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Origin of the Kleva Ni-Cu sulphide mineralisation in Småland, southeast Sweden

Bjärnborg, Karolina LU (2015) In Litholund Theses 25.
Abstract (Swedish)
Popular Abstract in Swedish

För cirka 1,8 miljarder år sedan, medan Skandinaviens urberg var under uppbyggnad, kristalliserade en järnrik magma till ett mörkt bergartskomplex av bergarterna gabbro och diorit. Denna magma hade bildats genom delvis uppsmältning av manteln under den dåvarande kontinentkanten, transporterats flera tiotals kilometer uppåt genom sprickor i jordskorpan och på vägen upp dragit med sig bitar av de omgivande bergarterna. Tack vare sammansättningen på mantelsmältan och de bergarter som på vägen inkorporerades i magman bildades en nickel-koppar-mineralisering bestående av metallrika svavelmineral. Denna mineralisering sitter i vad som idag kallas Klevaberget, 258 m.ö.h, som ligger cirka 13 km öster om... (More)
Popular Abstract in Swedish

För cirka 1,8 miljarder år sedan, medan Skandinaviens urberg var under uppbyggnad, kristalliserade en järnrik magma till ett mörkt bergartskomplex av bergarterna gabbro och diorit. Denna magma hade bildats genom delvis uppsmältning av manteln under den dåvarande kontinentkanten, transporterats flera tiotals kilometer uppåt genom sprickor i jordskorpan och på vägen upp dragit med sig bitar av de omgivande bergarterna. Tack vare sammansättningen på mantelsmältan och de bergarter som på vägen inkorporerades i magman bildades en nickel-koppar-mineralisering bestående av metallrika svavelmineral. Denna mineralisering sitter i vad som idag kallas Klevaberget, 258 m.ö.h, som ligger cirka 13 km öster om Vetlanda i Småland. Gruvan i Kleva var aktiv till och från mellan åren 1696 och 1919.

Magmatiska nickel-koppar-fyndigheter förekommer framförallt i Arkeiskt urberg som är mer än 2,5 miljarder år gammalt. I nordligaste Sverige och i Bergslagen finns ett antal fyndigheter av detta slag, men Kleva är den enda fyndigheten i sydöstra Sverige. nickel-kopparfyndigheter är ofta av stor ekonomisk betydelse, eftersom efterfrågan på metaller är stor idag. Kleva är en relativt liten fyndighet, och anses vara utbruten, men genom att studera dess magmatiska bildningssätt och hur yngre tektoniks aktivitet påverkat mineraliseringen kan man bättre förstå hur liknande fyndigheter skulle kunna se ut och var de kan återfinnas.

De svavelhaltiga malmmineralen i Kleva förekommer både som massiva kroppar, men även som spridda korn i gabbrobergarten och som sprickfyllnader. De är rika på nickel och koppar, men inte på ädelmetaller och platinum-grupp mineral, vilket brukar höra till denna typ av fyndighet. Det tyder på att malmmineral kristalliserat vid två tillfällen under mantelsmältans färd upp genom jordskorpan; det är endast den senare omgången malmmineral vi ser i Kleva, den tidigare som var rikare i platinum-grupp mineral återfinns förmodligen längre ner i jordskorpan.

Uran-bly-datering av mineralen zirkon och baddeleyit visar att värdbergarterna för fyndigheten är 1,79 miljarder år, alltså samtida med de graniter urberget domineras av i området. Baserat på malmmineralens och gabbrons relationer kan man konstatera att de i huvudsak bildades samtidigt. Dock har åldersbestämningar av malmmineralet pyrit visat att det vid minst två tillfällen efter kristallisationen, för cirka 1.6 och 1.4 miljarder år sedan, skett delvis omförflyttning och omkristallisation till sprickor i den massiva malmen och i gabbron. (Less)
Abstract
The Kleva Ni-Cu sulphide deposit is situated within a gabbro-diorite intrusive complex in southeast Sweden. The basement north of the intrusive complex is dominated by 1.81–1.77 Ga granites of the Palaeoproterozoic Transscandinavian Igneous Belt (TIB). Slightly older (1.83–1.82 Ga) rocks of the Oskarshamn Jönköping Belt, which hosts numerous syngenetic and epigenetic base metal mineralisations, occur just south of the Kleva intrusive complex. The aim of this PhD-thesis is to deduce the origin of the Kleva deposit, the mineralisation itself as well as its host rocks through geochemical, geochronological and petrological studies.

