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  • 1.
    Chmielowski, Riia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils
    Boliden Mines.
    Alteration patterns of the Kristineberg area as revealed by 3D geochemical modelling2014Conference paper (Refereed)
    Abstract [en]

    The Palaeoproterozoic Skellefte mining district in northern Sweden is one of the most important mining regions in Europe and, as a result of decades of exploration in this area, there is an extensive collection of geochemical analyses from drill holes in this area. This research compiles data from over 3,000 samples from the Kristineberg area of this district to create an overview of the alteration patterns in 3D, and, for the first time ever, this data is being compared with the regional structural 3D model, which has also been developed for this area, to determine to what extent the current structure dominates the alteration pattern. Structurally-constrained 3D interpolations of calculated alteration indexes of drill core and outcrop samples from the hydrothermally altered zones in this area reveals an excellent correlation (from surface to c. 1,000 m depth) between the zones of most intense alteration and the localization of massive sulphide deposits. The results furthermore suggest that most of the alteration zones at surface are continuous with alteration zones at depth (possibly even deeper than 1,000 m). Comparison of the geometries and spatial distribution of these 3D interpolation volumes with 3D-modelled regional faults and lithological contacts in the Kristineberg area suggest that the regional distribution of alteration zones is controlled to a significant extent by the regional structure of the area, in particular by major S-dipping faults. Consequently, the structurally- constrained 3D geochemical model presents a new and exciting tool for the identification of prospective 3D volumes in the Kristineberg area for deep exploration. In addition, the 3D approach will allow quantifications of the total budget of mass gain and loss during hydrothermal alteration in the Kristineberg area, which will allow fundamental questions regarding the nature of the hydrothermal systems and the source of elements to be answered.

  • 2.
    Chmielowski, Riia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils
    Boliden Mines, Exploration Department.
    Persson, Mac Fjellerad
    Boliden Mines.
    Fagerström, Pia
    Boliden Mines.
    3D modelling of hydrothermal alteration associated with VHMS deposits in the Kristineberg area, Skellefte district, northern Sweden2016In: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 51, p. 113-130Article in journal (Refereed)
    Abstract [en]

    This contribution presents a 3D assessment of metamorphosed and deformed, hydrothermally altered volcanic rocks, hosting the massive sulphide deposits of the Kristineberg area in the 1.9 Ga Skellefte mining district in northern Sweden, using six calculated alteration parameters: the Ishikawa alteration index, the chlorite–carbonate–pyrite index and calculated net mass changes in MgO, SiO2, Na2O and Ba. The results, which are also available as film clips in the Supplementary data, confirm inferences from geological mapping; namely that the sericite- and chlorite-rich alteration zones have complex and cross-cutting geometries and that most of these zones are semi-regional in extent and range continuously from surface to over a kilometre deep. The major known massive sulphide deposits occur proximal to zones characterised by coincidence of high values for the alteration index and chlorite–carbonate–pyrite index and large MgO gains, which corresponds to zones rich in magnesian silicates. These zones are interpreted as the original chlorite-rich, proximal parts the alteration systems, and form anomalies extending up to 400 m away from the sulphide lenses. In addition, the stratigraphically highest VHMS are hosted by rocks rich in tremolite, talc, chlorite and dolomite with lesser clinozoisite, which have high chlorite–carbonate–pyrite index and low–medium alteration index values, reflecting a greater importance of some chlorite-carbonate alteration at this stratigraphic level. Vectoring towards massive sulphide deposits in this area can be improved by combining the AI and CCPI indexes with calculated mass changes for key mobile elements. Of the ones modelled in this study, MgO and SiO2 appear to be the most useful.

