 37 Recommendations ...... 38 Bibliography ...... 40

Chapter 1: Introduction The Kiirunavaara ore body is one of the world’s largest magnetite-apatite mineralisation. It is famous worldwide for its size, quality and mining method. For more than a hundred years, the town of Kiruna has depended on its iron ores. More than a billion tonnes has already been mined out of Kiirunavaara alone. Despite its importance, there are still questions regarding its specific composition and the discussion regarding its origin is still one of the most intense debates in the science of economic geology. The importance of understanding this ore body, from mineralogical, structural and ore-genetical points of view is increasing as the production is advancing deeper and the demand for is increasing. Few previous studies have been carried out over the years to characterize the silicate of the Kiirunavaara iron ore, where the most recent studies mainly focused on the characterisation of REE- bearing minerals (Parak, 1973; Harlov et al., 2002; Edfelt, 2007; Smith et al., 2009). The silicate composition is important both for ore extraction purposes and also for calculating ore density, which affects the block modelling. This project aims towards creating a mineralogical characterisation for the Kiirunavaara ore body, focusing primarily on the silicate phases. By looking at composition, chemical environment and substitution mechanisms at work, links between mineral composition and bulk ore composition, as well as temperature and pressure of ore formation will be addressed. In this study, only silicates as gangue minerals and fissure fillings in the ore body itself will be examined. The study combines petrographical and a compositional characterisation using optical microscopy and electron microprobe analysis (EMPA) to achieve a broad classification of silicates. The focus will primarily be on amphiboles and micas, since these are most abundant, but data on titanite, allanite, chlorite, talc, and thorite will also be included. A smaller amount of analyses on carbonates, sulphates, phosphates and oxides are also included in order to achieve a broad characterization.

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Regional geology The Kiirunavaara iron ore, along with the other Kiruna-type ores in the area, is situated in the Precambrian Fennoscandian Shield, which is considered to be one of the most important ore- containing provinces in Europe (Bergman et al., 2007).

Figure 1: Simplified geological map of northern Norrbotten, from Bergman et al. (2001).

The geology of northern , northern Sweden, comprises an Archean basement, overlain by several magmatic and sedimentary formations (Bergman et al., 2001). The stratigraphically lowest units consist of late Archean and granitoids (Figure 2). These rocks are mainly exposed north from Kiruna, towards the Råstojaure and Naimakka area. However, they extend a lot further south at depth (Mellqvist et al., 1999). Above these units, two units of Paleoproterozoic age were deposited in the timespan 2.5 – 2.0 Ga (Figure 2), the Kovo Group and the Greenstone Group (Skiöld, 1986; Bergman et al., 2007). The former is defined as basal clastic metasedimentary rocks which consists of conglomerates and quartzites The Greenstone Group comprises mainly metabasalts and ultramafic rocks (Sundius, 1915; Bergman et al., 2001). The overlying rocks are metavolcanic Svecofennian rocks which are sub-divided into two units, the lower Porphyrite Group and the upper

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Kiirunavaara Group (Martinsson, 2004). The Porphyrite Group consists mainly of porphyric andesites with of . Stratigraphically equivalent to these are the Kurravaara conglomerates, which is a 50 – 300 m thick clastic bed, consisting mainly of intermediate to segments (Frietsch, 1979; Martinsson, 2004). The Kiirunavaara Group in Figure 2, hosts the apatite iron ores (AIO) and will therefore be Figure 2: Lithostratigraphy of Archaean and Paleoproterozoic units in the described in more detail Kiruna area, from Martinsson et al. (1999). below. Intruded into the supracrustal rocks are at least two older and two younger plutonic suites. The former two are the Haparanda Suite (1886 – 1873 Ma) and the Perthite Monzonite Suite (1879 – 1858 Ma), e.g., (Witschard, 1984; Mellqvist et al., 2003) where rocks of the former suite are mainly found in the eastern part of Norrbotten County and rocks of the Perthite Monzonite Suite are mainly found in the west. The Haparanda Suite rocks show a wide range of composition, from gabbro and towards granodiorite and subordinate granite. The Perthite Monzonite Suite rocks range from granitic and syenitoid compositions to large intrusions of gabbro. These suites have traditionally been kept separate because a tendency towards more alkaline compositions in the latter (Bergman et al., 2001) The two younger suites are the pegmatite associated Lina granites and the Granite-syenitoid- gabbroid association (Bergman et al., 2001). Both of them were deposited between 1.81 – 1.78 Ga e.g. (Skiöld et al., 1988; Romer, 1992; Öhlander & Skiöld, 1994; Bergman et al., 2001; Bergman et al., 2007). The compositions in the former suite are granitic to monzogranitic with a low content of minerals, whereas the composition of the Granite- syenitoid-gabbroid association ranges from granite to gabbro with a dominant chemical trend that is alkali-calcic (Bergman et al., 2001).

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Local Geology Studies on the host rocks (Kiirunavaara Group) to the ores have indicated a volcanic origin (e.g. Geijer, 1931a; Ekström & Ekström, 1997; Bergman et al., 2001) and an age of emplacement in the range 1.88 to 1.90 Ga (Cliff et al., 1990; Romer et al., 1994). The foot-wall rocks are part of the Hopukka Formation, which is considered to be a 300 – 1400 m thick flow of andesitic to trachyandesitic . The hanging wall rocks are interpreted as ryodacitic to ryolitic rocks with a pyroclastic origin, dominated by porphyritic tuff- lapillituff (Martinsson, 2004). They are distinguished from the Porphyrite Group through a generally more felsic composition and high contents of Ti and Zr. Close to the ore body, a zone of metasomatic alteration usually occurs, consisting mainly of skarn minerals that have replaced the host (Frietsch, 1978). However, the alteration of host rocks continues on a larger scale, particularly in the form of sodic alteration (Geijer & Ödman 1974). The has normally a red appearance which, in that case, indicates dissemination of hematite (cf. Groves et al., 2010).

Ore body description

The Kiirunavaara ore body, as well as the other magnetite-apatite ores in the region, were deposited during the Svecokarelian orogeny (Billström et al., 2010) in the range of 1.88 – 1.90 Ga (Cliff et al., 1990). The ore body is large, sheet-like and extends approximately 4km along strike. It is at least 1.7 km deep and varies in thickness between ca 50 and 200 m, contains more than 60 % Fe, and dips 60 - 70° towards east. It is crosscut by several dikes of diabase along with at least one dike of granophyre, which is older than the diabase (Cliff et al., 1990).

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Figure 3: Simplified model of the Kirunavaara ore body (LKAB) Apatite, and calcite are the most common gangue minerals. In addition micas, chlorite, pyrite, chalcopyrite, talc, anhydrite, gypsum, titanite and allanite are also present within the ore body in minor amounts. The content of impurities (i.e. non-iron oxides) in the ore body differs in between different parts, where the areas richest in phosphorus are located at the upper levels as well as in the northern end. The latter is known as Sjömalmen. The quality of the ore is divided in to five different categories: B1, B2, D1, D3 and D5. B-ore represents phosphorus-poor ore, whereas the D-ore is rich in P. B1 is the purest ore type and has an iron concentration of >65 % Fe. The B2 ore has an iron content <65 % and is characterized by its elevated content of silicates. Due to this fact, the B2 ore category is the focus for this study. The different types of D-ore are divided based on their phosphorous content.

