Ändra sökning
Avgränsa sökresultatet
1234567 151 - 200 av 540
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 151.
    Gee, David G
    et al.
    Uppsala University.
    Brekke, Harald
    Norwegian Petroleum Directorate.
    Lahtinen, Raimo
    Geological Survey of Finland.
    Sigmundsson, Freysteinn
    Nordic Volcanological Institute.
    Sundquist, Björn
    Uppsala University.
    Thybo, Hans
    University of Copenhagen.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Nordic geoscience and the 33rd International Geological Congress: introduction2008Ingår i: Episodes, ISSN 0705-3797, Vol. 31, nr 1, s. 4-8Artikel i tidskrift (Refereegranskat)
  • 152.
    Gonzalez, Maria Sinche
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Geochemical Model and Simulation of Water Balance for Mining Operations: Svappavaara Iron Mine2016Konferensbidrag (Övrigt vetenskapligt)
  • 153.
    Gonzalez, Maria Sinche
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Lamberg, Pertti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Geochemical Water Balance by Modeling and Simulation in Mining: Water Conscious Mining (WASCIOUS) Project2016Konferensbidrag (Övrigt vetenskapligt)
  • 154.
    Gonzalez-Jimenez, José Maria
    et al.
    Departamento de Mineralogía y Petrología (Universidad de Granada), Facultad de Ciencias, Spain.
    Plissart, Gaelle
    Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile.
    Garrido, Leonardo N.
    Department of Geology and Andean Geothermal Center of Excellence (CEGA), Universidad de Chile, Santiago, Chile.
    Padron-Navarta, Jose Alberto
    Géosciences Montpellier, CNRS and Univ. Montpellier (UMR5243), Montpellier, France.
    Aiglsperger, Thomas
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universidad de Barcelona (UB), Barcelona, Spain.
    Romero, Rurik
    Department of Geology and Andean Geothermal Center of Excellence (CEGA), Universidad de Chile, Santiago, Chile.
    Marchesi, Claudio
    Departamento de Mineralogía y Petrología (Universidad de Granada), Facultad de Ciencias, Spain.
    Moreno-Abril, Antonio Jesus
    Departamento de Mineralogía y Petrología (Universidad de Granada), Facultad de Ciencias, Spain.
    Reich, Martin
    Department of Geology and Andean Geothermal Center of Excellence (CEGA), Universidad de Chile, Santiago, Chile.
    Barra, Fernando
    Department of Geology and Andean Geothermal Center of Excellence (CEGA), Universidad de Chile, Santiago, Chile.
    Morata, Diego
    Department of Geology and Andean Geothermal Center of Excellence (CEGA), Universidad de Chile, Santiago, Chile.
    Titanian clinohumite and chondrodite in antigorite serpentinites from Central Chile: evidence for deep and cold subduction2017Ingår i: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 29, nr 6, s. 959-970Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Humite minerals, including Ti-rich, hydroxyl-dominant chondrodite and clinohumite, occur in Paleozoic antigorite serpentinite in the La Cabaña area, in the Chilean Coastal Cordillera (~38° 30 ′ S–73° 15 ′ W). This may be the first report from South America. Humite minerals are intergrown with Mn-rich olivine hosting antigorite blades in textural equilibrium, indicating a metamorphic origin. A comparison with previous results from piston-cylinder experiments and petrological studies of other high-P serpentinites constrains the formation conditions of the humite + olivine + antigorite assemblage to ca. 2.0–2.5 GPa and <600°C. Thus, the assemblage is interpreted as having formed during cold subduction of a segment of oceanic lithosphere to a depth >60 km, suggesting that the Paleozoic serpentinites were entrained into the mantle at higher P T conditions than those experienced by the spatially associated olivine–lizardite metadunites and enclosing metasedimentary rocks (subducted to < 30 km). During exhumation along the subduction channel, high- P serpentinites together with metadunites underwent tectonic mingling with metasediments of the accretionary prism, preserving their signature of distinct metamorphic trajectories. This could be similar to the tectonic evolution of blueschists and high-P amphibolites found as isolated blocks in the metasediments of the Chilean Coastal Cordillera.

  • 155. Gonzalez-Roldan, M.J
    et al.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Pascual, E.
    Alteration and metamorphism of synvolcanic intrusions associated with volcanic-hosted massive sulphide deposits in the Skellefte district, Sweden2005Ingår i: Abstracts, GAC-MAC meeting and IGCP-502 workshop, 2005, s. 70-Konferensbidrag (Övrigt vetenskapligt)
  • 156. González-Jiménez, José Maria
    et al.
    Proenza, Joaquin
    Pastor-Oliete, Miriam
    Saunders, Edward
    Aiglsperger, Thomas
    Pujol-Solà, Núria
    Melgarejo, Joan Carles
    Gervilla, Fernando
    Garcia-Casco, Antonio
    Precious metals in magmatic Fe-Ni-Cu sulfides from the Potosí chromitite deposit, eastern Cuba2020Ingår i: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Moa-Baracoa ophiolite in eastern Cuba is one of the few known ophiolites that display sulfide mineralization attributable to a magmatic origin in association with podiform-chromite ores hosted in the mantle-crust transition. These sulfide ores chiefly consist of Fe-Ni-Cu sulfides, namely pyrrhotite, pentlandite, chalcopyrite and cubanite partly altered to valleriite. The sulfide mineralization is located along the contact between the podiform-like chromite ores and intruding pegmatitic gabroic dykes. The detailed mineralogical study of the sulfide mineralization coupled with the first ever laser ablation ICP-MS analysis reveals that this sulfide mineralization show contents of the precious metals (Os, Ir, Ru, Pt, Re, Au, Ag) and other (semi)-metals (Co, Ni, Cu, Se, Te, Bi, Pb, As Sb) comparable to those sulfides from the magmatic sulfide deposits associated with mafic complexes hosted in the continental crust. The results obtained from this study confirm that Fe-Ni-Cu sulfides at Potosí are magmatic in origin, and very likely derived from the solidification of droplets of sulfide melt segregated by immiscibility from the intruding mafic melts once they interacted with the pre-existing chromitite at the mantle-crust transition zone of the ophiolite. The immiscibility of sulfide melt was achieved as a result of a progressive increase of fS2, very likely triggered by a set of circumstances, including the progressive fractionation of the intruding mafic melt leading to increase of aSiO2 and accumulation of volatiles as well as the crystallization of oxides. Two main generations of pentlandite were observed. One generation is primary in origin and it was locally exsolved along with pyrrhotite from monosulfide solid solution (MSS) during low-temperature cooling. The second type of pentlandite resulted from the reaction of MSS with coexisting droplets of Cu-and Ni-rich sulfide melt. LA-ICP-MS analysis reveals that most precious metals (Ru, Os, Ir, Re, Au, Ag) were concentrated along with the base-metal sulfides (BMS), although their distribution among the different BMS (pyrrhotite, pentlandite, chalcopyrite and cubanite) does not strictly follow the expected distribution according to the known melt-solid and solid-solid partition coefficients. Unlike the other analyzed PGEs, Pt was not preferentially concentrated in BMS but as discrete micrometer-sized sperrylite grains. The crystallization of sperrylite took place before and contemporaneous to sulfide segregation, and Pt-As nanoparticles probably played an important role in the Pt uptake as nucleation seeds for the formation of micron-sized sperrylite grains. These observations highlight the open-system nature of the ore forming system as well as the important role of arsenic in concentrating PGE in high-temperature silicate and sulfide melts.

  • 157.
    Guiral Vega, Juan Sebastian
    et al.
    Facultad de Minas, Universidad Nacional de Colombia, Medellín, Colombia.
    Rincon, Jonathan
    Facultad de Minas, Universidad Nacional de Colombia, Medellín, Colombia.
    Ordoñez-Carmona, Oswaldo
    Facultad de Minas, Universidad Nacional de Colombia, Medellín, Colombia.
    Geology of the southern part of Sabanalarga Batholith. Implications for terrane theory in the west of Colombia2015Ingår i: Boletín Ciencias de la Tierra, ISSN 0120-3630, nr 38, s. 41-48Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Colombian Andes are the product of the interaction of terranes with different geological affinity, such as the Western Cordillera, which is made up of blocks of oceanic affinity, that have been accreted to the western boundary of pre-existing terranes with continental affinity. The study area is geologically dominated by the Sabanalarga Batholith, which has at least two facies, gabro-diorite and tonalitie-granodiorite, that intrude the Barroso Formation. Both units have been affected strongly by regional faults generating large areas of mylonites closely related with hydrothermal alterations and mineralization occurrences. Due the clear intrusive relationship between the Sabanalarga Batholith and Barroso Formation, and due the Cauca-Almaguer fault cuts both units without separating them, it is suggested that the Terranes Theory must be reconsidered in this part of the country, because the Cauca-Almaguer fault do not correspond to the boundary between Calima Terrane and the terranes Arquía and Quebradagrande.

