MASTER'S THESIS. Rhenium in the Aitik Cu-Au-Ag-(Mo) deposit. Wondowossen Nigatu. Master of Science Exploration and Environmental Geosciences

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1 MASTER'S THESIS Rhenium in the Aitik Cu-Au-Ag-(Mo) deposit Wondowossen Nigatu Master of Science Exploration and Environmental Geosciences Luleå University of Technology Department of Civil, Environmental and Natural Resources Engineering

2 Rhenium in the Aitik Cu-Au-Ag-(Mo) deposit Wondowossen Bekele Nigatu Supervisor: Dr. Christina Wanhainen i

3 Table of Contents Table of Contents... ii List of Figures... iii List of Tables... iv Abstract... v Chapter 1 Introduction Background information Objective and scope of this study Rhenium Introduction Application and consumption of rhenium Demand and supply Price... 6 Chapter 2 Molybdenite within the Aitik deposit and its surrounding area General Geological setting and local geology Geology of the Aitik deposit Mineralization in the Aitik deposit Liikavaara Salmijärvi General occurrence of molybdenite Rhenium in molybdenite Chapter Sampling, sample preparation and analytical method Sampling Sample selection Sampling using Micro drilling Recovery of sample from drilling Sample weighting and molybdenite dissolving procedure Determination of rhenium abundance using ICP-MS analysis Chapter 4 Results Molybdenite within the three studied deposit Molybdenite distribution within the Aitik deposit Molybdenite distribution within the Salmijärvi deposit ii

4 4.1.3 Molybdenite in the Liikavaara mineralization Results of rhenium concentration in molybdenite Rhenium concentration against molybdenite grain size Rhenium concentration against molybdenite weight Rhenium concentration for each sampled area Rhenium concentration against major host rocks Rhenium concentration against mineral association Rhenium concentration with respect to molybdenite crystal habit Chapter 5 Discussion Causes of rhenium variation within molybdenite Comparison with other porphyry deposits Rhenium extraction from molybdenite: implications for the Aitik Cu-Au-Ag (Mo) deposit Acknowledgements References Appendix I: Measured grains of molybdenite Appendex II: Rough estimation of the money value of the Aitik rhenium List of Figures Figure 1 Location map of Aitik, Liikavaara and Salmijärvi deposits Figure 2 Percentage of rhenium demand sector Figure 3 Historic price of rhenium (Naumov 2007)... 7 Figure 4 A) Regional geology of northern Sweden. (Wanhainen et al.2003b) Figure 5 A) Different parts of the micro drilling equipment (Charlier et al.2006) B) Sample mounted for micro drilling C) Sample recovery D) weighting of sample using gold boat E) Digestion of sample using aqua regia Figure 6 Molybdenite associated with sulphide minerals Figure 7 Molybdenite within quartz-muscovite-sericite schist Figure 8 Euhedral molybdeinte grains within the QMD Figure 9 Molybdenite associated with alteration minerals in QMD Figure 10 Molybdenite within the QMD host rock Figure 11 Molybdenite grains with associated mineral assemblages within the QMD Figure 12 Molybdenite distribution within the major host rocks of the Salmijärvi deposit Figure 13 Molybdenite distributions within the Liikavaara deposit Figure 14 Molybdenite grain size measurement on the polished section Figure 15 Plots of rhenium concentration versus molybdenite grain size Figure 16 Molybdenite grain weight versus rhenium concentration Figure 17 A) Rhenium concentration within the north Aitik mine. B) Rhenium concentration within the south Aitik mine. C) Rhenium concentration within the Salmijärvi deposit. D) iii

5 Rhenium concentration within the Liikavaara deposit. E) Average rhenium concentration in molybdenite within the three deposits Figure 18 A) Rhenium concentration within the major host rocks of the Aitik deposit Figure 19 Average rhenium concentration of molybdenite within the major host rocks of the Salmijärvi deposit Figure 20 Rhenium concentration in molybdenite associated with alteration minerals in the Aitik deposit Figure 21 Rhenium concentration in molybdenite associated with opaque minerals within Aitik Figure 22 A) Rhenium concentration in molybdenite versus associated alteration minerals within the Salmijärvi deposit and B) Rhenium concentration in molybdenite versus associated ore minerals within Salmijärvi deposit Figure 23 A) Molybdenite crystal habit versus rhenium concentration in molybdenite within the Aitik deposit B) Average rhenium concentration in molybdenite versus crystal habits of molybdenite grains in the Aitik deposit C) Molybdenite crystal habit versus rhenium concentration in molybdenite within the Salmijärvi deposit D) Average rhenium concentration in molybdenite versus molybdenite crystal habits within the Salmijärvi deposit Figure 24 High rhenium containing molybdenite in the sericite-altered rock of the intrusive unit of the Aitik deposit Figure 25 A) Cu grade versus average rhenium content in molybdenite within the Aitik major host rocks. B) Au grade versus average rhenium content in molybdenite within the Aitik major host rocks Figure 26 Rhenium contents of grains of molybdenite projected on the contoured grade map of molybdenum at 300 m level in the Aitik deposit. Molybdenum grade map based on thousands of assays compiled by Boliden geologist Figure 27 Average rhenium concentration in molybdenite within the Aitik, Salmijärvi and Liikavaara deposits compared to Cu and Cu-Mo porphyry deposits of the world. Modified from Berzina et al. (2005) Figure 28 Average rhenium concentration in molybdenite within the Aitik, Salmijärvi and Liikavaara deposits compared to Mo-Cu porphyry deposits of the world. Modified from Berzina et al. (2005) Figure 29 Flow chart showing the recovery process of rhenium from a Cu-Mo ore. Modified from Naumov (2007) List of Tables Table 1 Summary of primary production of rhenium by country in kg from 2004 to 2009 (USGS)... 5 Table 2 Two years supply of rhenium from the recycling sector (Vulcan 2008) Table 3 Sample location and thin section ID Table 4 Molybdenite weight and known weight of rhenium added for isotope dilution Table 5 Rhenium concentration within molybdenite gains from the three studied deposits Table 6 Rhenium content (from this study) and Cu and Au grade within the major Aitik host rocks (Wanhainen 2005 and Wanhainen 2006) iv

6 Abstract The low-grade and high tonnage Aitik Cu-Au-Ag (Mo) deposit, the Salmijärvi deposit, and the Liikavaara deposit, which are situated at the mining district of the Norrbotten county, northernmost Sweden, are regarded as a porphyry deposit. Geologically the three deposits are situated in the continental domain of northern norrbotten, which comprises supracrustal series of meta-volcano-sedimentary rocks of paleoproterozoic age. These three deposits contain minor amounts of molybdenite. Rhenium, which is a unique element discovered back in 1925, naturally occur incorporated within the structure of molybdenite. The aim of this study was to determine the rhenium concentration within molybdenite and the genetic implication of the rhenium variation in different settings of molybdenite grains. In this study it has been possible to see significant variations of rhenium with different setting of molybdenite grain samples. In the Aitik deposit the rhenium concentration of molybdenite are higher in the quartz monzodiorite intrusive body (QMD) and in the quartzmuscovite-sericite schist than in the garnet-bearing biotite schist. In addition, the high rhenium-containing molybdenites are associated with rocks that are intensively sericite and biotite altered. Molybdenite in the Salmijärvi deposit contains an elevated amount of rhenium, especially in those rocks that are strongly altered by amphibole and biotite. Furthermore, the difference in degree of modification process that these two deposits seems to have undergone might have had an impact on the rhenium concentration of molybdenite, which has been seen from the relationship between the rhenium concentration in molybdenite and the crystal habit of the studied molybdenite grains. Based on the average rhenium concentration of the analysed molybdenite grains, the three studied deposits are similar to those Cu-Mo porphyry deposits of the world that are crustal in origin and show a sharp contrast in rhenium content of molybdenite with those Mo-Cu porphyry deposits of Climax-type. v