Kiruna type ore Apatite iron ore, also known as Kiruna-type ore (Geijer, 1931b) is a category of iron-deposits associated with volcanic rocks or high-level intrusions (Nyström & Henriquez, 1994), all of which have variable concentrations of magnetite-fluorapatite-actinolite and range in age between Proterozoic and Cenozoic (Hildebrand, 1986). They occur in several regions around the globe, e.g. Great Bear, Canada; El Laco, Chile; Bafq district, Iran, and Cerro de Mercado, Mexico (e.g. Naslund et al. 2002; Daliran et al. 2010, Geijer, 1931b). The main occurrences can be found in the Paleoproterozoic rocks of Sweden; the Mesoproterozoic 5 rocks of SE Missouri, United States and the Circum-Pacific fold belt of Peru and Chile (Frietsch & Perdahl, 1995; Geijer, 1931b). In Norrbotten county, Sweden, there are around 40 known deposits of this type and they are mainly concentrated in the Kiruna – Gällivare area (Bergman et al., 2001). This region holds one of the largest concentrations of magnetite-apatite ores in the world. They usually occur as tabular bodies that are intercalated in the middle-upper part with rocks of the Kiirunavaara Group (Geijer, 1910; 1931b; 1967; Frietsch, 1978; 1984). The origin of this group of iron deposits has been the target for an intense debate involving geologists from all over the world. Geijer (1931b; 1934) stated that the iron ore bodies are formed by magma differentiation, and deposited from late stage volatile-rich magmas. This was the dominating theory until Parak, (1973) stated that the origin was related to sedimentary exhalative processes. He based his theory mainly on structures and features of ore and host rocks that were, according to him, suggested sedimentary in origin along with chemical studies. After this, the debate has intensified, with Geijer & Ödman (1974), Bookstrom (1977) and Frietsch (1978; 1982) defending the theory of magma differentiation, while Parak (1973; 1975a; 1975b; 1984) maintaining his sedimentary exhalative theory. Meanwhile, Lundberg & Smellie (1979) argued that the ores are a product of liquid immiscibility derived from assimilation of iron rich material during formation. Hitzman, et al. (1992) claimed that these ore bodies instead are products of shallow level hydrothermal processes related to deep seated magmatism and should therefore, along with other ores with similar characteristics, be considered as a subgroup of Iron Oxide Copper Gold (IOCG) style deposits. Today the debate primarily stands between magmatic emplacement of volatile rich magmas (Nyström & Henriquez, 1994; Naslund et al., 2002; Harlov et al., 2002; Nyström et al., 2008) or through emplacement entirely by hydrothermal fluids, and therefore part of the large IOCG family (Einaudi & Oreskes, 1990; Hitzman et al., 1992; Barton & Johnson, 1996; Smith et al., 2009). An objection to a magmatic origin is, according to Barton & Johnson (1996), the low temperature mineral assemblages along with hydrothermal textures. However, this may be due to a later hydrothermal event (Cliff & Rickard, 1992) or that the ore body was subjected to successive stages of fluid rock interaction at different temperature conditions immediately following emplacement. In addition, numerous mainly textural features suggest similar rheological states of the ore and host rocks indicative of coeval magmas (U. B. Andersson pers comm. 2012).

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Methodology Sampling All samples were collected from drill cores, drilled from the 1060 level and downwards. The part of the ore body investigated here is therefore the one which will be mined after the opening of the new main haulage level 1365. The samples were chosen to represent the general characteristics of the ore body, both along its strike and regarding its different ore qualities. The local coordinate system has its Y-axis approximately in the north – south direction, with increasing numbers towards the south. 10 – 15 samples were collected within each of four different regions; (Y2 – Y6), (Y14 – Y18), (Y26 – Y30), (Y38 – Y42) (Fig. 4).

Figure 4: Map displaying prognoses for three levels of the ore body between the current- and the next main haulage levels. Sampling areas are marked by circles. Each digit after Y (e.g. Y1250) represents meters in distance. All different quality categories were also evenly represented with focus on the B2 ore, since it contains the highest amount of silica. Each sample was cut and polished into a thin section at Vancouver Petrographics Ltd, Vancouver, Canada. These were examined in a regular petrographic microscope for selection of samples to analyse with EMPA. Drillcore number, drillsite coordinates and sampled sections along the drillcore is presented in Appendix 1. Each sample was selected based on its geographical position and content of silicates along with its textural features. This resulted in only one sample in the region (Y2 – Y6), whilst for the other regions several samples were selected. In total, 16 samples were subjected to EMPA analysis.

Analysis Analysis was carried out at the Geological Survey of Finland, Espoo, using a CAMECA SX100 electron microprobe, with 5 WDS and one EDS spectrometers. 67 different areas 7 divided over 16 thin sections were chosen for analysis. On average, 3 different mineral grains were analysed in each area. This came to a total of 503 analyses in 198 different mineral grains. Four different analytical schemes were used for the different mineral groups in order to achive a good classification. One scheme was used for silicates, phosphates and oxides, one for REE-bearing silicates, one for carbonates and another for sulphides. The analytical results were presented as weight percentage of oxides which thereafter were recalculated to be presented as a chemical formula. All analyses in the form of oxides as well as a.p.f.u (atoms per formula unit) are given in Appendix 2. The analytical data from sulphides are disregarded in this study and therefore not included in Appendix 2.

Data processing Recalculation of data, from weight percentage of oxides into chemical formula, and plotting were carried out in MS Excel 2010. Information regarding molar weight of elements was collected from Wenk & Bulakh (2004). The amphibole formulas were calculated using a method based on 23 . The method was chosen based on the fact that the content was unknown from the EMPA. In order to use this method one assumption had to be made, namely that (OH,F,Cl) = 2 apfu (Hawthorne & Oberti, 2007). Nomenclature and plotting were according to Leake et al. (1997) and Deer et al., (1997). Mica formulas were recalculated based on 22 oxygen and plotted following Rieder et al., (1998) and Deer et al. (2003) Talc was also recalculated on the basis of 22 oxygen (Deer et al., 2009) Chlorites were calculated based on 28 oxygen (Zane et al., 1998). Zircon and thorite was normalised to two cations due to the presence of F. Allanites were recalculated based on 6 M + T cations, one of the methods recommended by Ercit (2002). A few assumptions had to be made using this method. Firstly, that there are no vacancies in the octahedral and tetrahedral sites. Secondly, that there is no substitution of O for OH. These assumptions are, according to Ercit (2002), supported by all structure refinements published to date. Titanite was calculated on the basis of three cations, assuming all Fe as FeIII+ principally following the schemes of Oberti et al. (1991) and Deer et al. (1997), with the additional assumptions that P is substituting for Si in the T-position and that V is substituting for Al and FeIII+. Carbonates were recalculated to two cations.

