Ryllshyttan is a Palaeoproterozoic lower amphibolite-facies poly-metamorphosed stratabound Zn-Pb-Ag-(Cu) + magnetite deposit. It is located in the Garpenberg inlier of the Bergslagen mining district of southern Sweden and produced ~ 1 Mt sulphide ore and ~ 0.4 Mt magnetite ore from the early 16th century until 1944.The Ryllshyttan area is dominated by metamorphosed calc-alkaline rhyolitic volcanics, transitional mafic intrusions and dolomitic marble. The later hosted the mined ores and is heterogeneously altered and metamorphosed to skarns of variable composition in proximity to the ores. The ore horizon is tightly F2-folded into a series of steeply plunging synclines and anticlines. F2-folds fold an earlier S1 foliation sub-parallel to bedding. Planar S1 foliations are included in pre S2 almandine porphyroblasts, suggesting inter-tectonic regional metamorphism (M1). A second phase of regional metamorphism (M2) outlived penetrative D2 deformation as shown by post S2 almandine porphyroblasts and regional statically recrystallised S2/S1 crenulation foliations. ENE-trending sub-vertical D3 shear zones outlasted regional metamorphism as shown by protomylonites cross-cutting M2 caused static recrystallization. Brittle shallow to steeply dipping F4 faults caused small reverse displacements in northern Ryllshyttan.The limestone ore-host formed after deposition of a syn-eruptive sub-aqueous rhyolitic mass-flow deposit which constitutes Ryllshyttan's stratigraphic footwall. Limestone formation by stromatolite growth in the photic zone was followed by subsidence to deeper water conditions and deposition of fine-grained rhyolitic sediments below wave base. The rhyolitic sediments periodically co-settled with hydrothermal-exhalative calcareous-ferruginous sediments, forming sedimentary mixtures which during metamorphism formed stratiform Ca-Fe-rich aluminous skarn beds. After burial, the stratigraphic succession was intruded by syn-volcanic peperitic rhyolite porphyries. The porphyries are crosscut by shallow level pre-D1 mafic sills and dykes. Emplacement of dolerite intrusions may be coeval with a period of mafic extrusive volcanism evident stratigraphically above Ryllshyttan. The entire stratigraphy is truncated by a microgranodiorite which represents the outermost part of the GDG batholith west of the Garpenberg inlier. Epigenetic formation of sulphide and magnetite ore occurred by replacement of a limestone unit. This occurred between emplacement of the mafic intrusions and microgranodiorite and is associated with pre-D1 K-Fe-Mg +/- Si alteration proximal (< 50 m) to the ore-zone. The alteration zones developed as chlorite-sericite zones but are now metamorphosed to porphyroblastic biotite-phlogopite +/- quartz schists with elevated concentrations of Zn, Pb, Cu and Mn. Distal (> 50 m) alteration is expressed by quartz-spessartine rocks formed by alteration and metamorphism of calcareousferruginous hydrothermal sediments and epidote-calcic clinoamphibole mottling and veining of rhyolitic volcanics. Alteration in the ore-zone is expressed by sphalerite and magnetite impregnated dolomitic marble, magnesian skarns and calcic skarns in the ore-zone. A zonation with proximal Fe-Mg alteration grading outwards with decreasing Fe/Mg-ratio to more distal Mn alteration is apparent. Though epigenetic sulphides appear to slightly post-date epigenetic magnetite, no significant hiatus is observed and both may have formed during the same event.The microgranodiorite is geochemically similar to syn-volcanic dacite intrusions proximal to the currently mined sulphide ores at Garpenberg. Na-Ca alteration has affected the microgranodiorite as well as adjacent volcanics, leading to the development of diopside-oligoclase assemblages. The timing of sulphide ore formation relative to the intrusive history indicate that ore formation occurred broadly synchronously at Garpenberg and Ryllshyttan during the evolution of a large marine felsic caldera complex but at different stratigraphic levels. Ryllshyttan displays features of both regionally metamorphosed, shallow marine, sub-seafloor replacement VMS deposits and metasomatic skarn deposits. These contrasting relationships may have resulted from a prograde hydrothermal evolution starting with early K-Mg-Fe +/- Si alteration, continuing with later Na-Ca alteration following a path of increasing temperature of the hydrothermal system and eventually ending with a transition to regional metamorphism and deformation during which already existing ores were significantly modified by deformation and fluid-assisted remobilization during the Svecokarelian orogeny.