7 Chapter 1 Introduction 1.1 Background information The Aitik Cu-Au-Ag-(Mo) low-grade porphyry deposit has been one of the major and most important mines in Europe since it started production in 1968 (Wanhainen et al. 2003b), after its dicovery in 1930.The mine is situated within the mining district of Norrbotten county, northernmost Sweden, which hosts world-class deposits such as the Kiruna and Malmberget apatite iron ores (Wanhainen et al. 2005a, Wanhainen et al. 2005, Martinsson and Wanhainen 2004). The Aitik mine is located 15 km south-east of the city of Gällivare and 60 km north of the Arctic Circle at geographic coordinate between N latitude and 21 0 E longitude (Fig. 1). The pit perimeter of the Aitik ore zone, containing veins and disseminated chalcopyrite, pyrite, pyrrhotite and magnetite with minor molybdenite, is approximately 3 km long in the north-south direction and 500 m wide in the east-west direction. The ore body as described by Wanhainen et al. (2003b) continues down to 400 m level in the southern pit, plunging towards north to at least 800 m depth (Wanhainen et al. 2003b). This important open pit mine has undergone several expansions through time in response to the world market outlooks since it came into production. The high demand of metal in the world followed by the expansion made by the owner, Boliden Mineral AB, increased the production in 2010 from 18 Mt to 28 Mt of ore grade material with a head grade of 0.27% of copper, 0.16 g/t of gold and 2.07 g/t of silver. In year 2014 the mine will increase production capacity to 36 Mt per year (New Boliden annual report 2010). The total ore reserve of the deposit was initially calculated to 450 Mt. However, the economic ups on the world market fuel the sub-economic mineralization zones (mineral resources) to be part of the mineral reserve, which significantly increase the grand amount of the ore reserve. According to the ore reserve estimation made in 2010, the remaining ore reserve of the mine is reported to 747 Mt of proven and probable ore material with a weighted average grade of 0.25% copper, 0.14 g/t gold, 1.7 g/t silver and 29.9 g/t molybdenum, which extends the mine life until the end of 2030 (New Boliden annual report 2010). Boliden Mineral AB is implementing a new circuit in the Aitik processing plant to handle the minor molybdenite content of the ore and have made test work to extract the byproduct molybdenum, which range in grade from to 0.008% Mo, from the dressed ore concentrate after the copper flotation process (Fatai 2008). 1

8 Figure 1 Location map of Aitik, Liikavaara and Salmijärvi deposits. 1.2 Objective and scope of this study The Aitik deposit is generally described as a low-grade, high-tonnage Cu-Au-Ag (Mo) porphyry style mineralization; with some overprinting signature IOCG type as described by Wanhainen et al. (2005). Like many of the porphyry systems in the world, Aitik also contains molybdenite as a by-product to the copper ore. Molybdenite naturally contains some rhenium incorporated in its structure (King 2004, Voudours et al. 2009) and almost all the production of rhenium reported in the world comes from the roasting of the molybdenite in porphry copper deposits (USGS 2008). Therefore, the main objective of this study is focusing on the distribution and abundance of rhenium within different settings of molybdenite within the Aitik ore, the Salmijärvi ore, which is located 600 m from the Aitik current open pit, and the Liikavaara deposit, which is located about 3.5 km east of the Aitik mine (Fig. 1). Moreover, this study will include some genetic aspects of the studied molybdenite and possible extraction methods of rhenium from molybdenite concentrate that are currently used by other mines of similar type and existing technology. 2

9 1.3 Rhenium Introduction The silver white and heavy metal rhenium is one of the rarest and most highly dispersed element and it was one of the two last metals to be discovered in the periodic table. Its discovery was achieved in 1925 by a team of German scientists, namely Otta Berg, Walter Norddack and Ida Tacke and it got its name from the famous river Rhine (Lipmann 2005). Its crustal abundance is estimated to be 7x10-8 %, which makes it one of the rarest trace elements and it is by a factor of five lower than that of the precious metal gold (Naumov 2007). Rhenium is known by its chemical property of having 8 valance states from -1 to +7 of which +4 and +7 are the most stable, and by two isotopes 185 Re (37.4%), which is stable and 187 Re (62.6%), which is radioactive. In the periodic table it is located adjacent to tungsten and platinum group metals and diagonally to molybdenum, and as a result to this it shares some features of its neighbors (Fleischer 1959) Application and consumption of rhenium The extraordinary high melting point (ca.3180 o C), the extremely high density (21020 kgm -3 ); which is only exceeded by Pt, Ir and Os, the no ductile to brittle transition temperature, the extremely stable and rigid character under stress, which is described as high modulus of elasticity, the high resistance to creep and oxidation, the exceptional resistance to chemical poisoning (Vulcan 2008) altogether makes rhenium one of the minor metals which serve multifunction in modern technology and is thus listed as one of few strategic metals of the world according to USGS report on Some of the most important application sectors of rhenium include: High-temperature superalloys: The high creep and oxidation resistance together with the high melting point behavior of rhenium has gained a great importance in the nickel-based superalloys, with a reported addition of 3 to 6% rhenium (Lipmann 2005). This is mainly used in single crystal high temperature superalloys turbine blades for aircraft engines and other land based turbine applications. Using rhenium alloy in turbine engines in aircraft industry has also attracted attention due to the prolonged engine life, high fuel-efficiency, and increased engine performance etc. This application sector accounts for 77% of the total rhenium consumption (USGS 2008). Alloy of rhenium and boron gives a compound called rhenium diboride (ReB 2 ), which is harder than diamond, and an alloy of rhenium with silicon gives a stable cluster which is proved to be very important in the future quantum computers and nanotechnology (Vulcan 2008). 3

10 Catalysts The second major application area of rhenium is as catalytic reforming in the production of high-octane hydrocarbons in petroleum refinery from chemical conversion of low octane naphtha together with platinum, the high-octane is important in the production of lead free petrol. Using rhenium for this purpose is much more appreciated with respect to environmental concern of today due to the fact that this metal is very resistant to chemical poisoning from nitrogen, sulfur and phosphorus caused by motor vehicles (Burch 1978). This application sector accounts for 15% consumption of the total rhenium production. Other use Other application areas of rhenium are in the production of crucibles, electrical contact where Re 2 O 7 is used on the contact surface to provide self cleaning of contact in critical switches (Naumov 2007), electromagnets, electron tubes and targets, heating elements, ionization gauges, mass spectrographs etc. These application areas accounts for 8% of consumption of the total rhenium production (Fig. 2). Figure 2 Percentage of rhenium demand sector Demand and supply The demand for rhenium has increased from 35,000 kg to 65,000 kg during the last ten years (Vulcan 2008). The three major consumers of rhenium are Cannon Musketon (Supplier of Rolls Royce), who consumes around 14 t, General Electric who consumes 14 t, and Pratt and Whitney who consumes 5-6 t of the total annual production (Naumov 2007). USA, being one of the largest producers of aerospace superalloys, is one of the biggest consumers of rhenium in the world and it has been reported that the consumption rate increases at a rate of 5.4% every year (USGS 2008). 4

11 Roskill s forecast based on the market analysis shows an increase of demand at an average rate of 5% per year from year 2009 to 2015 which increase the annual demand to 71,500 kg. Primary supply Around 80% of rhenium production comes from a primary production of copper ores, which commonly contain molybdenum as a by-product. Rhenium itself is a by-product of the molybdenite and extracted from the roasting of molybdenite concentrate. The porphyry copper ore belt which extends from Chile up to Arizona (USA) is the dominating suppliers of rhenium in the world. The company Molyment owns a roasting plant for molybdenite for production of its primary target metal molybdenum, which is also equipped with a circuit for rhenium recovery. Therefore, Molyment is the largest producer of rhenium in the world with estimated production capacity of 64% of the world supply (Lipmann 2009). The USGS mineral year book (Desiree 2011, Desiree 2008) on rhenium shows that Chile is the world s largest producer followed by USA and Kazakhstan (Table 1). Table 1 Summary of primary production of rhenium by country in kg from 2004 to 2009 (USGS) World primary production of rhenium by country Country Armenia Canada Chile Kazakhstan Peru Russia United States Poland NA NA NA NA NA 2400 Other Total Secondary supply Recycling of rhenium is considered as a secondary supply. Supply from recycling is dominated by the two major application areas of the bi-metallic catalysis and from alloys industries. The valuable platinum in the catalysts makes the recycling of rhenium viable. According to USGS s mineral commodity summaries released in January 2011 all spent platinum rhenium catalysts were recycled, which will have a great effect on the price of the primary supply (Desiree 2011). The short life cycle of turbine blades in jet engines from the alloy industry contributes to a great possibility of recycling. However, recycling from this industry can be achieved at extreme marginal value (Lipmann 2005). The high accumulation of scraps from the alloy sector will demand high technology to recycle rhenium, thus German companies such as 5

12 H.C.Starck GmbH and Haraeus Holding GmbH are now investigating in an economical way of scrap recycling (Desiree 2008). Two years supply from recycling (Table 2) has shown significant contribution of rhenium to the overall supply as presented in the following table (Vulcan 2008). Table 2 Two years supply of rhenium from the recycling sector (Vulcan 2008). Secondary rhenium production (t) Year Germany France/USA Estonia Czech Republic Other Countries Total Price Rhenium is one of the ten most expensive metals listed in the world. On the world market the price of rhenium is based on the long term agreement made between the consumer and producer, which is based on the basic grade of APR (Ammonium perrhenate), the most common form in which rhenium is precipitated, or the metal rhenium pellet produced, from which the price is issued by the London-based Minor Metals Trade association (MMTA) (Lipmann 2005). For the last three decades the historic price of rhenium has shown an irregular pattern caused by several factors as a function of demand and supply as described by Naumov (2007) (Fig. 3). 6