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Results Silicates Amphibole According to the present and former studies (Geijer, 1910), amphibole is by far the most abundant within the ore body,. It can be found in a wide range of parageneses within the ore and can only be considered as rare in the most iron-rich parts. Amphiboles occur in three different textural forms: subhedral crystals, situated in between areas of partly – fully brecciated magnetite, are often arranged in a flow-like pattern (Fig. 5), euhedral crystals that do not follow a flow-like pattern (Fig. 6) and large needle-like crystals in a magnetite (Fig.7), with a seemingly common direction of growth. Most of the third type descibed contain inclusions of magnetite within the crystal. At the edges, sphene crystals are sometimes found in contact with the magnetite. In some cases the middle part of the actinolites contain secondary gypsum and/or mica.

Figure 5: Zoned/un-zoned euhedral amphiboles in a B2- Figure 6: Subhedral amphiboles in stagnant, brecciated ore flow pattern. environment.

Figure 7: Large, needle-like crystals in magnetite matrix.

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The amphiboles are classified according to the nomenclature presented in Leake et al. (1997). According to them, all amphiboles with more than 1.5 Ca per formula unit within the B-site are to be classified as calcic amphiboles, which is the case for all samples analysed in this project. Furthermore, all samples show a Ti content <0,5 a.p.f.u and a (Na+K) content within the A-site <0,5 a.p.f.u which puts them into the nomenclature diagram presented in figure 6.

Figure 8: Amphibole compositions in the Kiirunavaara iron ore, presented in a nomenclature diagram for calcic amphiboles after Leake et al. (1997). The upper diagram displays samples without chemical zooning and the lower diagram displays the rim and core of samples with chemical zooning together with reference samples from Sierra La Bandera, Chile (Lledo, 2005).

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Only a few samples reached above a (Mg/(Mg+Fe2+)) ratio of 0.9 and, therefore, were classify as . Most other samples fall within the boundries of actinolite with only a few straddling the boundary to magnesiohornblende. The actinolites that display a zoning texture indicates an iron depletion towards the outer rim along with the depletion of Na and Al. Instead, the crystal rims are enriched in Ca, Mg and Si. The Kiirunavaara actinolites contain small but detectable amounts of Mn (0.01 – 0.03 a.p.f.u.), Na (0 – 0.45 a.p.f.u.), K (0 – 0.12 a.p.f.u.), P (0.01 – 0.02 a.p.f.u.) and Ti (0.01 – 0.03 a.p.f.u.)

Table 1: Representative samples of different composition of Kiirunavaara amphiboles. For the complete set, see Appendix 2.

B45-2-2-2 B23.2.1.1 B14.1.3.3 B8.2.2.2 B20.5.1.1 B20.5.1.1 Actinolite Actinolite Tremolite Core Rim SiO2 57.68 53.25 52.29 57.99 52.84 56.57 TiO2 0.30 0.15 0.10 0.00 0.27 0.00 Al2O3 0.46 2.43 2.71 0.25 2.47 1.04 V2O3 0.00 0.02 0.02 0.03 0.00 0.03 FeO 5.58 10.59 9.31 4.05 9.79 7.25 MnO 0.27 0.25 0.21 0.24 0.22 0.27 MgO 21.37 17.79 18.96 22.55 17.99 20.28 CaO 12.51 10.66 11.01 12.96 11.07 12.20 Na2O 0.00 1.16 1.11 0.00 1.18 0.41 K2O 0.02 0.54 0.53 0.02 0.56 0.04 P2O5 0.16 0.11 0.10 0.22 0.14 0.17

Total 98.12 97.03 96.39 98.32 96.59 98.38

Si 7.96 7.66 7.48 7.94 7.63 7.86 Ti 0.00 0.02 0.01 0.00 0.03 0.00 Al 0.07 0.41 0.46 0.04 0.42 0.17 V 0.00 0.00 0.00 0.00 0.00 0.00 Fe2+ 0.64 1.27 0.70 0.46 1.18 0.84 Fe3+ 0.00 0.01 0.41 0.00 0.00 0.00 Mn 0.03 0.03 0.03 0.03 0.03 0.03 Mg 4.39 3.82 4.05 4.60 3.87 4.20 Ca 1.85 0.64 1.69 1.90 1.71 1.82 Na 0.00 0.32 0.31 0.00 0.33 0.11 K 0.00 0.10 0.10 0.00 0.10 0.01 P 0.01 0.01 0.01 0.03 0.02 0.02

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Mica Mica is, according to this study, the second most abundant silicate mineral within the ore

Figure 9: Colorless from the third, Mg-rich Figure 10: Dark brown, iron-rich phlogopite from the group of mica. first mica group. body. It is present in a variety of textural positions within all parts of the ore. The crystals are most commonly anhedral – subhedral with a colorless (Fig. 9) or darkbrown color (Fig. 10) where the lighter aggregates tend to show a more clear pleochroism. They occur both enclosed within the magnetite, as bundles of grains in contact with magnetite breccia fragments and in some cases as in parallel-oriented flow-like textures, very similar to those of actinolite. These aggregates sometimes display alteration towards chlorite. Due to low to non existing octahedral Al and high to very high Mg/(Mg+Fe) ratio the micas in the Kiirunavaara ore classify as phlogopite of variable composition (Fig. 11). Three different groups can be distinguished (1, 2, 3 in Fig. 11 and representative analyses are given in Table 1)

Figure 11: Mica classification and nomenclature at Kiirunavaara. Samples plotted by thin sections. Diagram after (Deer et al. 2004).

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Table 2: Composition of representative samples from the three major mica compositional groups at Kiirunavaara. B32-2-1 represents group 1, B22-2-2 group 2 and B26-3-3 group 3.

B32-2-1 B22-2-2 B26-3-3 1 2 3 SiO2 39.09 41.99 44.59

Al2O3 1.93 0.80 0.33

TiO2 13.32 11.84 10.53

FeO 13.12 8.99 6.25

MnO 0.18 0.07 0.05

MgO 16.83 22.17 25.03

CaO 0.00 0.10 0.02

K2O 9.36 8.46 8.76

F 0.00 1.39 3.92

Cl 0.16 0.05 0.04

Total 94.12 95.40 97.91

Si 5.85 5.98 6.03 8.00 8.00 7.71 Al T 2.15 2.02 1.68 Al M 0.19 0.00 0.00 Ti 0.22 0.09 0.03 Fe 1.64 4.23 1.07 5.40 0.71 5.79 Mn 0.02 0.01 0.01 Mg 3.75 4.70 5.04 Ca 0.00 0.01 0.00 1.79 1.55 1.51 K 1.79 1.54 1.51 OH 3.96 3.34 2.25 F 0.00 4.00 0.64 4.00 1.74 4.00 Cl 0.04 0.01 0.01

Group 1 is characterised by relatively high Fe, Al, Ti, Mn, K and Cl contents, while group 2 is lower in these elements but higher in Si, Mg and F content. Group 2 does not contain any octahedral Al. Group three is even higher in Si, Mg and F content. The variation in F and Cl is relatively significant (see Table 2, Appendix 2 and Fig. 12). F shows a strong positive corelation with Mg/(Mg+Fe), where as Cl has anegative correlation.

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Figure 12: The F and Cl content in Kiirunavaara mica. Plotted by thin section.