  • 158.
    Gumsley, Ashley P.
    et al.
    Lund University.
    Chamberlain, Kevin R.
    University of Wyoming.
    Bleeker, Wouter
    Geological Survey of Canada.
    Söderlund, Ulf
    Lund University.
    de Kock, Michiel O.
    University of Johannesburg.
    Kampmann, Tobias Christoph
    Lund University.
    Larsson, Emilie R.
    Lund University.
    Bekker, Andrey
    University of Johannesburg.
    The timing of the Palaeoproterozoic Great Oxidation Event using Dykes, Sills and Volcanics of the Ongeluk Large Igneous Province, Kaapvaal Craton2016Ingår i: Acta Geologica Sinica, ISSN 1000-9515, E-ISSN 1755-6724, Vol. 90, nr S1, s. 67-68Artikel i tidskrift (Refereegranskat)
  • 159.
    Gumsley, Ashley Paul
    et al.
    Lunds universitet.
    Chamberlain, Kevin
    University of Wyoming.
    Bleeker, Wouter
    Geological Survey of Canada.
    Söderlund, Ulf
    Lund Universitet, Department of Geology, GeoBiosphere Science Centre, Lund University.
    Kock, Michiel Olivier de
    University of Johannesburg.
    Kampmann, Tobias Christoph
    Lund Universitet.
    Larsson, Emilie
    Lund Universitet.
    U-Pb TIMS and in-situ SIMS dating of baddeleyite and zircon from sub-volcanic sills of the Ongeluk Formation (Transvaal Supergroup) in the Griqualand West sub-basin, Kaapvaal Craton, with implications for Snowball Earth and the Great Oxygenation Event2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Great Oxygenation Event (GOE) in the Paleoproterozoic coincides with a complex series of glacial episodes preserved in supracrustal successions on the world’s cratons. These Paleoproterozoic glacial rocks are bracketed in age between 2.46 and 2.22 Ga, based on the glacial record in the Huronian Supergroup on the Superior Craton in Canada). In southern Africa, the cover successions of the western Kaapvaal Craton preserve possible glacial correlatives of the Huronian Supergroup in the Griqualand West sub-basin of the Transvaal Supergroup. This potential correlative is the glacial diamictites of the Makganyene Formation. The Makganyene Formation is in turn conformably overlain by the Ongeluk Formation, a series of subaqueous mafic volcanic rocks with a putative age of ca. 2.22 Ga. However, both local and global correlations using glacial units of the Transvaal and Huronian supergroups are hampered by a lack of robust well-placed geochronological data. The timing of the Ongeluk Formation itself has been challenged. Here, the sub-volcanic sills of the Ongeluk volcanic rocks have been dated using U-Pb in-situ SIMS analysis on baddeleyite to ca. 2.43 Ga. This has been coupled with ID TIMS dating and paleomagnetism studies on the coeval Westerberg Sill Suite. This suggests that the Ongeluk Formation volcanic rocks, and the immediately underlying Makganyene Formation glacial deposits, are approximately 200 Myr older than generally assumed. These new ages lend support to three glacial epochs around the GOE, of which the first was low-latitude in the Makganyene Formation. The Makganyene diamictites could correlate to diamictites from the Duitsland Formation in the more eastern Transvaal sub-basin of the Transvaal Supergroup, with a significant revision of regional stratigraphic correlations, that is in itself not without challenges. In such a scenario, the Ongeluk volcanic rocks could be correlated with the Bushy Bend volcanics, and not the ≤ 2.25 Ga Hekpoort Formation volcanics. This new magmatic event may be linked with the evolution of the Vaalbara continent, the Kenorland supercontinent, and global environmental changes related to magmatism and weathering in the Paleoproterozoic Era.

  • 160.
    Guntoro, Pratama Istiadi
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Tiu, Glacialle
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Ghorbani, Yousef
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Lund, Cecilia
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Rosenkranz, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Application of machine learning techniques in mineral phase segmentation for X-ray microcomputed tomography (µCT) data2019Ingår i: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 142, artikel-id 105882Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    X-ray microcomputed tomography (µCT) offers a non-destructive three-dimensional analysis of ores but its application in mineralogical analysis and mineral segmentation is relatively limited. In this study, the application of machine learning techniques for segmenting mineral phases in a µCT dataset is presented. Various techniques were implemented, including unsupervised classification as well as grayscale-based and feature-based supervised classification. A feature matching method was used to register the back-scattered electron (BSE) mineral map to its corresponding µCT slice, allowing automatic annotation of minerals in the µCT slice to create training data for the classifiers. Unsupervised classification produced satisfactory results in terms of segmenting between amphibole, plagioclase, and sulfide phases. However, the technique was not able to differentiate between sulfide phases in the case of chalcopyrite and pyrite. Using supervised classification, around 50–60% of the chalcopyrite and 97–99% of pyrite were correctly identified. Feature based classification was found to have a poorer sensitivity to chalcopyrite, but produced a better result in segmenting between the mineral grains, as it operates based on voxel regions instead of individual voxels. The mineralogical results from the 3D µCT data showed considerable difference compared to the BSE mineral map, indicating stereological error exhibited in the latter analysis. The main limitation of this approach lies in the dataset itself, in which there was a significant overlap in grayscale values between chalcopyrite and pyrite, therefore highly limiting the classifier accuracy.

  • 161.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Forsling, Willis
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Öhlander, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Norrländsk vattenkraft och gruvnäring: två svenska välståndsbyggare2009Ingår i: Thule: Kungl. Skytteanska samfundets årsbok 2009, Umeå: Kungl. Skytteanska samfundet , 2009, s. 331-345Kapitel i bok, del av antologi (Övrig (populärvetenskap, debatt, mm))
  • 162.
    Hamberg, Roger
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Bark, Glenn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Maurice, Christian
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Alakangas, Lena
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Release of arsenic from cyanidation tailings2016Ingår i: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 93, s. 57-64Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At a gold mine in northern Sweden, gold occurring as inclusions in pyrrhotite and arsenopyrite is leached by cyanidation of the ore. The main sulphide minerals in the ore are pyrrhotite and arsenopyrite. Effluents from the cyanidation process are treated with Fe2(SO4)3 to form Fe-precipitates suitable for the co-precipitation of As. The aim of this study was to perform static and kinetic leaching tests on the ore and tailings to define geochemical processes governing As mobility. Sequential leaching tests suggested that the majority of dissolved As deriving from the sulphide fraction in the ore was incorporated in newly formed Fe-precipitates in the tailings. The mobility of As in the tailings was therefore mainly dependent on the stability of these As-bearing Fe-precipitates. Weathering cell tests (WCT) involving 31 weekly cycles of wetting and air exposure were conducted to assess the stability of the As in the tailings under accelerated weathering conditions. The first stage of the WCT was characterized by a pH ≈ 5 and low As leaching, probably driven by the dissolution of amorphous Fe-As species. In the second stage of the WCT, leaching of Fe, S and As increased and the pH decreased to <3.5. An increase of the leachate’s molar Fe/S-ratio suggested that pyrrhotite oxidation was occurring. The falling pH destabilized As-bearing Fe-precipitates, causing further As release. The total As release during the WCT corresponded to only a small proportion of the tailings’ total As content. The accelerated As-leaching observed towards the end of the WCT could thus indicate that its release could increase progressively over time.

  • 163.
    Hansen, Jonathan
    et al.
    Fraunhofer Development Centre X-ray Technology EZRT, Fürth Germany.
    Voland-Salamon, Virginia
    Fraunhofer Development Centre X-ray Technology EZRT, Fürth Germany.
    Kampmann, Tobias Christoph
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Firsching, Markus
    Fraunhofer Development Centre X-ray Technology EZRT, Fürth Germany.
    Samodviga, Oleksiy
    Fraunhofer Development Centre X-ray Technology EZRT, Fürth Germany.
    Ennen, Alexander
    Fraunhofer Development Centre X-ray Technology EZRT, Fürth Germany.
    Uhlmann, Norman
    Fraunhofer Development Centre X-ray Technology EZRT, Fürth Germany.
    Sensor fusion and correlation of X-ray tomography and XRF data for drill core analysis2019Ingår i: International Symposium on Digital Industrial Radiology and Computed Tomography – DIR2019, 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    State of the art analysis techniques on drill cores for exploration purposes, including X-ray fluorescence (XRF), laser-induced breakdown spectroscopy (LIBS) or Raman spectroscopy are used to derive mineralogical information. Since this sensor data corresponds to materials that occur on the surface of the core, inclusions (e.g. diamonds) cannot be detected. In addition, information outside of the measurement position is not taken into account and may lead to misinterpretation or the miss of certain elements. X-ray computed tomography (CT) and radioscopy provide data about the entire sample as well as inlying structures based on X-ray absorption. As a drawback, CT is time-consuming and the material information is not explicit.For the enhancement of geological interpretation, we propose to apply sensor data fusion techniques in order to unite both depth information as well as reliable material data information from surface measurement techniques. This leads to more substantial information of the drill core.For further insights in the feasibility we investigate the correlation of XRF data at varying abstraction levels with CT data, i.e. grey value information.The applied XRF technique involves the fact that the data is not acquired continuously but discrete point by point. This is accompanied by the circumstance that the spatial resolution of the acquired data has a different magnitude than the CT-data. Both facts result in the challenge to register the XRF data coming from a one-dimensional scan line with a micro-CT volume. The experiments must be planned in a way that location and orientation of the scan data are well-known and reproducible.In the experiments, the acquired and registered data of a defined drill core is analysed with respect to correlation and fusion capability. The experimental setup will be presented and results will be discussed.