  • 3.
    Chmielowski, Riia
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils
    Persson, Mac Fjellerad
    Boliden Mines.
    Fagerström, Pia
    Boliden Mines.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    3D geochemical modelling of hydrothermal alteration related to 1.89 Ga VHMS-type deposits, Kristineberg area, Skellefte District2013In: Mineral deposit research for a high-tech world: Proceedings of the 12th Biennial SGA Meeting, 12-15 August 2013, Uppsala, Sweden, Uppsala: Sveriges Geologiska Undersökning , 2013, p. 66-69Conference paper (Refereed)
    Abstract [en]

    A 3D geochemical model of the Kristineberg area of the Skellefte District, Sweden, is currently under construction, utilizing data from more than 1600 regionally distributed whole-rock lithogeochemical samples. The model will improve our understanding of the formation the VHMS deposits in this area. The model is built by mapping geochemical variations in 3D, and using this as a basis for modelling hydrothermal alteration in the unsampled portions of the rock column. A better understanding of the geometry, intensity, vectors of transport, and zonation of the hydrothermal zones in 3D will aid deep exploration for massive sulphide deposits in the Kristineberg area, and may potentially lead to new discoveries.

  • 4.
    Frank, Katherine S
    et al.
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Spry, Paul
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Raat, Hein
    Boliden Mines.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    O'Brien, Joshua J
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Whole Rock-Rare Earth Element and Magnetite Chemistry as Guides to Exploration for Metamorphosed Base Metal Sulfide Deposits in the Stollberg Ore Field, Bergslagen, Sweden2014Conference paper (Other academic)
    Abstract [en]

    The Stollberg ore field (~12 Mt), 50 km W of the giant Garpenberg Zn-Pb-Ag-(Cu-Au) district (>100 Mt) occurs in the regional Stollberg F2 syncline within 1.9 Ga bimodal felsic and mafic rocks metamorphosed to the amphibolite facies. Sulfide mineralization is hosted by volcanic rocks and skarn and consists of massive to semi-massive sphalerite-galena and pyrrhotite (with subordinate pyrite, chalcopyrite, arsenopyrite, and magnetite). The trace element composition of magnetite, which locally forms ore-grade masses and occurs as a common accessory in most rocks types at Stollberg, has previously proven to be a pathfinder in the exploration for ore deposits elsewhere and is evaluated here along with the rare earth element (REE) chemistry of altered rocks. At Stollberg, the dominant country rocks are metamorphosed rhyolitic pumice breccia and rhyolitic ash-silt-sandstone with minor amphibolite sills. On the eastern side of the Stollberg syncline, mineralization at Stollberg and Dammberget occurs as stratabound replacement of limestone/skarn that grades into iron formation spatially related to garnet-biotite and gedrite-albite alteration. At Gränsgruvan on the western side of the syncline, sulfides occur in a silicified zone along with garnet-biotite and quartz-garnet-pyroxene alteration. Although the Tvistbo and Norrgruvan deposits along the north end of the syncline are small, they show geological characteristics that are transitional to deposits found on the western and eastern side of the syncline in that the ore is hosted by skarn rock and associated with quartz-garnet-pyroxene alteration. The Gränsgruvan deposit more closely resembles deposits found at Garpenberg than those located on the eastern limb of the Stollberg syncline. Whole-rock analyses of altered and unaltered host rocks suggest that most components were derived from a felsic volcaniclastic component and that elements were immobile during alteration. These rocks (including altered rocks in the stratigraphic footwall) are light REE enriched, heavy REE depleted, and show negative Eu anomalies, whereas mineralized rocks (Fe- and base metal-rich) and altered rocks in the ore zone show the same REE pattern but with positive Eu anomalies. Trace element compositions (using LA-ICP-MS techniques) of magnetite in high-grade ore, limestone/skarn, massive magnetite, and garnet-biotite, gedrite-albite, garnet-pyroxene alteration show a range of compositions. Such ranges in composition are inconsistent with previous studies in other ore fields that suggest the composition of magnetite can be used to define compositional fields characteristic of ore deposit type (e.g., Al+Mn vs. Ti+V wt. %) or approximate temperature of the ore-forming fluid. Magnetite in garnet-biotite and gedrite-albite alteration spatially associated with Dammberget typically contains > 200 ppm Ga, > 10 ppm Sn, and Ti/V ratios of >10 whereas magnetite in garnet-biotite alteration associated the smaller Cederkreutz deposit contains < 25 ppm Ga, < 2 ppm Sn, and Ti/V ratios < 0.1. Magnetite in garnet-biotite alteration associated with the Gränsgruvan deposit contains > 10 ppm Sn, 20 to 180 ppm Ga, and Ti/V ratios of 0.1 to 2. These and other trace element compositions of magnetite as well as REE patterns of altered host rocks show potential as exploration guides to ore in the Stollberg district.