13 Figure 3 Historic price of rhenium (Naumov 2007). The strong demand growth of rhenium has forced the price to increase by a factor of ten in the last five years (Vulcan 2008), before the economic down turn affected all metal prices around the world in During that period the highest price of rhenium recorded, with a peak in august 2008, were 12,000 $/kg. This was followed by downward correction as a function of economic crises leading to a decreased price of $/kg at the mid 2009 as reported by the Roskill int. (web). The recovery in the price of most metals seems to include rhenium from mid 2009 to mid 2010, and as a result a kilogram of rhenium was sold at a price of $ during this period. According to the assessment made by Roskill an increase in price of rhenium is expected as a function of an increasing demand by 5% per year from 2009 to This is especially driven by the superalloys sector, which accounts for the large consumption of the metal for the production of a new generation turbine blades. 7

14 Chapter 2 Molybdenite within the Aitik deposit and its surrounding area 2.1 General Baltic shield is a well endowed and important mineral source by containing several world class deposits (Wanhainen et al. 2006, Wanhainen et al. 2005). Among the most important and major ore deposit types in the Baltic shield, which accounts for a significant metal supply, is the low-grade, high-tonnage porphyry Cu-Au-Ag-(Mo) deposits (Wanhainen et al. 2003b, Lundmark et al. 2005, Weihed 2001). This porphyry-style of mineralization within the region occurs close to the Archaean-Proterozoic palaeoboundary (Lundmark et al. 2005). Below the Archaean craton (Fig. 4A) several discrete porphyry-style deposits have been discovered (Lundmark et al. 2005, Martinsson and Wanhainen 2004). The porphyry-style mineralization in the region mainly includes the Tallberg calc-alkaline porphyry type Cu - Au ± Mo deposit, located within the Skellefte district (Lundmark et al. 2005), the Grånberget quartz-feldspar granitic intrusion-related deposit south of Skellefteå (Lundmark et al. 2005, Weihed 2001), the Pikkujärvi deposit in the western part of northern Norrbotten, which is genetically related to the perthite-monzonite suite of granitoids (Lundmark et al. 2005), the Vaikijaur deposit related to Jokkmokk granitoid, which is located at the juvenile Proterozoic crust (Lundmark et al. 2005), and the Aitik Cu-Au-Ag-(Mo) porphyry deposit (Wanhainen et al. 2005a). Porphyry-style mineralization occurring close to the major Aitik deposit mainly include the Nunisvaara mineralization, which is located 10 km west of Aitik, the Nautanen deposit, which is located 15 km NNW of Aitik, and the Liikkavaara deposit located 3.5 km east of Aitik. These deposits are described as being related to the regional Nautanen Deformation zone, which runs in a north-northwest direction (Martinsson and Wanhainen 2004). 8

15 2.2 Geological setting and local geology The geology of Aitik and its surrounding areas are characterized by supracrustal series of palaeoproterozoic rocks of an age of ca Ga, which are metamorphosed at amphibolite facies thus forming gneisses and schists (Öhlander and Nisca 1985, Martinsson and Wanhainen 2004). They are thought to have a palaeoproterozoic volcano-sedimentary origin (Wanhainen et al. 2005, Monro 1988). The palaeoproterozoic succession, which is underlain by a 2.8 Ga Archaean granitoid gneiss basement exposed at the northernmost part of the region (Fig. 4A), was intruded by two generations of granitoids (Wanhainen et al. 2005, Monro 1988). These calc-alkaline to alkali-calcic granitic, gabbroic and dioritic intrusions regarded as belonging to the Haparanda and perthite-monzonite suites, intruded during the events elapsed between Ga (Wanhainen et al. 2005), and are mainly intermediate in composition (Wanhainen et al. 1999). This arc-related magmatism are suggested to have occurred due to subduction beneath the Archaean continent during the Svecokarelian orogeny (Lundmark et al. 2005, Öhlander and Nisca 1985).These two intrusive suits were described to occur in different tectonic environments, where the Aitik intrusion, genetically related to the Haparanda suite, occurs within a compression environment in a volcanic arc setting (Wanhainen and Martinsson 1999). The area was later affected by further extensive magmatism generated by orogenic deformation and metamorphism giving two generations of granitoid intrusion between Ga (Wanhainen et al. 2005). Monro (1988) describes these intrusions as the younger Lina granites, which is characterized by quartz, microcline, albite and minor biotite associated with abundant pegmatite dykes, and the older granitoid (Jyryjoki granite) characterized by plagioclase phenocrysts in a fine grained groundmass. The Lina granite suit is the most widespread intrusive body surrounding the Aitik deposit (Wanhainen et al. 2005). The supracrustal rocks and the intrusive rocks are suggested to have undergone metamorphism at amphibolites facies with strong decrease in degree of metamorphism from west to east across the major Nautanen Deformation zone (Monro 1988, Martinsson and Wanhainen 2004) Geology of the Aitik deposit The Aitik deposit geology is generally built up by calc-alkaline, intermediate rocks (Wanhainen and Martinsson 1999). Based on structural boundaries and copper grades the stratigraphic succession of the Aitik mine is divided into three categories (Wanhainen et al. 2005a), which includes the footwall, the main ore zone, and the hanging wall (Fig. 4C). Footwall zone In terms of copper grade the footwall zone of the Aitik deposit is characteristically a low grade zone ranging in copper grade from 0.10% in the most eastern part to 0.26% towards the ore zone (Wanhainen et al. 2006). The lithology of the footwall is subdivided into four units according to Monro (1988), these include: 9

16 The fine-grained grey quartz-biotite gneiss unit, which is characterized by a low copper grade and disseminated chalcopyrite overlaying a porphyritic quartz monzodiorite intrusion, which is located at the southern part of the Aitik deposit (Monro 1988, Wanhainen et al. 2006). This unit exhibits slight sericitization and scapolitization (Monro 1988). The second lithologic unit which is localized at the central and northern part of the Aitik footwall side is the hornblende schlieren biotite gneiss as described by Monro (1988). It is mainly characterized by fine-grained quartz and biotite. This unit exhibits veinlets of magnetite cross-cut by hornblende (Monro 1988). In terms of copper mineralization it is described as a barren unit. The footwall quartz monzodiorite is regarded as the main mineralizing intrusion for the Aitik porphyry system. It outcrops extensively in the south-eastern part of the mine and also intercepts at depth in the northern footwall (Wanhainen et al. 2006). This unit is regarded as the main intrusive unit together with micro-quartz monzodiorite, which is described as the associated phase of the main intrusion according to petrographic descriptions made by Wanhainen et al. (2006). The quartz monzodiorite consists of grey, fine-grained, porphyritic rocks with slightly elongated plagioclase phenocrysts, which compositionally contain An30 An35 (Andesin), and make up 7% of the unit (Monro 1988, Wanhainen et al. 2006). The matrix consists of plagioclase, biotite, K-feldspar and quartz, where the preferred orientations of the biotite laths indicate an earlier and later foliation as described by Monro (1988) and Wanhainen et al. (2005a). According to Monro (1988), the core part of this unit exhibit sericite alteration. The mineralization in this unit is characterized by veinlets and a disseminated nature of chalcopyrite, pyrite and magnetite (Wanhainen et al. 2006, Monro 1988). The micro-quartz monzodiorite unit characterized by its finer grain size, is dominantly localized at the western part of the intrusion. This unit has a similar composition as the main intrusion apart from the dominance of k-feldspar and less abundance of biotite (Wanhainen et al. 2006). The contact between this unit and the main intrusion as describe by Wanhainen et al. (2006) is distinct to gradational and exhibit a grain size of coarsening toward the center of the unit, which makes this unit to be considered as younger than the main unit (Wanhainen et al. 2005). The last unit in the stratigraphic column of the footwall side is, according to Monro (1988), the coarse-grained amphibole-epidote-feldspar gneiss, which is fault-bounded with the main ore zone in the eastern part of the footwall. This unit characteristically exhibit strong foliation (Monro 1988). Main ore zone The main ore zone within the Aitik mine contain lithologic units with copper grades greater than 0.26%. Generally the main ore zone is subdivided into two major lithologic units which are strongly altered (Monro 1988, Wanhainen et al. 2003a). These are: Garnet-bearing biotite schist and gneiss and 10