  • 164.
    Hedin Baastrup, Hugo
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Structural Reconnaissance Mapping of the Nasa Basement Window, Southern Norrbotten Caledonides2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Too few documentative descriptions exist from the reactivated Proterozoic Nasa Basement window in Sweden. This re-exposed crustal piece predominantly consisting of 1.8 Ga granite and volcanic basement rock lack structural evidences on maps. The Western Gneiss region gave example of how rocks in extreme cases may experience protolith overprinting through collisional vertical granite basement subduction to eclogite ambient conditions, which would give traces in metamorphic quartz (coesite), muscovite, pyroxene and kyanite, and increased densities. Preliminary indications from literature points towards a locally passive Nasa Basement with limited translation, but because of too little documentation it cannot be assured metamorphic inertia under fluid absence has been unimportant in the basement evolution. To address this highly structural issue, field reconnaissance mapping and sampling was carried out, and aimed to achieve a structural characterisation of historic deformation back to Proterozoic time. Observations were collected from 166 outcrop vicinities, and 17 of 27 carefully examined thin sections aimed to describe microscopic structures, in addition to mineral relation to metamorphic minerals. Collected evidences in this project encompass a Proterozoic macroscopic concentric fold with axis striking NW-SE, as well as, mesoscopic folds striking WNW-ESE. Tectonic movements record syn-collisional top-SE and post- collisional top-SW translation, which truncate weakly shortened and foliated blocks. Basement blocks locally preserve igneous coarse but weakly recrystallized texture fabrics. Overall optically produced paleothermometry indicates low- to medium grade facies conditions of deformation, through widespread bulging recrystallization, occasional subgrain rotation and rare grain boundary migration in quartz. Feldspar response to deformation is brittle and rarely ductile. Hydrous biotite, chlorite and epidote are abundant. Mineralogy together with an observed average density of 2,6 g/cm3 can possibly reject the idea of unreacted local continental subduction to eclogite depths, due to the overall presence of hydrous mineral phases. Top-to-the shear sense proves Caledonian reactivation, but Bourguer anomaly indicates at least locally an important limited translation. NW-SE striking lineaments and strikes of foliation show best accordance with lineaments mapped in Norway and alignment with tectonic contacts in the Baltica interior, and do so show the best examples of candidates for Proterozoic structures.

  • 165.
    Herrington, Richard
    et al.
    NHM.
    Piercey, Steve
    Laurentian University.
    Franklin, Jim
    Franklin Geoscience.
    Crawford, Tony
    CODES.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Tectonic settings of VMS deposits2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Modern and ancient volcanogenic or volcanic-hosted (VMS or VHMS deposits) have been usefully divided into five broad lithostratigraphic groups: 1) Bimodal-mafic; 2) Mafic; 3) Pelitic-mafic; 4) Bimodal-felsic and 5) Siliciclastic-felsic. This classification relates to the entire volcano-sedimentary cycle or assemblage within a district, using principles of sequence stratigraphy, not only the type of immediate host or footwall. Such a classification avoids using straight empirical metal ratios or more parochial nomenclature based on deposit-scale features but by necessity provides only broad models for the definition of sub-types.The tectonic settings of many VMS deposits are well defined, and classic examples are found forming at modern spreading ridges, which includes oceanic ridges, thickened oceanic crust and sedimented oceanic ridges and continental margin rifts. Modern arcs are also host to VMS deposits and due to problems of preserving spreading ridges in the geological record, it is the rifted arc settings that provide the best examples of the deposit type in the ancient record such as; nascent arcs - ophiolites; primitive volcanic arcs; complex oceanic arcs and mature volcanic arcs. The five lithostratigraphic groups can be linked to many of these tectonic settings directly although there are some important VMS camps where the broad criteria fit specific lithostratigraphic settings (e.g. Mt Read, Tasmania; Iberian Pyrite Belt) in Bimodal Felsic and Siliciclastic Felsic settings respectively) but that the literature suggests that a simple supra-subduction arc setting is not appropriate for either case. These types of tectonic settings are probably unknown in the modern crust and thus it follows that some of the potential settings for VMS deposits found in the geological record may not have a modern analogue.In this paper wesuggest that whilst strict definition of tectonic settings for each lithostratigraphic group of VMS deposits may not be possible, very specific lithogeochemical signatures of volcanic rocks relate to each of the settings. These rock types are all indicative of high-temperature melting and extension for each of the specific lithostratigraphic associations. Other work suggests that these specific magma types may be forming in a less proscriptive range of tectonic settings to that previously recorded and are simply indicative of a special set of rifting or arc to rifting conditions. This further suggests that VMS deposits may form in settings outside the normal spreading ridges and arcs and that we may able to extend the range of tectonic settings for the formation of VMS deposits accordingly. Following on from this, the recognition of some of these critical lithogeochemical magma types in tectonic settings previously considered less favourable for VMS deposits may lead to the discovery of new prospective belts.

  • 166.
    Hällström, Lina
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Alakangas, Lena
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Geochemical characterization of W, Cu and F skarn tailings at Yxsjöberg, Sweden2018Ingår i: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 194, s. 266-279Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Little attention has been paid to tailings from skarn ore deposits and their environmental impact, even though they can contain elevated concentrations of elements of potential concern together with sulfides and fluorite. Historical skarn tailings at Yxsjöberg, Sweden, containing e.g. Be, Bi, Cu, F, Sn, S, W, and Zn were geochemically characterized as a first step to evaluate the environmental impact and the potential to re-mine the tailings. The tailings were deposited between 1897 and 1963 in the Smaltjärnen Repository without dams or a complete cover, and have been in contact with the atmosphere for >30 years. Four vertical cores throughout the tailings were taken and divided into 134 subsamples, which were analyzed for total concentrations and paste pH. Selected samples from different depths were mineralogically characterized using optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), Raman vibrational spectroscopy, and X-ray diffraction (XRD). Minerals, hand-picked from drilled rock cores, were analyzed for the element content, and a modified Element to Mineral Conversion (EMC) that pinpoints the quantitative distribution of elements between the minerals in the tailings was carried out. The average concentrations of Be, Bi, Cu, Sn, Zn, W, F and S in the tailings were 284, 495, 946, 559, 301, and 960 ppm, and 1.9 and 1.2 wt%, respectively. The tailings has reached a late stage development due to pyrrhotite oxidation resulting in low pH (<4) in the uppermost tailings, and formations of secondary minerals such as gypsum, hydrous ferric oxides (HFO) and orthogonal calcite. Secondary pyrite and magnetite, formed from monoclinic pyrrhotite was detected, and different weathering rates of secondary pyrite, hexagonal and monoclinic pyrrhotite was indicated, with secondary pyrite as the most stable and monoclinic pyrrhotite as the least. The rare and easily-weathered mineral danalite (Fe4Be3(SiO4)3S) was found in the drilled rock cores and by XRD in the tailings. However, the mineral could not be found by optical microscopy or SEM-EDS. This suggests that the mineral has been weathered to a great extent, which poses a high risk of releasing elements of potential concern to the groundwater since danalite contains approximately 40% of the total Be and Zn concentrations in the tailings. Fluorine was mainly found in fluorite, Cu in chalcopyrite, and Bi in bismuthinite; which all showed signs of weathering in acidic condition in the uppermost part, subsequent with decreased concentrations, followed by accumulation peaks deeper down in the tailings correlated with Al. Tungsten was mainly found in scheelite; most grains were unweathered, but a few grains had altered rims or HFO on the mineral surfaces. Tin was mainly found in ferrohornblende, hedenbergite and grossular. Beryllium, Cu, F, and Zn has high potential to be released to the surrounding environment from the Smaltjärnen Repository, while W, Bi and Sn are relatively stable in the tailings. Most of the scheelite is intact and re-mining could, therefore, be a suitable remediation method that would both reduce the environmental impact and simultaneously support the supply of critical raw materials in the EU.

  • 167.
    Hällström, Lina
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Alakangas, Lena
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Scheelite weathering and tungsten (W) mobility in historical oxidic-sulfidic skarn tailings at Yxsjöberg, Sweden2020Ingår i: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    More knowledge of the geochemical behavior of tungsten (W) and associated contamination risks is needed. Therefore, weathering of scheelite (CaWO4) and secondary sequestration and transport of W to groundwater in historical skarn tailings and surface water downstream of the tailings were studied. The tailings contained 920 mg/kg W, primarily in scheelite. Mineralogical and geochemical analyses were combined to elucidate the geochemical behavior of W in the tailings, and water samples were taken monthly during 2018 to monitor its mobility. In the tailings, a large peak of W was found at 1.5 m depth. There, 30 wt%. of W was present in easily reducible phases, indicating former scheelite weathering. Currently, W is being released from scheelite to water-soluble phases at 2.5 m depth. The release of WO42− is hypothetically attributed to anion exchange with CO32− released from calcite neutralizing acid produced from pyrrhotite oxidation in the upper tailings and transported downwards to pH conditions > 7. Higher concentrations of dissolved W were found in the groundwater and particulate W in downstream surface water than in reference water, but they were lower than current contamination thresholds. Tungsten showed correlations with hydrous ferric oxides (HFO) in both the tailings and surface water.

