Sweden 2017 Fieldtrip Report

Transcription

1 Sweden 2017 Fieldtrip Report Where mining meets moose

2 Cardiff SEG Sweden th 19 th June Andrew Martin, Hannah Stephenson, Jamie Price and Andrew Dobrzanski With thanks to Wolfgang Maier, SRK Consulting and all the mine contacts at Boliden and LKAB, without your support this trip would not have been possible.

3 Exploration is the engine that drives innovation. Innovation drives economic growth. So Acknowledgments let's all go exploring -Edith Widder Cardiff SEG would like to acknowledge the support of the SEG Stewart R. Wallace fund and SRK Consulting (UK) for making this trip financially viable. We would also like to acknowledge the following staff from various mines we visited during our trip: Rodney Allen, Birgir Voigt, Johan Olsson, Ulf Andersson, Jakob Fahlgren and Peter Karlsson. We are eternally grateful for your willingness, enthusiasm and hospitality during our respective mine visits. It was a truly great trip and immensely enjoyable thanks to your support. On behalf of the SEG Student Chapter please accept our sincerest thanks for all your hard work and effort! We also thank Wolf Maier for facilitating the initial contact to many of the mines. Participants The SEG Cardiff gang at Nora Karr REE prospect, Sweden (photo: Andrew Martin) Name Year of Study Institution Andrew Martin 2 nd year PhD Cardiff University Hannah Stephenson 3 rd year PhD Cardiff University Jamie Price 1 st year PhD Cardiff University Aled Evans MESci Cardiff University Vlad Simov MSc Cardiff University Sion Kinson 3 rd year BSc Geology Cardiff University Marcus Read 3 rd year BSc Exploration Cardiff University John Condron 3 rd year BSc Exploration Cardiff University Ellie Capuano 3 rd year BSc Exploration Cardiff University Jacob Garland 2 nd year BSc Exploration Cardiff University Zac Mattin 2 nd year BSc Exploration Cardiff University Andrew Dobrzanski 2 nd year PhD Edinburgh University

4 Overview Day 1 12 th June: Meet at Main Building Earth entrance no later than 04:30 depart for LHR. Heathrow (T5) to Stockholm BA JUN LHR ARN PM drive Stockholm to Skellefteä Stay Skellefteä Camping Day 2 13 th June: Kanberg Au Te (BMS) Mine, Skellefteä. Visit led by Birger Voigt. Arrive at mine for 08:30 until 16:00 Stay Skellefteä Camping Day 3 14 th June: Aitiki Cu mine, Aitik/Gällivare area. Arrive 08:30. 10:00 Mine introduction, 11:00 Core, 12:00 lunch, 14:00 mine tour. Visit led by Peter Karlsson Stay Gällivare Camping Day 4 15 th June: Kiruna Fe apatite Mine, Kiruna Arrive 09:00, depart 16:00. Visit to be led by Ulf Andresson Stay Gällivare Camping Day 5 16 th June: Renström BMS Mine, Skellefteä Visit led by Jakob Fahlgren, Arrive 08:00, depart 16:00 Stay Skellefteä Camping Day 6 17 th June: Drive Skellefteä to Nora Stay Nora Camping (leave 06:30) Day 7 18 th June: Nora Kärr REE prospect Depart 09:00 for the field until 17:00 Stay Nora Camping Day 8 19th June: Garpenberg Zn Cu Pb Mine (AM). Arrive Garpenberg at 08:00, visit led by Rodney Allen. 15:00. Depart for LHR BA JUN ARN LHR This ambitious itinerary involved driving from Stockholm to Kiruna and then back to Nora in southern Sweden. During the trip we covered over 3500 km! Luckily given the stunning scenery and midnight sun this wasn t an issue. We visited some world class deposits including the world s largest underground Fe mine and Europe s biggest Cu mine. Generally each day would start with a safety briefing, a tour of the core shed, lunch then a trip down the mine followed by a tour of any processing or work shop facilities.