The Palaeoproterozoic Skellefte mining district in northern Sweden covers an area of 120 by 30 km and is one of the most important mining districts in Europe, producing mainly Zn, Cu, Pb, As and Au from volcanogenic massive sulfide (VMS) and orogenic gold deposits.Detailed mapping of structures and stratigraphy within the sedimentary Vargfors Group combined with a structural analysis revealed a syn-extensional fault pattern of NW-SE-trending normal faults and associated NE-SW-trending transfer faults, creating the segmented sedimentary Vargfors basin. It comprises distinct fault-bound compartments, which incluence the sedimentary stratigraphy in each of these compartments.Syn-rift subsidence affected the sedimentary conditions from near-shore to shallow submarine environment.Intensive fault movements associated with mafic volcanic activity along these faults resulted in the rapid uplift of the oldest phase of the Jörn intrusive complex and/or subsidence of its surrounding areas. Subsequent erosion of the intrusive rocks led to the formation of a tonalite to granodiorite bearing conglomeratic sequence, representing an alluvial fan. Further uplift to the north of the district resulted in the erosion of Arvidsjaur volcanic rocks and the formation of a braided river system. Subsidence of the intrusive complex and/or a sedimentary coverage on top of the same caused a break in sedimentation of tonalite to granodiorite clasts. Stratigraphical evolution of the sedimentary rocks and the Vargfors Group - Skellefte Group contact relationships show that rifting started in the centre and proceeded with time towards SE and NW. Subsequent basin inversion resulted in the reactivation of the existing normal faults along a carbonate-rich basal layer forming asymmetric synclines. Primary geometries of sedimentary strata within each fault-bound compartment controlled their deformation styles. Furthermore, strain was partitioned into the faults, forming high strain zones along the basin margins, where foliations parallel the main faults, and low strain domains in the core of the basin, where foliation is oblique to the main structural grain of the basin. This oblique foliation is either a result of a rotating stress field or a transpressional regime. This case study on basin inversion gives implications for accretion processes along the Svecokarelian Craton margin as well as forthe formation of VMS-deposits and their possible transposition. Basic modelling of the main geological boundaries in the central Skellefte district was performed by integrating data from regional to outcrop scale using the GoCAD (Paradigm) software platform. Available data included geographical and geological data, which were imported from ArcGIS (ESRI) as well as drill-hole data, seismic profiles, resistivity and gravimetry profiles and EM-profiles. Creation of the main geological boundaries utilized GoCAD and SPARSE (Mirageoscience) algorithms, whereas structural geological data was exclusively modelled with SPARSE. Furthermore, this study provides a base for refining the 3-dimensional model and developing a 4-dimensional model, showing the geological evolution of the Skellefte district.