  • 168.
    Imana, Marcello
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Epithermal and porphyry style mineralization of the central Andes2005Ingår i: Proceedings of the 2005 Field Workshop, 2005Konferensbidrag (Refereegranskat)
  • 169. Imana, Marcello
    et al.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Barrett, Tim J.
    Volcanic stratigraphy, chemical stratigraphy and alteration system of the Storliden massive sulphide deposit, Skellefte district, northern Sweden2005Ingår i: Mineral Deposit Research, Meeting the Global Challenge: Proceedings of the 8th Biennial SGA meeting / [ed] Jingwen Mao; Frank P. Bierlein, New York: Encyclopedia of Global Archaeology/Springer Verlag, 2005, s. 627-630Konferensbidrag (Refereegranskat)
  • 170. Imana, Marcello
    et al.
    Barrett, Tim J.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Volcanic sequence, chemostratigraphy and alteration at the Storliden Zn-Cu deposit, Skellefte District, northern Sweden2005Ingår i: GAC-MAC-CSPG-CSSS [joint Meeting], Halifax, 2005 : building bridges - across science, through time, around the world: abstracts, St. John's: Geological and Mineralogical Association of Canada, 2005, s. 92-Konferensbidrag (Övrigt vetenskapligt)
  • 171.
    Ivarsson, Filip
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Characterization of Fe-rich skarns and fluorapatite-bearing magnetite occurrences at the Zinkgruvan Zn-Pb-Ag and Cu deposit, Bergslagen, Sweden2019Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Zinkgruvan is a stratiform Zn-Pb-Ag and Cu sulphide deposit hosted by Paleoproterozoic strata in southern Bergslagen, Sweden. The deposit underwent medium-high grade regional metamorphism during the Svecokarelian orogeny, including partial melting of the host succession. Subordinate zones of semi-massive to massive magnetite and Fe-rich skarns occur in marble stratigraphically below the stratiform Zn-Pb-Ag ore but have so far not been described in detail in the scientific literature.

    This thesis presents results from detailed geological drill core logging, light optical microscopy (LOM) and scanning electron microscopy (SEM), which have been integrated with results from electron microprobe analysis (FE-EMPA) and whole-rock lithogeochemical analysis to provide a comprehensive description of the magnetite mineralization. Samples from the formerly mined magnetite deposits Västerby, Garpa and Åmme - distal to Zinkgruvan - have also been studied to allow for a comparison. The combined dataset has been used to 1) discuss the genesis of the magnetite mineralizations, including their relationship to base metal sulphide mineralization, and 2) evaluate potential vectors to Zn-Pb-Ag and Cu mineralization based on variations in the magnetite deposits.

    The semi-massive to massive magnetite, adjacent and associated Fe-rich skarn at Zinkgruvan are located in the stratigraphic upper part of the marble host. Three different varieties of magnetite mineralization can be defined: 1) semi-massive to massive magnetite mineralization in marble, 2) magnetite-bearing veins and 3) retrograde magnetite after olivine. Detailed optical microscopy has revealed a positive spatial correlation between aluminium spinel, apatite, magnetite and graphite. Semi-massive to massive magnetite mineralization at Zinkgruvan is enriched in P2O5, ΣREELa-Lu and Mn relative to a carbonate precursor. A positive correlation exists between P2O5 and ∑REELa-Lu, suggesting apatite and monazite are the primary REE-bearing minerals. The fact that the samples with highest P2O5 and ∑REELa-Lu are all Fe-rich rocks suggest the enrichment of the latter is related to the event which formed the Fe mineralization. Magnetite mineralization from the historic iron mines NW of Zinkgruvan share several key attributes with magnetite mineralization at Zinkgruvan. These include: 1) magnetite is the only iron oxide, 2) lithological and mineralogical similarities, including spatial association with marble, 3) equally high whole-rock Fe content, 4) equally high Mn (1-4 wt.% MnO), 5) equally high Eu anomalies (Eu/Eu* = 1.1- 2.8, avg. 1.75), and 6) local presence of sphalerite mineralization. Bending of the tectonic foliation from c. E-W to NW in the western part of Zinkgruvan suggest these magnetite mineralizations may be located along the same trend as those at Zinkgruvan.

    The normal calc-silicate mineralogy in Zinkgruvan marble (e.g. diopside, forsterite, phlogopite) can be explained by prograde regional metamorphic reactions between silicates and dolomite or calcite in impure carbonate rocks with a variable content of detrital siliciclastic and volcaniclastic material. However, the stratabound magnetite mineralization and associated Fe-rich skarns cannot be fully accounted for by this model. It is plausible that the Fe-rich skarns can be explained by similar reactions but involving more Fe-rich carbonates (ferrodolomite, ankerite, siderite). In the absence of quartz, siderite is known to thermally decompose into magnetite and graphite at temperatures above 465° C, whereby siderite-rich rocks may have been precursor to the semi-massive to massive magnetite mineralization. A recent genetic model suggests that the ore-forming fluids which formed Zinkgruvan where similar to those which formed McArthur-type SEDEX deposits. The presented results are consistent with this model, since e.g. siderite is a common alteration mineral in alteration envelopes to such deposits. Hence, magnetite mineralization, Zn-Pb-Ag and Cu-ore may all be related to the same pre-metamorphic hydrothermal system.

    The current genetic model places the magnetite mineralization at Zinkgruvan proximal to a fossil hydrothermal vent zone (the Burkland discontinuity). It is plausible that the magnetite mineralization mined at surface lay along the northern continuation of the Burkland discontinuity. Based on the assumption that the Burkland Cu-mineralization is most proximal and the old iron mines at Åmme are most distal along this structure, variations in whole-rock lithogeochemistry, mineral chemistry and mineralogy have been used to define nine vectors to economic Zn-Pb-Ag and Cu ore as is mined at Zinkgruvan.

     

  • 172.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Bland stromatoliter och urtidsvulkaner vid Sala silvergruva2017Ingår i: Geologiskt Forum, ISSN 1104-4721, Vol. 93, s. 4-9Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 173.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    EXplORE: Master programme in Exploration2018Konferensbidrag (Övrigt vetenskapligt)
  • 174.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Genetic models for the Bergslagen sulfide deposits: The importance of continuously improving ore genetic models for exploration in mature mining districts2018Konferensbidrag (Övrigt vetenskapligt)
  • 175.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Salbergets skatter2006Ingår i: Geologiskt forum, ISSN 1104-4721, Vol. 13, nr 50, s. 7-Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 176.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Structural, stratigraphic and ore genetic significance of stromatolites in the Sala stratabound Zn-Pb-Ag deposit, Bergslagen, Sweden2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Sala is Sweden's most famous silver mine, with production from 1500 AD of about 450 tonnes of silver from 5 MT of ore and waste. The ores comprise vein, skarn and breccia-fill sphalerite-galena within dolomite and show similarities to other stratabound volcanic- and limestone-hosted Zn-Pb-Ag ores in Bergslagen, such as Garpenberg. The Sala dolomite contains several stromatolite occurrences, one being the type-locality for Swedish stromatolites. In this presentation, the first detailed account of stromatolites within the Sala Mine is given along with a discussion on the structural geological, stratigraphic and ore genetic significance of the stromatolites. The stromatolites display a wide range of morphologies, occurring as microbial mats, domal shapes, digitate forms as well as columns. They are best preserved in the southern part of the mine and are less conspicuous in the northern part. Stromatolitic way-up indicators reinforce earlier interpretations that the ore is hosted by a major syncline whose axis is parallel to the plunge of the mineralization. Furthermore, the stromatolites provide evidence that the planar intensely Chl-Phl-Srp-Di-Tr-Cal-Qz altered layers which transect the dolomite are concordant to bedding. These altered rocks drape stromatolitic structures, suggesting they are altered siliceous sedimentary rocks. Stromatolites also allow recognition of discordant, altered layers that are mineralogically similar to the siliceous sedimentary rocks but lack diopside and tremolite. These layers are interpreted as shear zones. The most significant is the Storgruvan Shear Zone, which parallels the strike of the deposit. Previously, these two contrasting geological features were lumped together under the loosely defined Swedish mining term 'sköl'. Way-up determinations from the stromatolites suggest that sphalerite ore mainly occurs stratigraphically below galena ore. The relationships between the shapes of workings, stromatolitic layers and altered siliceous interbeds suggest a stratigraphic control on the hydrothermal plumbing system during ore formation. Sphalerite vein-networks that occur adjacent to well-preserved stromatolitic textures suggest that ore formation was not completely texturally destructive. Skarn and sphalerite locally mimic stromatolitic laminae and form infillings in stromatolitic vugs. Although some ore is tectonically remobilized, ore displaying similar deformation patterns to the host-rock has also been observed. Thus, early to pre-orogenic ore formation is indicated. The ore may initially have formed epigenetically by sub-sea floor infiltration of metalliferous fluids into a buried stromatolite reef with volcaniclastic interbeds. Ore minerals precipitated as massive sulphide lenses and semi-massive vein-networks with long dimensions parallel to bedding. Because of later tectonic modification, ore is now concentrated in the axial plane of the Sala Syncline and in the vicinity of the Storgruvan Shear Zone.