5 Kankberg Mine- Introduction Owned by: New Boliden Commodity: Au Te Development Stage: Underground Geological Setting/Genetic Model: VHMS Location and Access: 8.3km northeast of Boliden Geological Domain: Fennoscandian Shield First Operational: mining Cu Zn, 2012 mining Au Te The Kankberg Au Te mine is located 8.3 km north of the town of Boliden, in the Skellefte mining district of central Sweden (Figure 2). The deposit has a very interesting history, including multiple phases of operation for different resources. Kankberg was first operated as an open cast Cu Zn mine from , once more from and most recently reopened as an underground Au Te mine in In a rather unique manner, the Kankberg Au Te deposit was in fact discovered at 350m depth, beneath the coexisting and previously exploited Kankberg Cu Zn deposit. At present, the Kankberg Au Te mine produces 10% of the world s tellurium supply and is one of the only deposits where tellurium is a direct product of mining activity. The total ore reserves at Kankberg are reported at 3.5million tonnes, with an average gold grade of 3.5g/t and tellurium grade of 200g/t (Boliden, 2014). This equates to a typical gold production per annum of 1,150 kg, and tellurium production of 40 tonnes. Tellurium is increasingly important with the explosion of renewable energy technologies, used predominantly as an alloying element in steel and as a semi conductor in solar cells. Kankberg is also one of the most advanced mines in the world, both in terms of connectivity and automation. The Skellefte mining district in which the Kankberg mine is situated is a world renowned locality for volcanic hosted massive sulphide (VHMS) deposits, in addition to porphyry Cu Au, epithermal Au and orogenic Au deposits. As such, more than 50% of all the gold produced in Sweden comes from the Skellefte district. The district comprises both supracrustal and intrusive igneous rocks of Paleo proterozoic ( Ga) age, formed in a volcanic arc setting and later deformed during the Svecokarelian orogeny (Figure 1). Abundant shear zones have developed syn extensionally and have acted as conduits for hydrothermal ore forming fluids (Kathol & Weihad, 2005). Most of the VHMS deposits in the region are massive to semi massive, pyrite dominated Zn Cu Pb Au Ag systems, typically assigned to the bimodal felsic classification and situated near the top of the meta volcanic sequence, proximal to overlying metasedimentary rocks (Allen et al., 1996). The Kankberg mine is located in a folded and strongly altered package of felsic volcanic rocks, metasediments, breccias and felsic shallow level intrusions (Figure 2) associated with an Island arc setting. Sediments are intruded by quartzfeldspar porphyries, interpreted as syn sedimentary shallow intrusions. The Kankberg VHMS deposit has two distinct zones of alteration; one with a strong Si Al alteration assemblage including topaz, andalusite, sericite and corundum and the other with a more typical VMS alteration assemblage. Alteration zones, from proximal to distal in relation to gold mineralisation, comprise quartz andalusite, silicification, seritisation, chlorite biotite (± garnet) and calcite (Wasström et al., 1999). The occurrence of garnet porphyroblasts and metamorphic biotite indicate upper greenschist metamorphic facies, whilst andalusite, topaz and corundum were likely derived from metamorphism of Al rich clays (Wasström et al., 1999). Sulphide mineralisation at Kankberg is typically disseminated and dominated by pyrite and pyrrhotite, with lesser sphalerite, chalcopyrite, arsenopyrite and galena. Gold bearing minerals include petzite (Ag 3AuTe), electrum (AuAg), calaverite (AuTe 2) and sylvanite (AuAgTe 4) and are frequently <5 m in size, though some grains >50 m have been identified. Gold bearing minerals are irregularly distributed and hosted by a range of phases including andalusite, muscovite, chlorite, rutile, corundum, pyrite, molybdenite and löllingite. Other tellurium bearing minerals containing no gold include native tellurium (Te), altaite (PbTe), coloradoite (HgTe), tellurbismuthite (Bi 2Te 3) hessite (Ag 2Te), frohbergite (FeTe 2) and melonite (NiTe 2) (Wasström et al., 1999).

6 Figure 1: Simplified geological map of the Skellefte district with the location of base and precious deposits metal deposits labelled, including Kankberg (outlined). After Hallberg et al. (2015). Figure 2: Local geology of the Kankberg area (SGU, 2015).