Rockliden is a polymetallic Zn-Cu volcanic-hosted massive sulphide (VHMS) deposit. It is located in north-central Sweden about 150 km south of the Skellefte ore district. Two major challenges to mining and production were identified soon after Rockliden was discovered in the 1980’s. Firstly, the geographic distance to Boliden’s main ore deposits and existing concentrator in the Skellefte district will set additional financial and logistic constrains for the processing of the ore. Secondly, the locally high Sb grade in the ore potentially lowers the quality of the Cu-Pb concentrate sent to the Cu smelter. To face the second challenge to mining and production, it is necessary to use information from three disciplines: ore geology, mineral processing and process metallurgy. The three disciplines build the geometallurgical framework of the Rockliden ore characterisation. The purpose of this investigation is to outline which mineralogical factors are the cause of the elevated Sb content in the Cu-Pb concentrate. Determining such factors will help to predict the Sb content of this product and thus outline the tools required before decisions may be reached with regard to selection between various processing alternatives for the Rockliden ore. Hydrometallurgical treatment of the Cu-Pb concentrate has previously been studied by Awe (2013) and it was found that alkaline sulphide leaching can be used to lower the Sb content.A qualitative characterisation of the ore forms the main focus of this licentiate thesis. Minerals have been identified and their chemical composition has been obtained with micro-analytical tools (SEM/EDS &amp; EPMA/WDS) to study the mineralogical distribution of major (e.g. Zn, Cu, Fe), penalty (e.g. Sb) and bonus (e.g. Ag) metals. Furthermore, mineral textures and associations have been studied in ore samples by optical microscopy and SEM/BSE imaging. Ore types are preliminary classified based on the sulphide mineralogy, i.e. the relative content of pyrite, pyrrhotite, magnetite, sphalerite and chalcopyrite estimated by reflected light microscopy. As sphalerite and chalcopyrite form the main Cu- and Zn-bearing minerals at Rockliden, the content of these two minerals can be approached with element-to-mineral conversion based on standard drill core assays (including S, Cu, Zn, Pb, As, Sb and Ag). The mineralogy of Sb-bearing minerals is complex and a single thin section can contain more than three different Sb-bearing phases. Thus, the element-to-mineral conversion is not applicable in directly calculating the modal mineralogy of the Sb-bearing mineral fraction based on drill core assays. Additionally, it is shown that the mineral association of the Sb-bearing minerals is complex. Products from initial flotation tests have been studied and the preliminary conclusion is that the complex intergrowths with various minerals influence the distribution of Sb-bearing minerals between the flotation products. Thus, a more detailed petrographic study on the massive sulphides and their host rocks was conducted. The sulphide and non-sulphide mineralogy of the host rocks and ore types are shown to be variable. It is also shown that the host rock types can be distinguished based on their trace element eochemistry, supporting the geological classification based on drill core logging.Based on petrographic and mineralogical observations done in this study, potential process-relevant rock-intrinsic factors are outlined. However, to evaluate the impact of such parameters on the beneficiation process, these parameters have to be quantified throughout the Rockliden deposit and this is the focus of continued studies. SEM-based automated mineralogy tools will be essential in measuring the important parameters such as modal mineralogy and mineral liberation. Quantitative information will then be used in a larger framework to build a geometallurgical model usable for production planning.

The Aitik mine is a large Cu-Au producer in Europe with an annual production of 28 million tons of ore and a planned expansion of production to 36 million tons of ore until year 2013. Large ongoing investments are done in the mine and a new processing plant is built to manage the capacity increase. The mine is situated 15 kilometers from the town Gällivare, in northern Norrbotten, Sweden. The ore is a large porphyry type deposit with low grades of disseminated copper (0,27 %) and gold (0,16 ppm). Porphyry copper ores usually have low recoveries when flotation is used as an extraction method and also the Aitik mine has shown historically low gold recoveries (< 50 %).The Aitik deposit is situated in 1.9 Ga Svecofennian volcanic and sedimentary rocks formed in a volcanic arc environment and later deformed and metamorphosed at amphibolite facies. The main ore zone consists of biotite and muscovite schist and gneisses. A thrust fault divides the main ore zone from the hanging wall that contains feldspar