17 Quartz-muscovite-sericite schist Garnet-bearing biotite schist and gneiss; this unit is localized towards the footwall side of the pit and it is the most abundant unit (Wanhainen et al. 2005a). It is mainly characterized by 1-2% garnet porphyroblast within a matrix of feldspar, which is dominantly plagioclase of andesine composition (Monro 1988), biotite, amphibole, quartz, and disseminated ore minerals with 2% accessory minerals such as tourmaline, apatite, fluorite, and titanite which are disseminated throughout the groundmass (Wanhainen et al. 2005a, Monro 1988). The metamorphic assemblage containing garnet, amphibole, chlorite, sericite and biotite and the later hydrothermal alteration assemblage consisting of amphibole, scapolite, epidote, k-feldspar, garnet and quartz are the overprinting result of the early biotite, plagioclase and minor quartz at this part of the main ore zone as described by Wanhainen et al. (2005a). Furthermore, Wanhainen et al. (2005) describe the association between the early biotite with the opaque phase occurring as inclusion with the later fresh porphyroblast garnet together with feldspar, quartz, and sulphides. This part of the main ore zone is cross-cut by quartz stockwork systems, pegmatite dykes, and barite dykes that are formed as a result of hydraulic fracturing (Monro 1988). Mineralization associated with this lithologic unit is mainly characterized by disseminated chalcopyrite, pyrite and pyrrhotite (Wanhainen et al. 2005a) with copper grades attaining the highest values > 0.6% (Wanhainen et al. 2003b). Quartz-muscovite-sericite schist; this lithologic unit interfingers with the garnet-bearing biotite schist and it is located towards the hanging wall side of the pit. It is characterized by a strongly foliated muscovite-rich matrix containing also quartz, biotite, microcline and plagioclase (Wanhainen et al. 2005a). This part of the main ore zone exhibits a low content of ferromagnesian minerals and higher amounts of quartz and muscovite, pyrite and magnetite, which are disseminated throughout the unit (Wanhainen et al. 2005a, Monro 1988).The pyrite to chalcopyrite ratio in this unit is greater than that of the garnet-bearing biotite schist (Monro 1988). Hanging wall side of the Aitik deposit The hanging wall side of the Aitik deposit is separated from the main ore zone by a thrust, which runs parallel to the regional Nautanen Deformation zone (Wanhainen et al. 2005a).The contact between the main ore zone and the hanging wall is therefore characterized by an abrupt change both in mineralization as well as in rock unit (Wanhainen et al. 2003b). The rock units that conceal the Aitik ore body in the hanging wall side as described by Wanhainen et al. (2005a) is mainly fine-grained grey-greenish to grey-brownish feldspar-biotiteamphibole gneiss containing magnetite and titanite as accessory minerals. The groundmass contains plagioclase, biotite, amphibole, and quartz, that are partly altered to k-feldspar, sericite, chlorite, epidote, scapolite and tourmaline (Wanhainen et al. 2005a). 11

18 Minor mafic intrusion of metagabbro occurs in the hanging wall side as a porphyritic unit with plagioclase phenocrysts. This lithology exhibit deformation patterns characterized by small scale folds and elongated phenocrysts of plagioclase (Wanhainen et al. 2005a). The hanging wall side of the Aitik deposit is generally barren except for the presence of trace amounts of molybdenite within younger pegmatite dykes (Wanhainen et al. 2003, Wanhainen and Martinsson 1999). Pegmatite dykes in the Aitik deposit Two generations of pegmatite dykes of mainly quartz, k-feldspar and plagioclase, which vary in size from m wide, occur within the Aitik deposit (Wanhainen et al. 2003a, Wanhainen et al. 2005a). The first generation of pegmatite dykes are oriented parallel to the major N-S foliation of the Aitik deposit and they are approximately 1.85 Ga old (Wanhainen et al. 2005). These pegmatites are either deformed or undeformed as described by Wanhainen et al. (2003). The second generation of pegmatite dykes cross-cuts the major foliation and are oriented in an E-W direction. These younger of pegmatite dykes are undeformed in place with an approximate age of 1.73 Ga (Wanhainen et al. 2005). The pegmatite dykes occurring in the ore zone contain chalcopyrite and pyrite with significant amounts of molybdenite (Wanhainen et al. 2003b). Stockwork and hydrothermal breccias Typical features of a porphyry style mineralization such as quartz stockworks and hydrothermal breccias occur with greater intensity in the south-eastern part of the Aitik open pit as described by Wanhainen et al The stockwork system is made up of two sets of quartz veins based on their constituent and these are deformed and oriented randomly. The first set of quartz veins are characterized by grey-white quartz with disseminated grains of pyrite, magnetite, and chalcopyrite, while the second set consists of biotite, chalcopyrite and pyrite (Wanhainen et al. 2005a) Mineralization in the Aitik deposit The Aitik deposit is generally regarded as a magmatic-hydrothermal deposit in which the mineralization is spatially and temporally related to the intrusion of 1.89 Ga old quartz monzodiorite (Wanhainen et al. 2005) with a pronounced remobilization of metals caused by polyphase deformation and metamorphism (Wanhainen et al. 2005). Based on the current copper cut-off grade the mineralized zone has extended from the main ore zone, which include the garnet-bearing biotite schist and the quartz-muscovitesericite schist, to the sub-economic part of the intrusive body in the footwall zone (New Boliden annual report 2010). The major ore minerals within the Aitik deposit are mainly chalcopyrite and pyrite followed by minor pyrrhotite, magnetite, bornite, molybdenite and chalcocite (Wanhainen et al. 2003). Metal distribution patterns in the Aitik deposit exhibit spatial compositional variation in both horizontal and vertical profiles (Wanhainen et al. 2003b, Monro 1988). Monro (1988) presents the distribution of the chalcopyrite to pyrite ratio which changes from 1:1 in the 12

19 lower part of the main ore body to 1:2 and 1:4 in the upper part of the ore zone, which manifest the metal zoning in support of the porphyry system associated with a mineralizing intrusive body Liikavaara The Liikavaara mineralization, which is located 3.5 km east of the Aitik mine (Fig. 4B), was discovered at the same time as the Aitik deposit (Monro 1988, Martinsson and Wanhainen 2004). The main host rock at this deposit is a biotite-amphibole gneiss and schist that has undergone mainly chlorite alteration (Martinsson and Wanhainen 2004). The mineralized zone contains chalcopyrite, pyrrhotite, and pyrite as major constituents and magnetite, sphalerite, galena, and molybdenite in minor amounts (Monro 1988). The copper grade in this deposit varies from 0.2 to 5.3 % down to a depth of 240 m with an average grade of 0.58% Cu, 0.2 g/t Au, and 8 g/t Ag (Monro 1988, Martinsson and Wanhainen 2004) The bedrock in this deposit as described by Martinsson and Wanhainen (2004) is dominated by arenitic sediments with minor amphibolitic units and granitoid intrusions, the latter containing quartz, feldspar, sericite, biotite, and chlorite, with microcline, calcite, epidote, tourmaline and apatite as accessory minerals Salmijärvi The Salmijärvi deposit is located 600 m south of the Aitik mine (Fig. 4B).The host rocks to this mineralization comprises three units that seems to be strongly altered and metamorphosed than the Aitik ore body (Nordin, 2005). Moreover these three main units are less tectonically affected, although exhibiting similar foliation and folding (Nordin, 2005). Based on the degree of alteration and on mineral assemblage these units are grouped into: Amphibole-biotite gneiss: This host rock contains mainly amphibole and minor biotite with sporadic magnetite and pyrite, and molybdenite as an accessory constituent. Veins of feldspar, quartz and sulphide are a characteristic feature of this rock. Biotite-amphibole gneiss: This unit is characterized by dominant amounts of biotite and minor amphibole with veins of quartz, zeolites and epidot with abundant molybdenite associated with magnetite, pyrite and chalcopyrite. K-feldspar altered gneiss: This host rock is mainly associated with amphibole-biotite gneiss and garnet-biotite gneiss, with molybdenite as an accessory mineral. This rock unit exhibit strong potassic alteration. 13

20 A C B Figure 4 A) Regional geology of northern Sweden. (Wanhainen et al.2003b) B) Geology of the Aitik, Salmijärvi, and Liikavaara area (Martinsson and Wanhainen 2004) C) Geology of the Aitik deposit (Martinsson and Wanhainen A 2004) 2.3 General occurrence of molybdenite Porphyry systems are the most important source for copper and molybdenum in the world. According to Sinclair (2007) these deposits alone accounts for 60 to 70% of world copper production and for more than 95% of molybdenum production. Based on the relative contents of copper and molybdenum, the porphyry deposits containing molybdenum are divided into two major categories (Berzina et al. 2005); the Cu ± Mo deposits, characterized by containing copper ores as a major constituent and molybdenum as minor, and Mo ± Cu deposits, which are described as climax type of porphyry deposits with significant amounts of molybdenum and minor copper (Berzina et al. 2005, Stein et al. 2001). In the copper 14