  • 177.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The origin of iron ores in Bergslagen, Sweden, and their relationships with polymetallic sulphide ores2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The Bergslagen mining district of southern Sweden is one of Europe’s classic mining districts with more than 1 000 years of mining history. One of the typical features of Bergslagen is a spatial association between Zn-Pb-Ag-(Cu-Au) sulphide deposits and magnetite-rich Fe oxide deposits. The relationship between these two deposit types has been discussed intensely for more than a century, yet there are still many uncertainties to be resolved. In this thesis, the origin of Fe oxide deposits in Bergslagen and their relationship with polymetallic sulphide deposits is investigated. Detailed investigations have been undertaken at a number of Fe oxide and polymetallic sulphide deposits in the Garpenberg and Stollberg areas, where sulphides and Fe oxides are spatially associated. The deposits studied at Garpenberg include the Ryllshyttan stratabound Zn-Pb-Ag-(Cu) + magnetite deposit, the Smältarmossen calcic Fe skarn deposit, the Lappberget stratabound Zn-Pb-Ag-(Cu-Au) deposit and stratiform Fe-rich exhalites near the Ryllshyttan deposit. At Stollberg, the investigation has mainly focused on studying the regional geological framework of the ore deposits. The research project was based on detailed geological mapping and drill core logging. The ores, their host rocks and the associated hydrothermal alteration envelopes have been further studied by a combination of optic microscopy, electron microprobe mineral chemical analysis, radiometric dating and whole rock lithogeochemical analysis. The results reveal that several different types of Fe oxide deposits may be defined in the Garpenberg and Stollberg areas 1) synsedimentary-exhalative Fe oxide deposits, 2) carbonate replacement-type deposits that are locally spatially associated with polymetallic sulphide deposits, and 3) contact metasomatic Fe skarn deposits proximal to syn-volcanic intrusions. For most of the studied ore deposits, several different stages of ore formation or modification of pre-existing ores are recognized, based on textural evidence and cross-cutting relationships between hydrothermal alteration, stratigraphy, intrusive events and structures. Zoning in ore metals, mineralogy and alteration geochemistry occurs both on deposit-scale and on a regional scale in all studied areas. The zonation patterns have been studied in detail in an attempt to elucidate whether geochemical, mineralogical and mineral chemical vectors may be identi¿ed, which would aid mineral exploration where Fe oxide and polymetallic sulphide deposits co-exist. Radiometric dating indicates that the studied deposits at Garpenberg, despite being markedly different from each other in style and setting, formed during a short time span at 1892 ±4 Ma. The possibility that all studied deposit-types formed at slightly different times and/or at different depths within a large igneous system is explored. Based on stratigraphic evolution, the distribution and character of hydrothermally altered zones as well as the characteristics of the ore deposits themselves, it is inferred that the sequence of ore types 1-3 above reflects generally increasing depths of ore formation and/or proximity to causative intrusions. Documented overprinting relationships and the co-existence of all deposits at similar stratigraphic levels indicate that multiple stages of ore formation during active volcaniclastic sedimentation, burial and intrusion of magmas to shallow crustal levels in an evolving extensional basin must be considered. Continuous burial during volcaniclastic sedimentation in an extensional tectonic setting (e.g. a backarc basin on continental crust) combined with the frequent intrusion of magma to shallow crustal levels, resulted in the stratigraphic succession hosting stratiform Fe oxide mineralization (type 1) being subjected to seawater-dominated hydrothermal convection cells. This led to formation of type 2replacement-style Fe oxide and polymetallic sulphide mineralizations. During continued burial, these deposits were subsequently affected by local or widespread intrusion-associated metasomatism that formed contact metasomatic Fe skarn deposits. The ores were later subjected to polyphase ductile deformation under low P amphibolite facies metamorphic conditions during the Svecokarelian orogeny. The polymetallic sulphide ores especially, were substantially modi¿ed and remobilized in the hinge zones of folds, into ore shoots parallel with axial surfaces and locally into the ENE-trending, sheared short limbs of folds. Sulphide remobilization partly coincided with retrograde alteration of anhydrous, Fe-rich skarns to more hydrous, magnetite-rich skarns, thus locally leading to the formation of high-grade magnetite mineralization proximal to massive sulphide deposits.

  • 178.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The origin of the Ryllshyttan stratabound Zn-Pb-Ag-(Cu) + magnetite deposit, Garpenberg, Bergslagen, Sweden2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 179.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The relationship between polymetallic sulfide deposits and Fe oxide deposits in the Garpenberg area2018Konferensbidrag (Övrigt vetenskapligt)
  • 180.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    VectOre - Exploration criteria for polymetallic sulphide deposits and industrial carbonates2018Konferensbidrag (Övrigt vetenskapligt)
    Abstract [sv]

    Videopresentation: https://www.youtube.com/watch?v=dw1o-J8BzuM

  • 181.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Volcanic stratigraphy of the Ryllshyttan Zn-Pb-Ag-(Cu) + magnetite deposit, Bergslagen, Sweden2009Ingår i: Smart science for exploration and mining: proceedings of the 10th Biennial SGA Meeting, Townsville, Australia, 17th-20th August 2009 / [ed] Patrick Williams, Townsville, Qld: James Cook University of North Queensland , 2009, s. 448-450Konferensbidrag (Refereegranskat)
    Abstract [en]

    The previously mined Ryllshyttan Zn-Pb-Ag-(Cu) + magnetite deposit comprised approximately 1 Mt sphalerite-dominated massive sulphide ore and about 200 000 tons of massive to semi-massive skarn-limestone hosted magnetite ore. Ryllshyttan belongs to the Bergslagen ore district of south central Sweden, a Palaeoproterozoic igneous province renowned for its abundance and diversity of Fe-oxide and sulphide mineralisations. Ryllshyttan's ore-bodies are hosted by a carbonate horizon partially altered to skarns of tremolite, diopside-salite and andradite. The ore horizon itself is enclosed by volcanics and intrusions belonging to the earliest Svecokarelian igneous rocks (~ 1.9 Ga BP). The stratigraphy follows a first order volcanic cycle with an evolution from juvenile rhyolitic mass flow deposition to deposition of rhyolitic ash-siltstones intercalated with ferruginous-calcareous chemical and/or hydrothermal sediments. Observations suggest that iron oxides started to accumulate syngenetically at the time of host-rock formation. In contrast, sulphides are associated with discordant Mg +/- K +/- Si alteration that also overprints some intrusions. Consequently, sulphide mineralization and the earliest iron oxide mineralization are attributed to separate events.

  • 182.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Multistage ore formation at the Ryllshyttan marble and skarn-hosted Zn-Pb-Ag-(Cu) + magnetite deposit, Bergslagen, Sweden2015Ingår i: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 69, s. 217-242Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Numerous magnetite skarn deposits and marble- and skarn-hosted base metal sulphide deposits occur in polydeformed and metamorphosed, felsic-dominated metavolcanic inliers in the Palaeoproterozoic Bergslagen region of south-central Sweden, including the Ryllshyttan magnetite and Zn-Pb-Ag-(Cu) sulphide deposit, approximately 2.5 km SW of the large Garpenberg Zn-Pb-Ag-(Cu-Au) deposit. The Ryllshyttan deposit, from which approximately 1 Mt of Zn-rich massive sulphide ore and 0.2 Mt of semi-massive magnetite were extracted, is located near a transition between magnesian skarn and dolomitic marble. The host unit consists of a 10-20 m-thick former calcitic limestone of likely stromatolitic origin that is commonly pervasively altered to skarn, locally hosting magnetite skarn deposits. The ore-bearing unit is one of several mineralised marble units within a more than 1 km-thick, felsic-dominated metavolcanic succession that includes a metamorphosed, large caldera-fill pyroclastic deposit, 800 m stratigraphically above the Ryllshyttan host succession. The Garpenberg stratabound Zn-Pb-Ag-(Cu)-(Au) deposit is located higher in the stratigraphy, just below the caldera fill deposits. The metavolcanic succession is bounded to the NW by a large granitoid batholith and intruded by a microgranodiorite pluton less than a 100 m from the Ryllshyttan deposit. Magnetite laminae in bedded skarns and metavolcanic rocks in the hanging wall of Ryllshyttan indicate an early (syngenetic) accumulation of Fe-rich exhalites. In contrast, the sulphide mineralisation consists of stratabound replacement-style ore associated with dolomitisation of the host and with discordant K-Mg-Fe±Si alteration of volcanic rocks and early porphyritic intrusions in the footwall and hanging wall. The microgranodiorite that intrudes the host succession crosscuts the K-Mg-Fe±Si alteration envelope and is overprinted by Na-Ca alteration (diopside and plagioclase-bearing mineral associations) that also overprints K-Mg-Fe±Si-altered rocks. The Na-Ca alteration is interpreted to be associated with the formation of calcic and magnesian iron skarn deposits semi-regionally at a similar stratigraphic position. Despite superimposed amphibolite facies regional metamorphism and substantial syn-D2-D3 remobilisation of sulphides concurrent with retrograde alteration of skarn assemblages, cross-cutting field relationships indicate that the Ryllshyttan magnetite and Zn-Pb-Ag-(Cu) sulphide deposit results from protracted VMS-style hydrothermal activity including early seafloor mineralisation (Fe-rich exhalites), closely followed by sub-seafloor carbonate-replacement-style mineralisation (base metal-bearing massive sulphides). Both mineralisation styles were overprinted by contact metasomatism associated with the formation of abundant magnetite skarn deposits during the emplacement of granitoid intrusions. As for other deposits in the Bergslagen region, the ore-forming system at Ryllshyttan thus has similarities to both metamorphosed VMS deposits and metasomatic Fe and Zn skarn deposits. Our results suggest that the sequence of volcanic, intrusive and hydrothermal events in this region is compatible with prograde heating of a long-lived hydrothermal system, wherein a shift from a convective seawater-dominated system to a contact metamorphic and/or metasomatic environment occurred during the early stage of the 1.9-1.8 Ga Svecokarelian orogeny. This model partly resolves the controversy regarding genesis of the iron oxide and base metal sulphide deposits in Bergslagen, as we recognise that these deposits have a complex history of alteration, metamorphism, deformation and (re)mobilisation, and no unique established genetic model can account for all their features.