biotite amphibole gneiss. In the footwall the feldspar biotite amphibole gneiss also is found and an intrusion of quartz montzodiorite.In this study, horizontal and vertical zoning patterns were recognized in data based on the block model that consist of drill cores and drill ship samples since the mine started 1968. The vertical zoning shows a decrease in high (> 0,6 % Cu) copper grade areas and an increase in high (>0,3 ppm Au) areas towards the depth. An increase in the amphibole content is seen in the biotite gneiss towards depth. The gold mineralized areas are trending northeasterly and plunging northeast, and for copper north-northwest. The horizontal zoning can be seen in the middle of the ore zone where a high-grade area of disseminated sulfides in potassic altered biotite gneiss/schist exists. Further towards the hanging wall, a low grade, strongly sericite altered and pyrite-rich schist is common.Gold-rich areas are found close to the hanging wall in strongly sericite schist altered rock and in a part of a biotite schist that are strongly affected by K feldspar and epidote alteration and quartz and pyrite growth, but also in the amphibole rich parts close to the footwall. Copper dominated mineralization is mainly developed towards the hanging wall, as disseminated and massive veins of chalcopyrite. The rich dissemination in the centre of the ore body is suggested to be a part of the primary mineralization, and the locally higher concentrations in veins would originate from later remobilization. To get a better knowledge of how gold occurs at Aitik and how to increase the gold recovery during mining a detailed mineralogical investigation was done. This revealed that there is a change in gold associations towards depth. Commonly associated minerals with gold at 600 m and below are K-feldspar, biotite, plagioclase, quartz, chalcopyrite and pyrite. At higher levels in the mine gold is most commonly associated with chalcopyrite and pyrite. There is also a change in gold content in alloys towards depth where the gold decreases in electrum and amalgam but the amount of native gold grains increases. As the average gold and copper grades are relatively constant at the different levels in the mine this means that the gold associations that are not connected to sulfides (chalcopyrite) are going to tailings from the deeper part of the mine and the gold recovery as a consequence is lower today. Some other copper-gold deposits have implemented several different recovery methods to extract the gold from the ore, an example from Bajo de la Alumbrera (Chryssoulis 2001), Argentina with a similar ore type as Aitik have a combination of gravity and flotation in their recovery process. Based on the results on the mineralogy and the mineral associations it would be possible to combine additional recovery methods as gravimetric methods to the flotation that are used today. Lime used in the process might have a depressive affect on gold and should be further investigated. The Aitik deposit is interpreted to have a mixed origin, with an early porphyry copper style of mineralization overprinted by a later and minor iron-oxide Cu-Au (IIOCG) system (Wanhainen 2005). Gold bearing fluids at Aitik were compared with those at the minor epigenetic Cu-Au deposits Liikavaara East, Fridhem, Jårbojoki and Muorjevaara, that occur in the Nautanen deformation zone. According to earlier studies high salinity fluids are connected to the copper mineralization and in this study a connection between gold and CO2 is suggested based on the positive correlation between CO2 and gold that could be found in all deposits. However, the carbonic fluids varied in composition and includes pure CO2, CO2-CH4, CO2-H2O, or CO2 present as calcite in aqueous inclusions. The highest gold grades were associated with CO2 in silicates and CO2-CH4 in sulphides.

The Gällivare area is situated in northern Norrbotten, Sweden, and hosts the Aitik Cu-Au deposit and the Malmberget Fe deposit. In addition, more than 17 mineral prospects and mineralizations are present, among these the currently developed Nautanen Cu-Au deposit. All deposits are hosted within Paleoproterozoic volcanic and volcano-sedimentary successions intruded and surrounded by multiple generations of intrusive suites, including large bodies of ultramafic to mafic layered complexes. Detailed field mapping combined with geochemical and petrological investigations and geochronology have revealed suites of igneous rocks ranging in composition from ultramafic-mafic, intermediate to felsic. Main key igneous rocks include 1) tholeiitic, ultramafic-mafic layered intrusive complexes; 2) calc-alkaline mafic to intermediate plutonic and volcanic units; 3) calc-alkaline, mafic-intermediate dykes and sills; 4) calc-alkaline and shoshonitic granitoids. U-Pb multigrain zircon SIMS analysis combined with lithogeochemical investigations suggest two magmatic episodes at 1.88 