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A rock magnetic study of the Åkerberg gold deposit, northern Sweden

Dahlenborg, Lars (2007) In Dissertations in Geology at Lund University
Department of Geology
Abstract
A rock magnetic study has been preformed of the Åkerberg gold deposit, located 30 km NE of Boliden
in northern Sweden. The gold mineralization is located to a zone of subparallel quartz veins in a layered gabbro.
Ground surveys show a lowering of the magnetic properties at the ore zone. This thesis addresses the factors causing
the anomaly by investigating the magnetic properties of different parts of the gabbro. The thesis is also concerned
with displacement of tectonic blocks, which is indicated by tilted magmatic layers in the immediate surroundings
of the ore zone. Thermal and alternating field demagnetization and susceptibility and thermomagnetic
measurements have been conducted on the samples collected at the ore zone and in... (More)
A rock magnetic study has been preformed of the Åkerberg gold deposit, located 30 km NE of Boliden
in northern Sweden. The gold mineralization is located to a zone of subparallel quartz veins in a layered gabbro.
Ground surveys show a lowering of the magnetic properties at the ore zone. This thesis addresses the factors causing
the anomaly by investigating the magnetic properties of different parts of the gabbro. The thesis is also concerned
with displacement of tectonic blocks, which is indicated by tilted magmatic layers in the immediate surroundings
of the ore zone. Thermal and alternating field demagnetization and susceptibility and thermomagnetic
measurements have been conducted on the samples collected at the ore zone and in distant parts relative to the ore
zone. ChRM-directions have been analyzed with principal component analyses and one Virtual Geomagnetic Pole
(VGP) was calculated. Mineral composition was examined with a Scanning Electron Microscope and conventional
microscopy in both transmitted and reflected light. This study shows that the sampled outcrop distant to the ore
zone is magnetite poor and that the gabbro lacks magnetite in the ore zone and in immediate surrounding areas. The
NRM (Natural Remanent Magnetization) in the ore zone is carried by monoclinic pyrrhotite. The magnetic anomaly
over the ore zone is caused by a lower amount of pyrrhotite compared to the surrounding areas. This study also
indicates that the NRM carried by monoclinic pyrrhotite in the ore zone and in the distant parts of the gabbro was
acquired during the same event. The timing of this event, however, is unclear since only one VGP could be calculated. (Less)
Abstract (Swedish)
En bergartsmagnetisk studie har utförts på en guldmineralisering som är belägen vid Åkerberg,
30 km Nordöst om Boliden, i norra Sverige. Mineraliseringen är bunden till en zon av subparallella kvartsgångar i
en magmatiskt lagrad gabbro. Markbundna totalfältsmätningar av magnetismen visar en negativ anomali över
malmzonen. I detta arbete har de magnetiska egenskaperna av området kring malmen, samt områden av gabbron
som är mindre eller inte alls påverkade av malmlösningar undersökts. Arbetet syftar till att fastställa vad som orsakar
anomalin. Detta arbete adresserar även tektoniska blockrörelser, vilket har observerats genom lutande lagring i
närheten av malmzonen. Termisk- och växelströmsavmagnetisering har utförts på prover som... (More)
En bergartsmagnetisk studie har utförts på en guldmineralisering som är belägen vid Åkerberg,
30 km Nordöst om Boliden, i norra Sverige. Mineraliseringen är bunden till en zon av subparallella kvartsgångar i
en magmatiskt lagrad gabbro. Markbundna totalfältsmätningar av magnetismen visar en negativ anomali över
malmzonen. I detta arbete har de magnetiska egenskaperna av området kring malmen, samt områden av gabbron
som är mindre eller inte alls påverkade av malmlösningar undersökts. Arbetet syftar till att fastställa vad som orsakar
anomalin. Detta arbete adresserar även tektoniska blockrörelser, vilket har observerats genom lutande lagring i
närheten av malmzonen. Termisk- och växelströmsavmagnetisering har utförts på prover som inhämtats från malmzonen
och mindre påverkade delar av gabbron. Utifrån dessa mätningar har olika vektorriktningar av NRM
(Naturlig Remanent Magnetisering) analyserats och en så kallad VGP (Virtual Geomagnetic Pole) har beräknats.
Ytterligare provundersökningar har varit susceptibilitet och termomagnetiska mätningar. Provernas mineralogiska
sammansättning har undersökts med ett svepelektronmikroskop samt genom konventionell mikroskopering, så som
i genomfallande och reflekterande ljus. Arbetet visar att magnetit som allmänt är ett av de vanligaste magnetiska
mineralen, förekommer mycket sparsamt i de mindre påverkade delarna av gabbron (Fågelberget 1), samt att magnetit
saknas i malmzonen och dess omgivning (Åkerberg 1 och Åkerberg 2). Det magnetiska mineralet i malmzonen
är istället monoklin magnetkis. Den magnetiska anomalin är orsakad av en mindre mängd monoklin magnetkis
i malmzonen jämfört med omgivande delar. Denna studie visar också att monoklin magnetkis i malmområdet, samt
i mindre påverkade delar av gabbro, fick sin nuvarande NRM vid samma tidpunkt. Tidpunkten när detta hände har
dock inte gått att fastställa då endast en VGP kunde beräknas. (Less)
Please use this url to cite or link to this publication:
author
Dahlenborg, Lars
supervisor
organization
alternative title
En bergartsmagnetisk studie av Åkerbergs guldgruva, norra Sverige
year
type
H1 - Master's Degree (One Year)
subject
keywords
NRM, gold ore, pyrrhotite, magnetite, Åkerberg, guldmalm, magnetkis, magnetit
publication/series
Dissertations in Geology at Lund University
report number
208
language
English
id
2338090
date added to LUP
2012-02-02 15:32:09
date last changed
2012-02-02 15:32:09
@misc{2338090,
  abstract     = {A rock magnetic study has been preformed of the Åkerberg gold deposit, located 30 km NE of Boliden
in northern Sweden. The gold mineralization is located to a zone of subparallel quartz veins in a layered gabbro.
Ground surveys show a lowering of the magnetic properties at the ore zone. This thesis addresses the factors causing
the anomaly by investigating the magnetic properties of different parts of the gabbro. The thesis is also concerned
with displacement of tectonic blocks, which is indicated by tilted magmatic layers in the immediate surroundings
of the ore zone. Thermal and alternating field demagnetization and susceptibility and thermomagnetic
measurements have been conducted on the samples collected at the ore zone and in distant parts relative to the ore
zone. ChRM-directions have been analyzed with principal component analyses and one Virtual Geomagnetic Pole
(VGP) was calculated. Mineral composition was examined with a Scanning Electron Microscope and conventional
microscopy in both transmitted and reflected light. This study shows that the sampled outcrop distant to the ore
zone is magnetite poor and that the gabbro lacks magnetite in the ore zone and in immediate surrounding areas. The
NRM (Natural Remanent Magnetization) in the ore zone is carried by monoclinic pyrrhotite. The magnetic anomaly
over the ore zone is caused by a lower amount of pyrrhotite compared to the surrounding areas. This study also
indicates that the NRM carried by monoclinic pyrrhotite in the ore zone and in the distant parts of the gabbro was
acquired during the same event. The timing of this event, however, is unclear since only one VGP could be calculated.},
  author       = {Dahlenborg, Lars},
  keyword      = {NRM,gold ore,pyrrhotite,magnetite,Åkerberg,guldmalm,magnetkis,magnetit},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {A rock magnetic study of the Åkerberg gold deposit, northern Sweden},
  year         = {2007},
}