There are also distinguishing textural features that separates the groups from one another. The group rich in Fe are typically dark brown without a clear pleochroism. This group is commonly associated with dolomite, calcite and actinolite. It is in this group that the chlorite- altered are usually found. The colorless, more pleochroitic aggregates are usually present together with grains of apatite.

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Chlorite Chlorite is less common compared to actinolite and mica within the ore samples of the present study, in contrast to the common occurrence reported by (Harlov et al., 2002). Most of the chlorite are present as alteration lamellae within grains. The rest consist of only chlorite and are present either as pale/palebrown (Fig. 13) aggregates or dark blue grains (Fig. 14).

Figure 13: Pale brown chlorite in magnetite. Figure 14: Chlorite alteration lamellae within mica.

Compositionally, the chlorite shows a wide range in Fe, Mg and Al contents. However, the composition is relatively homogenous within each thin section and follow a similar compositional trend between the samples as the coexisting micas. The chlorite is, however, even more enriched in Fe compared with the mica within the same thin section. It is classified as pycnochlorite, diabantite and pennine (Fig. 15). All chlorite is somewhat enriched in Mn (0.05 – 0.33 a.p.f.u.), and most of them in Ti. The enrichment in Mn follows the content of Fe, only the most Mg-rich aggregates lack any content of Ti. Figure 15: Classification diagram after Hey (1954) of Kiirunavaara chlorites and comparative samples from Deer et al. (1992). Kirunavaara chlorites are plotted by thin- section. 15

DHZ1 DHZ2 DHZ3 DHZ4 DHZ5 DHZ6 B1.1.2 B2.5.1 B33.5.1 B35.2.2 B42.5.1 SiO2 27.12 25.62 25.07 22.64 32.73 32 SiO2 28.19 28.70 29.39 30.42 34.27 TiO2 0.88 0.12 - 0 - TiO2 0.00 0.70 1.05 0.10 0.05

Al2O3 27.68 21.19 19.78 18.6 7.96 12.9 Al2O3 19.66 14.18 13.77 13.74 15.74 Cr2O3 - - - - 8.31 - Cr2O3 0.00 0.02 0.00 0.00 0.00 FeO 1.24 21.55 35.8 2.29 12.5

Fe2O3 0.2 3.88 3.5 4.43 - - FeO 14.85 24.00 28.42 21.10 6.07 MnO 0.54 0.35 0.5 38.93 0.02 0.13 MnO 0.35 0.92 0.36 0.51 0.16 NiO - - - - 0 - NiO 0.05 0.04 0.04 0.13 0.03 ZnO - - - - - 30.4 ZnO 0.03 0.04 0.01 0.03 0.00 MgO 30.96 15.28 1.11 1.48 34.88 4.4 MgO 23.40 18.27 15.18 20.46 32.48 CaO - 0.16 1.04 - - - CaO 0.13 0.08 0.09 0.16 0.07 Na2O - 0 0.18 - - - Na2O 0.00 0.00 0.00 0.00 0.00 K2O - 0 0.93 - - - K2O 0.00 0.11 0.18 0.01 0.00

Total 87.74 88.91 88.03 86.08 86.19 92.33 Total 86.69 87.25 88.59 86.74 89.04

Number of Number of ions Si 5.01 5.45 5.56 5.36 6.39 7.09 Si 5.68 6.08 6.25 6.34 6.38 Ti 0.00 0.14 0.02 0.00 0.00 0.00 Ti 0.00 0.11 0.17 0.02 0.01 Al 6.03 5.31 5.17 5.19 1.83 3.37 Al 4.67 3.54 3.45 3.38 3.45 Cr 0.00 0.00 0.00 0.00 1.28 0.00 Cr 0.00 0.00 0.00 0.00 0.00 Fe3+ 0.19 3.83 6.64 0.00 0.37 2.32 Fe3+ 0.01 0.03 0.04 0.02 0.01 Fe2+ 0.08 0.06 0.08 0.79 0.00 0.00 Fe2+ 2.38 4.22 5.01 3.66 0.93 Mn 0.08 0.06 0.09 7.80 0.00 0.02 Mn 0.06 0.16 0.07 0.09 0.03 Ni 0.00 0.00 0.00 0.00 0.00 0.00 Ni 0.01 0.01 0.01 0.02 0.00 Zn 0.00 0.00 0.00 0.00 0.00 4.97 Zn 0.00 0.01 0.00 0.00 0.00 Mg 8.53 4.84 0.37 0.52 10.16 1.45 Mg 7.03 5.77 4.81 6.36 9.02 Ca 0.00 0.04 0.25 0.00 0.00 0.00 Ca 0.03 0.02 0.02 0.04 0.01 Na 0.00 0.00 0.08 0.00 0.00 0.00 Na 0.00 0.00 0.00 0.00 0.00 K 0.00 0.00 1.55 0.00 0.00 0.00 K 0.00 0.03 0.05 0.00 0.00

Table 3: Table comparing Kiirunavaara chlorite analyses with sample number (on the right hand side, cf. Appendix 2) with examples of chlorite analyses from Deer et al. (1992). The sums of oxides in these are calculated without water content, for comparative reasons.

DHZ1: Mg-Al chlorite talc-serpentine schist, Camberousse, Savoy, France.

DHZ2: Mg-Fe chlorite, chlorite-epidote-albite schist, Limebury Point, Salcombe Estuary, South Devon, UK.

DHZ3: Fe-chlorite, vein in granite, Silent Valley quarry, east Mourne mountains, Northern Ireland.

DHZ4: Manganeese chlorite, ore, Benallt mine, Rhiw, Caernarvonshire, Wales, UK.

DHZ5: Chromian chlorite, Gumushane, Turkey.

DHZ6: Zinc chlorite, calcite vein in breccia containing altered andesite and -vesuvianite skarn, Chillagoe, Queensland, Australia.

For full list of sample references, see Deer, Howie & Zussman (1992) p. 336

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Talc and clay-minerals Only minor amounts of talc were encountered during the present study, even though mapping has shown it to be a common mineral. It was encountered in two different settings. They are situated mainly together with amphiboles in the same setting as traces of clay-minerals and also in pores of porous magnetite matrix along with dolomite and mica.

Talc in the Kiirunavaara ore show small variations in chemical composition. It mainly consists of Si and Mg along with fairly high amounts of Fe (FeO 3.65-5.22 %; ferroan talc) and trace amounts of Al, Mn and Ca (cf. Harlov et al., 2002). Appreciable amounts of F (up to 2.19 wt %) is also documented (see Appendix 2). The only varying trend that has been observed is that the Fe-content is higher when talc is present as a fine grained matrix in association with amphibole rather than with dolomite and mica. In the latter environment, elevated contents of Mg are instead observed. In the table below, typical samples of Kiirunavaara talc are given together with examples from Deer et al. (1992).

Probable clay minerals have been analysed (see Appendix 2) with compositions in the range

48 – 59 % SiO2, 11 – 15 % Al2O3 and 9 -12 % FeO as dominating oxides. Minor elements consist of Mg, Ca, Na and K in falling order along with traces of S, P and Cl. These have not been investigated further

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Table 4: Representative analyses of Kiirunavaara talc compared to example analyses from Deer, Howie and Zussman (1992).