and 1.80 Ga, respectively, with coeval mafic-felsic magmatism including the generation of voluminous layered complexes. Based on their MORB-type, tholeiitic character, these layered complexes are suggested to have formed in an extensional setting, preferentially in a back-arc environment. U-Pb multigrain zircon SIMS analysis and field mapping also reveal that granitoids in the area range from 1886 to 1779 Ma with the oldest granitoids containing mafic enclaves. This suggests magma interaction between basic and felsic magma sources. Geochemical data suggest generation of granitoids in a volcanic arc environment in a mainly post-collisional setting. Results suggest the formation of layered complexes and a volcanic arc system in an extensional setting followed by a subsequent compressional phase of arc accretion producing post-collisional granitoids. The 1.88 Ga event that generated the ultramafic-mafic layered complexes is associated with a back-arc setting generated in response to 1.90 Ga NNE trending subduction. The later event at ~1.80 Ga generating voluminous mafic-felsic units is associated with the TIB event which is also coupled to the regional IOCG overprint. / The Gällivare area is situated in northern Norrbotten, Sweden, and hosts the Aitik Cu-Au deposit and the Malmberget Fe deposit. In addition, more than 17 mineral prospects and mineralizations are present, among these the currently developed Nautanen Cu-Au deposit. All deposits are hosted within Paleoproterozoic volcanic and volcano-sedimentary successions intruded and surrounded by multiple generations of intrusive suites, including large bodies of ultramafic to mafic layered complexes. Detailed field mapping combined with geochemical and petrological investigations and geochronology have revealed the role of intrusive igneous events and their control on ore formation. Main key igneous rocks include 1) tholeiitic, ultramafic-mafic layered intrusive complexes; 2) calc-alkaline mafic to intermediate plutonic and volcanic units; 3) calc-alkaline, mafic-intermediate dykes and sills; 4) calc-alkaline and shoshonitic granitoids. U-Pb multigrain zircon SIMS analysis combined with litho-geochemical investigations suggest two magmatic episodes at 1.88 and 1.80 Ga, respectively, with coeval mafic-felsic magmatism including the generation of voluminous layered complexes. Based on their MORB-type, tholeiitic character, these layered complexes are suggested to have formed in an extensional setting, preferentially in a back-arc environment. U-Pb multigrain zircon SIMS analysis and field mapping also reveal that granitoids in the area range from 1886 to 1779 Ma with the oldest granitoids containing mafic enclaves. This suggests magma interaction between basic and felsic magma sources. Geochemical data suggest generation of granitoids in a volcanic arc environment in a mainly post-collisional setting. Results suggest the formation of layered complexes and a volcanic arc system in an extensional setting followed by a subsequent compressional phase of arc accretion producing post-collisional granitoids. The 1.88 Ga event that generated the ultramafic-mafic layered complexes is is associated with a back-arc setting generated in response to 1.90 Ga NNE trending subduction. The later event at ~1.80 Ga generating voluminous mafic-felsic units is associated with the TIB event also coupled to the regional IOCG overprint.

The Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, situated in the Palaeoproterozoic (1.9–1.8 Ga) Bergslagen lithotectonic unit in the south-western part of the Fennoscandian Shield, is one of the major base and minor precious metal sulphide deposits in Sweden. Host rocks to the deposit as well as the ores and altered rocks were metamorphosed and affected by heterogeneous ductile strain during the Svecokarelian orogeny the total duration of which was 2.0–1.8 Ga. These processes both reworked the mineral assemblages of the original hydrothermal alteration system and reshaped the structural geometry of the deposit, following formation of the ores and the associated hydrothermal alteration.In order to study primary geological and ore-forming processes at Falun, it is necessary firstly to investigate the nature of the tectonothermal modification. In this licentiate thesis, a three-dimensional modelling approach is used in order to evaluate geometric relationships between lithologies at the deposit. This study demonstrates the polyphase character (D1 and D2) of the strong ductile deformation at Falun. The major rock-forming minerals in the silicate alteration rocks are quartz, biotite/phlogopite, cordierite, anthophyllite, chlorite, and minor almandine and andalusite. On the basis of microstructural investigations, it is evident that these minerals grew during distinct periods in the course of the tectonic evolution, with major static grain growth between D1 and D2, and also after D2. Furthermore, the occurrence