  • 183.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    SIMS U-Pb zircon age constraints on the ages of syn-volcanic iron oxide and Zn-Pb-Cu-(Ag-Au) sulphide deposits, Garpenberg, Bergslagen, Sweden2011Konferensbidrag (Refereegranskat)
  • 184.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The Geology of the Ryllshyttan Zn-Pb-Ag-(Cu) + magnetite deposit in the Bergslagen Ore District, Southern Sweden2010Konferensbidrag (Övrigt vetenskapligt)
  • 185.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The origin of iron ores in Bergslagen and their relationships with polymetallic sulphide ores2010Ingår i: FoU-seminarium vid SGU 19–20 april 2010: dokumentation, Uppsala, 2010, s. 6-10Konferensbidrag (Övrigt vetenskapligt)
  • 186.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The origin of skarn beds, Ryllshyttan Zn–Pb–Ag + magnetite deposit, Bergslagen, Sweden2011Ingår i: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 103, nr 1-4, s. 49-78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thin- to medium-bedded, stratiform calc-silicate deposits (banded skarns) are a peculiar, but important, component of the supracrustal successions in the Palaeoproterozoic Bergslagen mining district of central Sweden. They are referred to as “skarn-banded leptites” in the literature and are common in areas and at stratigraphic levels that contain iron oxide and base metal sulphide deposits. The stratigraphic hanging wall of the stratabound Ryllshyttan Zn–Pb–Ag + magnetite deposit at Garpenberg, contains approximately 100–150 m of interbedded aluminous skarn beds and rhyolitic ash-siltstones. The skarn beds are mineralogically variable and dominantly composed of grandite, spessartine, epidote, actinolite, quartz, clinopyroxene, and locally magnetite. Integrated field-mapping, and whole-rock lithogeochemical, microscopic and mineral chemical analyses suggest that the stratiform skarn beds are the products of at least two discrete hydrothermal events and subsequent metamorphism. The first event comprised accumulation in a quiescent subaqueous environment, below wave base, of calcareous and ferruginous sediments rich in Fe, Mn, Ca, and Mg. These chemical sediments were deposited concurrently with rhyolitic ash-silt sedimentation, thus forming a (now metamorphosed) laminated calcareous Fe formation with both a detrital rhyolitic component and rhyolitic siltstone interbeds. Positive Eu-anomalies and negative Ce-anomalies for normalized rare earth element analyses of skarn beds suggest that the iron may have been derived from exhalation of hot and reduced hydrothermal fluids, which upon mixing with more oxidized seawater, precipitated Fe oxides and/or carbonates that settled from suspension to the seafloor. The size of the positive Eu-anomalies of the chemical sediments are modified by the content of rhyolitic volcaniclastic material, which has a negative Eu anomaly, such that positive Eu-anomalies are only observed in skarn beds that possess a minor volcaniclastic component. Subsequently, the calcareous Fe formations were subjected to post-depositional alteration by hydrothermal fluids, locally yielding more manganoan and magnesian assemblages. The Mn-alteration is manifested by lateral gradations from epidote-grandite-clinopyroxene±magnetite rocks into significantly more Mn-rich quartz-spessartine rocks and massive andradite rocks over distances of less than 10 cm within individual skarn beds. Magnesian alteration is manifested by the development of discordant zones of pargasite para-amphibolites and formation of stratiform pargasite rocks texturally similar to the interlaminated grandite-epidote-ferroan diopside rocks. The latter increase in abundance towards the Ryllshyttan deposit and are associated with pre-metamorphic/pre-tectonic K–Mg–Fe±Si alteration (now biotite-phlogopite-garnet-cordierite-pargasite rocks) that is related to base metal mineralization. The zone of Mn- and Mg-altered skarn beds extends beyond the zone of pervasive K–Mg–Fe±Si alteration around Ryllshyttan. This suggests that the skarn bed progenitors, or their sedimentary contacts against rhyolitic ash-siltstones, acted as conduits to outflowing hydrothermal fluids. The chemical and mineralogical imprint, imposed on affected beds by alteration, may serve as indicators of proximity to intense K–Mg–Fe±Si alteration envelopes around other base metal sulphide deposits in Bergslagen. The last recorded event comprised syn-tectonic veining of competent massive andradite skarn beds. The veins contain quartz-albite-epidote-ferroan diopside-actinolite assemblages.

  • 187.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Timing and setting of skarn and iron oxide formation at the Smältarmossen calcic iron skarn deposit, Bergslagen, Sweden2013Ingår i: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 48, nr 3, s. 313-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Abundant iron oxide deposits including banded iron formations, apatite iron oxide ores, and enigmatic marble/skarn-hosted magnetite deposits occur in the Palaeoproterozoic Bergslagen region, southern Sweden. During the last 100 years, the latter deposit class has been interpreted as contact metasomatic skarn deposits, metamorphosed iron formations, or metamorphosed carbonate replacement deposits. Their origin is still incompletely understood. At the Smältarmossen mine, magnetite was mined from a ca. 50-m-thick calcic skarn zone at the contact between rhyolite and stratigraphically overlying limestone. A syn-volcanic dacite porphyry which intruded the footwall has numerous apophyses that extend into the mineralized zone. Whole-rock lithogeochemical and mineral chemical analyses combined with textural analysis suggests that the skarns formed by veining and replacement of the dacite porphyry and rhyolite. These rocks were added substantial Ca and Fe, minor Mg, Mn, and LREE, as well as trace Co, Sn, U, As, and Sr. In contrast, massive magnetite formed by pervasive replacement of limestone. Tectonic fabrics in magnetite and skarn are consistent with ore formation before or early during Svecokarelian ductile deformation. Whereas a syngenetic-exhalative model has previously been suggested, our results are more compatible with magnetite formation at ca. 1.89 Ga in a contact metasomatic skarn setting associated with the dacite porphyry.

  • 188.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Timing of volcanism, hydrothermal alteration and ore formation at Garpenberg, Bergslagen, Sweden2011Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 133, nr 1-2, s. 3-18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The timing of Palaeoproterozoic magmatism in the Garpenberg area in the Bergslagen region of the Fennoscandian shield has been constrained by secondary ion mass spectrometry (SIMS) U-Pb zircon dating of metamorphosed igneous rocks. Volcanism is constrained by igneous crystallisation ages of 1895 ± 4Ma for a syn-volcanic rhyolite porphyry intrusion and 1893 ± 3Ma for a rhyolitic pumice breccia. Granite and microgranodiorite, which intruded into the stratigraphy, are dated at 1895 ± 3 and 1894 ± 4 Ma, respectively. The identical U-Pb ages suggest rapid geological evolution from the emplacement of volcanics, their burial and subsidence to 2-5 km depths and intrusion by granitoids. The timing of metamorphism and the extent of metamorphic resetting of titanite have been evaluated. SIMS titanite 207Pb-206Pb ages from the same samples as the zircon yield younger ages. Although errors are large in individual analyses and fractions, a weighted average of 59 analyses from four samples yields a 207Pb-206Pb age of 1858 ± 14 Ma, interpreted as the age of regional metamorphism. The results add constraints to the timing of sulphide and iron oxide mineralisation at Garpenberg. The rhyolite porphyry is intruded into a syngenetic iron formation. Its crystallisation age provides a minimum age for syngenetic iron oxide deposits at Garpenberg. The major Zn-Pb sulphide deposits are accompanied by alteration envelopes. Units formed before alteration yield similar igneous crystallisation ages as intrusions post-dating alteration. It is concluded that both iron oxide and sulphide mineralisation formed within the same age-span as the dated units

  • 189.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney L.
    Volcanic Resources AB.
    Skogsmo, Göran
    Björka mineral AB.
    Vorbrodt, Nils
    Björka mineral AB.
    Bäckström, Mattias
    Björka mineral AB.
    An updated genetic model for metamorphosed and deformed, c. 1.89 Ga magnesian Zn-Pb-Ag skarn deposits, Sala area, Bergslagen, Sweden2019Ingår i: Proceedings of the 15th SGA Biennial Meeting, 27-30 August 2019, Glasgow, Scotland, Life with Ore Deposits on Earth, 2019, Vol. 1, s. 166-169Konferensbidrag (Refereegranskat)
    Abstract [en]

    This contribution presents an updated view on the genesis of stratabound Zn-Pb-Ag mineralization in the Sala area, Bergslagen, Sweden. Integrated legacy and new geological, geochemical and geophysical data reveal that the deposits are hosted by a complex array of magnesian skarn-altered zones in dolomitic marble. These mineralized zones parallel early faults and metavolcanic interbeds in the host marble, and converge downwards in the stratigraphy adjacent to a 1.89 Ga calc-alkaline granite-granodiorite batholith. Prograde alteration involved formation of early barren ferroan diopside- and forsterite-bearing skarns. Mineralization is mainly associated with subsequent alteration to tremolite, chlorite, serpentine, magnetite and calcite. The hydrous associations overlap mineralogically with assemblages formed during subsequent greenschist facies regional metamorphism between 1.87 Ga and 1.8 Ga. However, ferroan diopside and forsterite are unique to the alteration system, and indicate mineralization in conjunction with an early, high T, metasomatic alteration event at 1.89 Ga. The Sala deposits can be classified as Zn skarn deposits, albeit atypical in the magnesian nature of the skarns and the lack of minerals with essential Mn. The Fe and Mn content in magnesian silicates and carbonates is however sufficient to induce clear enrichment haloes of these elements around the deposits. The magnesian nature of the skarns probably reflect formation in a shallow marine continental backarc tectonic setting, and an importance of seawater in early pre-skarn alteration stages, such as dolomitization.