  • 5.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bland stromatoliter och urtidsvulkaner vid Sala silvergruva2017In: Geologiskt Forum, ISSN 1104-4721, Vol. 93, p. 4-9Article in journal (Other (popular science, discussion, etc.))
  • 6.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Salbergets skatter2006In: Geologiskt forum, ISSN 1104-4721, Vol. 13, no 50, p. 7-Article in journal (Other (popular science, discussion, etc.))
  • 7.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Structural, stratigraphic and ore genetic significance of stromatolites in the Sala stratabound Zn-Pb-Ag deposit, Bergslagen, Sweden2008Conference paper (Other academic)
    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.

  • 8.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The origin of iron ores in Bergslagen, Sweden, and their relationships with polymetallic sulphide ores2011Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 9.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The origin of the Ryllshyttan stratabound Zn-Pb-Ag-(Cu) + magnetite deposit, Garpenberg, Bergslagen, Sweden2009Licentiate thesis, comprehensive summary (Other academic)
    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.

  • 10.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Volcanic stratigraphy of the Ryllshyttan Zn-Pb-Ag-(Cu) + magnetite deposit, Bergslagen, Sweden2009In: 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, p. 448-450Conference paper (Refereed)
    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.

  • 11.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Multistage ore formation at the Ryllshyttan marble and skarn-hosted Zn-Pb-Ag-(Cu) + magnetite deposit, Bergslagen, Sweden2015In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 69, p. 217-242Article in journal (Refereed)
    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.

  • 12.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    SIMS U-Pb zircon age constraints on the ages of syn-volcanic iron oxide and Zn-Pb-Cu-(Ag-Au) sulphide deposits, Garpenberg, Bergslagen, Sweden2011Conference paper (Refereed)
  • 13.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The Geology of the Ryllshyttan Zn-Pb-Ag-(Cu) + magnetite deposit in the Bergslagen Ore District, Southern Sweden2010Conference paper (Other academic)
  • 14.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The origin of iron ores in Bergslagen and their relationships with polymetallic sulphide ores2010In: FoU-seminarium vid SGU 19–20 april 2010: dokumentation, Uppsala, 2010, p. 6-10Conference paper (Other academic)
  • 15.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The origin of skarn beds, Ryllshyttan Zn–Pb–Ag + magnetite deposit, Bergslagen, Sweden2011In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 103, no 1-4, p. 49-78Article in journal (Refereed)
    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.

  • 16.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Timing and setting of skarn and iron oxide formation at the Smältarmossen calcic iron skarn deposit, Bergslagen, Sweden2013In: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 48, no 3, p. 313-339Article in journal (Refereed)
    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.

  • 17.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Timing of volcanism, hydrothermal alteration and ore formation at Garpenberg, Bergslagen, Sweden2011In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 133, no 1-2, p. 3-18Article in journal (Refereed)
    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

  • 18.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sädbom, Stefan
    Lovisagruvan AB.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Bergslagen & Broken Hill2017In: Geologiskt Forum, ISSN 1104-4721, no 94, p. 24-28Article in journal (Other (popular science, discussion, etc.))
  • 19. Jansson, Nils
    et al.
    Chmielowski, Riia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    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, Skellefte2013In: Mineral deposit research for a high-tech world: Proceedings of the 12th Biennial SGA Meeting, 12–15 August 2013, Uppsala, Sweden, 2013, p. 545-548Conference paper (Refereed)
  • 20.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Erismann, Fabian
    Boliden Mineral AB, Exploration Department, 776 98 Garpenberg.
    Lundstam, Erik
    Boliden Mineral AB, Exploration Department, 776 98 Garpenberg.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Evolution of the paleoproterozoic volcanic-limestone-hydrothermal sediment succession and Zn-Pb-Ag and iron oxide deposits at Stollberg, Bergslagen region, Sweden2013In: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 108, no 2, p. 309-335Article in journal (Refereed)
    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

  • 21.
    Jansson, Nils F.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Structural evolution of the Palaeoproterozoic Sala Stratabound Zn-Pb-Ag carbonate-replacement deposit, Bergslagen, Sweden2017In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 139, no 1, p. 21-35Article in journal (Refereed)
    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.

