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Stephens, Michael
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Publications (10 of 21) Show all publications
Saintilan, N. J., Spangenberg, J. E., Chiaradia, M., Chelle-Michou, C., Stephens, M. B. & Fontboté, L. (2019). Petroleum as source and carrier of metals in epigenetic sediment-hosted mineralization. Scientific Reports, 9, Article ID 8283.
Open this publication in new window or tab >>Petroleum as source and carrier of metals in epigenetic sediment-hosted mineralization
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8283Article in journal (Refereed) Published
Abstract [en]

Sediment-hosted ore deposits contribute a significant amount (up to 65%) of the global resources of lead and zinc. Among them, the Mississippi-Valley type deposits and related oil fields often comprise large-scale hydrothermal systems where regional host rocks are stained with disseminated liquid petroleum (crude oil) and other organic compounds. Current models for the formation of those epigenetic Pb-Zn sulphide deposits consider that metals are mostly leached from basement rocks and their detrital erosional products, and transported by oxidized basinal hydrothermal fluids as chloride complexes. Sulphide precipitation mainly occurs when these basinal brines interact with fluids rich in reduced sulphur species produced mostly by thermochemical sulphate reduction (TSR) mediated by hydrocarbons. Here, using organic geochemistry and Pb isotopes, we provide evidence that petroleum and associated water were key for the formation of sulphide mineralization in the world-class sandstone-hosted ore deposit at Laisvall, not only by supplying reduced sulphur but also by contributing metals in significant amounts. The lead originally found in bitumen of the Alum Shale Formation was transported —during an arc-continent collisional event— by liquid petroleum and associated water to the site of sulphide mineralization. The alteration of petroleum by TSR made lead available for precipitation as sulphide. The petroleum-associated lead represents 40 to 60% of the metal budget in the deposit, the remainder being sourced by leaching of basement rocks.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-74506 (URN)10.1038/s41598-019-44770-7 (DOI)000470075600032 ()31164692 (PubMedID)2-s2.0-85066605437 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-20 (johcin)

Available from: 2019-06-13 Created: 2019-06-13 Last updated: 2019-08-23Bibliographically approved
Bender, H., Ring, U., Almqvist, B., Grasemann, B. & Stephens, M. B. (2018). Metamorphic Zonation by Out‐of‐Sequence Thrusting at Back‐Stepping Subduction Zones: Sequential Accretion of the Caledonian Internides, Central Sweden. Tectonics, 37(10), 3545-3576
Open this publication in new window or tab >>Metamorphic Zonation by Out‐of‐Sequence Thrusting at Back‐Stepping Subduction Zones: Sequential Accretion of the Caledonian Internides, Central Sweden
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2018 (English)In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 37, no 10, p. 3545-3576Article in journal (Refereed) Published
Abstract [en]

Exhumation of the high‐grade metamorphic Seve Nappe Complex and its emplacement between lower‐grade nappes has been related to wedge extrusion in the central Scandinavian Caledonides. To test this hypothesis, the kinematic evolution of the Caledonian nappe pile is studied by systematic structural mapping in central and northern Jämtland, Sweden. Structural data, combined with petrological and quartz microstructure observations, document pervasive top‐to‐the‐ESE, foreland‐directed shearing under progressively decreasing metamorphic grade across the entire nappe pile. Mylonitic foliation, foliation‐parallel boudinage, and abundant top‐to‐the‐ESE and rare, scattered top‐to‐the‐WNW shear‐sense indicators imply foreland‐directed general shear. This deformation regime caused exhumation by concurrent thrusting and vertical ductile thinning. We propose a specific succession of in‐ and out‐of‐sequence thrusts that generated the metamorphic zonation. Our model envisions in‐sequence propagation of thrusts during exhumation of the Seve Nappe Complex, related to subduction of Baltica beneath a volcanic arc within Iapetus. Concurrently, Iapetus subducted beneath Laurentia farther to the west. When Iapetus was closed, Baltica subduction stepped westward and continued beneath Laurentia. The back stepping of subduction at the onset of continental collision caused out‐of‐sequence propagation of the orogenic wedge. Thrusting cut downsection across the existing tectonostratigraphy, emplacing units of lower metamorphic grade above the high‐grade Seve Nappe Complex. This imbrication generated the present metamorphic zonation of the Caledonian nappe pile during sustained convergence between Laurentia and Baltica.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
Keywords
Caledonian orogeny, collisional tectonics, kinematic evolution, out‐of‐sequence thrusting
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-71752 (URN)10.1029/2018TC005088 (DOI)000450992300009 ()2-s2.0-85053468243 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-26 (johcin)