  • 190.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Volcanic Resources AB.
    Skogsmo, Göran
    Björka Mineral AB.
    Vorbrodt, Nils
    Björka Mineral AB.
    Bäckström, Mattias
    Björka Mineral AB.
    Geological controls on light dolomite deposits related to polymetallic sulphide deposits, Sala area, Bergslagen, Sweden: insights from whole-rock lithogeochemistry, spectrophotometry and magnetic susceptibility2019Ingår i: Geophysical Research Abstracts, 2019, Vol. 21, s. 1-, artikel-id 9056Konferensbidrag (Övrigt vetenskapligt)
  • 191.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Sädbom, Stefan
    Lovisagruvan AB.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Bergslagen & Broken Hill2017Ingår i: Geologiskt Forum, ISSN 1104-4721, nr 94, s. 24-28Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 192. Jansson, Nils
    et al.
    Chmielowski, Riia
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Hermansson, Tobias
    Boliden Mines.
    Persson, Mac Fjellerad
    Boliden Mines.
    Berglund, Alexandra
    Boliden Mines.
    Kruuna, Annika
    Boliden Mines.
    Skyttä, Pietari
    Bachmann, Kai
    TU Bergakademie Freiberg.
    Gutzmer, Jens
    TU Bergakademie Freiberg.
    Recent advances in structural geology, lithogeochemistry and exploration for VHMS deposits, Kristineberg area, Skellefte2013Ingår i: Mineral deposit research for a high-tech world: Proceedings of the 12th Biennial SGA Meeting, 12–15 August 2013, Uppsala, Sweden, 2013, s. 545-548Konferensbidrag (Refereegranskat)
  • 193.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Erismann, Fabian
    Boliden Mineral AB, Exploration Department, 776 98 Garpenberg.
    Lundstam, Erik
    Boliden Mineral AB, Exploration Department, 776 98 Garpenberg.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Evolution of the paleoproterozoic volcanic-limestone-hydrothermal sediment succession and Zn-Pb-Ag and iron oxide deposits at Stollberg, Bergslagen region, Sweden2013Ingår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 108, nr 2, s. 309-335Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Stollberg Zn-Pb-Ag and magnetite mining field is located in the Bergslagen region of the Fenno -scandian Shield. The main Stollberg ore deposits comprise a chain of orebodies that occur discontinuously for5 km along a prominent marble and skarn horizon. Orebodies mainly contain magnetite and combinations ofsphalerite, galena, pyrrhotite, and lesser pyrite and chalcopyrite within marble and skarn. Previously, the twomain limestone (marble) units in the Stollberg area were regarded as structural repetitions of one single horizon.Based on sedimentary and volcanic facies and structural analysis, the mineralized Stollberg limestone isnow shown to be the uppermost of two different limestone units within a ca. 3-km-thick Paleoproterozoic (∼1.9Ga) volcanosedimentary succession. Approximately 2 km of preserved footwall stratigraphy is recognized belowthe Stollberg limestone, as opposed to ca. 500 m in previous structural models. This new interpretation hasallowed the stratigraphic evolution prior to the mineralizing event and extent of the Stollberg hydrothermal systemto be investigated in detail.After formation of the Staren limestone ca. 1 km below Stollberg, the depositional basin subsided to belowwave base, while adjacent areas were uplifted and eroded. This led to the deposition of a ca. 600-m-thick, shallowing-upward sedimentary sequence in which normal-graded subaqueous mass flow deposits pass upward topolymict limestone-volcanic breccia-conglomerates. This sequence is attributed to progradation of a fan deltadepositional system. The breccia-conglomerates are overlain by ca. 500 m of juvenile rhyolitic pumice brecciathat is interpreted as a major pyroclastic deposit. Conformably above is the Stollberg ore host, which comprisesplanar-stratified, rhyolitic ash-siltstone interbedded with Fe-Mn-rich hydrothermal sedimentary rocks andlimestone, all deposited below wave base. This ore host package is extensively altered to skarn and mica schist.The thickness, extent, and homogeneous composition of the rhyolitic pumice breccia below the ore host suggestthat volcanism was accompanied by caldera subsidence and that the Stollberg ore deposits formed withinthe caldera structure. The ore host is overlain by planar-stratified, rhyolitic ash-siltstone and subordinate sedimentarybreccias deposited below wave base from turbidity currents and suspension.Skarns in the Stollberg ore host unit are interpreted as metamorphosed mixtures of variably altered rhyolite,limestone, and hydrothermal sediments. Whole-rock contents of Al, Ti, Zr, Hf, Nb, Sc, Th, Ta, U, and heavyrare-earth elements are highly correlated in skarns, limestone, magnetite mineralization, and variably alteredrhyolites in the Stollberg succession, suggesting that these elements were supplied by a felsic volcaniclasticcomponent and were immobile during alteration. The felsic volcaniclastic component is calc-alkaline and characterizedby negative Eu anomalies and light rare-earth element enrichment. Strong positive Eu anomalies areonly observed in limestone, skarn, and iron ore in the Stollberg ore host, i.e., in samples rich in Mn, Ca, andFe.The Stollberg ore deposits are interpreted as metamorphosed, hydrothermal-exhalative and carbonate replacement-type mineralization. The hydrothermal-exhalative component formed first by accumulation of sedimentsrich in Mn and Fe, coeval with limestone formation during waning volcanism. Burial of the hydrothermal systemby sediments of the stratigraphic hanging wall led to a gradual shift to more reducing conditions. At thisstage, the Stollberg limestone interacted with more sulfur rich hydrothermal fluids below the sea floor, producingstrata-bound, replacement-type Zn-Pb-Ag sulfide and additional iron oxide mineralization

  • 194.
    Jansson, Nils F.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Structural evolution of the Palaeoproterozoic Sala Stratabound Zn-Pb-Ag carbonate-replacement deposit, Bergslagen, Sweden2017Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 139, nr 1, s. 21-35Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A structural investigation of the Sala Zn–Pb–Ag deposit in the Bergslagen mining district of southern Sweden shows that it is associated with two tectonic structures: the N–NW-trending Storgruveskölen shear zone (SSZ), which is parallel to the strike of the mined ore bodies, and the F1 Sala syncline with a fold hinge plunging c. 35° towards NNW, which is parallel to the plunge of the entire mineralised system. The Sala syncline was refolded by F2 folds, leading to flattening and local reversals in the plunge of F1 folds and the ore bodies. Field evidence suggests that the SSZ represents both a phase of D3 reverse dip-slip shearing and a later (D4) phase of dextral strike-slip reactivation. However, a high concentration of pre- to syn-D1skarn- and sulphide-bearing vein networks and breccias adjacent to the SSZ, which are gradational into the mined massive sulphide ore bodies, suggest that stages in the formation of the SSZ predated D3 and D4. It may consequently constitute a reactivated pre- to syn-D1 structure. The distribution of breccia and hydrothermal alteration together with the highly discordant nature of the deposit are consistent with a pre- to syn-D1 timing of ore formation, involving of cross-stratal fluid flow along the proto-SSZ and subordinate fluid flow parallel to volcanic interbeds in the host carbonate rock. Three δ34S determinations on sphalerite (2.1–2.4‰) and galena (1.2‰), respectively, are consistent with a magmatic source for ore sulphur, as has been suggested for many other sulphide deposits in Bergslagen.

  • 195.
    Jansson, Nils F.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Kampmann, Tobias C.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Contrasting fluid types involved in the genesis of ca. 1.89 Ga, syngenetic polymetallic sulfide deposits, Falun and Zinkgruvan, Bergslagen, Sweden2017Ingår i: Mineral Resources to Discover / [ed] Mercier Langevin, P; Dube, B; Bardoux, M; Ross, PS; Dion, C, Society for Geology Applied to Mineral Deposits , 2017, s. 613-616Konferensbidrag (Refereegranskat)
    Abstract [en]

    Metamorphosed polymetallic sulfide deposits in Bergslagen, Sweden, are currently divided into 1: Strata bound volcanic-associated limestone-skarn Zn-Pb-Ag-CuAu sulfide deposits (SVALS) and 2: Stratiform ash-siltstonehosted Zn-Pb-Ag sulfide deposits (SAS). It has not been completely resolved if these deposit types formed from similar hydrothermal fluids. Recent investigations at the Falun SVALS deposit and the Zinkgruvan SAS deposit suggest that fluids of contrasting pH, fO(2), salinity and T were involved in their origin. Whereas Falun formed by cooling and neutralization of acidic (pH<4), hot (300-400 C) and reducing fluids carrying metals and sulfur together, Zinkgruvan formed by reduction of oxidized brines at a near-neutral pH. Falun is a vent-proximal, synvolcanic carbonate-replacement deposit with similarities to VMS and skarn deposits, whereas Zinkgruvan is a post-volcanic, exhalative deposit with similarities to some SEDEX deposits. Our results suggest that the different character of SVALS and SAS deposits in part are functions of fundamental differences in fluid chemistry, controls on sulfide precipitation and relationship to volcanism.