  • 22.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kampmann, Tobias Christoph
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Contrasting fluid types involved in the genesis of ca. 1.89 Ga, syngenetic polymetallic sulfide deposits, Falun and Zinkgruvan, Bergslagen, Sweden2017In: Mineral Resources to Discover: Proceedings of the 14th SGA Biennial Meeting, Québec City, Canada, Society for Geology Applied to Mineral Deposits , 2017, Vol. 2, p. 613-616Conference paper (Refereed)
    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.

  • 23.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Malmström, Lars
    Zinkgruvan Mining.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A comment on the occurrence of gallium and germanium in the Zinkgruvan Zn-Pb-Ag-(Cu) deposit, Bergslagen, Sweden2016In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 4, p. 533-535Article in journal (Refereed)
    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.

  • 24.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sädbom, Stefan
    Lovisagruvan AB.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    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 genesis2018In: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 113, no 3, p. 699-739Article in journal (Refereed)
    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.

  • 25.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    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, Sweden2016In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 82, p. 285-308Article in journal (Refereed)
    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.

  • 26.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Boliden Mineral AB, Exploration Department.
    Malmström, Lars
    Zinkgruvan Mining AB.
    Geochemical vectors for stratiform Zn-Pb-Ag sulfide and associated dolomite-hosted Cu mineralization at Zinkgruvan, Bergslagen, Sweden2018In: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 190, p. 207-228Article in journal (Refereed)
    Abstract [en]

    The Zinkgruvan deposit is the largest stratiform Zn-Pb-Ag mineralization in Sweden. The most recent genetic model attributes ore formation to the discharge of oxidized, near-neutral pH, metalliferous brines into a reduced basin, forming laterally extensive, stratiform sulfide mineralization on the seafloor. It has a known strike extent of 5 km and is underlain by a regionally extensive zone of K-altered metavolcanic rock and dolomitic marble, the latter hosting Cu-(Co-Ni) replacement mineralization near the inferred hydrothermal vent to the stratiform sulfides. The deposit is stratigraphically overlain by migmatized,  pyrrhotite- and graphite-rich pelite that is in turn overlain by a banded almandine-biotite-quartz-ferrosilite-bearing unit at the base of an regionally extensive metasedimentary succession. These laterally continuous units are interpreted as metamorphosed organic-rich sulphidic mudstone and silicate-dominated Fe formation, respectively.

    The favorable stratigraphic interval contains anomalously high Zn, Pb, Ag, Cu, K2O/(K2O+Na2O), Mn, Co, Tl, Ba and B relative to adjacent metatuffite. However, only Zn, Pb, Ag, K2O/(K2O+Na2O) and Mn are significantly enriched relative to adjacent strata beyond the known lateral extent of the ore. Elevated copper, Co and Tl only occur in the vent-proximal part of the deposit, whereas anomalous enrichments of Ba and B are sporadic and occur mainly in the stratigraphic footwall. Many elements such as Si, Fe, Mg, Ca and Cs are of limited use in vectoring due to low enrichment factors relative to inferred background compositions and/or strong lithological controls on their distribution.

    Although ore metal (Zn, Pb and Ag) enrichments are the best quantitative and qualitative guides to ore, K, Mn and Co enrichments also provide corroborative support. The most useful elements for vectoring have been synthesized into exploration indices. The Modified Sedex Metal Index (MSMI; Zn+3Pb+100Ag) is a vector towards stratiform Zn-Pb-Ag mineralization, whereas MSMI2 [Zn+3Pb+10(Cu+Co)] alsoallows targeting of proximal Cu mineralization.