21 dominant systems the copper grade ranges from 0.2 to 1%, while in the second group the grade of molybdenum ranges from 0.07 to 0.3% (Sinclair 2007). Molybdenum within the porphyry belt of northern Sweden has been reported to occur in significant amounts. At Nunisvaara for example, molybdenum occurs with an ore grade of 0.3% Mo as described by Monro (1988). Öhlander and Nisca (1985) described the occurrence of molybdenite in the continental domain of northern Sweden as genetically related to granitic intrusions intersected by deep-sited faults. Thus a model for the occurrence of molybdenite in the supracrustal province of northern Sweden as proposed by Öhlander and Nisca (1985) states that; when a rising fertile granitic intrusion, enriched with incompatible molybdenum, reach a regional fluid focusing structure, an aqueous phase is generated followed by precipitation of molybdenite associated with pegmatite and aplite dykes. 2.4 Rhenium in molybdenite Rhenium seldom forms minerals of its own, except in the Kudryakyi volcano in Russia where it condenses from vapor as rhenium sulphide (Naumov 2007). The highest rhenium concentrations commonly occur in molybdenite, which is associated with chalcopyrite in Cu- Mo sulphide ores (Terada et al. 1971). The range of rhenium concentration in molybdenite from the porphyry copper systems, which account for more than 95% of the molybdenum source, has been described to vary from ppb level to thousands of ppm (Berzina et al. 2005, Voudouris et al. 2009). This is due to the fact that rhenium naturally occurs incorporated within the structure of molybdenite (Voudouris et al. 2009). The strong chemical affinity of rhenium with molybdenite lies in their similar ionic radius, especially for speciation of Re +4 which isomorphically can substitute Mo +4 in molybdenite (MoS 2 ), where Mo +4 has resulted from the reduction of Mo +6 during deposition of the sulphide at reducing conditions (Fleischer 1959, Stein et al. 2003). Rhenium concentration from the molybdenite source of two major porphyry systems, the Cu-Mo and the Climax Mo-Cu, shows significant difference (Berzina et al. 2005). The first deposit type, which is characterized by a relatively low quantity of molybdenite, tends to contain higher concentrations of rhenium than the Climax type which contains higher amounts of molybdenite (Berzina et al. 2005, Stein et al. 2003). This is due to the fact that small amounts of molybdenite will consume all the limited rhenium budget from the oreforming fluids whereas this will be diluted within the high volume of molybdenite-richer magma (Stein et al. 2001). Generally concentration of rhenium in molybdenite is a combination of several interplaying factors such as; composition of parent magmas (ore-forming fluids) and host rocks (Berzina et al. 2005, Stein et al. 2001, Voudouris et al.2009), source of the host rocks and metals (Stein et al. 2001), concentration of molybdenite within the parent magma enriched with rhenium (Stein et al. 2001, Berzina et al. 2005), degree of oxygen and chloride fugacity of the fluid (Selby and Creaser 2001, Berzina and Korobeinikov 2007), and changes in chemical and physical condition during crystallization (Berzina et al. 2005). 15

22 Chapter 3 Sampling, sample preparation and analytical method 3.1 Sampling The studied samples were collected in year 2007 by C.Wanhainen from drill core sections within 17 drill cores from the Liikavaara, Salmijärvi, and Aitik deposits, and from the Aitik open pit. Samples were taken from different lithologies and alteration- and mineralization assemblages. Polished thin sections were prepared from the samples by Vancouver Petrographics Ltd, Canada, after careful documentation of wall rock, alteration- and mineralization phases present. 3.2 Sample selection Of the 23 polished thin sections prepared, 17 thin sections together with their copy of rock chips, and two open pit samples from a NS trending pegmatite and an EW trending (younger) pegmatite, were selected for rhenium content determination within molybdenite grains (table 3). Selection of representative grains of molybdenite was done based on thin section studies, performed using a high magnification Nikon Microscope at the Division of Geosciences at Luleå University of Technology, Sweden. In order to prepare representative molybdenite grains for analysis, criteria such as molybdenite grain size, mineral association and crystal habit of molybdenite were set up. A total of 27 molybdenite grains were selected for chemical analysis using Isotope dilution mass spectrometry at the Earth sciences Department of Durham University, UK. Due to the fact that all the thin sections were 30 µm and less in thickness, grains of molybdenite were extracted from the rock chips using micro drilling equipment at the Durham University laboratory. 3.3 Sampling using Micro drilling Grains of molybdenite from the rock chips were extracted using a micro drilling equipment (Micro mill manufactured by New Wave (Charlier et al. 2006)) integrated with a computer using a Micro mill software at Arthur Holmes Isotope Geology Laboratory at Durham University, UK. The Micro drill instrument contains three basic parts such as a Binocular Microscope, a High speed drill chunk with adjustable tungsten carbide or diamond drill bits (Charlier 2006), and a XYZ stage with all the components integrated with a workstation allowing high precision of ±1 µm collar location movement of the drill and depth of drilling (Fig. 5A). Rock chips containing grains of molybdenite were first attached and mounted with double sided tape on the sample plate stage (Fig. 5B). Micro drilling operation were performed on the samples using a 30 µm in diameter drill bit with 40 µm depth of drilling, after an adjustment made using the integrated software for precise collar of the grains. Drilling at several collar spots were performed depending on the grain size of the chosen molybdenite grains to extract the maximum amount of molybdenite cutting (separate). After drilling was performed on one sample, cleaning with ultrasonic bath in ethanol (Charlier et al. 2006) and/or replacing of the 16

23 drill bit to avoid contamination were carried out before proceeding to the next micro sampling. 3.4 Recovery of sample from drilling Recovery of the molybdenite separate from the drilling was done using a flotation technique with high purity water (MilliQ) by a µl micropipette which sucked up the floated molybdenite grains (Fig. 5C), or a dry separation technique using high magnification microscope (Selby et al. 2001). For the samples recovered by the first method all the water must evaporate before weighting. However, during this course of work the dry separation technique was used for most of the samples due to the strong association of the molybdenite grains with impurities such as quartz, biotite, amphibole and ore minerals (chalcopyrite, pyrite and magnetite) in order to extract pure molybdenite for analysis. A B C D E Figure 5 A) Different parts of the micro drilling equipment (Charlier et al.2006) B) Sample mounted for micro drilling C) Sample recovery D) weighting of sample using gold boat E) Digestion of sample using aqua regia. 17

24 3.5 Sample weighting and molybdenite dissolving procedure To measure the weight of the recovered spikes of molybdenite and prepare for analysis a gold boat prepared and measured for its weight using Metler Todeo UMT2 balance was used (Fig. 5D). The extracted molybdenite was transferred into the gold boat and their weight were measured together. By calculating back from the weight of the gold boat the difference gave the weight of the sample. The weight of the samples extracted for analysis range from to mg (table 4). After weighting of all samples, the samples were transferred to a 3.5 ml screw-cap beaker and concentrated HCl acid of 0.25 ml was added to the beaker and heated using a hotplate with a temperature of ca.80 0 C for more than 12hr in order to decompose and separate the sample from the gold boat. The screw-cap beaker had to be sealed properly during this process (Fig. 5E). This reaction was only dissolves some part of molybdenite. After separating the molybdenite from the gold boat, it was transferred back to the beaker for isotope dilution. At this stage, spikes of a known amount of 185 Re, which was prepared with respect to proportional amounts of measured molybdenite weight (table 4) and isotopically normal osmium (Selby and Creaser 2001), were added to the beaker containing the sample. Normal HNO 3 was also added to the beaker containing the solution and sealed properly. To facilitate the reaction, the beakers were let into the hotplate, which was adjusted to a temperature of ca C for about 24 hr. The reaction between HNO 3 and HCl will form aqua regia, which effectively dissolve or digest molybdenite, which incorporates unknown amount of rhenium. The osmium, which is highly volatile in nature, was escaped from the solution at early stage. Before preparing the solution for reading, the beaker was cooled down and then heated to a temperature of 80 o C for another 24 hr to dry the sample. This process removes all the molybdenite, leaving isotopic rhenium. Table 3 Sample location and thin section ID Location Thin section Drillhole Meter x y z Northern Am Aitik Agm Agm Agm Am Southern Am Aitik Am Agm Am Pegmatite dykes Salmijärvi Liikavaara P-EW P-NS Sm Sgm Sgm Sm Sm Sg Lgm

25 Table 4 Molybdenite weight and known weight of rhenium added for isotope dilution Sample ID Lab code Gold boat weight (mg) Gold Boat + Moly weight (mg) Moly weight (mg) Agm Sample Agm Sample Am Sample sample Sgm Sample P-EW Sample Am sample Sm sample Sm Sample Sm Am Smplae Sample Sample Sample Sample Sm Sample Lgm Am Sample Sample Sampe Sampe Am Sample Agm Sampple Agm Sample Sgm Sample Sample P-NS Sample Sg Spot Spot Added 185 Re Spike (µl =mg) 19

26 3.6 Determination of rhenium abundance using ICP-MS analysis The dry samples, which contain rhenium, were diluted with 0.12 ml HNO 3 of normal concentration for ICP-MS analysis. During the analysis a solution of HNO 3 were used as blank for cleaning in order to avoid contamination and calibrate the measurement for proceeding sample analysis. A standard diluted solution of 1 ppb rhenium was also used before and after the analysis of each sample in order to check the precision of the analysis. The data from these analyses generated a spread sheet containing information on isotopic ratio and abundance of both isotopes of rhenium with software integrated with the instrument. Finally, the concentration of rhenium from individual molybdenite grains was calculated from the generated data. 20