of F2 sheath folds along steeply south-south-east plunging axes is suggested as a key deformation mechanism, forming cylindrical, rod-shaped ore bodies which pinch out at depth. The sheath folding also accounts for the same stratigraphic level (footwall) on both the eastern and western sides of the massive sulphide ores. A major, sulphide-bearing high-strain zone defines a tectonic boundary at the deposit and bounds the massive sulphide ores to the north.The geological evolution in the Falun area involved emplacement of felsic sub-volcanic intrusive and volcanic rocks and some carbonate sedimentation; followed by hydrothermal alteration, ore formation and the intrusion of dykes and plutons of variable composition after burial of the supracrustal rocks. Secondary Ion Mass Spectrometry (SIMS) U-Pb (zircon) geochronology of key lithologies in and around the Falun base metal sulphide deposit indicates a rapid sequence of development of different magmatic pulses with individual age determinations overlapping within their uncertainties. The intense igneous activity, as well as the feldspar-destructive hydrothermal alteration and ore formation are constrained by two 207Pb-206Pb weighted average (zircon) ages of 1894 ± 3 Ma for a sub-volcanic host rock not affected by this type of alteration and 1891 ± 3 Ma for a felsic dyke, which cross-cuts the hydrothermally altered zone and is also unaffected by this alteration. All other ages, including the granitic plutonic rocks, fall in the interval between these ages.The lithological, structural and geochronological observations have implications for the environment and the conditions of ore formation at the Falun deposit. Several aspects argue for an ore system resembling a classic volcanogenic massive sulphide (VMS) system in terms of type of alteration, metal zonation, the pyritic character of massive sulphides and an inferred vent-proximal location in relation to the convection-driving magmatic system. The bowl-shaped, sub-seafloor feeder part of such a system might have served as an initial inhomogeneity in the strata for the later development of strong stretching along steep axes and sheath fold formation during ductile strain. Possible discordant relationships along the margins of the massive sulphide ores, coupled with the syn-magmatic, pre-tectonic timing of ore formation are in accordance with a general VMS-type model for the Falun base metal sulphide deposit. These results provide a compromise solution to the previous debate around two opposing models of strictly syn-genetic vs. epigenetic, post-deformational carbonate-replacement processes for ore formation at the deposit. / The Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, situated in the Palaeoproterozoic (1.9–1.8 Ga) Bergslagen lithotectonic unit in the south-western part of the Fennoscandian Shield, is one of the major base and minor precious metal sulphide deposits in Sweden. Host rocks to the deposit as well as the ores and altered rocks were metamorphosed and affected by heterogeneous ductile strain during the Svecokarelian orogeny (2.0–1.8 Ga). These processes both reworked the mineral assemblages of the original hydrothermal alteration system and reshaped the structural geometry of the deposit, following formation of the ores and the associated hydrothermal alteration.In order to study primary geological and ore-forming processes at Falun, it is necessary firstly to investigate the nature of the strong tectonothermal modification. In this licentiate thesis, a three-dimensional modelling approach is used in order to evaluate geometric relationships between lithologies at the deposit. This study demonstrates the polyphase character (D1 and D2) of the ductile deformation at Falun. The major rock-forming minerals in the silicate alteration rocks are quartz, biotite/phlogopite, cordierite, anthophyllite, chlorite, and minor almandine and andalusite. On the basis of microstructural investigations, it is evident that these minerals grew during distinct periods in the course of the tectonic evolution, with major static grain growth between D1 and D2, and also after D2. Furthermore, the occurrence of F2 sheath folds along steeply south-south-east plunging axes is suggested as a key deformation mechanism, forming cylindrical, rod-shaped ore bodies which pinch out at depth. The sheath folding also accounts for the same stratigraphic level on both the eastern and western sides of the massive sulphide ores. A major, sulphide-bearing high-strain zone defines a tectonic boundary inside the deposit and bounds the massive sulphide ores to the north. A precursor to this zone can have played a central role as a metal-bearing fluid conduit during ore genesis, prior to reactivation of the zone in the ductile regime.The geological evolution in the Falun area involved emplacement of felsic volcanic and sub-volcanic rocks and some carbonate sedimentation, followed by ore