B27.3.3 B20.4.1 DHZ1 DHZ2 DHZ3

SiO2 62.49 61.23 61.71 62.5 62.69

Ti2 0,01 0,04 0,09 - -

Al2O3 0.02 0.22 0.3 0.5 0.49

Cr2O3 0.00 0.00 - 0.1 -

V2O3 0.00 0.01 - - - FeO 3.75 5.19 4.09 1.32 0.76 MnO 0.03 0.07 - 0.01 - MgO 29.21 27.59 29.09 30.8 29.93 CaO 0.13 0.10 - - 0.3

Na2O3 0.00 0.00 - - 0.03

K2O 0.02 0.00 - - 0.02 NiO 0.02 0.10 - - - ZnO 0.03 0.08 - - - F 1.52 0.25 - - - Cl 0.00 0.03 - - -

Total 96.60 94.90 95.28 95.35 94.22

Si 7.89 7.96 7.95 7.95 8.02 Ti 0.00 0.00 0.01 - - Al 0.00 0.03 0.05 0.07 0.07 Cr 0.00 0.00 - 0.01 - V 0.00 0.00 - - - Fe 0.40 0.56 0.44 0.14 0.08 Mn 0.00 0.01 - 0.00 - Mg 5.49 5.35 5.58 5.84 5.71 Ca 0.02 0.01 - - 0.04 Na 0.00 0.00 - - 0.01 K 0.00 0.00 - - 0.00 Ni 0.00 0.01 - - - Zn 0.00 0.01 - - - F 0,61 0,10 - - - OH 3.39 3.88 4.00 3.99 4.61 Cl 0.00 0.01 0.00 0.00 0.00

DHZ1: Talc, talc--chlorite schist, Gran Paradiso, Cogne, Italy. DHZ2: Talc, Contact-metamorphosed schist, south-west Alpe Zocca, Italy. DHZ3: Talc orebody, Trimouns, French Pyrenees.

For complete list of sample references, see Deer, Howie & Zussman (1992), p329.

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Titanite Titanite is relatively common in small quantities. It grows mainly in bundles of small crystals 0.05mm – 0.1mm, most often along the edges of magnetite units (Fig 16), but do sometimes occur as bundles of more subhedral – euhedral crystals, usually adjacent to a mass of magnetite (Fig. 17). In addition to the major cations Ca, Ti and Si the Kiirunavaara titanites are characterised by significant abundances of Fe, V, light REE, F and P. Previous titanite analyses from Kiirunavaara have been carried out by Smith et al. (2009). The Kiirunavaara titanites are plotted along with Kiruna-group samples of titanites from Smith et al. (2009) (Fig. 31). There is a clear correlation between samples in the present study and the samples from Smith et al. (2009). Both data sets are consistently low in Al and relatively high in REE, compared to representative analyses in Deer et al. (1997), but the compositional spread is much larger in the present data set.

Figure 16: Fe-poor, Ti-rich type of titanite crystals. Ca Figure 17: Fe-rich, Ti-poor type of titanite 50 μm in diameter.

Allanite The shape of allanites is subhedral and highly irregular. It typically grows in bundles adjacent to clusters of magnetite crystals (Fig. 18). The color is reddish with a tint of brown. The only samples localised in this investigation are associated with phosphorus-rich environments, shown in sample B1.1.1, where the allanite crystals grow in a matrix of apatite (Fig 18).

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Figure 18: Bundles of allanites adjacent to magnetite crystals. The Kiirunavaara allanites show a relatively large compositional variation (Fig. 19). For example, the range in FeII+/(FeII++Mg) is from 0.52 to 0.91, and the ratio of VIFe3+ to VIAl is high, putting them closer to the ferriallanite , rather than allanite s.s. Total REE range from 0.73 to 0.93 a.p.f.u. The Kirunavaara allanites also contains minor Ti (0.01 – 0.07 a.p.f.u.), Mn (0.01 – 0.08 a.p.f.u.), V (0.00 – 0.02 a.p.f.u.) , Y (0.00 – 0.02a.p.f.u.), F(0.06 – 0.28 a.p.f.u.) and P (0.00 – 0.01 a.p.f.u.), along with traces of Th.

Figure 19: Compositional classification of the Kiirunavaara allanites of this study. Additional data from Holtstam et al.(2003) and Smith et al. (2009). Diagram after Holtstam et al. (2003).

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Epidote Only one sample of epidote was analysed in this study (see Appendix 2). It is, according to the classification scheme in Deer et al. (1992), classified as epidote s.s. It contained traces of Mn, Ti, Sr and P.

Zircon and thorite Two zircon crystals and two thorite/ crystals were analysed in this study. They were found in two different thin sections: one zircon crystal and one thorite crystal in each. Both of these thin sections are silicate rich and poor in phosphorus. The zircons are about 0.05 – 0.1 mm in diameter and display a zoning texture. The color is dark brown and partly opaque. Thorites/huttonites however, are completely opaque but similar in size.

Figure 20: Zircon and thorite crystals (ca 50 μm in diameter) from Kiirunavaara. A faint radioactive halo is observed in the surrounding phlogopite around the latter. The Kirunavaara zircons contain minor quantities of Al, Fe, Mn, Ca and Hf. The thorites contain a wide range of elements in addition to Th, Si and O. Most significant is the content of U and Ce; between 3 – 4 wt% of UO2 and 4 – 6 wt% Ce2O3. Other elements in minor and trace quantities in thorite are Fe (0.03 – 0.06 a.p.f.u), Ca (0.04 – 0.08 a.p.f.u), Ba (0.00 – 0.01 a.p.f.u.), Y (0.00 – 0.01 a.p.f.u.), L-REE (0.01 – 0.11 a.p.f.u.) See Appendix 2.

Feldspar and quartz Other silicates that were analysed in present study were quartz and feldspar. One sample of feldspar and three samples of quartz were analysed. The feldspar did not contain any K and only traces of Ca. Therefore it is albite. All of the analysed quartz contained trace amounts of Fe, Al, Ca, Ti and Cr (see Appendix 2).

21

Carbonates Three different types of carbonates have been found: calcite, Fe-bearing dolomite and . Dolomite and ankerite are distinguished, according to Chang et al. (1996), by their (Fe2+/(Mg+Fe2+) ratio where a ratio >0,2 is to be characterized as ankerite. The calcites were found in fissures, crosscutting homogeneous or brecciated magnetite while dolomites and ankerites Figure 21: Large calcite grains within magnetite. were found both within magnetite breccia

Figure 22: Small grains of ankerite.

and silicate dominated environments. The texture of calcite is most commonly subhedral and the size seems to vary with the width of the fissure which it is filling. Dolomite and ankerite tend to be more anhedral in shape and commonly smaller in grain size compared to calcite. The different phases are most often easy to distinguish by their and twinning, which is clear in calcite and most often missing in dolomite and ankerite. All calcite, subject to this study, contain a certain amount of Mg, Fe and Mn, between 0.88 – 1.4 Figure 23: Relationship between different carbonates wt% MnO, 0.08 – 1.41 wt% MgO and 0.06 – regarding Mg, Fe and Mn. Plotted vs. Ca. 1.13 wt% FeO (see Appendix 2).