U-Pb age determination of zircon dates igneous crystallisation to 1.79 Ga, which is the age of the Kleva... (More)
The Kleva Ni-Cu sulphide deposit is situated within a gabbro-diorite intrusive complex in southeast Sweden. The basement north of the intrusive complex is dominated by 1.81–1.77 Ga granites of the Palaeoproterozoic Transscandinavian Igneous Belt (TIB). Slightly older (1.83–1.82 Ga) rocks of the Oskarshamn Jönköping Belt, which hosts numerous syngenetic and epigenetic base metal mineralisations, occur just south of the Kleva intrusive complex. The aim of this PhD-thesis is to deduce the origin of the Kleva deposit, the mineralisation itself as well as its host rocks through geochemical, geochronological and petrological studies.

U-Pb age determination of zircon dates igneous crystallisation to 1.79 Ga, which is the age of the Kleva intrusive complex and confirms its temporal association with the voluminous TIB magmatism. Major- and trace element systematics are in accordance with a basaltic magma that formed through partial melting of a metasomatically refertilised mantle wedge underneath an Andean-type continental magmatic arc. Lu-Hf signatures of zircon, together with other rocks of Palaeoproterozoic Fennoscandia indicate alternating stages of extension and compression across the subduction zone, facilitating ascent of the mafic magma. Evidence for contamination of the magma through crustal assimilation during its ascent are inconclusive. Low IPGE/Ni together with high S/Se, indicate sulphide melt saturation prior to final emplacement, possibly induced by crustal contamination. Nb/La vs La/Sm indicate contamination with mid-crustal rocks, and radiogenic Os of magmatic pyrite suggests <10% contamination with Archean crust. OJB aged rocks are thus unlikely contaminants, despite the numerous rock inclusions of similar geochemical composition within the intrusive complex. δ34S of Kleva mineralised rocks and the country rocks corresponds with the mantle range, and local or mantle origin of S can neither be proven nor rejected.