Available from: 2018-11-26 Created: 2018-11-26 Last updated: 2018-12-10Bibliographically approved
Kampmann, T. C., Jansson, N. F., Stephens, M. B., Olin, P. H., Gilbert, S. & Wanhainen, C. (2018). Syn-tectonic sulphide remobilization and trace element redistribution at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen, Sweden. Ore Geology Reviews, 96, 48-71
Open this publication in new window or tab >>Syn-tectonic sulphide remobilization and trace element redistribution at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen, Sweden
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2018 (English)In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 96, p. 48-71Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Falun deposit, Bergslagen, Fennoscandian Shield, sulphide remobilization, LA-ICP-MS, trace elements
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-61672 (URN)10.1016/j.oregeorev.2018.04.010 (DOI)000434004700004 ()2-s2.0-85045259948 (Scopus ID)
Projects
Structural evolution, hydrothermal alteration and tectonic setting of the Falun base metal and gold deposit, Bergslagen region, Sweden
Funder
The Geological Survey of Sweden (SGU), 61-1441/2011
Note

Validerad;2018;Nivå 2;2018-04-16 (andbra)

Available from: 2017-01-27 Created: 2017-01-27 Last updated: 2018-06-28Bibliographically approved
Saintilan, N. J., Stephens, M., Spikings, R. A., Schneider, J. C., Chiaradia, M., Spangenberg, J. E., . . . Fontboté, L. (2017). Polyphase vein mineralization in the Fennoscandian Shield at Åkerlandet, Järvsand, and Laisvall along the erosional front of the Caledonian orogen, Sweden. Mineralium Deposita, 52(6), 823-844
Open this publication in new window or tab >>Polyphase vein mineralization in the Fennoscandian Shield at Åkerlandet, Järvsand, and Laisvall along the erosional front of the Caledonian orogen, Sweden
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2017 (English)In: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 52, no 6, p. 823-844Article in journal (Refereed) Published
Abstract [en]

The Åkerlandet, Järvsand, and Laisvall deposits in Sweden are calcite-fluorite-sulfide vein deposits and occurrences located close to the current erosional front of the Caledonian orogen and hosted by crystalline basement rocks in the Fennoscandian Shield. At Laisvall, basement-hosted veinlets occur beneath Ediacaran to Cambrian sandstones that host a strata-bound Pb-Zn deposit. The mineralized fractures at Åkerlandet and Järvsand occur along fault systems oriented N–S to NNW–SSE. Veins or veinlets strike NNW–SSE and NW–SE at Åkerlandet, NNE–SSW at Järvsand, and NNW–SSE and NNE–SSW to NE–SW at Laisvall. At Åkerlandet and Järvsand, fractures acted as conduits for hydrothermal fluids of variable composition and formed during separate tectonic events. At Åkerlandet, the fault zone with NNW–SSE strike shows kinematic indicators consistent with ~NE–SW bulk horizontal extension. At Järvsand, the calcite-fluorite-galena veins formed along R-Riedel shears related to the host N–S to NNW–SSE fault system. The kinematic indicators are consistent with ~NW–SE bulk horizontal extension, similar to the extensional deformation during the later part of the Caledonian orogeny (Silurian to Devonian). At Åkerlandet, adularia-quartz deposition was followed by sphalerite ± galena and finally by precipitation of fluorite and calcite. 40Ar-39Ar thermochronology of a single adularia sample did not yield a well-defined plateau age but the gas released at higher temperatures suggests an early Tonian (980 to 950 Ma) crystallization age, i.e., during the later part of the Sveconorwegian orogeny, although the data do not exclude other less likely interpretations. Previous fluid inclusion microthermometry and geochronological studies and new petrographic and geochemical results suggest that sphalerite ± galena mineralization formed from saline, relatively oxidizing, moderate-temperature, and slightly acidic hydrothermal fluids, either during the Ediacaran or the Middle Ordovician. Metals and H2S were derived from local basement rocks. Based on petrographic evidence, rare earth element composition, and S, C, and O isotope data, fluorite and calcite precipitated under near neutral and relatively reducing conditions. Occurrence of solid bitumen in veins at Åkerlandet and C and O isotope data of calcite at Åkerlandet and in the Laisvall basement veinlets suggest that the precipitation of calcite and fluorite was triggered by interaction of hot and evolved hydrothermal fluids (87Sr/86Sr = 0.718–0.732) with organic matter. Structural, petrographic, and geochemical data at Laisvall suggest that the basement structures hosting calcite-fluorite ± pyrite veinlets were utilized in the Middle Ordovician as the plumbing system for the oxidizing, slightly acidic, metal-bearing brines that caused the economic Pb-Zn mineralization in the overlying sandstones