formation and hydrothermal alteration as well as the intrusion of dykes and plutons of variable composition. U-Pb zircon geochronology of key lithologies in and around the Falun base metal sulphide deposit indicates a rapid sequence of development of different magmatic phases with individual age determinations overlapping within their uncertainties. The igneous activity is constrained between a zircon U-Pb concordia age of 1899 ± 7 Ma for a sub-volcanic host rock and a zircon 207Pb-206Pb weighted average age of 1891 ± 3 Ma for a felsic dyke, with all other reliable ages, including the quartz-rich plutonic rocks, falling in the interval between them. This interval also included the hydrothermal alteration and ore formation at Falun.It is suggested that the bowl-shaped, sub-seafloor feeder part of a high-sulphidation and Au-bearing volcanogenic massive sulphide ore system, with replacement of carbonates and (sub)-volcanic rocks, served as an initial inhomogeneity in the strata for the later development of strong stretching along steep axes and sheath fold formation during ductile strain. The observation of discordant relationships along the margins of the massive sulphide ores, coupled with the syn-magmatic, pre-tectonic timing of ore formation, corroborate this hypothesis, providing a compromise solution to the previous debate around two opposing models of strictly syn-genetic vs. epigenetic, post-deformational carbonate-replacement processes of ore formation at the Falun base metal sulphide deposit. / Structural evolution, hydrothermal alteration and tectonic setting of the Falun base metal and gold deposit, Bergslagen region, Sweden

Closer monitoring of hydrogeochemical changes in the Cascade volcanic arc has been in effect since 2009 to track recent volcanic unrest. This study analyzes data collected from several sites across this region from 2009 to 2016 using a program called MATLAB to create spectrograms using Fourier analysis to find anomalies or correlations from previous Cascade studies. Results showed consistent diurnal and yearly signals, but did not clearly follow any trends. The findings in this study add to the support of using Fourier analysis along with baselines for hydrogeochemical data to compare future volcanic, earthquake, and tectonic events.

The discovery of new mineral deposits is essential to meet the increasing demand for metals in our society. The Skellefte mining district in Northern Sweden is one of the main producers of polymetallic ores of Cu, Zn, Pb,Ag, Au, and Te in Europe. Discovery of new deposits in the Skellefte district has become increasingly challenging due to exhaustion of near surface deposits, and general difficulties when applying traditional exploration methods at depth. This has stimulated an interest in alternative methods, such as utilizing the trace element chemistry of sulphide minerals (e.g. pyrite) in metasedimentary and metavolcanic rocks to vector in on massive sulphide deposits. Meanwhile, there is a near complete paucity of trace element data from the massive sulphide deposits of the Skellefte district, and a global shortage of data from Palaeoproteroizoic, polydeformed and metamorphosed volcanogenic massive sulphide deposits (VMS). The Rävliden North Zn-Pb-Cu-Ag VMS deposit in the western most part of the Skellefte district, offers a great opportunity for combine in-situ trace element studies with paragenetic analysis to assess if vectors to mineralisation can be defined, and the effects of deformation and metamorphism. The deposit is hosted at the transition from the mainly felsic metavolcanic rocks of the Skellefte group to the mainly pelitic metasedimentary and mainly mafic – intermediate metavolcanic rocks of the Vargfors group. Rävliden North was significantly affected by deformation and greenschist – lower amphibolite facies metamorphism during the 1.88 – 1.86 Gadeformation phases of the Svecokarelian orogeny. Sphalerite-rich mineralisation associated with pyrrhotite, galena, pyrite and Ag-minerals is situated structurally and stratigraphically above stringer-type chalcopyrite-richmineralisation with lesser pyrrhotite, pyrite and minor amounts of Ag-minerals. Analysis of the textural and structural paragenesis of the mineralisations in the deposit show that sulphides range from aligned sub-parallel to three foliations (SC, S2, S2L), to hosted by tectonic structures such as tension gashes, piercement veins, veinlets, breccias and plastically deformed sulphide ore with rounded tectonoclasts (‘ball ore’). Sulphide occurrences associated with quartz veinlets and sulphide-cemented breccias cross-cutting poly-stage ductile structures could be the result of remobilisation under brittle conditions during the late stages of the Svecokarelian orogeny or afterwards. In-situ minor and trace element data from sphalerite, pyrite, sulphosalts, tellurides, antimonides and amalgams indicate trace element distribution patterns