7 Day 2: Kankberg Au Te BMS deposit Kankberg 13 th June 2017 We arrived at the Kankberg mine site just outside Skellefte, northern Sweden at 08:00 in the morning for a day led by mine geologist Birgir Voigt. The day started with a safety briefing followed by an introduction to the mine geology. Kankberg is an unusual mineral deposit, the primary commodities mined are Au and Te. Kankberg is one of only serval mines in the world where Te is mined as a primary commodity. The deposit was originally mined for base metal sulphides (BMS) in the 1960 s via an open pit. The mine now operates using underground cut and fill mining at a depth of 500 m. Annual ore production is 320 kt/y. Reserves are 3.1 Mt with a 0.4 Mt resource (open at depth). Current grade is 4.1 g/t Au and 186 g/t Te. There is no set genetic model that accounts for the significant Te enrichment at Kankberg, research is ongoing to understand deposit paragenesis. After the safety briefing we headed to the run of mine (ROM) pad to hunt for some Au and tellurides. The ore is bright white in colour with various highly coloured flecks, mostly topaz, fuchsite and fluorite. Disseminated pyrite and silicification is common throughout (Figure 1A). Vlad struck lucky finding a beautiful sample with native Au grains. Tellurides are small <<1mm and occur as grey shiny elongate minerals infilling cracks. Tellurides are rare however some good samples were found (Figure 1B). All ore is centrally processed at Boliden via a hot acid leach. After a search around the ROM pad we headed down to the 400m production level. The mine is accessed via a decline which doubles up as a haulage road to the surface. Ore is transported in traditional dump trucks to the surface. When in the mine we visited an exploration drift as the current production area was in operation. The drift doubled as a ventilation shaft for the mine. We often learn about the fluorescent nature of minerlas in the classroom or see exhibits in museums but what s the point? Can this be used in industry? Kankberg is the ultimate example of why fluorescent minerals are useful in industry. These minerals are key in mapping alteration zones within the mine. High power short wavelength UV lamps are used to identify alteration zones. Scapolite, topaz and apatite which are invisible to the naked eye are easily visible under UV light at Kankberg (Figure 1C). 2 cm Tellurides After an hour or so underground we returned to the surface and headed to Boliden for lunch followed by a tour of the core shed. The core was beautiful, some of the best we ve seen. Due to the silicified nature of the core, core recovery was excellent >90%. Sulphides, mainly pyrrhotite and chalcopyrite were readily observed in disseminated and semi massive morphologies. Tellurides were readily observable in the core reaching an impressive size of up to 2 cm in some cases! Birgir then explained to us the process followed at Boliden for logging core and the software used. We then turned off the lights and had another look at the core under UV light, as in the mine, UV light can be used to map alteration. An excellent start to the trip! Figure 1A: Students on the ROM pad Figure 1B: A superb sample contain tellurides Figure 1C: Mineral fluorescing under UV light

8 Aitik Mine Introduction Owned by: New Boliden Commodity: Cu Au Ag Development Stage: Open cast, in operation Geological Setting/Genetic Model: Porphyry Cu Location and Access: 17 km east of Gällivare Geological Domain: Fennoscandian Shield First Operational: 1968 The Aitik Cu Au Ag mine is located in northern Sweden, 17km east of the town of Gällivare and 100km north of the Arctic Circle (Figure 3). Aitik is currently Sweden s largest open cast copper mine and is one of the largest Au rich porphyry copper deposits in the world. The deposit currently has a total mineral resource of 1846 Mt, with an average grade of 0.15% Cu, 0.09g/t Au, 0.8g/t Ag and 18g/t Mo, returning an operating profit of 222 million SEK ( 19.6million) in 2016 alone. The processing plant at the mine produces a Cu concentrate (average grade of 27 29% Cu, 8g/t Au and 250g/t Ag), which is sent via rail to the Rönnskär smelter east of Skellefte. The Aitik mine has an average annual production of 60,000 tonnes of Cuin concentrate, tonnes of Ag and tonnes of Au (Nordin et al., 2007). Since mining of the Aitik deposit commenced in 1968, over 500 Mt of ore have been mined from a 3 km long, 1 km wide and 450 m deep open pit, in addition a further >500Mt of waste rock was removed in order to expose the ore body. The geology of the Aitik deposit can be subdivided into three main zones; the hanging wall, the footwall complex, and the main ore zone (Figure 4). The hanging wall is predominantly banded hornblende gneisses whilst the footwall is composed of a quartz monzodiorite. The intervening ore zone is composed of three units, a biotite gneiss, muscovite schist and a biotite schist, all of which are highly altered, deformed and progressively grade into one another. Geochemical studies of the schists indicate that their protoliths were intermediate volcaniclastic rocks (Wanhainen and Martinsson, 1999). Younger pegmatites and intermediate dykes discordantly cross cut the hanging wall, footwall and ore zones, and are often focussed along zone margins. Host Rocks and Mineralisation The hornblende banded gneiss footwall is a >250m thick, finely banded unit with a mineralogy dominated by hornblende, biotite and quartz with lesser plagioclase and scapolite porphyroblasts with accessory tourmaline and magnetite. Crucially, no sulphides or associated Figure 3: Geology of the region surrounding the Aitik deposit. (Wanhainen et al., 2006). mineralisation is present. This unit has been tectonically emplaced over the main ore zone via a thrust evident at the contact. The boundary between the hornblende banded gneiss and main ore zone is highly fractured, and intruded by pegmatitic dykes up to 40m wide (Nordin et al., 2007).