Place, publisher, year, edition, pages
Springer, 2017
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-61418 (URN)10.1007/s00126-016-0698-0 (DOI)000405602500003 ()2-s2.0-85007164444 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-08-16 (andbra)

Available from: 2017-01-13 Created: 2017-01-13 Last updated: 2018-07-10Bibliographically approved
Kampmann, T. C., Jansson, N., Stephens, M., Majka, J. & Lasskogen, J. (2017). Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen ore district, Fennoscandian Shield, Sweden (ed.). Economic geology and the bulletin of the Society of Economic Geologists, 112(5), 1111-1152
Open this publication in new window or tab >>Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen ore district, Fennoscandian Shield, Sweden
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2017 (English)In: 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) Published
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.

Place, publisher, year, edition, pages
Society of Economic Geologists, 2017
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-5137 (URN)10.5382/econgeo.2017.4504 (DOI)000426874300005 ()2-s2.0-85021135933 (Scopus ID)329616f3-a1ac-49e9-8cfe-bee49ce58aa3 (Local ID)329616f3-a1ac-49e9-8cfe-bee49ce58aa3 (Archive number)329616f3-a1ac-49e9-8cfe-bee49ce58aa3 (OAI)
Projects
Structural evolution, hydrothermal alteration and tectonic setting of the Falun base metal and gold deposit, Bergslagen region, Sweden
Funder
The Geological Survey of Sweden (SGU)
Note

Validerad;2017;Nivå 2;2017-06-05 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-05-04Bibliographically approved
Johansson, Å. & Stephens, M. (2017). Timing of magmatism and migmatization in the 2.0–1.8 Ga accretionary Svecokarelian orogen, south-central Sweden (ed.). International journal of earth sciences, 106(3), 783-810
Open this publication in new window or tab >>Timing of magmatism and migmatization in the 2.0–1.8 Ga accretionary Svecokarelian orogen, south-central Sweden
2017 (English)In: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 106, no 3, p. 783-810Article in journal (Refereed) Published
Abstract [en]