27 Chapter 4 Results 4.1 Molybdenite within the three studied deposit Molybdenite distribution within the Aitik deposit In this study, molybdenite grains from representative major host rocks and alteration types of the Aitik deposit have been characterized based on their relative grain size, crystal habit, mineral associations including other opaque minerals and their distribution. Mode of molybdenite occurrence in northern Aitik In the northern Aitik open pit, two samples, which are representative of the main host rocks, were characterized for the occurrence and distribution of molybdenite. The first sample (Agm ) is from the garnet-bearing biotite schist, which is localized towards the footwall side of the pit. In this sample three grains of molybdenite are identified, which Figure 6 Molybdenite associated with sulphide minerals. are associated with rock forming minerals such as biotite, amphibole, and plagioclase, and with the ore minerals pyrite and magnetite. The other sample (Am ) is taken from the quartzmuscovite-sericite schist and contains disseminated grains of molybdenite (> 60 grains) which varies in grain size from small (0.01 mm2) to large (0.58 mm2) (Fig. 6). The molybdenite grains in this sample shows anhedral, subhedral and euhedral crystal habits, which occurs as inclusion and together with the associated host minerals quartz, plagioclase, Figure 7 Molybdenite within quartz-muscovite-sericite and biotite laths, and minor schist amount of muscovite (Fig 7). Pyrite and chalcopyrite are observed in association with the molybdenite in this sample. 21

28 Mode of molybdenite occurrence in southern Aitik A total of seven samples representative of the main host rocks from the southern part of the Aitik open pit were studied. Three of them are from the quartz monzodiorite intrusive body (QMD), two of them are representative of the garnetbearing biotite schist and the two remaining are representative of the quartz-muscovite-sericite schist. Figure 8 Euhedral molybdeinte grains within the QMD. Two of the samples from the quartz monzodiorite intrusive rock (Am and Agm ) are mainly characterized by having similar molybdenite distribution, and contain about 13 molybdenite grains with subhedral to euhedral crystal habit (Fig 8). These molybdenite grains are mainly associated with epidote and amphibole occurring in a groundmass of mainly k-feldspar and quartz (Fig. 9). In these two Figure 9 Molybdenite associated with alteration minerals in samples a minor amount of QMD. sulphides in association with the molybdenite grains are observed. The third sample (Am ) from this host rock contains one big grain of molybdenite which occurs within a groundmass of plagioclase. This euhedral grain is partly replaced by alteration minerals such as epidote, biotite, and garnet. Molybdenite occurrence in one of the samples (Am ) from the garnet-bearing biotite schist are characterized by large grains which are perfectly euhedral and elongated in crystal habit occurring by partly replacing quartz and sitting together with host mineral assemblages 22 Figure 10 Molybdenite within the QMD host rock.

29 (mainly plagioclase ± quartz ± biotite ± muscovite ± garnet). Some of the grains contain biotite and garnet inclusions. In the second sample from this unit (Am ) molybdenite grains, most of them rather small in size, occur associated with the main rock forming minerals of the host rock such as quartz and biotite and with the alteration minerals amphibole and epidote (Figs. 10 & 11). Grains of molybdenite in this thin section occur either by replacing the associated alteration minerals or as inclusions. Molybdenite grains in this sample are dominantly associated with chalcopyrite and with minor pyrite. Figure 11 Molybdenite grains with associated mineral assemblages within the QMD. Two samples which are taken from the quartz-muscovite-sericite schist contain relatively few molybdenite grains. In the first sample (Agm ), six grains of molybdenite exhibits a subhedral to euhedral crystal habit. The molybdenite grains occur in association with quartz, biotite and garnet, and with sulphide minerals such as chalcopyrite and pyrite. The second sample from this unit (Agm ) has only one large grain of molybdenite. This molybdenite grain is partly replacing chalcopyrite in a quartz vein Molybdenite distribution within the Salmijärvi deposit Identification and characterization of molybdenite from this deposit was performed by studying two samples from each category of the main host rocks. A total of six samples were studied in order to describe the mode of molybdenite occurrence from this mineralization. Molybdenite in amphibole-biotite gneiss In the first sample (Sgm ) of amphibole-biotite gneiss, small grains of molybdenite occur within amphibole as fracture filling (identification from this sample only made using the available rock chip). The second sample (Sm ) is characterized by > 80 grains of molybdenite ranging in grain size from small (0.01 mm 2 ) to medium (0.04 mm 2 ) with anhedral to euhedral crystal habits. The mode of molybdenite occurrence with respect to associated mineral assemblages of the host rock, which include amphibole ± biotite ± quartz ± garnet, are by sitting together, as inclusions, and partly by replacing them. Sulphide minerals such as chalcopyrite and pyrite are the dominant ore minerals that are associated with molybdenite grains in this sample (Figs. 12A-B). 23

30 Molybdenite in biotite-amphibole gneiss In the first sample (Sm ) several grains of molybdenite are aligned in a certain preferred direction. These grains are mainly anhedral, and occur as inclusions within alteration minerals such as amphibole and epidote (Figs. 12C-D). Magnetite is the dominant ore mineral associated with most grains of molybdenite, but and some molybdenite grains are also associated with pyrite and chalcopyrite. The second sample (Sm ) contains about 14 grains of molybdenite which varies in grain size ( mm 2 ). They are strongly associated with chalcopyrite and pyrite in a groundmass which containing biotite ± amphibole ± quartz ± epidot. Molybdenite grains in this sample mainly occur as inclusions within the associated minerals. Molybdenite in k-feldspar altered host rock About seven molybdenite grains are identified in the first sample (Sm ).These are associated with mineral assemblages such as quartz, plagioclase, and muscovite. Some of the molybdenite grains in this sample occur as inclusions and some of them by partly replacing the associated minerals. Minor amounts of chalcopyrite are also associated with molybdenite. In the second sample from this unit (Sg ) about 13 molybdenite grains occur associated with k-feldspar, biotite, muscovite, and quartz in decreasing order. Magnetite is the dominant ore mineral associated with molybdenite grains of this sample followed by chalcopyrite (Figs. 12E-F). 24

31 A B C D E F Figure 12 Molybdenite distribution within the major host rocks of the Salmijärvi deposit. A) Molybdenite with associated ore minerals (chalcopyrite, pyrite and magnetite) in amphibolebiotite gneiss B) Alteration mineral (amphibole) associated with molybdenite in amphibole-biotite gneiss C) Molybdenite with associated ore minerals (pyrite and chalcopyrite) in biotite-amphibole gneiss D) Molybdenite associated with alteration minerals (biotite ± amphibole ± epidote ± muscovite) in biotite-amphibole gneiss E) Molybdenite with associated ore minerals (magnetite and chalcopyrite) in k-feldspar altered host rock F) Moybdenite with associated minerals assemblage (k-feldspar ± plagioclase ± quartz ± biotite) in k-feldspar altered host rock Molybdenite in the Liikavaara mineralization From this mineralization, one sample from a 5 m wide section of quartz vein and aplite, which contains chalcopyrite and pyrite, was included. In this sample several grains of molybdenite with anhedral to euhedral crystal habits are exhibited. Mineral assemblages that are associated with molybdenite grains include microcline, quartz and plagioclase with minor amounts of pyrite and chalcopyrite (Figs. 13A-B). 25

32 Figure 13 Molybdenite distributions within the Liikavaara deposit. A) Molybdenite associated with sulphide minerals (chalcopyrite and pyrite). B) Molybdenite associated with alteration mineral assemblages (k-feldspar ± plagioclase ± quartz). 4.2 Results of rhenium concentration in molybdenite Rhenium concentration of molybdenite samples from the three studied deposits (Liikavaara, Salmijärvi, and Aitik deposits) shows significant variations as summarized in Table 5. In order to be able to study the cause of rhenium variation, results will be presented separately for the three deposits and comparisons between them are made using the average rhenium concentration in molybdenite. Presentation of the rhenium content are mainly based on the mode of molybdenite occurrence of the selected grains using the descriptions and measurements made on thin sections or polished sections of the samples (Fig 14) and from the extracted weight of molybdenite during Micro-sampling. The analytical results of the rhenium concentration contain an error factor determined during ICP-MS analysis for each sample as presented in table 5. However, diagrams and graphs presented in this study do not take into account this error factor. Figure 14 Molybdenite grain size measurement on the polished section 26

