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  • 1.
    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.

  • 2.
    Romer, Rolf L.
    Luleå tekniska universitet.
    Caledonian upgrading of Proterozoic low-grade base-metal deposits in northern Sweden1994In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 50, no 4, p. 271-285Article in journal (Refereed)
    Abstract [en]

    Proterozoic sulfide deposits within the basement of northern Sweden have lead isotopic compositions that fall on a mixing line in the206Pb/204Pb-207Pb/204Pb diagram. These deposits contain a highly radiogenic Phanerozoic lead component that was leached from the Proterozoic basement at around 0.4 Ga during the Caledonian orogeny. Within the Proterozoic deposits, the less radiogenic lead isotopic compositions occur in undeformed and little deformed sections, while the more radiogenic lead isotopic compositions are observed along fault, fracture, and shear zones. These zones with radiogenic Phanerozoic lead also have higher contents of lead, zinc, and gold, respectively, than the other parts of the deposits, which suggests that these metals were introduced together with the radiogenic lead at a much later event than the metals in the unaltered Proterozoic deposit. The Proterozoic deposits acted as traps for metal additions along Caledonian reactivated fault and shear zones in the Proterozoic basement.

  • 3.
    Romer, Rolf L.
    Luleå tekniska universitet.
    Sandstone-hosted lead-zinc mineral deposits and their relation to the tectonic mobilization of the baltic shield during the Caledonian orogeny: a reinterpretation1992In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 47, no 1, p. 67-85Article in journal (Refereed)
    Abstract [en]

    Sandstone-hosted lead-zinc impregnation deposits in Scandinavia occur in Vendian to Cambrian and, locally, Ordovician sandstones that rest unconformably on the deeply eroded Baltic Shield. The sandstones are overthrust by the Caledonian nappes or form part of the lowermost Caledonian thrust units. Sandstone-hosted lead-zinc deposits, that occur along the present erosional front of the Caledonides, contain galena and sphalerite cementing fractures and pore space. The deposits formed by fluid-mixing processes in the sandstones. Early ore genetic models considered the ore-hosting sandstones, because of the positive correlation between ore grade and palaeo-permeability, as main aquifer for the metalliferous fluids that were interpreted to be either ground-waters or hot basinal brines driven out from geosynclinal sediments during the Caledonian orogeny. It is suggested here that the distribution of sandstone-hosted lead-zinc deposits is controlled by Caledonian reactivated basement structures, as the ores overlay faults and lithologic discontinuities in the basement. The geographic distribution of the Scandinavian sandstone-hosted lead-zinc deposits coincides with areas that show both extensive thrust sheets of the Lower Allochthon unit at the front and basement culminations in the interior of the Caledonian orogen. These areas are characterized by deeper thrusting levels and probably more intense reactivation of basement faults, which made the basement more susceptible to large-scale fluid migration. Metalliferous fluids emerging from Caledonian reactivated basement faults mixed with fluids in the sedimentary cover, which resulted in metal precipitation. The lead-zinc deposits in sandstones that formed by these processes occur selectively in the lowermost permeable cover.

  • 4.
    Romer, Rolf L.
    Luleå tekniska universitet.
    Vesuvianite: new tool for the U-Pb dating of skarn ore deposits1992In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 46, no 4, p. 331-341Article in journal (Refereed)
    Abstract [en]

    Vesuvianites from the Early Proterozoic Björntjärn tungsten skarn deposit in northern Sweden were dated with the U-Pb and Pb-Pb methods. Low206Pb/204Pb values make the U-Pb dating of vesuvianite rather sensitive to the common lead correction. However, the combination of Pb-Pb and U-Pb data on the same material permits the deduction of precise ages on Proterozoic vesuvianites. Vesuvianite can be used to date the formation of skarn mineralizations and possibly also the metamorphism and metasomatism of argillaceous limestones

  • 5.
    Romer, Rolf L.
    et al.
    Luleå tekniska universitet.
    Smeds, Sten-Anders
    Institute of Earth Sciences, Mineralogy-Petrology, Uppsala University.
    Cerny, P.
    Department of Geological Sciences, University of Manitoba.
    Crystal-chemical and genetic controls of U-Pb systematics of columbite-tantalite1996In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 57, no 3-4, p. 243-260Article in journal (Refereed)
    Abstract [en]

    Columbite-tantalite can accommodate considerable amounts of uranium and excludes lead almost completely. It is thus potentially suited for U-Pb dating. Discordias generally yield closely constrained upper intercept ages. Yet, in a few cases, the U-Pb system of columbite-tantalite gives poorly constrained ages due to excess scatter or inverse discordance. These anomalous features do not show any relation with gross mineral chemistry or pegmatite fractionation. Recrystallization or the presence of exsolutions and inclusions generally do not result in anomalous and scattered U-Pb systematics, unless the inclusions are uraninite or secondary Nb, Ta-bearing phases. Open-system behavior of uraninite, whose occurrence seems to be related to the local host-rock-influenced redox conditions during pegmatite crystallization, often results in inverse discordance. Secondary Nb, Ta-bearing phases that accept Pb and U derived from uraninite inclusions into their structure may inherit this inverse discordance.

  • 6.
    Tole, Ilda
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Mechanochemical activation of natural clay minerals: an alternative to produce sustainable cementitious binders – review2019In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 113, no 4, p. 449-462Article in journal (Refereed)
    Abstract [en]

    Mechanochemical activation can be defined as a process able to induce structural disorder through intensive grinding. In certain conditions, it may increase the chemical reactivity of the processed material. The process is extensively utilized in extractive metallurgy, synthesis of nanocomposites or pharmacology. It is also considered an environmentally friendly alternative to activate kaolinitic clay avoiding high calcination temperature. This paper aims to give a comprehensive overview of the process, its evolution, process parameters and applications. The paper focuses on the mechanochemical treatment of natural clay minerals, aiming at their transformation into cementitious or pozzolanic materials. It provides a summarized review of the theories related to the mechanochemistry and discusses commonly used models. The paper also analyzes various key factors and parameters controlling the mechanochemical activation process. The optimization and control of the several factors, as the filling ratio, the grinding media, the velocity, the time of grinding, etc., can promote developments and new research opportunities on different fields of application. Examples of applications, with a special focus on mechanochemically activated clay minerals and their use as cementitious binders, are listed as well.

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