The Palaeoproterozoic (2.0–1.8 Ga) Svecokarelian orogen in central Sweden consists of a low-pressure, predominantly medium-grade metamorphic domain (central part of Bergslagen lithotectonic unit), enclosed to the north and south by low-pressure migmatite belts. Two periods of metamorphism (1.87–1.85 and 1.83–1.79 Ga) are known in the migmatite belts. In this study, new U–Th–Pb ion microprobe data on zircon and monazite from twelve samples of locally migmatized gneisses and felsic intrusive bodies determine both protolith and metamorphic ages in four sample areas north of Stockholm, inside or immediately adjacent to the medium-grade metamorphic domain. Two orthogneiss samples from the Rimbo area yield unusually old protolith ages of 1909 ± 4 and 1908 ± 4 Ma, while three orthogneisses from the Skutskär and Forsmark areas yield more typical protolith ages between 1901 ± 3 and 1888 ± 3 Ma. Migmatized paragneiss samples from this and two earlier studies contain a significant detrital component sourced from this 1.9 Ga magmatic suite. They are interpreted to be deposited contemporaneously with or shortly after this magmatism. Migmatization of the paragneiss at Rimbo was followed by intrusion of leucogranite at 1846 ± 3 Ma. Even in the other sample areas to the north (Hedesunda-Tierp, Skutskär and Forsmark), metamorphism including migmatization is constrained to the 1.87–1.85 Ga interval and penetrative ductile deformation is limited by earlier studies in the Forsmark area to 1.87–1.86 Ga. However, apart from a metamorphic monazite age of 1863 ± 1 Ma, precise ages were not possible to obtain due to the presence of only partially reset recrystallized domains in zircon, or highly discordant U-rich metamict and altered metamorphic rims. Migmatization was contemporaneous with magmatic activity at 1.87–1.84 Ga in the Bergslagen lithotectonic unit involving a mantle-derived component, and there is a spatial connection between migmatization and this magmatic phase in the Hedesunda-Tierp sample area. The close spatial and temporal interplay between ductile deformation, magmatism and migmatization, the P–T metamorphic conditions, and the continuation of similar magmatic activity around and after 1.8 Ga support solely accretionary rather than combined accretionary and collisional orogenic processes as an explanation for the metamorphism. The generally lower metamorphic grade and restricted influence of the younger metamorphic episode, at least at the ground surface level, distinguishes the central part of the Bergslagen lithotectonic unit from the migmatite belts further north and south.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-9980 (URN)10.1007/s00531-016-1359-3 (DOI)000398931600001 ()2-s2.0-84978036316 (Scopus ID)8b872cd6-9178-41c0-90eb-9798d8fff59d (Local ID)8b872cd6-9178-41c0-90eb-9798d8fff59d (Archive number)8b872cd6-9178-41c0-90eb-9798d8fff59d (OAI)
Note

Validerad; 2017; Nivå 2; 2017-03-29 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-11-15Bibliographically approved
Kampmann, T. C., Stephens, M. & Weihed, P. (2016). 3D modelling and sheath folding at the Falun Zn-Pb-Cu-(Au-Ag) massive sulphide deposit and implications for exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden (ed.). Paper presented at . Mineralium Deposita, 51(5), 665-680
Open this publication in new window or tab >>3D modelling and sheath folding at the Falun Zn-Pb-Cu-(Au-Ag) massive sulphide deposit and implications for exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden
2016 (English)In: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 51, no 5, p. 665-680Article in journal (Refereed) Published
Abstract [en]

The Falun pyritic Zn-Pb-Cu-(Au-Ag) deposit, situated in the Palaeoproterozoic (1.9–1.8 Ga) Bergslagen lithotectonic unit in the south-western part of the Fennoscandian Shield, is one of the major base metal sulphide deposits in Sweden. Altered rocks and ore types at Falun have been metamorphosed and deformed in a heterogeneous ductile manner, strongly modifying mineral assemblages in the original hydrothermal alteration system and the geometry of the deposit. Using a combined methodological approach, including surface mapping of lithologies and structures, drill core logging and microstructural investigation, the polyphase character (D1 and D2) of the ductile deformation is demonstrated and a 3D model for the deposit created. F2 sheath folding along axes that plunge steeply to the south-south-east, parallel to a mineral stretching lineation and the dip direction of the S2 foliation, is suggested as a key deformation mechanism forming steeply plunging, rod-shaped ore bodies. This is in contrast to previous structural models involving fold interference and, in turn, has implications for near-mine exploration, the occurrence of hanging-wall components to the ore body being questioned. Typical rock-forming minerals in the Falun alteration aureole include quartz, biotite/phlogopite, cordierite, anthophyllite and minor almandine, andalusite and chlorite, as well as dolomite, tremolite and actinolite. Where observable, the silicate minerals in the alteration rocks show growth patterns during different phases of the tectonothermal evolution, considerable static grain growth occurring between D1 and D2 and even after D2. A major high-strain zone, characterized by the mineral assemblage talc-chlorite-(quartz-biotite/phlogopite) defines a boundary between northern and southern structural domains at the deposit, and is closely spatially associated with the polymetallic massive sulphide ores. A possible role as a metal-bearing fluid conduit during ore genesis is discussed.