33 Table 5 Rhenium concentration within molybdenite gains from the three studied deposits. Location Sample ID Lab code Moly weight (mg) Calculated Re abundace (ppm) Rock description Agm ± 5.6 Bt(am)-schist with cm-wide sulf-qtz-fsp-veins. MoS 2 in 0.5 cm wide ccp-am-fsp-vein. North Aitik Am ± ± 23.5 Homogeneous ms-schist with sporadic 0.5 cm wide qtz-fsp-veins (brittle), weak sulfimpregnation, and rich MoS 2 - impregnation. Average Brittle and qtz-altered dm of ms-schist rich in 20 ± 1.01 Agm sulf-mag and with some MoS2-grains 4 m wide qtz-vein in ms-schist. MoS2 in qtz Agm ± 4.53 and in crack filled with ep-cal-chl m wide vein of qtz, fsp, bt and, tur in bt(am)- Am schist South Aitik Am ± 8.1 Altered QMD. Alteration = kfs, am, ttn, ep, py, ccp, (mag), c. 5 m ± ± 4.8 1m wide vein of qtz, fsp, bt and tur in bt(am)- Am ± 12.6 schist Am ± 4.2 Homogeneous QMD with sporadic sulf-bearing qtz-veins. MoS2 and zeol on the edge of a 3 cm wide am-qtz-sulf-clot Agm ±48.8 Am-fsp-ttn-altered QMD Average Aitik P-EW ± cm wide, east-west cross-cutting pegmatite dike dipping 90 deg. Pegmatite P-NS ± 0.4 Deformed, north-south striking pegmatite dike. Average Sgm ± 1.6 Homogeneous am(bt)-gneiss with sporadic ammag-py-clots with MoS 2 Sm ± 5.8 Kfs-vein with MoS 2 in am(bt)-gneiss ± dm of mag-sulf-qtz-am-ep-altered homogeneous bt(am)-gneiss. Rich in fine Salmijärvi Sm ± 10.9 grained MoS ± cm wide qtz-zeol-ep-vein with sporadic MoS 2 - Sm ± 52.9 grains and rich in mag-py-ccp. Bt(am)-gneiss ± Am-bt-gneiss with fsp-qtz-am-sulf-veining and Sgm ± 8.9 a 1 dm sulf-clot with MoS ± 3.4 Kfs-altered grt-bt-gneiss with common MoS 2 Sg ± 2.9 of variable size. Average Lgm ± 0.7 5m wide section of with quartz veins and fine grained aplite dyke with ccp and py.mos 2 Liikavaara ± 3.2 within bt-schist Average

34 Mineral abbreviations: bt = biotite, am = amphibole, ms = muscovite, qtz = quartz, fsp = feldspar, kfs = potassium feldspar, tur = tourmaline, grt = garnet, ep = epidote, zeo = zeolite, QMD = quartz monzodiorite, cal = calcite, chl = chlorite, ttn = titanite, Sulf = sulfide, py = pyrite, ccp = chalcopyrite, mag = magnetite Rhenium concentration against molybdenite grain size The molybdenite grain size was measured using the software integrated with the optical microscope at the Division of Geosciences, Luleå University of Technology, Sweden (Fig. 14). In order to be able to see possible relationships between molybdenite grain size and the concentration of rhenium within the measured molybdenite grain, a relation graph was constructed (Fig.15 ) for the three deposits, including 21 grains of molybdenite (Appendix I). The regression line drawn from these samples gives a weak and positive correlation coefficient of 0.2. Figure 15 Plots of rhenium concentration versus molybdenite grain size Rhenium concentration against molybdenite weight Molybdenite grain weight was measured during extraction of molybdenite separates for ICP-MS analysis at the Department of Earth Sciences, Durham University, UK. Diagrams showing the rhenium content against molybdenite weight were produced using 27 molybdenite grains from 18 samples (Fig. 16). The regression line drawn from the correlation between the rhenium content and their respective molybdenite weights gives a positive correlation coefficient of as calculated and drawn in figure

35 Figure 16 Molybdenite grain weight versus rhenium concentration Rhenium concentration for each sampled area The rhenium concentration of molybdenite grains in the three studied deposits, ranges from few tens of ppm to thousands of ppm. The variation in rhenium content in molybdenite within Aitik (subdivided into north and south Aitik), Salmjärvi and Liikavaara, are presented separately (Fig. 17A-D) and the average rhenium content are used when comparing the three deposits (Fig. 17E). A B 29

36 C D E Figure 17 A) Rhenium concentration within the north Aitik mine. B) Rhenium concentration within the south Aitik mine. C) Rhenium concentration within the Salmijärvi deposit. D) Rhenium concentration within the Liikavaara deposit. E) Average rhenium concentration in molybdenite within the three deposits. The rhenium concentration within molybdenite grains of the three studied deposits is characterized by a complex pattern (Fig. 17A-D). In the northern part of the Aitik ore (Fig. 17 A) the rhenium content of 5 molybdenite grains ranges from 48.9 ppm to ppm, while in the southern part of the Aitik ore the rhenium content of 10 grains of molybdenite ranges from 20 ppm to ppm (Fig. B). The average rhenium concentration of the molybdenite in the Aitik deposit is 213 ppm (Fig. 17E). In the Salmijärvi deposit the rhenium concentration in molybdenite, on the basis of 10 molybdenite grains (Fig. 17C), ranges from 43.9 ppm to ppm with an average content of 452 ppm. Two grains of molybdenite from the Liikavaara deposit contains a rhenium value of 45.6 ppm and ppm (Fig. 17D) with an average content of 160 ppm Rhenium concentration against major host rocks The major host rocks of the Aitik deposit, which include the footwall intrusion, the garnet-bearing biotite schist, the quartz-muscovite-sericite schist, and the pegmatite dykes, are 30

37 plotted against their rhenium concentration in molybdenite (Fig. 18A) and the average rhenium content within these main rocks is plotted for comparison in Fig. 18B. A B Figure 18 A) Rhenium concentration within the major host rocks of the Aitik deposit. B) Average rhenium concentration within the major host rocks of the Aitik deposit. As can be seen in the first graph (Fig. 18 A) the rhenium concentration of the molybdenite in the footwall intrusive unit (QMD), based on three grains of molybdenite, ranges from 84.4 ppm to ppm with an average content of ppm. The rhenium content of the garnetbearing biotite schist, based on six molybdenite grains, ranges from 42.6 ppm to ppm with an average content of ppm. The rhenium value in the older pegmatite dyke (NS trending) from one sample of molybdenite grain is 61.3 ppm, while the molybdenite grain from the younger pegmatite dyke contains ppm of rhenium. In the quartz-muscovite- 31

38 sericite schist the rhenium concentration, based on four molybdenite grains, varies between 20 ppm to ppm with an average rhenium content of ppm. The major rock units of the Salmijärvi deposit, which are grouped according to the extent of alteration, are plotted against their rhenium concentration in Fig. 17C and the average rhenium content of these host rocks are shown in Fig. 19. Figure 19 Average rhenium concentration of molybdenite within the major host rocks of the Salmijärvi deposit. The rhenium concentration in the main host rocks of the Salmijärvi deposit exhibits an irregular pattern (Fig. 17C). In the rock unit described as biotite-(amphibole) gneiss the rhenium content, based on four molybdenite grains, ranges from 91.9 ppm to ppm. The rhenium concentration in molybdenite from three molybdenite grains selected from the amphibole-(biotite) gneiss unit ranges from 45.9ppm to ppm. In the k-feldspar altered gneiss the rhenium content of three analysed grains ranges from 59.9 ppm to ppm. The average rhenium content calculated from the biotite-(amphibole) gneiss is the highest with a value of ppm, which is due to the elevated rhenium contents in two molybdenite grains (Fig. 19). This value is the maximum rhenium concentration observed in this study. The amphibole-(biotite) gneiss and k-feldspar gneiss exhibit lower average values of ppm and ppm respectively (Fig. 19A) Rhenium concentration against mineral association Alteration mineral assemblages and ore minerals associated with the analyzed molybdenite grains are plotted against the rhenium concentration for samples from the Aitik and Salmijärvi deposits as shown in Figs

39 Figure 20 Rhenium concentration in molybdenite associated with alteration minerals in the Aitik deposit. In the Aitik deposit, the rhenium content of molybdenite that are dominantly associated with quartz ranges from 20 ppm to ppm. The rhenium content of molybdenite associated with plagioclase exhibits a higher value in the range of ppm to ppm. The rhenium content of molybdenite associated with alteration minerals such as biotite, amphibole, epidot, and k-feldspar are characterized by lower values as shown in figure 20. Figure 21 Rhenium concentration in molybdenite associated with opaque minerals within Aitik. Molybdenite grains associated with the ore minerals pyrite and chalcopyrite in the Aitik deposit exhibit different ranges of rhenium concentration (Fig 21). In four grains of molybdenite associated with pyrite, the rhenium content ranges from 48.1 ppm to ppm, 33