9 The main ore zone dips approximately 45 to the west and consists of muscovite and biotite rich schists and gneisses. The uppermost quartzmuscovite schist is typically 200m thick and characterised by a strongly foliated matrix. The gradational contact with underlying biotite schist is distinguished by a greater dominance of biotite relative to muscovite. The lowermost part of the main ore zone is biotite gneisses, with the same mineralogy and mineralisation as the biotite schists, but with a larger grain size, gneissose banding and zones of spessartine almandine garnet (Nordin et al., 2007). The dominant footwall lithology is a quartz monzodiorite up to 600 metres in thickness, with textures varying from medium grained equigranular to strongly porphyritic in places. The unit contains compositionally zoned plagioclase phenocrysts typically 7 9mm in size, amongst a finer grained matrix of plagioclase, quartz, biotite and lesser sericite. Multiple generations of stockwork mineral veining (mm cm wide) occur in the monzodiorite unit, including quartz, quartztourmaline, gypsum fluorite and zeolite bearing veinlets. A zircon U Pb age of 1887 ± 8 Ma has been determined for this unit by (Wanhainen et al., 2006), thus the intrusion is Paleo Proterozoic in age. Sulphide mineralisation in the uppermost muscovite schist is dominated by pyrite and chalcopyrite, with lesser pyrrhotite and molybdenite (py > cpy > po). Sulphides occur as both blebs along foliation planes and as veinlets in the host schist. A sulphide rich zone is present at the upper contact of the muscovite schist, varying from 5 40m thick and bearing 20 25% sulphides and enriched gold, copper and molybdenum concentrations. In the biotite schist, there are equal proportions of pyrite and chalcopyrite, both occurring as veinlets, clots and disseminations throughout the host schist (Nordin et al., 2007). Chalcopyrite predominantly occurs in the matrix of the host schists rather than latestage alteration minerals, indicating that mineralisation was emplaced during the early stages of petrogenesis (Wanhainen et al., 2006). Mineralisation grades typically increase towards the margins of the ore zone, with low grade rocks in the core of the deposit (Wanhainen et al., 2006). Gold is present as native Au, electrum (AuAg) and amalgam (AuHg), with a change from dominantly sulphide related gold, to groundmass related gold with depth. Genesis of the Aitik Deposit Figure 4: Geology of the Aitik deposit (Wanhainen & Martinsson, 1999). The plutonic and volcaniclastic host rocks at Aitik belong to the Haparanda Intrusive Suite and Porphyrite Group of comagmatic rocks, respectively (Wanhainen and Martinsson, 1999; Wanhainen et al., 2006). These rocks were generated during the subduction of oceanic crust beneath the Archaean Karelian Craton during the Svecokarelian orogenic event at ~1.9Ga. Upon emplacement of the quartz monzodiorite intrusive, contemporaneous high salinity hydrothermal fluids were released, responsible for potassic alteration of the intrusive body, chalcopyrite pyrite mineralisation and quartz stockwork formation (Nordin et al., 2007). The mineralised quartz monzodiorite of the footwall at Aitik is suggested to represent an apophyse (extension) of a larger intrusion at depth. As noted by Wanhainen et al. (2006), disseminated sulphide mineralisation associated with a subvolcanic intrusion, itself subject to brecciation, potassic alteration and stockwork veining, are characteristics typical of porphyry copper deposits. However, other features of the main ore zone at Aitik is not consistent with a typical porphyry system. Rather, it has been suggested that Aitik is a hybrid porphyry copper IOCG mineralising system, based on the characteristics of the high salinity ore fluids, the mineralisation styles and the prolonged evolution (160Ma; Re Os molybdenite) of the deposit (Wanhainen et al., 2006; Nordin et al., 2007). Furthermore, the intrusive complex associated with mineralisation at Aitik is similar to that of smaller IOCG deposits in the Norbotten region dated at 1.8Ga, suggesting the Gällivare area is a transition between regions dominated by two contrasting deposit types (Martinsson, 2004; Nordin et al., 2007).

10 Day 3: Aitik Cu Mine Aitik 14 th June 2017 In the morning we left Skellefte at 05:00 heading for Aitik which is located just south of Gallivare in Lapland. We arrived at 08:30 for our introduction and safety briefing. Aitik was the first large open pit many of the students has visited, it was an excellent opportunity for them to see the contrast in mining methods from the previous day at Kankberg. Our guide for the day was mine geologist Peter Karlsson. Aitik was discovered in 1930 by the occurrence of chalcopyrite rich boulders. Aitik is currently undergoing a phase of expansion with Boliden aiming to double production In the future from 18 to 36 Mt/year. The average feed grade is 0.24 % Cu, 0.14 g/t Au and 2.15 g/t Ag. Currently the open pit is 450 m deep, 4km long and km wide (Figure 2A). Aitik provides an excellent case study for the economies of scale low grade but large volume. After our introduction we headed into the base of the open pit (north pit). The scale of the pit was immense, we were as deep in AItik as we were in Kankberg the day before! Ore transport to the surface is achieved by a series of conveyor belts. Ore is blasted and transported to two in pit jaw crushers and then transported to the surface via 6 km of underground and over ground conveyors. Once in the pit we hunted for some of the spectacular ore. Samples were plentiful. The main ore mineral is chalcopyrite with various copper secondaries e.g. bornite. The ore is spectacular hosting cm scale garnets, massive chalcopyrite and various alteration minerals. Gold is refractory and occurs within pyrite. Whilst in the pit we were treated to a tour of a diamond drilling rig operated by a Finnish contractor Kati. It was an excellent experience that allowed the students to talk to drillers about the process of diamond coring. Peter explained that the current hole was for exploration purpose to see how far the mineralisation extended downwards (Figure 2B). After our tour of the open pit we headed back to the surface to the core shed to look at some typical core. The core was beautiful it contained cm size garnets, amphibole and orthoclase feldspar. Or mineralogy was dominantly chalcopyrite with covellite and bornite. Unlike Kankberg traditional alteration mapping was used at Aitik. The final stop of the day was to the engineering workshops to get up close and personal with some of the haul trucks and large excavators. We were lucky enough to be able to have a photo in the bucket of one of the large electric shovels used in the open pit. To give an ideal of scale the bucket fitted all 12 of us in with room to spare! The haul trucks used at the mine are mainly cat 795F, these are big! They have a payload of 345 metric tons. Aitik has 25 of these haul trucks costing $5 million each. It was great for everyone to see the contrast in machines used in open pit mines compared with underground operations and appreciate the costs involved in moving so much material. Figure 2A: The Aitik north pit Figure 2B: Kati drill rig Figure 2C: Core with large garnets Figure 2D: Group photo next to a CAT 795F

11 Kirunavaara Mine Introduction Owned by: Luossavaara Kiirunavaara Aktiebolag (LKAB; a state owned company) Deposit Type: Apatite iron oxide ore or Kiruna Type Ore Minerals: Magnetite and hematite Mining Method: Underground, sub level caving open stoping Sweden is the largest producer of iron ore in Europe (providing 90% of the supply); it is sourced from two principal regions the Kiruna Malmberget province in the north and Bergslagen in central Sweden. The Kiruna municipality is situated in the province of Lapland, around 145 km north of the Arctic Circle, and is the northernmost town in Sweden! This high latitude means that between May and July the sun doesn t set and there are no daylight hours between December to January. This results in a harsh climate, with corresponding temperature shifts from an average of 18.6 C in January and highs of 19.3 C in July. Kiruna is the type locality for apatite iron oxide ore; as the name implies, besides iron, these deposits contain abundant phosphates such as fluorapatite and REE silicates, which may constitute significant reserves of REEs. The origin of this ore type is controversial and several fundamentally different modes of formation have been suggested including: direct magmatic segregation (via crystallisation), magmatic hydrothermal replacement and hydrothermal precipitation such as that producing IOCG deposits. A U Pb zircon age of 1880 ± 3 Ma has been obtained from crosscutting granophyric dikes and as such represents a minimum age for the deposit. The Kiruna mine exploits a high grade magnetite deposit approximately 4 km long, averaging 80 m wide, dipping at around 70 and orientated in an N S direction. The orebody is tabular and concordant with the host rock, following the contact between a thick pile of trachyandesite lava and overlying pyroclastic rhyodacite (see Figure 5). There are 2 main ore types, which differ based on their phosphate contents, the main ore contaminant. 20% of the orebody is comprised of apatite rich magnetite known as D ore, whereas 80 % is composed of apatite poor, high iron content magnetite known as B ore. B ore represents the best quality ore containing % P and 68 % Fe. The Kiruna deposit was first discovered in outcrop in 1696, however a permanent mine was not established unit Initial open pit mining ceased in 1962 with a total production of 209 Mt. Currently, it represents the largest underground iron ore mine in the world recovering ore from depths of > 1 km using sub level caving (stoping); the main haulage road is on the 1045 m level (see Figure 6). The mine produces around 24 Mt of iron ore per year, which is processed in facilities adjacent to the mine in a three stage process, dressing concentration pelletisation. The endproducts from the processing mill are small rounded iron ore balls known as pellets. These are transported via a rail line to the harbours of Lulea on the east coast of Sweden and Narvik on the west coast of Norway. The majority of the ore is shipped to steel mills in Europe but some is shipped to the Middle and Far East. The continued operation and growth of this mine is dependent on the successful relocation, decommissioning and reconstruction of central parts of the nearby town. The settlement at Kiruna, whose existence and prosperity rely on the mine, is literally being undermined and the current town centre requires moving 3 km to the east. Ground deformation became apparent and it was decided that the present municipal centre would have to be relocated to counter mining related subsidence. This work began on the 24 th May 2017 by beginning to move the first of 8 heritage buildings.

12 Figure 5: A geological map of the Kiruna area including the location of the main ore deposits. (Martinsson and Wanhainen, 2000) Figure 6: A schematic profile view of the Kiruna mine plan. Highlighted are the production levels and the ground deformation resulting from the extraction at depth.

13 Day 4: Kiruna Fe Mine Kiruna 15 th June We started the morning with an hour and a half drive north the furthest north the Cardiff SEG has ever been! We arrived at Kiruna at 08:30 where we met Ulf Andersson who was our guide for the day. Before heading in the mine we were lucky enough to view some small historically mined IOCG deposits in the surrounding area. Deposits were characterised by crosscutting magnetite veins within mafic rocks with a hydrothermal overprint; aegerine was common and very beautiful. Apatite and hematite veins cross cut the body creating some spectacular textures. There was also an exceptionally good view over Kiruna (Figure 3A) We then headed to the town hall of Kiruna (Figure 3B) for some geo tourism. Due to the mining method used at Kiruna the town is subsiding. Gradually over the next 10 years the whole town will have to be moved. It was very interesting to think that the mine is so profitable that it s viable to move a whole town! We then headed to the mine site for an excellent lunch before heading underground. Kiruna is the world s largest underground Fe ore mine; the very fact you can mine such an inexpensive commodity underground and make a profit is testament to the efficiency LKAB apply at Kiruna. The deposit is an iron oxide copper gold (IOCG) or Kiruna type deposit, it is the largest known deposit of its type. The ore is massive magnetite which is cross cut by 1 3 m thick apetite pyrite veins (Figure 3H). Annual production of pellets and fines is 33 Mt/y. 3A 3B 3C 3D Figure 3A: The view over Kiruna 3B: The gang in the Kiruna town hall 3C: The underground cinema 3D: Group photo is a recently blasted drift