that can be related to primary ore formation followed by subsequent redistribution during the main phases of metamorphism and deformation. Sphalerite from the stringer-type chalcopyrite-rich mineralisation has a higher In, Co, Cu content, and a lower Mn content compared with sphalerite from the sphalerite-rich mineralisation. This trace element zonation resembles that of common VMS deposits, and is thus interpreted as retained from primary mineralisation. The Feand Cd content in sphalerite shows little variation in the sphalerite-rich mineralisation compared with the chalcopyrite-rich mineralisation, and do not exhibit any systematic variation relative to deformation textures. This can be explained by syn-metamorphic recrystallisation that could have equilibrated the composition of sphalerite. Sulphosalts, tellurides, antimonides, and amalgams are associated with galena and chalcopyrite in syn- to post-tectonic structures relative the main phase of deformation. The Ag-mineralogy seem to have formed during the retrograde phase of metamorphism as exsolutions from α-galena when temperatures decreased from 500 to 200C. However, LA-ICP-MS imaging of pyrite grains reveal co-precipitation of early syngenetic pyrite, base metalsulphides, and silver-rich minerals, and subsequent syn-metamorphic pyrite growth and remobilisation of the latter. This suggest that besides causing a significantly higher Ag content in paragenetically younger mineralisation types, syn-metamorphic remobilisation may have not extensively modified the mineralisations at Rävliden North. Sphalerite associated with low temperature Ag-sulphosalt-, zeolite- and calcite-bearing veinlets and breccias in the stratigraphic hanging wall contain the highest contents of Ga, Ge, Sb and Cu in the area. Comparison with sphalerite in similar style of mineralisation in the Lycksele-Storuman area, west of Kristineberg, suggest a contemporaneous origin. They possibly formed as a result of a mineralising event related to the opening of the Iapetus Ocean (0.7 – 0.5 Ga) or the waning stages of the Timanian orogeny (0.6 – 0.5 Ga). Although unrelated to the VMS deposit, the late-stage veins in the stratigraphic hanging wall of Rävliden North can still be of some aid during mineral exploration as they likely contain some components that were sourced locally via remobilisation (e.g. Ag and Sb).

In this project, two key study areas in the northwestern Fennoscandian Shield are under investigation. The “Western supracrustal belt” and “Central Kiruna area” are both located along lithotectonically comparable Rhyacian-Orosirian metasupracrustal belts and both areas are characterized by iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG)-style mineralizations and related hydrothermal alterations. The area is in general well studied but the structural evolution remains unresolved. In order to build a structural framework for the Kiruna area, the number of deformation events, kinematics, geometries, mineralogy and interrelationships of the dominant structures are under focus in this study. The paired structural-alteration configuration is targeted in order to constrain the relative timing of dominant structures and mineral alteration parageneses in order to use these systems as structural vectors of mineralized systems. Furthermore, the Orosirian stratigraphy is re-evaluated in order to constrain the pre-compressional geological history of the study areas. This is important as it controls the character of the structural development during subsequent compression forming the sub-surface architecture as we see today. The Orosirian stratigraphy suggests the development of a syn-extensional basin in Kiruna where iron oxide-apatite deposits were emplaced. This basin was subsequently inverted accompanied by shearing, folding, and faulting during D1 and D2, refolded during D3, and further fractured during D4. The shortening directions inferred during the deformation events suggest a clockwise rotation of the stress field from NE-SW (D1) to E-W (D2) and finally NNW-SSE (D3). Regional scapolite ± albite alteration is interpreted to be coeval with regional amphibole + magnetite alteration during D1. Mineral alteration parageneses linked to D2 is more potassic in character and often structurally controlled by shear zones. As a regional generalization, the potassic dominated D2-alteration is characterized by sericite ± epidote ± biotite ± chlorite ± magnetite ± sulphide ± K-feldspar. Fe- and Cu-sulphides are concentrated into brittle D2-structures suggesting that a IOCG-style of mineralization can be linked to the potassic D2 event. This implies that iron oxide-apatite emplacement can be linked to the basin development phase, whereas epigenetic Fe- and Cu-sulphides are linked to the basin inversion-phase of the geological evolution, and hence, separated in time and probably not directly genetically linked in Kiruna.

No description available.