  • 196.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Kampmann, Tobias Christoph
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Contrasting fluid types involved in the genesis of ca. 1.89 Ga, syngenetic polymetallic sulfide deposits, Falun and Zinkgruvan, Bergslagen, Sweden2017Ingår i: Mineral Resources to Discover: Proceedings of the 14th SGA Biennial Meeting, Québec City, Canada, Society for Geology Applied to Mineral Deposits , 2017, Vol. 2, s. 613-616Konferensbidrag (Refereegranskat)
    Abstract [en]

    Metamorphosed polymetallic sulfide deposits in Bergslagen, Sweden, are currently divided into 1: Stratabound volcanic-associated limestone-skarn Zn-Pb-Ag-Cu-Au sulfide deposits (SVALS) and 2: Stratiform ash-siltstone hostedZn-Pb-Ag sulfide deposits (SAS). It has not been completely resolved if these deposit types formed from similar hydrothermal fluids. Recent investigations at the Falun SVALS deposit and the Zinkgruvan SAS deposit suggest that fluids of contrasting pH, ƒO2, salinity and Twere involved in their origin. Whereas Falun formed by cooling and neutralization of acidic (pH<4), hot (300-400ºC) and reducing fluids carrying metals and sulfur together, Zinkgruvan formed by reduction of oxidized brines at a near-neutral pH. Falun is a vent-proximal, synvolcanic carbonate-replacement deposit with similarities to VMS and skarn deposits, whereas Zinkgruvan is a post-volcanic, exhalative deposit with similarities to some SEDEX deposits. Our results suggest that the different character of SVALS and SAS deposits in part are functions of fundamental differences in fluid chemistry, controls on sulfide precipitation and relationship to volcanism.

  • 197.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Malmström, Lars
    Zinkgruvan Mining.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    A comment on the occurrence of gallium and germanium in the Zinkgruvan Zn-Pb-Ag-(Cu) deposit, Bergslagen, Sweden2016Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, nr 4, s. 533-535Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Zinkgruvan deposit has been included in compilations of exceptionally Ga- and Ge-endowed deposits in Sweden. Available published data sets do however not support a substantial enrichment in Ga and Ge. In this contribution, we investigate the Ga- and Ge-endowment based on a whole-rock lithogeochemical data and ore grade analyses from the deposit. Based on our results, we find it highly unlikely that a Ga-endowment exists in the ore. A Ge-endowment may exist, but we find no evidence of Ge grades at the 1,000 ppm level that have been reported previously.

  • 198.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Sädbom, Stefan
    Lovisagruvan AB.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Billström, Kjell
    Swedish Museum of Natural History.
    Spry, Paul G
    Iowa State University.
    The Lovisa stratiform Zn-Pb deposit, Bergslagen, Sweden: Structure, stratigraphy, and ore genesis2018Ingår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 113, nr 3, s. 699-739Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Medium- to high-grade metamorphosed, 1.9 Ga, stratiform, syngenetic Zn-Pb±Ag sulfide deposits comprise an economically important type of ore deposit in the Bergslagen lithotectonic unit of the Fennoscandian shield. The Lovisa Zn-Pb deposit occurs in a metamorphosed succession of rhyolitic ash-siltstone, rhyolitic mass flow deposits, limestone and iron formation, deposited at a stage of waning volcanism in Bergslagen.

    Accessory graphite, absence of Ce anomalies in shale-normalized rare-earth element (REE) data, and absence of hematite in Mn-rich iron formations stratigraphically below the Lovisa Zn-Pb deposit indicate a suboxic-anoxic depositional environment. The uppermost Mn-rich iron formation contains disseminated, inferred syngenetic Pb-Ag mineralization with mainly negative δ34S values in sphalerite and galena (-6.1 to -1.9‰).

    Deposition of this iron formation terminated during a pulse of explosive felsic volcanism. The Lovisa Zn-Pb deposit is interpreted to have formed in an alkali-rich brine pool developed immediately after this volcanic event, based on lithogeochemical and stratigraphic evidence. The first stage of mineralization deposited stratiform sphalerite mineralization with mainly positive δ34S values (-0.9 to +4.7‰). This was succeeded by deposition of more sphalerite-galena stratiform mineralization with δ34S values close to 0‰ (-2.1 to +1.5‰). The more galena-rich mineralization partitioned strain and was partly remobilized during later ductile deformation.

    The stratigraphic context, sulfide mineralogy, sulfur isotopes and alteration geochemistry suggest that the metalliferous fluids and the depositional environment were H2S-deficient (S-poor or SO42--dominant). The source of sulfur is interpreted to have been a mixture of H2S derived from bacterial and thermochemical seawater sulfate reduction, and sulfur derived from leaching of volcanic rocks, with the latter becoming more important over time.

    Lovisa formed in a setting where basin subsidence was periodically punctuated by the deposition of thick, syn-eruptive felsic volcaniclastic massflow deposits. Coeval volcanism was likely important for driving hydrothermal activity and supplying a reservoir of metals and sulfur. However, the high rate of deposition of volcaniclastic sediment in Bergslagen also precluded the establishment of long-lived, deep and anoxic environments favorable for accumulation of organic matter and H2S. This stratigraphic pattern is common in Bergslagen and may explain why large stratiform Zn-Pb deposits are uncommon in the region and restricted to the uppermost part of the metavolcanic succession, directly stratigraphically beneath post-volcanic pelitic rocks.

  • 199.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Wanhainen, Christina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Thomas, Helen
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Persson, Mac
    Boliden Mineral.
    Sand, Anders
    Boliden Mineral.
    Textural and chemical characterization of sulphide minerals for improved beneficiation and exploration, Skellefte district, Sweden2019Ingår i: SGU rapport 2019:10 FoU-seminarium / [ed] Nelly Aroka, Lars-Ove Lång, Uppsala, 2019, s. 48-Konferensbidrag (Övrigt vetenskapligt)
  • 200.
    Jansson, Nils
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Allen, Rodney
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Billström, Kjell
    Swedish Museum of Natural History.
    Malmström, Lars
    Zinkgruvan Mining AB.
    Genesis of the Zinkgruvan stratiform Zn-Pb-Ag deposit and associated dolomite-hosted Cu ore, Bergslagen, Sweden2016Ingår i: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 82, s. 285-308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Zinkgruvan, a major stratiform Zn-Pb-Ag deposit in the Paleoproterozoic Bergslagen region, south-central Sweden, was overprinted by polyphase ductile deformation and high-grade metamorphism (including partial melting of the host succession) during the 1.9-1.8 Ga Svecokarelian orogeny. This complex history of post-ore modification has made classification of the deposit difficult. General consensus exists on a syngenetic-exhalative origin, yet the deposit has been variably classified as a volcanogenic massive sulfide (VMS) deposit, a sediment-hosted Zn (SEDEX) deposit, and a Broken Hill-type (BHT) deposit. Since 2010, stratabound, cobaltiferous and nickeliferous Cu ore, comprising schlieren and impregnations of Cu, Co and Ni sulfide minerals in dolomitic marble, is mined from the stratigraphic footwall to the stratiform Zn-Pb-Ag ore. This ore type has not been fully integrated into any of the existing genetic models. Based on a combination of 1) widespread hematite-staining and oxidizing conditions (Fe2O3>FeO) in the stratigraphic footwall, 2) presence of graphite and reducing conditions (Fe2O3<FeO) in the ore horizon and hangingwall and 3) intense K-feldspar alteration and lack of feldspar-destructive alteration in the stratigraphic footwall, we suggest that both the stratiform Zn-Pb-Ag and the dolomite-hosted Cu ore can be attributed to the ascent and discharge of an oxidized, saline brine at near neutral pH. Interaction of this brine with organic matter below the seafloor, especially within limestone, formed stratabound, disseminated Cu ore, and exhalation of the brine into a reduced environment on the sea floor produced a brine pool from which the regionally extensive (> 5 km) Zn-Pb-Ag ore was precipitated.

    Both ore types are characterized by significant spread in δ34S, with the sulphur in the Cu ore and associate marble-hosted Zn mineralization on average being somewhat heavier (δ34S = -4.7 to +10.5 ‰, average 3.9 ‰) than that in the stratiform Zn-Pb-Ag ore (δ34S = -6 to +17 ‰, average 2.0 ‰). The ranges in δ34S are significantly larger than those observed in syn-volcanic massive sulphide deposits in Bergslagen, for which simple magmatic/volcanic sulphur sources have been invoked. Mixing of magmatic-volcanic sulfur leached from underlying volcanic rocks and sulfur sourced from abiotic or bacterial sulfate reduction in a mixing zone at the seafloor could explain the range observed at Zinkgruvan.

    A distinct discontinuity in the stratigraphy, at which key stratigraphic units stop abruptly, is interpreted as a syn-sedimentary fault. Metal zonation in the stratiform ore (decreasing Zn/Pb from distal to proximal) and the spatial distribution of Cu mineralization in underlying dolomitic marble suggest that this fault was a major feeder to the mineralization. Our interpretation of ore-forming fluid composition and a dominant redox trap rather than a pH and/or temperature trap differs from most VMS models, with Selwyn-type SEDEX models, and most BHT models. Zinkgruvan has similarities to both McArthur-type SEDEX deposits and sediment-hosted Cu deposits in terms of the inferred ore fluid chemistry, yet the basinal setting has more similarities to BHT and felsic-bimodal VMS districts. We speculate that besides an oxidized footwall stratigraphy, regionally extensive banded iron formations and limestone horizons in the Bergslagen stratigraphy may have aided in buffering ore-forming brines to oxidized, near-neutral conditions. In terms of fluid chemistry, Zinkgruvan could comprise one of the oldest known manifestations of Zn and Cu ore-forming systems involving oxidized near-neutral brines following oxygenation of the Earth’s atmosphere.

1234567 151 - 200 av 540
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf