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Location: 30 km NW from Skellefteå, Sweden
Finnforsvägen 4BolidenSweden936 32
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Boliden Area Operation (Renström, Kristineberg, and Kankberg mines) is 100% owned by Boliden Mineral AB.
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Renstrom Geology The rocks in the Skellefte district were formed approximately 1.9 Ga during a period of active volcanism. The felsic magmas intruded as shallow (subvolcanic) intrusions (dykes and sills) at and close to the surface, where they mixed and mingled with wet sediments and mass-flows derived from volcanic slopes resulting in hyaloclastic brecciation and peperites. The active volcanic region also initiated a convection of solutions within the deposited package which enabled the dissolution and transportation of metals and minerals. These solutions also altered the rocks both physically, through (hydro-) brecciation and fragmentation, and chemically resulting in the heavily altered rocks present today. After the main volcanic period, regional deformation took place within the Skellefte district. The brittle deformation accommodated for fractures and fissures, which would be filled by mafic magmas forming andesitic and basaltic dykes.The Renström area is located 15km west of Boliden, in the eastern part of the Skellefteå district. The Renström area has a volcanically complex and multiply deformed rock sequence. Rock types include a large range of basaltic andesite to rhyolite volcanic facies. Juvenile basaltic andesite, dacite and rhyolite volcanoclastic facies are particularly abundant and these have been intruded by numerous basaltic, andesitic dacitic and rhylitic sills and doms. The area has two main generations of folding with a complex interference pattern, and several generations of faults and intrusions.The Renström area is one of the most intensely mineralized parts of the Skellefte district and the Renström deposit is one of the most important deposits due to its size (>10 million tonnes), grade (high Zn, Au, Ag values) and metallurgical characteristics (medium grained; low arsenic and antimony contents). The ores in the Renström deposit are associated with strong chlorite, dolomite, sericite and silica alteration.Mineralization The Renström mineralization consists of several smaller lenses, which are all characterized by massive to semimassive pyrite-sphalerite dominated ores with subordinate massive to semimassive pyrite-chalocopyrite ore and local stringer-type pyrite-chalocopyrite±pyrrhotite mineralization. The main ore minerals are pyrite, sphalerite, galena, chalcopyrite, pyrrotite and arsenopyrite with minor tetrahedrite-tennantite, other sulphosalts, electrum and amalgam (Helfrich, 1971; Kläre, 2001). Ores in the Renström area have higher zinc, gold, silver and lead contents and lower sulphur and arsenic content than most volcanic-hosted massive sulfide ores in the Skellefte district.Kristineberg Geology The Kristineberg Camp is located on the western extent of the Skellefteå district. The area stretches roughly 100 km from the village of Kristineberg in the west to the village of Boliden in the east. The Skellefte district hosts more than 85 VHMS deposits, of which 26 have been, or are currently hosting mining operations. Mineralization of the Kristineberg Camp are considered examples of VHMS.MineralisationsMineralization at Kristineberg is typically hosted in steeply-gently dipping chlorite schist lenses, with a gentle plunge towards the southwest. These can be broadly split into chlorite schist hosted and Ag-Pb “remobilized” mineralization. Chlorite schist hosted mineralization generally contains sulphide mineralization that is semi-massive to massive in nature with variable abundances of economically important minerals: chalcopyrite (CuFeS2), sphalerite ((Zn, Fe)S) and galena (PbS), with minor silver and gold. The schists themselves contain variable amounts of muscovite, quartz, chlorite, phlogopite, biotite, cordierite, andalusite, pyrite and magnetite. The chlorite schists appear as lenses within colloquially named “quartzites” which are hypothesized to be highly altered rhyolitic to dacitic rocks (Barrett & MacLean, 2000). Chlorite, cordierite, sericite and andalusite as well as quartz, overprint the original rock textures making primary rock identification difficult. Chlorite schist hosted mineralisation generally contains sulphide mineralisation that is semimassive to massive in nature with variable abundances of economically important minerals: chalcopyrite (CuFeS2), sphalerite ((Zn, Fe)S) and galena (PbS), with minor silver and gold. The schists themselves contain variable amounts of muscovite, quartz, chlorite, phlogopite, biotite, cordierite, andalusite, pyrite and magnetite. The chlorite schists appear as lenses within colloquially named “quartzites” which are hypothesised to be highly altered rhyolitic to dacitic rocks (Barrett & MacLean, 2000). Chlorite, cordierite, sericite and andalusite as well as quartz overprint the original rock textures making primary rock identification difficult.RävlidenRävliden constitutes a sub-vertical to steeply south-dipping, 5m to 25m wide and 150 m high mineralized lens, or system of lenses, with a length extent of at least 900 m along plunge (Jansson & Fjellerad Persson, 2014). Mineralization types can be split broadly into two categories: massive to semi-massive sphalerite-dominated mineralization and breccia-type Cu>Zn mineralization.Nyliden, a new satellite depositThe Nyliden deposit is sub-vertical to steeply North dipping, 5-30 m wide and 250 m high mineralized lens or system of lenses, with a strike extent of at least 500m along strike. The mineralization is bound to a black shale layer that overlies a succession of andesitic to dacitic volcanic and volcaniclastic rocks. The ores are comprised mainly of stringers and semi-massive to massive pyrite with varying amounts of chalcopyrite, sulfosalts of the tetrahedrite-tennantite solid solution and rare bornite. Sphalerite-rich domains are usually found in shallower parts of mineralization but lack continuity.Kankberg Geology The Kankberg Mine lies within the eastern part of the Skellefte mining field, one of the most important mining regions in Sweden, where Boliden has been active since the 1920s.The host rock in the Kankberg area is dominated by volcanic rocks of primarily dacitic, andesitic and minor rhyolitic compositions forming both coherent and volcaniclastic rock types. The magmas forming these volcanics and breccias intruded as shallow (subvolcanic) domes, dykes and sills and extruded as lavas at the surface where they mixed with sediments and mass flows derived from volcanic slopes. The associated magmatic-hydrothermal system both strongly altered and brecciated the host rocks and transported minerals and metals to sites of deposition.After the major volcanic and hydrothermal period ended the area was subsequently deformed and folded. This resulted in a dominantly vertical trend of the rocks and structures. At a later stage, brittle deformation took place. Fractures and fissures were intruded by mafic magma forming basaltic and andesitic dykes, which are common in the Kankberg area.MineralizationGold mineralization is hosted in a complex mix of volcanic rocks consisting primarily of quartz-feldspar porphyry, volcaniclastics and breccias. The host rocks are strongly altered by silicification, andalusite ± topaz alteration and to a varying degree sericitization. The strong alterations form a highly competent body, which is surrounded by dacites. The contact zone is characterized by sericite ± chlorite alteration associated with pyrite ± pyrrhotite.The economic mineralization is contained in ‘metallic’ minerals primarily located within the quartz-andalusite ± topaz alteration. It includes fine-grained native gold alloyed with silver at proportions of between 0 to 20%. More commonly, gold occurs as gold-tellurides including petzite (Ag3AuTe2), calaverite (AuTe2) and sylvanite (AuAgTe4). Another common telluride is tellurobismuthite (Bi2Te3). Several more telluride minerals have been identified through microscopy.
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