40 while in seven grains of molybdenite that are associated with chalcopyrite the rhenium content ranges from 42.6 ppm to ppm. A B Figure 22 A) Rhenium concentration in molybdenite versus associated alteration minerals within the Salmijärvi deposit and B) Rhenium concentration in molybdenite versus associated ore minerals within Salmijärvi deposit. In the Salmijärvi deposit the rhenium content in molybdenite grains associated with rocks that are strongly amphibole altered ranges from 148 ppm to ppm (Fig 22A). Molybdenite grains associated with quartz contain rhenium in ranges of 91.9 ppm to ppm, whereas molybdenite grains associated with k-feldspar have rhenium contents ranging from 59.9 ppm to ppm. Low contents of rhenium are detected in grains of molybdenite 34

41 that are associated with biotite and garnet (Fig. 22A). Molybdenite within the Salmijärvi deposit are dominantly associated with pyrite (Fig 22B), with a rhenium content that ranges between 91.9 ppm and ppm. The rhenium content of molybdenite grains associated with chalcopyrite exhibit a value ranging from 59.9 ppm to ppm. Two molybdenite grains associated with magnetite show rhenium contents that range with a wide interval of 45.9 ppm to ppm Rhenium concentration with respect to molybdenite crystal habit The crystal habit of molybdenite grains from the Aitik and Salmijärvi deposits are plotted against their rhenium concentration based on the description made from thin sections (Fig. 23A-D). In the Aitik deposit, grains of molybdenite with anhedral crystal habit show rhenium contents that range from 20 ppm to ppm with an average value of 85.8 ppm. Molybdenite grains with subhedral crystal habit exhibit rhenium contents in the range of ppm to ppm with an average value of ppm. Molybdenite grains with euhedral crystal habit exhibit rhenium contents ranging from 42.6 ppm to ppm, with an average value of ppm (Fig. 23A-B) In the Salmijärvi deposit, the rhenium concentration of molybdenite grains with euhedral crystal habit ranges from 59.9 ppm to ppm with an average content of ppm. Molybdenite grains with anhedral crystal habit exhibit considerably higher rhenium contents ranging from 45.9 ppm to ppm with an average value of ppm (Fig. 23C-D). A B 35

42 C D Figure 23 A) Molybdenite crystal habit versus rhenium concentration in molybdenite within the Aitik deposit B) Average rhenium concentration in molybdenite versus crystal habits of molybdenite grains in the Aitik deposit C) Molybdenite crystal habit versus rhenium concentration in molybdenite within the Salmijärvi deposit D) Average rhenium concentration in molybdenite versus molybdenite crystal habits within the Salmijärvi deposit. 36

43 Chapter 5 Discussion 5.1 Causes of rhenium variation within molybdenite In the studied deposits, Aitik, Salmijärvi and Liikavaara, the rhenium content of the molybdenite separates varies significantly (Fig. 17). The average rhenium concentration of molybdenite in the Salmijärvi deposit, as compared to the others, are relatively high with an average value of ppm followed by molybdenite separates from the Aitik deposit with an average value of 213 ppm (Fig. 17 E). Samples from the Liikavaara mineralization were few and their average rhenium content are low (160 ppm). Figure 24 High rhenium containing molybdenite in the sericitealtered rock of the intrusive unit of the Aitik deposit The host rock is one of the controlling factors for rhenium concentration in molybdenite (Voudours et al. 2009, Berzina et al. 2005). In Aitik, elevated concentrations of rhenium are associated with the footwall intrusion and the quartzmuscovite-sericite schist, which exhibit a nearly similar average content (Fig. 18B). These highrhenium containing molybdenite grains are found in intensively sericite-altered parts of these rock units (Fig. 24). In the garnet-bearing biotite schist, where a potassic alteration is prominent (Wanhainen and Martinsson 2003), the rhenium content in molybdenite are relatively low as compared to the other two major host rocks (Fig. 18B). Thus, it seems as if the hydrothermal alteration of the ore could be partly responsible for the variation and/or enrichment of rhenium, a phenomenon also described by Berzina and Korobeinikov (2007), where elevated rhenium concentrations are associated with rocks which have undergone intense sericite alteration instead of potassic alteration. Molybdenite grains in different generations of pegmatite dykes in the Aitik deposit also contain variable concentrations of rhenium. The younger pegmatite contains higher amounts of rhenium in molybdenite than the older one (Fig. 18A). Generally it seems as if the rhenium-enriched molybdenite in the Aitik deposit shows a complex pattern and could possibly be the result of magmatic, hydrothermal and metamorphic processes elapsing at the interval between 1.88 Ga and 1.73 Ga, i.e. after the main porphyry Cu-Au mineralizing event at 1.89 Ga (Wanhainen et al. 2005; Wanhainen et al. 2003b). In the Salmijärvi deposit, the biotite-(amphibole) gneiss, which is strongly biotite altered, exhibits the highest rhenium concentrations in molybdenite compared to the amphibole- (biotite) gneiss, which is intensely amphibole altered, and the k-feldspar altered gneiss 37

44 (Fig.19). The difference in rhenium concentration between the two deposits could possibly be explained by the different degree of alteration on the host rocks (Nordin, 2005). Although modified and remobilized, the metals within the Aitik deposit exhibits a distribution pattern typical for porphyry systems in both horizontal and vertical profile (Wanhainen et al.2003b, Wanhainen et al. 2005, Wanhainen et al. 2006). This study shows that the average rhenium concentration within molybdenite seems to follow this metal distribution pattern with the gradual change of main lithologic units (Fig. 18). Apparently, the copper grade within the major host rocks of the deposit (Wanhainen et al. 2005), and the rhenium content of the molybdenite shows a negative and strong correlation of (Table 6 and Fig. 25A). On the contrary, the rhenium content of molybdenite shows a weak and negative correlation of (Table 6 and Fig. 25B) with gold grade within the major host rocks of the deposit (Wanhainen et al. 2005, Wanhainen et al. 2006). Furthermore, the rhenium content of molybdenite does not show a correlation pattern with the grade of molybdenum estimated at 300 m level (Fig. 26). This comparison was, however, not possible to draw any conclusions from due to the small number of molybdenite grains that are considered for this study, and due to the different sampling levels that are projected on the 300 m level of the molybdenum grade map (Fig. 26). However, it can be used as reference for a block model evaluation of rhenium that might be performed in the future. Table 6 Rhenium content (from this study) and Cu and Au grade within the major Aitik host rocks (Wanhainen 2005 and Wanhainen 2006). Major host rock Aitik Calculated Re abundace (ppm) Cu grade in % Au in ppm Quartz-muscovite-sercite schist 310,33 0,40 0,60 Garnet-bearing bt-schist 115,76 0,60 0,30 Intrusive body (QMD) 333,87 0,18 0,04 Figure 25 A) Cu grade versus average rhenium content in molybdenite within the Aitik major host rocks. B) Au grade versus average rhenium content in molybdenite within the Aitik major host rocks. 38

45 Legend Figure 26 Rhenium contents of grains of molybdenite projected on the contoured grade map of molybdenum at 300 m level in the Aitik deposit. Molybdenum grade map based on thousands of assays compiled by Boliden geologist. With regard to crystal habit of molybdenite grains, the rhenium content of molybdenite in the Aitik and Salmijärvi deposits are characterized by significant variation implying that the degree of modifying processes (Wanhainen 2005a), such as metamorphism and deformation, have probably played an important role. In the Aitik deposit, elevated rhenium content of molybdenite grains are dominantly associated with a well-developed euhedral crystal habit (Fig. 21B), while in Salmijärvi, a high rhenium content of molybdenite are dominantly associated with an anhedral crystal habit (Fig. 21D). The well-developed crystal habit in the Aitik deposit could indicate the extent of the lower degree of the modifying process leading to re-crystallization of molybdenite and an upgraded amount of rhenium, while in the Salmijärvi deposit, the high rhenium content associated dominantly with an anhedral crystal habit of molybdenite could indicate a higher degree of late modifying processes destroying the already re-crystallized grains. In addition, the high rhenium concentration in the Salmijärvi molybdenite could possibly be a result of additional introduction of rhenium during dehydration melting of biotite/amphibole during high degree of metamorphism (Stein et al. 2006). The association of the high-rhenium molybdenite grains with oxide minerals (magnetite) further indicates more favorable oxidizing conditions for mobilization of rhenium as compared to the Aitik deposit (Voudours et al. 2009). The rhenium concentration of molybdenite has been described to be characterized by heterogeneity (Terada et al 1971, Selby and Creaser 2004). In this study, molybdenite grain size and weight were used to study the relationship between the rhenium content and the molybdenite crystal. From this study it can be concluded that the grain size of molybdenite and the rhenium content have a positive but weak correlation (Fig. 15), while the molybdenite weight and the rhenium content shows a significant positive correlation (Fig. 16). Therefore, by looking at the grain size on the surface of molybdenite (e.g. in the drill core) it cannot be 39