National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-9197 (URN)10.1007/s00126-016-0638-z (DOI)000377024500007 ()2-s2.0-84955598369 (Scopus ID)7c293c1b-cd76-47eb-85c5-e1cf3a56f6d9 (Local ID)7c293c1b-cd76-47eb-85c5-e1cf3a56f6d9 (Archive number)7c293c1b-cd76-47eb-85c5-e1cf3a56f6d9 (OAI)
Projects
Structural evolution, hydrothermal alteration and tectonic setting of the Falun base metal and gold deposit, Bergslagen region, Sweden
Note
Validerad; 2016; Nivå 2; 20150212 (tobkam)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Saintilan, N. J. D., Spangenberg, J. E., Samankassou, E., Kouzmanov, K., Chiaradia, M., Stephens, M. & Fontboté, L. (2016). A refined genetic model for the Laisvall and Vassbo Mississippi Valley-type sandstone-hosted deposits, Sweden: constraints from paragenetic studies, organic geochemistry, and S, C, N, and Sr isotope data (ed.). Paper presented at . Mineralium Deposita, 51(5), 639-664
Open this publication in new window or tab >>A refined genetic model for the Laisvall and Vassbo Mississippi Valley-type sandstone-hosted deposits, Sweden: constraints from paragenetic studies, organic geochemistry, and S, C, N, and Sr isotope data
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2016 (English)In: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 51, no 5, p. 639-664Article in journal (Refereed) Published
Abstract [en]

The current study has aimed to refine the previously proposed two-fluid mixing model for the Laisvall (sphalerite Rb-Sr age of 467 ± 5 Ma) and Vassbo Mississippi Valley-type deposits hosted in Ediacaran to Cambrian sandstone, Sweden. Premineralization cements include authigenic monazite, fluorapatite, and anatase in the Upper Sandstone at Laisvall, reflecting anoxic conditions during sandstone burial influenced by the euxinic character of the overlying carbonaceous middle Cambrian to Lower Ordovician Alum Shale Formation (δ 13Corg = −33.0 to −29.5 ‰, δ 15Norg = 1.5 to 3.3 ‰, 0.33 to 3.03 wt% C, 0.02 to 0.08 wt% N). The available porosity for epigenetic mineralization, including that produced by subsequent partial dissolution of pre-Pb-Zn sulfide calcite and barite cements, was much higher in calcite- and barite-cemented sandstone paleoaquifers (29 % by QEMSCAN mapping) than in those mainly cemented by quartz (8 %). A major change in the Laisvall plumbing system is recognized by the transition from barite cementation to Pb-Zn sulfide precipitation in sandstone. Ba-bearing, reduced, and neutral fluids had a long premineralization residence time (highly radiogenic 87S/86Sr ratios of 0.718 to 0.723) in basement structures. As a result of an early Caledonian arc-continent collision and the development of a foreland basin, fluids migrated toward the craton and expelled Ba-bearing fluids from their host structures into overlying sandstone where they deposited barite upon mixing with a sulfate pool (δ 34Sbarite = 14 to 33 ‰). Subsequently, slightly acidic brines initially residing in pre-Ediacaran rift sediments in the foredeep of the early Caledonian foreland basin migrated through the same plumbing system and acquired metals on the way. The bulk of Pb-Zn mineralization formed at temperatures between 120 and 180 °C by mixing of these brines with a pool of H2S (δ 34S = 24 to 29 ‰) produced via thermochemical sulfate reduction (TSR) with oxidation of hydrocarbons in sandstone. Other minor H2S sources are identified. Upward migration and fluctuation of the hydrocarbon-water interface in sandstone below shale aquicludes and the formation of H2S along this interface explain the shape of the orebodies that splay out like smoke from a chimney and the conspicuous alternating layers of galena and sphalerite. Intimate intergrowth of bitumen with sphalerite suggests that subordinate amounts of H2S might have been produced by TSR during Pb-Zn mineralization. Gas chromatograms of the saturated hydrocarbon fraction from organic-rich shale and from both mineralized and barren sandstone samples indicate that hydrocarbons migrated from source rocks in the overlying Alum Shale Formation buried in the foredeep into sandstone, where they accumulated in favorable traps in the forebulge setting.