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Table 5: Representative analyses of the three different phases of carbonate minerals within the ore body. CO2 is calculated.

1 2 3

CaO 51.74 28.90 28.58 MgO 1.41 15.76 15.42 FeO 1.13 5.74 8.05 MnO 1.40 2.94 1.28

CO2 44.20 46.45 43.62 Total 100.00 100.00 100.00

Number of ions on the basis of 2 cations

Ca 1.86 1.00 0.94 Mg 0.07 0.76 0.71 Fe 0.03 0.16 0.21 Mn 0.04 0.08 0.03

B1-4-2 Calcite B17-3-2 Dolomite B27-5-3 Ankerite

Sulphates and phosphates The sulphates and phosphates found in the present study are; gypsum, anhydrite, apatite and monazite. Apatite and monazite exists in close relationship with magnetite whereas gypsum and anhydrite are localised as secondary minerals in fissures. Anhydrite is also known

Figure 24: Apatite and monazite (inclusions within Figure 25: Anhydrite and gypsum in brecciated apatite) in fissure cutting through magnetite breccia. magnetite.

23 through core logging as a contact phase between the ore body and host rock. Apatite and monazite contain traces of Fe. Monazite is of the species monazite-(Ce), with Ce as the dominating cation (Chang et al., 1996). Apatite and monazite in Kiirunavaara have been studied extensively by Harlov et al. (2002). The gypsum contains traces of Fe, Cl and P, and anhydrite traces of P, Sr and Fe (Appendix 2).

Oxides Oxide minerals analysed in the present study include magnetite, hematite and . (Appendix 2). One sample of each mineral species was analyzed. The rutile contained 1.66 –

1.8 % FeO and 0.78 – 0.85 % V2O3. V was also found in magnetite (0.12 – 0.29 %). Other traces of elements within the Fe-oxides were close to or below the detection limits. This was also the case for Ti.

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Discussion Silicates Amphibole There are many substitution mechanisms involved in calcic amphiboles (Deer et al., 1997). Calcic amphiboles have four octahedral cation positions in the structure, M1,2,3,4, where M4 is dominantly occupied by Ca, and the other three by Mg, Fe2+, and Mn. Only insignificant amounts of Fe3+ are present in the Kiirunavara amphiboles according to the formula charge balancing. Important substitutions for the Kiirunavaara amphiboles are: [M]Mg = [M]Fe2+, as seen in the variation in the Mg/(Mg+Fe2+) ratio in Fig. 6, and: [M1,2,3](Mg,Fe, Mn)2+ + [T]Si4+ = [M1,2,3]Al3+ + [T]Al3+, the so called tschermak substitution (Deer et al., 1997) (Fig. 26A). T represents the tetrahedral site. However, since the amount of Al in the T position is often larger than in the M position and Al approaches a 1:1 substitution with Si (Fig. 26B) an additional mechanism has to be invoked. The increase of Al also correlates with an increase in the alkalis suggesting the operation of: [T]Si4+ = [M4,A](Na,K)+ + [T]Al3+ However, also Ca decreases with an increase of the alkalis (Fig. 26C) and this may be related to: [M4]Ca2+ = [M4](Na)+ + [A](Na ,K)+. Thus, filling of the poorly filled A site in the Kiirunavaara actinolites is related to a concomitant substitution of Al in the T position and Na in the M4 position. Not all the variation in Ca, however, can be explained by this variation. Since Ca does not fill the M4 position in the Kiirunavaara actinolites (<2 a.p.f.u., see Appendix 2), it is also filled partly with (Mn,Mg,Fe) (Fig. 24D) according to: [M4]Ca2+ = [M4](Mg,Fe,Mn)2+. However, due to the simultaneous incorporation of Na in the M4 position the (Mg,Fe, Mn) in M4 (>5 a.p.f.u.) is only roughly correlated with a decrease in Ca.

25

Figure 26: Plots illustrating substitution mechanisms operating in the Kiirunavaara actinolites. A. Si+Mg+Fe (Incl. Mn) vs. Al. B. Si vs. Al. C. Ca vs. Na+K. D. Ca vs. Mg+Fe+Mn. Explanations in the text.

As described, some of the amphiboles are intergrown with magnetite, usually displaying an orientation along a flow pattern. This suggests that some of the amphiboles formed slowly together with magnetite. Similar observations of actinolite crystals have been made in the stratabound iron deposit of Sierra La Banderra, Chile, by Lledo (2005). Figure 27 and 28 shows the pattern in Kirunavaara and Sierra La Banderra respectively.

Figure 27: Actinolite crystals (ca 2 mm long, 0.4 mm Figure 28: Actinolite crystals (ca 2-6 mm long and 0.5 wide )from Sierra La Banderra, intergrown with mm wide) from Kiirunavaara, intergrown with a crystals of magnetite (Lledo, 2005). matrix of magnetite.

26

The amphiboles that are inter-grown with magnetite display a composition close to that of the rim of the zoned amphiboles. More specifically, depletion of Al, Ti, Na and K along with enrichment in Si, Ca and Mg, whereas amphiboles located in more silicate rich parts tend to instead mimic the core composition of those zoned crystals. According to an experimental study perfomed by Lledo & Jenkins (2008) actinolites of similar composition, Ca > 1,7 a.p.f.u. and Fe-number of 0.22 (0.04 – 0.25 for Kiirunavaara actinolites) were shown to be stable at temperatures up to 850° at 1 kbar and 900° at 4 kbar. It should be noted, however, that was always present during these experiments which has not been observed in the present study, however, reported by Geijer (1910). In the absence of pyroxene the experimental actinolite stabilities should be regarded as upper limits (D. Jenkins, pers comm. 2012). The correlation in both composition and textural relationship between the actinolites of Kirunavaara and Sierra La Banderra, indicates a similar origin, at least regarding the ones intergrown with magnetite. Lledo (2005) has shown that P-Fe-rich magma can exist down to 600˚C and coexist with actinolite at low pressure. This is in agreement with the volcanic- subvolcanic character of the Kiirunavaara deposit and the flow-textured actinolites.

Mica and chlorite The Kiirunavaara mica is typically high in Mg over Fe, i.e. phlogopitic (see Fig. 11). Group 3 mica has the lowest Fe contents. The latter is mostly texturally associated with apatite and magnetite and may thus be in equilibrium with the ore, while the more Fe-rich phlogopites appear to have equilibrated together with more late stage carbonates. Substitution mechanisms operating in mica are very complex (see Fleet, 2003), and the compositional variation in the Kiirunavaara mica is substantial. However, the dominating chemical variation observed relates to the Mg/(Mg+Fe) ratio (Fig. 11), mainly representing the simple octahedral substitution: [6]Mg2+ = [6]Fe2+. A small part of Fe may be Fe3+, but this is impossible to determine with the EMPA technique. The other main variation concerns Al (Fig. 27). The Cl-rich (see below) phlogopites are richer in Al and have Al such that Si/Al<3/1 (see Appendix 2), as well as in excess of the tetrahedral position indicating the operation of: [6](Mg,Fe)2+ + [4]Si4+ = [6]Al3+ + [4]Al3+. Contrastingly, in the F-rich mica, this mechanism is reversed to such an extent that Si/Al>3/1. This may be partly compensated by: 27

[6](Mg,Fe)2+ + 2[4]Al3+ = [6]□ + 2[4]Si4+ or [A]K+ +[4]Al3+ = [A]□ + [4]Si4+ (□ represents vacancy).