14 We accessed the mine via a decline making a pit stop at the visitor s centre where we were shown a short video on the formation of kiruna (Figure 3C). It was a maze underground with over 5000 km of track. We had the opportunity to collect some Fe ore pellets the end product produced at Kiruna (Figure 3F). After this we descended to the 1045 m production level. The mining method employed at Kiruna is sublevel open stoping. A series of parallel drifts are drilled from the footwall into the ore body, sequentially a fan shape is blasted in the roof of the drift causing the area above to cave in. The ore is then dropped through a series of ore passes and grizzlies to the 1045 production level. As series of automated full size trains then transport the ore to the crushers before they are hoisted via a skip raise system to the surface. To ensure maximum efficiency LKAB have developed a water based drilling technique using the Wasser drill, this drill enables them to drill holes with deviation of less than 1 degree (Figure 3G). This leads to optimum ore fragmentation and reduces costs. We were fortunate enough to have access to two recently blasted drifts, one within high grade B ore magnetite the other in the higher phosphate D ore zone which was cross cut by a beautiful apatite pyrite vein (Figure 3D). Digital software is used for grade control on a portable tablet device (Figure 3E). After every blast the face is mapped and a grade assigned. Shotcrete is applied to all stopes to ensure maximum safety. 3E 3F 3G 3H Figure 3E: Mine geologists demonstrating grade control software 3F: Pick n Mix geology style Fe pellets 3G: Students inspecting blast holes in drift face 3H: Apatite pyrite vein

15 Renström Mine Introduction Owned by: Boliden AB Commodity: Polymetallic Zn Cu Pb Au Ag Mining Method: Underground, cut and fill The Renström mine located in the Boliden area, also comprising the underground Kristineberg and Kankberg mines and the Maurliden open pit, in the eastern part of the Skellefte district (see Figure 7). This World famous mining district hosts > 85 pyritic Zn Cu Au Ag massive sulphide deposits of which 27 have been or are currently being exploited. These are found within a ca. 200 km long belt of Early Proterozoic (1.89 Ga) terrain comprising metavolcanics and metasediments intruded by several granitoid bodies. Ore deposits in the Renström area are hosted in volcanic rocks ranging in composition from basaltic andesite to rhyolite (see Figure 7). The rhyolite rocks associated with the deposit are interpreted as part of a rhyolite cryptodometuff volcano and the ores occur in the proximal (near vent) part of this volcano. The ores are interpreted to have formed by sub seafloor replacement because the ore lenses are present within rapidly deposited pumiceous beds rather than in slowly deposited siltstone facies. Interpreting the host rock assemblage of the ore deposit at Renström is complicated because it lies within a corridor of deformation adjacent to the Renström fault zone. This comprises a 400 m wide zone of steeply westward dipping shears and faults, intruded by high Mg basaltic andesite dikes. Therefore, most rocks are moderately to strongly foliated and/or lineated and all have been metamorphosed to greenschist facies. Identifying ore bearing horizons within strongly altered rocks is facilitated by the use of lithogeochemistry and induced polarization which is frequently used to test the interpretations of rock types and stratigraphic correlations. The Renström orebodies consist of numerous, thin (0.5 to 5 m), sub vertical, massive to semi massive sulphide lenses (mostly pyrite and sphalerite). Mineralogically the ores are straightforward with pyrite, sphalerite, chalcopyrite, galena, arsenopyrite and minor tetrahedrite present. In addition gold and silver occur as native metals or as the alloy electrum. Ores in the Renström area have higher Zn, Au, Ag and Pb contents and lower S and As then most volcanichosted massive sulphide ores in the Skellefte field. Subsequent deformation has resulted in extreme elongation of the ore lenses and a variety of ore textures including recrystallized, mylonitic and fine grained cataclastite. The mine opened in 1952 and has extended to 1,445 metres depth making it the deepest mine in Sweden. It exploits 2 main ore lenses, above the 600 m level, the A and B lenses. The B lens merges downwards with the A lens, and they continue to the 1750 m level. The A B lenses and Deep Zones occur near the hinge of a very tight to isoclinal anticline fold. There is no metal zonation within and between the different ore lenses. The ores are typically surrounded by a complex pattern of partly stratabound strong chlorite, sericite and silica alteration, commonly with zones of disseminated pyrite ± other sulphides. The deposit was discovered following the identification of glacial boulders with sulphide disseminations, which were found in the Renström area in Follow up work involved electromagnetic ground surveys, tracing of glacial boulders back to their source and trenching performed in Since 1992 Boliden has invested in exploration activities in order to extend the current ore reserves, this lead to the discovery of the Renström Deep Zone. Recent extensive regional and within mine geological mapping and drilling has extended the ore resource in the Renström main lens down to 1750 m.

16 Figure 7: An overview geological map of the Skellefte District, see Renström mine depicted towards the east. (Tavakoli et al., 2016)

17