    The banded iron formation and the pyrrhotite- and graphite-rich pelite of the stratigraphic hangingwall are consistently enriched in base metals (e.g. 500-1000 ppm Zn), total S and Mn throughout the entire Zinkgruvan area. However, these units are not known to grade laterally along strata into economic base metal sulfide mineralization, and they are not obviously products of the same hydrothermal system which formed the stratiform Zn-Pb-Ag deposit.

    In a vent-distal setting, the somewhat spurious metal anomalies of the hangingwall units can be difficult to distinguish from those of the favorable interval. The favorable stratigraphic interval can, however, be recognized by also taking into account that positive Zn anomalies are mainly coincident with positive anomalies in both K and Mn only in the favorable interval. Furthermore, samples from the favorable interval generally have Co/Ni > 1 and displays a positive Co/Ni vs. Zn trend, whereas samples of the pyrrhotite- and graphite-rich pelite have Co/Ni < 1 and define a negative Co/Ni vs. Zn trend. Thus, the index (Co/Ni)*Zn allows easy detection of weak Zn anomalies associated with the stratiform Zn-Pb-Ag mineralization.

  • 27.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB, Bromma.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Malmström, Lars
    Zinkgruvan Mining.
    Oxidized Brines Inferred in the Formation of c. 1.9 Ga Stratiform Zn-Pb-Ag and Dolomite-Hosted Cu Ores, Zinkgruvan, Bergslagen, Sweden2015In: Mineral Resources in a Sustainable World / [ed] A.S. Andre-Mayer; M. Cathelineau; P. Muchez; E. Pirard; S. Sindern, 2015, p. 1925-1928Conference paper (Refereed)
    Abstract [en]

    Zinkgruvan is an elusive Palaeoproterozoic stratiform Zn-Pb-Ag deposit which has been discussed in the context of sediment-hosted Zn-Pb (SEDEX), volcanic-hosted massive sulphide (VHMS) and Broken Hill-type (BHT) deposits. In this contribution, we address the chemistry of the ore-forming fluid, the nature of the depositional environment and the controls on ore formation based on a review of previous work complemented with new geological data from a stratigraphically underlying dolomite-hosted, zinciferous, cobaltiferous and nickeliferous Cu ore. We conclude that both deposit types can be explained as the product of a saline, oxidizing metalliferous brine which formed Cu mineralization by interaction with reduced pore waters, prior to exhalation into an anoxic brine pool, forming the stratiform Zn-Pb-Ag deposit. Our inference of fluid composition differs from many inferences on the chemistry of hydrothermal fluids involved in the formation of typical VHMS and BHT deposits, but is similar to that inferred for Proterozoic sediment-hosted Zn-Pb deposits in the McArthur basin, Australia.

  • 28.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Malmström, Lars
    Zinkgruvan Mining.
    Oxidized Brines Inferred in the Formation of c. 1.9 Ga Stratiform Zn-Pb-Ag and Dolomite-Hosted Cu Ores, Zinkgruvan, Bergslagen, Sweden2015Conference paper (Other academic)
    Abstract [en]

    Zinkgruvan is an elusive Palaeoproterozoic stratiform Zn-Pb-Ag deposit which has been discussed in the context of sediment-hosted Zn-Pb (SEDEX), volcanic-hosted massive sulphide (VHMS) and Broken Hill-type (BHT) deposits. In this contribution, we address the chemistry of the ore-forming fluid, the nature of the depositional environment and the controls on ore formation based on a review of previous work complemented with new geological data from a stratigraphically underlying dolomite-hosted, zinciferous, cobaltiferous and nickeliferous Cu ore. We conclude that both deposit types can be explained as the product of a saline, oxidizing metalliferous brine which formed Cu mineralization by interaction with reduced pore waters, prior to exhalation into an anoxic brine pool, forming the stratiform Zn-Pb-Ag deposit. Our inference of fluid composition differs from many inferences on the chemistry of hydrothermal fluids involved in the formation of typical VHMS and BHT deposits, but is similar to that inferred for Proterozoic sediment-hosted Zn-Pb deposits in the McArthur basin, Australia