National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-15402 (URN)10.1007/s00126-015-0627-7 (DOI)000377024500006 ()2-s2.0-84971324388 (Scopus ID)ee8d2a7b-6e14-417d-a4ca-c4c69af94602 (Local ID)ee8d2a7b-6e14-417d-a4ca-c4c69af94602 (Archive number)ee8d2a7b-6e14-417d-a4ca-c4c69af94602 (OAI)
Note
Validerad; 2016; Nivå 2; 20151222 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Kampmann, T., Jansson, N., Stephens, M. & Majka, J. (2016). 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, Sweden (ed.). Paper presented at European Geosciences Union General Assembly : 18/04/2016 - 22/04/2016. Geophysical Research Abstracts, 18
Open this publication in new window or tab >>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, Sweden
2016 (English)In: Geophysical Research Abstracts, ISSN 1029-7006, E-ISSN 1607-7962, Vol. 18Article in journal, Meeting abstract (Refereed) Published
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-31438 (URN)59bc06dd-24a3-4e85-a08e-a9f8d4254539 (Local ID)59bc06dd-24a3-4e85-a08e-a9f8d4254539 (Archive number)59bc06dd-24a3-4e85-a08e-a9f8d4254539 (OAI)
Conference
European Geosciences Union General Assembly : 18/04/2016 - 22/04/2016
Projects
Structural evolution, hydrothermal alteration and tectonic setting of the Falun base metal and gold deposit, Bergslagen region, Sweden
Note

Godkänd; 2016; 20160425 (tobkam)

Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-30Bibliographically approved
Kampmann, T., Stephens, M., Ripa, M., Hellström, F. & Majka, J. (2016). Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U-Pb geochronology on zircon and monazite (ed.). Paper presented at . Precambrian Research, 278, 52-68
Open this publication in new window or tab >>Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U-Pb geochronology on zircon and monazite
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2016 (English)In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 278, p. 52-68Article in journal (Refereed) Published
Abstract [en]

U–Th–Pb (zircon and monazite) ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the Palaeoproterozoic, Falun base metal sulphide deposit in the Bergslagen lithotectonic unit, Fennoscandian Shield, Sweden, and, thereby the timing of mineralisation. Hydrothermal alteration and mineralisation at Falun are constrained to a short interval of several million years between a 207Pb/206Pb weighted average age of 1894 ± 3 Ma for a rhyolitic sub-volcanic rock in the felsic volcanic to sub-volcanic host rock suite, and a 207Pb/206Pb weighted average age of 1891 ± 3 Ma for a post-sulphide, porphyritic dacite dyke. Magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 ± 3, 1894 ± 2 Ma and 1893 ± 3 Ma. The felsicsub-volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties, indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity, and burial of the supracrustal rocks.Two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the Falun deposit yield 207Pb/206Pb weighted average ages of 1831 ± 8 Ma and 1822 ± 5 Ma, respectively. These ages fall well within the temporal range of a younger1.84–1.81 Ga (M2) metamorphic episode during the 2.0–1.8 Ga Svecokarelian orogeny, with the older episode (M1) inside the Bergslagen lithotectonic unit at around 1.86 Ga. This shows the major influence of the M2 event in the north-western part of this unit, leading to a complete resetting of the U–Th–Pb isotopesystem in monazite.

National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-3483 (URN)10.1016/j.precamres.2016.03.011 (DOI)000375812000004 ()2-s2.0-84962135514 (Scopus ID)14fb5419-c9f2-4921-bc28-1ed578ee92e6 (Local ID)14fb5419-c9f2-4921-bc28-1ed578ee92e6 (Archive number)14fb5419-c9f2-4921-bc28-1ed578ee92e6 (OAI)
Projects
Structural evolution, hydrothermal alteration and tectonic setting of the Falun base metal and gold deposit, Bergslagen region, Sweden
Note
Validerad; 2016; Nivå 2; 20151014 (tobkam)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
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