Figure 29: Plot of Si + (Mg+Fe+Mn) vs. Al illustrating substitutional mechanism in the Kiirunavaara micas. Discussion in the text.

The minor Ti appears positively correlated with Al and Cl and lower total octahedral occupancy (see Fig. 29; Appendix 2), suggesting that: 2[6](Mg,Fe)2+ = [6]Ti4+ + [6]□ and [6](Mg,Fe)2+ + [4]Si4+ = [6]Ti4+ + [4]Al3+ are viable minor substitutions. It appears also possible from the analytical data that the variation in the fill of the interlayer cation site may at least partly be related to: [A]K+ + [6](Mg,Fe)2+ = [A]□ + [6](Al,Fe)3+ and/or 2[A]K+ + [6](Mg,Fe)2+ = 2[A]□ + [6]Ti4+. A small group of micas appears to contain Si and (Mg,Fe) in excess of the tetrahedral and octahedral positions, respectively (see Fig. 29).

The tendency that has been noticed in the Kiirunavaara mica to become enriched in F in Mg- rich mica and instead enriched in Cl in Fe-rich mica, is known as Fe-F avoidance (or Mg-Cl avoidance) (Fleet et al., 2003). According to him, enrichment in F occurs in dry environments. Foley et al. (1986) noticed in their experiments on the effects of F on the stability of phlogopite an increase in the temperature stability of phlogopite when F was added to the system. They also noticed that the increase in F in the phlogopite itself was proportional to the enrichment in Si together with depletion of Al. The same phenomenon is encountered by the author when comparing samples from different groups of Kiirunavaara mica. 28

This could be an indicator of two separate crystallization events and/or environments of Kiirunavaara mica, one at drier, higher T, enriched in Mg and F, and another at more hydrous, lower T, enriched in Fe. The compostion of the chlorites in the Kiirunavaara ore is considerably poorer in Al than those in metapelitic and felsic rocks, partly overlapping those of metabasic rocks, while the Mg-numbers are higher than most felsic rocks and overlapping those in metapelites and metabasic rocks (cf. Zane et al., 1998) The chlorites mimic the compostion of the coexisting phlogopite in respective sample, suggesting equilibration in a similar envirnment or replacement of the mica. Most chlorites contain detectable amount of Cl.

Talc and clay-minerals The talc in Kiirunavaara shows small variations in chemical composition: a feature common for talc in general (Deer et al., 2009). The main substitution observed is Fe replacing Mg and F replacing OH. (cf. Deer et al., 2009). Only insignificant FeIII+ appears to be present. Talc is a relatively late phase harboring F and small amounts of Cl, often associated with dolomite.

29

Titanite Previous titanite analyses of Kiirunavaara have been carried out by Smith et al. (2009). There is a substantial overlap in composition between samples in the present study and the samples from Smith et al. (2009). Both are high in Fe, typically low in Al, and relatively high in Y + REE, compared to representative analysis in Deer et al. (1997). All titanite crystals, analysed in this study, have been observed at the rims of magnetite or in bundles at a close distance from the magnetite which indicates a later formation than the magnetite itself. Figure 28 displays Fe vs. Ti content in titanites, plotted by thin section.

Figure 30: Kirunavaara titanites Fe vs. Ti. Plotted by thin section. The titanites which contain the lowest amount of Fe are more transparent in color and precipitated onto the magnetite rims whereas the ones containing the highest amount of Fe usually grow in bundles at some distance from the magnetite and have a more reddish character. There is a concomittant increase in Fe+Al+V and a decrease in Ti in the compositional spectrum of the Kiirunavaara titanites, also crudely co-varying with Y-REE (Fig. 31). This suggests that the following substitution mechanism is important:

30

Figure 31: Compositional diagrams of the presently investigated Kiirunavaara titanites compared to Kiruna-group titanites from Smith et al. (2009).

[7]Ca2+ + [6]Ti4+ = [7](Y,REE)3+ + [6](Fe,Al,V)3+.

However, this cannot account for all the Fe+Al+V found in the titanites, but the following mechanism roughly seems to account for the remaining trivalent cations:

[6]Ti4+ + O2- = [6](Fe,Al,V)3+ + F- based on the co-increasing fluorine contents.

The Kiirunavaara titanites do always contain P in small amounts. P seems to increase along with an increase of V. However, no satisfying substitution mechanism where P is involved has been found during the present study. Although there is a semi-continuous compositional spread in the titanite data: two compositional and textural groups can be discerned. This may be an indication of two different generations of titanites, which is also the conclusions by Smith et al. (2009) and Storey et al. (2007), based on data from samples of the associated Porphyry Group. Smith et al. (2009) came to the conclusion, by U-Pb isotopic analysis of titanite grains in the

31

Kiirunavaara hanging wall, that two separate events formed the titanites. One (1894±35 Ma) related to the iron ore formation and the other, at c. 1780 Ma, related to a late stage hydrothermal event. However, it could also be an indication of penecontemporaneous growth in two different environments. The Kiirunavaara samples show a larger compositional spread compared with samples from Smith et al. (2009). This could be due to the larger amount of titanite analyses in the present study. The correlation between the two studies is except for this matter relatively good and is shown in figure 31.

Allanite The compositional overlap between the Kiirunavaara, Nautanen, and Rakkurijärvi allanite- ferriallanites points towards a similar environment of formation, presumably from a relatively late fluid-enriched stage. This contrasts with the ferriallanites from the Bastnäs deposit which show an even higher content of FeIII+ (Fig. 19). The Kiirunavaara allanite-ferriallanites also range towards relatively low Fe2+/(Fe2+ + Mg) ratios.

Zircon and thorite Zircon in Kirunavaara has been described before both by Geijer (1910) and Parak (1973b). The zircons analyzed in the present study are encountered in Si-rich and P-poor environments in contradiction to the earlier observation done by Geijer (1919) who claimed that zircon is restricted to apatite. This was however, already questioned by Parak (1973b) who showed that zircon exists in both P-rich and P-poor parts of the ore body. Zircons can be formed in both igneous and metamorphic environments. Even hydrothermal zircons are claimed to have been observed though their existence is still debated (Hoskin & Schaltagger, 2003). Igneous zircon often displays a pattern called oscillatory zoning (Shore & Fowler, 1996). This pattern seems to exist in the Kiirunavaara zircon although its small grain size makes it difficult to determine. There are many different trace element patterns that can determine the origin of zircon. Most of these elements are however, below the detection limit in the present study and are therefore not applicable in this regard.