  • 29.
    Kampmann, Tobias Christoph
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils F.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Stephens, Michael B.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Olin, Paul H.
    CODES ARC Centre of Excellence and TMVC ARC Research Hub, University of Tasmania.
    Gilbert, Sarah
    CODES ARC Centre of Excellence and TMVC ARC Research Hub, University of Tasmania.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Syn-tectonic sulphide remobilization and trace element redistribution at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen, Sweden2018In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 96, p. 48-71Article in journal (Refereed)
    Abstract [en]

    Mineralization types at the Palaeoproterozoic Falun base metal sulphide deposit are predominantly pyritic Zn-Pb-Cu-rich massive sulphide mineralization, disseminated to semi-massive Cu-Au mineralization, auriferous quartz veins, and mineralized shear zones of talc-chlorite-dominated schist. The massive and disseminated to semi-massive sulphide mineralization types were subject to polyphase ductile deformation (D1 and D2) and metamorphism under low-P, lower-amphibolite facies conditions, which led to the development of ore textures and paragenetic relationships indicating both mechanical and chemical remobilization of sulphides. In the massive sulphide mineralization, rare inclusion-rich pyrite occurs as relic cores inside inclusion-poor metamorphosed pyrite. Imaging and spot analysis using multielement laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) reveal that inclusion-poor pyrite was depleted in trace elements, which were originally present as non-stoichiometric lattice substitutions or in mineral inclusions. The inclusion-rich pyrite was shielded from depletion and, at least partly, retained its initially higher trace element concentrations, including Au.

    Gold is also associated with chalcopyrite in the disseminated to semi-massive Cu-Au mineralization and in the system of auriferous quartz veins hosted therein, the latter being also affected by the D2 ductile strain. It is inferred that emplacement of the vein system took place after the peak of metamorphism, which occurred between D1 and D2, but prior to and possibly even shortly after completion of the D2 deformational event. Similarities in trace element signatures in chalcopyrite are compatible with the interpretation that the quartz veins formed by local chemical remobilization of components from the Cu-Au mineralization. Transport of liberated Au from pyrite during grain growth in the massive sulphide mineralization may have upgraded the Au endowment in the quartz veins, leading to the additional formation of native gold in the veins. A strong correspondence between elements liberated from pyrite (e.g. Pb, Bi, Se and Au) and those forming discrete and characteristic mineral phases in the quartz veins (Pb-Bi sulphosalts, native gold) supports this hypothesis.

    Trace element signatures for the main sulphide minerals pyrite, chalcopyrite, sphalerite and galena are similar to previously published data from other metamorphosed massive sulphide deposits. The association of the Falun mineralization with elevated Bi is reflected by its occurrence in sulphide minerals (e.g. galena) and in abundant mineral inclusions of Pb-Bi sulphosalts (e.g. weibullite), especially in the disseminated to semi-massive Cu-Au mineralization. Elevated Sn concentrations in the lattice and/or as cassiterite inclusions in chalcopyrite, sphalerite and galena are compatible with a hot, acidic and reducing fluid during formation of the syn-volcanic, base metal sulphide mineralization and associated host-rock alteration.

  • 30.
    Kampmann, Tobias Christoph
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Stephens, Michael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Majka, Jarosław
    Uppsala universitet, AGH University of Science and Technology, Mickiewicza.
    Lasskogen, Jonas
    Boliden Mineral AB.
    Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen ore district, Fennoscandian Shield, Sweden2017In: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 112, no 5, p. 1111-1152Article in journal (Refereed)
    Abstract [en]

    The Paleoproterozoic Falun Zn-Pb-Cu-(Au-Ag) pyritic sulfide deposit in the Bergslagen ore district, Sweden, is enveloped by hydrothermally altered rocks metamorphosed to the lower amphibolite facies. Immobile-element ratios suggest that the alteration precursors were volcanic rocks of mainly rhyolitic to dacitic composition. Least altered examples of these rocks plot along magmatic fractionation trends outlined by late- to post-ore feldspar-phyric metadacite dikes and post-ore granitoid plutons, consistent with a comagmatic relationship between these calc-alkaline, coeval (<10-m.y.) suites. Dolomite or calcite marble, as well as diopside-hedenbergite or tremolite skarn, form subordinate but important lithologic components in the hydrothermally altered zone. Marble occurs as fragments in the massive pyritic sulfide mineralization, suggesting that at least some mineralization formed by carbonate replacement.