Sulphide melt segregated from an evolved magma and partially accumulated into massive lenses, which is in accordance with a magmatic conduit setting. The mineralisation contains massive, net-textured and disseminated sulphides of typical magmatic association and is interpreted to be contemporaneous with silicate melt crystallisation, consistent with a Re-Os 1.71 ±0.2 Ga isochron for massive pyrite with magmatic texture. Re-Os isochrons of secondary pyrite indicate metamorphic disturbance of the mineralisation at least twice; at c. 1.61 Ga and 1.39 Ga, which can be linked to orogenic events further to the south and west. The mineralisation was heterogeneously affected by tectonic disturbance, resulting in remobilisation of chalcopyrite into veins, plastic deformation of sulphides and host rock, micro-faulting and brittle deformation of oxides and sulphides and recrystallisation of pyrite in fractures. To summarise, the deposit is an example of a subduction related magmatic Ni-Cu mineralisation affected by multi-stage deformation and alteration. (Less)
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author
supervisor
opponent
  • Billström, Kjell, Museum of Natural History, Stockholm
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Palaeoproterozoic, Fennoscandia, geochronology, geochemistry, sulphide remobilisation, gabbro–diorite, mantle, arc, ore genesis, Ni-Cu sulphide deposit
in
Litholund Theses
volume
25
pages
186 pages
publisher
Department of Geology, Lund University
defense location
Pangea, Geocentrum II
defense date
2015-12-11 09:15
ISSN
1651-6648
ISBN
978-91-87847-07-3 (print)
978-91-87847-08-0 (pdf)
language
English
LU publication?
yes
id
da102143-e862-424a-a03a-ee097e31e129 (old id 7852663)
date added to LUP
2015-11-20 13:25:24
date last changed
2016-09-19 08:44:50
@phdthesis{da102143-e862-424a-a03a-ee097e31e129,
  abstract     = {The Kleva Ni-Cu sulphide deposit is situated within a gabbro-diorite intrusive complex in southeast Sweden. The basement north of the intrusive complex is dominated by 1.81–1.77 Ga granites of the Palaeoproterozoic Transscandinavian Igneous Belt (TIB). Slightly older (1.83–1.82 Ga) rocks of the Oskarshamn Jönköping Belt, which hosts numerous syngenetic and epigenetic base metal mineralisations, occur just south of the Kleva intrusive complex. The aim of this PhD-thesis is to deduce the origin of the Kleva deposit, the mineralisation itself as well as its host rocks through geochemical, geochronological and petrological studies.<br/><br>
U-Pb age determination of zircon dates igneous crystallisation to 1.79 Ga, which is the age of the Kleva intrusive complex and confirms its temporal association with the voluminous TIB magmatism. Major- and trace element systematics are in accordance with a basaltic magma that formed through partial melting of a metasomatically refertilised mantle wedge underneath an Andean-type continental magmatic arc. Lu-Hf signatures of zircon, together with other rocks of Palaeoproterozoic Fennoscandia indicate alternating stages of extension and compression across the subduction zone, facilitating ascent of the mafic magma. Evidence for contamination of the magma through crustal assimilation during its ascent are inconclusive. Low IPGE/Ni together with high S/Se, indicate sulphide melt saturation prior to final emplacement, possibly induced by crustal contamination. Nb/La vs La/Sm indicate contamination with mid-crustal rocks, and radiogenic Os of magmatic pyrite suggests &lt;10% contamination with Archean crust. OJB aged rocks are thus unlikely contaminants, despite the numerous rock inclusions of similar geochemical composition within the intrusive complex. δ34S of Kleva mineralised rocks and the country rocks corresponds with the mantle range, and local or mantle origin of S can neither be proven nor rejected.<br/><br>
Sulphide melt segregated from an evolved magma and partially accumulated into massive lenses, which is in accordance with a magmatic conduit setting. The mineralisation contains massive, net-textured and disseminated sulphides of typical magmatic association and is interpreted to be contemporaneous with silicate melt crystallisation, consistent with a Re-Os 1.71 ±0.2 Ga isochron for massive pyrite with magmatic texture. Re-Os isochrons of secondary pyrite indicate metamorphic disturbance of the mineralisation at least twice; at c. 1.61 Ga and 1.39 Ga, which can be linked to orogenic events further to the south and west. The mineralisation was heterogeneously affected by tectonic disturbance, resulting in remobilisation of chalcopyrite into veins, plastic deformation of sulphides and host rock, micro-faulting and brittle deformation of oxides and sulphides and recrystallisation of pyrite in fractures. To summarise, the deposit is an example of a subduction related magmatic Ni-Cu mineralisation affected by multi-stage deformation and alteration.},
  author       = {Bjärnborg, Karolina},
  isbn         = {978-91-87847-07-3 (print)},
  issn         = {1651-6648},
  keyword      = {Palaeoproterozoic,Fennoscandia,geochronology,geochemistry,sulphide remobilisation,gabbro–diorite,mantle,arc,ore genesis,Ni-Cu sulphide deposit},
  language     = {eng},
  pages        = {186},
  publisher    = {Department of Geology, Lund University},
  school       = {Lund University},
  series       = {Litholund Theses},
  title        = {Origin of the Kleva Ni-Cu sulphide mineralisation in Småland, southeast Sweden},
  volume       = {25},
  year         = {2015},
}