32

Figure 32: Euhedral zircon. According to Klein & Hurlbut (1999), zircons always contain a small amount of Hf which also is the case for the samples in this study. Klein & Hurlbut (1999) also states that zircons commonly contains some Th and U which causes some structural damage to the crystal lattice. The thorites encountered in Kiirunavaara are only called thorites for simplicity reasons. The fact is that they may as well be huttonite which is the polymorph of ThSiO4 that is stable in temperatures above 1210 ° – 1225 °C at 1 atm or 780 °C at 200 MPa (Harlov et al., 2005). Huttonite is isostructural with monazite and has been proven stable at much lower temperatures (300 ° – 900 °C at 200 – 1000 MPa) when grown on natural monazite (Harlov et al., 2005). Because of the choice of analytical method, distinction in between the two is not possible in the present study.

Carbonates Since carbonates have been found with different compositions corresponding to different settings and grain size, one can assume that there are at least two generations of carbonates within the ore body. One generation appears to have precipitated early, together with silicates and magnetite, dominated by dolomite and ankerite, while the other (calcite) post-dates the magnetite, filling up fissures within the most iron rich (B1) part of magnetite. According to Chang et al. (1996), the ankerite subject to the present study is close to the Mg-rich end composition of ankerite, Ca(Mg0.8Fe0.2)(CO3)2. This puts them relatively close to the dolomite side of the spectrum. Chang et al. (1996) also states that dolomite usually appears along with calcite, ankerite and siderite.

33

34

Conclusions Amphibole All amphiboles are calcic amphiboles which show a continuous range in composition that for the most part fall in the actinolite field.

Compositional zoning is noticed in several instances, such that core compositions are richer in Fe, Al, and alkalis, whereas the rims are richer in Si, Ca, Mg.

Similarly, amphiboles crystallized together with magnetite are relatively enriched in Si, Ca, and Mg but relatively depleted in Fe, alkali elements and Al, while amphibole crystallized together with other minerals display the opposite relationship.

The chemical variation is dominated by the following two substitution mechanisms: [M1,2,3]Mg = [M1,2,3]Fe2+ and [M1,2,3](Mg,Fe)2+ + [T]Si4+ = [M1,2,3]Al3+ + [T]Al3+,

The Kiirunavaara actinolite demonstrates a clear textural and compositional similarity with actinolites from Sierra La Banderra, Chile, which is an indicator for similar origin. This, along with experiments on the stability of actinolite, suggests a possible magmatic crystallization.

Mica All mica is to be classified as phlogopite.

Three groups of mica are distinguished by composition. Group one is enriched in Fe, Al, Ti, Mn, K and Cl whereas group two is enriched in Si, Mg, and F, and group three shows an even higher enrichment in these elements than group two. This division is clearly visible through each groups F content.

The compositional variation is complex but appears dominated by the following substitutions vectors: [6]Mg2+ = [6]Fe2+, [6](Mg,Fe)2+ + [4]Si4+ = [6]Al3+ + [4]Al3+, and [6](Mg,Fe)2+ + 2[4]Al3+ = [6]□ + 2[4]Si4+.

35

Fe-rich phlogopites are associated with carbonates and actinolites, whereas Mg-rich phlogopites are associated with apatites.

Chlorite Chlorites show a wide range in Fe, Mg and Al contents.

The composition is however, locally similar in between crystals and follows the same compositional trend as coexisting mica.

Talc Talc in Kiirunavaara mainly consists of Si and Mg, along with fairly high amounts of Fe.

The only variation trend that has been observed is an elevated Fe-content when talc is associated with amphiboles, whereas higher Mg talc is present together with dolomite and mica.

Titanite The Kiirunavaara titanites are characterised by significant abundances of Fe, V, lightREE, F and P.

The following two substitution mechanisms are dominating in the titanites: [7]Ca2+ + [6]Ti4+ = [7](Y,REE)3+ + [6](Fe,Al,V)3+ and [6]Ti4+ + O2- = [6](Fe,Al,V)3+ + F-

Two groups with differences in texture and composition are found. The content of Fe and Ti is the clearest distinguishing factor.

Zircon and thorite Zircon and thorite observed in this study co-exists in Si-rich and P-poor environments.

The texture of zircons appears to be oscillatory, which indicate an igneous origin.

Carbonates Three different types of carbonates are found: calcites, Fe-bearing dolomites, and ankerites.

All carbonates in Kiirunavaara contain Fe, Mg and Mn to some extent.

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The different compositions are related to variable textural settings, indicating two different generations of carbonates. One dolomitic – ankeritic, hosted in brecciated magnetite environments and the other calcitic, precipitated in fissures within magnetite.

Sulphates and phospates The sulphates and phosphates encountered in this study are gypsum, anhydrate, apatite and monazite.

Apatite and monazite exists in close relationship to magnetite, whereas gypsum and anhydrate occur as late stage minerals in fissures.

In general No distinction between mineral compositions in the P-rich and P-poor ore parts, which was one of the objectives of this study, has been revealed.

The chemical variation within mineral species is more likely related to textural differences (local chemical equilibrium) than to bulk composition of the ore sections.

Curiously, P is widely present in low amounts within several minerals, notably actinolite, titanite, anhydrite and gypsum.

The textures and compositions suggest changing chemical environment and conditions during silicate crystallization in the Fe-ore.

Actinolite shows textural evidence of early precipitation, together with magnetite and apatite and experiments have shown that actinolite of this composition may be in equilibrium with a Fe-P melt at 850° at 1 kbar and 900° at 4 kbar.

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Recommendations Further mineralogical work on the ore body is recommended, especially with focus on sulphides, which have not been considered in the present study nor have been significantly studied before. Sulphides are not only important for the same aspects as the minerals in this thesis, but also because of their economic potential. Further study regarding clay minerals is also recommended, since they were only touched upon in the present work. The composition, occurrence and extent of clay minerals play an important structural role within the ore body and its surrounding rocks. A study with the focus on the mineralogical-geochemical link between the nodule-bearing trachyandesite in the foot-wall and the ore is also recommended. This could reveal new clues in the understanding of the ore formation.

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Appendix 1

Drillcore X- Y- Z- number Sample number Section start Section end coordinate Coordinate Coordinate 6289 B1 122,2 125 6877,440 3968,821 1037,688 6289 B2 228 228,8 6877,440 3968,821 1037,688 6036 B8 332,55 332,6 6631,500 1597,320 1041,410 6274 B14 198,5 201,5 6617,189 2779,745 1061,684 6058 B17 149 150,8 6503,220 1397,970 1039,740 6172 B20 153 156 6517,230 2685,223 1065,032 6176 B22 26 29 6507,408 2884,539 1061,437 6176 B23 43 46 6507,408 2884,539 1061,437 6040 B26 221 223 6530,300 1695,090 1043,410 6040 B27 168,5 171,5 6530,300 1695,090 1043,410 6040 B28 151,5 153,5 6530,300 1695,090 1043,410 6462 B32 504 507 6482,450 210,250 1027,450 6407 B33 17,4 20,6 Unknown Unknown Unknown 6407 B35 65 68 Unknown Unknown Unknown 6243 B42 105 108 6617,501 2784,240 1062,711 6243 B45 197 200 6617,501 2784,240 1062,711

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