    Mass-change calculations suggest that the hydrothermally altered volcanic rocks gained Mg and Fe and generally lost Ca, K, and Na. Proximal, quartz-anthophyllite-rich altered rocks additionally gained Si, whereas several types of biotite-rich altered rocks lost this element. These mass changes along with mineral chemical data for anthophyllite, biotite, cordierite, and garnet, and the common occurrence of quartz indicate that chloritization, sericitization, and silicification were the dominant premetamorphic alteration styles. A zonation from distal sericitized and silicified volcanic rocks to intermediate sericitized rocks, partly overprinted by chloritization (Mg-rich chlorite), and proximal siliceous and intensely chloritized (Fe-rich chlorite) rocks has been identified. Furthermore, mass changes in more peripheral parts of the altered zone toward the southeast of the deposit suggest that the alteration weakens gradationally toward the volcanic and subvolcanic rocks surrounding the deposit. These patterns represent vectors toward mineralization.

    Intensely chloritized rocks, largely represented by a single, rhyolitic precursor, envelop the central pyritic massive sulfide bodies to the east, south, and west, supporting a structural model in which the massive sulfide mineralization formed the stratigraphically highest preserved unit in the center, surrounded in a tubular manner by stratigraphic footwall rocks. The northern side represents a portion of the footwall, which was separated by a major shear zone. These spatial relationships also have implications for near-mine exploration, since quartz-rich footwall rocks locally host disseminated to semimassive stockwork Cu-Au mineralization.

    Cooling of a hot (300°–400°C), acidic (pH ≤4) and reducing fluid carrying metals and sulfur is suggested for formation of stockwork Cu-Au vein mineralization and hydrothermal alteration in the stratigraphic footwall. The Zn-Pb-Cu-rich massive sulfide mineralization is inferred to have formed by fluid neutralization upon interaction with carbonates and mixing with cooler seawater upon fluid entry into porous pumice breccia in a subseafloor setting. Dissolution processes, primary porosity in the pumice breccia, and secondary porosity produced during synvolcanic faulting are all suggested to have contributed to the creation of space necessary for the formation of the massive sulfide mineralization. Falun differs from other deposits of the same type in Bergslagen mainly in the high pyrite content of the massive sulfide mineralization, the absence of related Fe oxide deposits, as well as the dominant replacement of volcaniclastic sediments compared to carbonates. The types of host rocks, the inferred premetamorphic feldspar-destructive alteration types, and the style of mineralization and alteration zonation at the deposit are reminiscent of pyritic volcanogenic massive sulfide (VMS) deposits. However, the importance of chemical trapping by fluid-limestone interaction, as well as the spatial association with subordinate skarn alteration constitute important differences to a classic VMS model.

  • 31.
    Kampmann, Tobias
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Stephens, Michael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Majka, Jarosław
    Uppsala universitet.
    Systematics of hydrothermal alteration at the volcanic-hosted Falun Zn-Pb-Cu-(Au-Ag) deposit: implications for ore genesis, structure and exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden2016In: Geophysical Research Abstracts, ISSN 1029-7006, E-ISSN 1607-7962, Vol. 18Article in journal (Refereed)
  • 32.
    O'Brien, Joshua J
    et al.
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Spry, Paul
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Raat, Hein
    Boliden Mines, Exploration Department.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Frank, Katherine S
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The major-trace element chemistry of garnet in metamorphosed hydrothermal alteration zones, Proterozoic Stollberg Zn-Pb-Ag-(Cu-Au) ore field, Bergslagen district, Sweden: implications for exploration2014Conference paper (Other academic)
    Abstract [en]

    Altered and exhalative rocks are used as exploration guides to ore deposits since they are generally more extensive than the massive sulfide target. Major and trace element compositions of silicates (e.g., garnet) and oxides (e.g., gahnite and magnetite) in meta-exhalites have recently been used as a vectoring tool in the search for metamorphosed massive sulfide deposits. Here, we evaluate the major-trace element chemistry of garnet in altered (i.e., gedrite-albite, garnet-biotite, and garnet-pyroxene-carbonate alteration) and unaltered (i.e. rhyolitic ash-siltstone) rocks spatially associated with volcanogenic massive sulfide Zn-Pb-Ag-(Cu-Au) and magnetite deposits in the Stollberg ore field (metamorphosed to the amphibolite facies), to determine the spatial distribution of major/trace element compositions of garnet and the potential of garnet chemistry as a guide to ore. Garnet in garnet-biotite alteration (extends intermittently for ~8 km along strike) and high-grade sulfides is Fe-rich (almandine) whereas garnet in skarn and garnet-pyroxene alteration contains significantly higher amounts of Ca (grossular), and Mn (spessartine). Concentrations (425 analyses) of trace elements in garnet were obtained from 38 samples in the Dammberget (n = 14), Gränsgruvan (n = 17), and Tvistbo (n = 7) deposits. Garnet contains elevated concentrations of Sc, Ti, V, Cr, Co, Zn, Ga, Ge, Y, and rare earth elements (REEs). Chondrite-normalized rare earth element patterns of garnet are depleted in light REEs (LREEs) and enriched in heavy REEs (HREEs). Garnet in sulfide-bearing altered rocks (i.e., garnet-biotite and garnet-pyroxene alteration) show a strong positive Eu anomaly, regardless of its major element composition, and contains elevated Zn (> 100 ppm) and Ga (> 15 ppm) contents, and low concentrations of Ti (<200 ppm). Garnet-biotite alteration adjacent to unaltered rhyolitic ash-siltstone contains garnet which is LREE depleted, HREE enriched, and typically shows no Eu anomaly, or in some cases, minor negative Eu anomalies. In sulfide-free quartz-garnet-pyroxene rocks, garnet possesses no Eu anomaly and contains elevated concentrations of Ga (> 10 ppm), Sc (> 5 ppm), and Ti (> 100 ppm), but low concentrations of Co (< 1 ppm), Cr (< 5 ppm), and V (< 20 ppm). Garnet in gedrite albite alteration exhibits a relatively flat chondrite-normalized REE profile, and contains elevated (> 10 ppm) Sc content, and low concentrations of V (< 2 ppm), Cr (< 3 ppm), and Zn (< 30 ppm). Garnet in mafic dikes and marbles contain the highest Cr (> 10 ppm), Co (> 5 pm), V (25-250 ppm) and Ti contents, whereas garnet in rhyolitic ash-siltstone typically shows no Eu anomaly, and low concentrations of Zn (< 100 ppm), Ga (< 15 ppm), Cr (< 5 ppm), and V (< 3 ppm). Garnet in massive sulfides and sulfide-bearing alteration assemblages can be distinguished from sulfidepoor or sulfide-free rocks of the same alteration type on the basis of their positive Eu anomaly, and Zn, Ga, and Ti content, which suggests garnet chemistry may be used as a vectoring tool to ore in the Stollberg ore field, and elsewhere in the Bergslagen district.

  • 33.
    Spry, Paul
    et al.
    Department of Geological and Atmospheric Sciences, Iowa State University.
    O'Brien, Joshua J
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Frank, Katherine S
    Department of Geological and Atmospheric Sciences, Iowa State University.
    Teale, GS
    Teale & Associates.
    Koenig, A
    U.S. Geological Survey, Denver Federal Center.
    Jansson, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Raat, Hein
    Boliden Mines, Exploration Department, Boliden Mines.
    Trace element compositions of silicates and oxides as exploration guides to metamorphosed massive sulphide deposits:examples from Broken Hill, Australia, and Stollberg, Sweden2015Conference paper (Other academic)
1 - 33 of 33
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