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Borrkärnekartering av en Zn-Ag-Pb-mineralisering vid Stenbrånet, Västerbotten

Åkerman, Jonas (2007) In Examensarbeten i geologi vid Lunds universitet
Department of Geology
Abstract (Swedish)
Stenbrånet är ett område strax väster om Bastuträsk i utkanten av gruvdistriktet Skelleftefältet i
Västerbotten, norra Sverige. Tidigare undersökningar gjorda av Boliden Mineral AB har visat på förekomst av en
skivformad kropp kraftigt anrikad på Zn, Ag och Pb. Studier av tunnslip och borrkärnor som karterats i detta arbete
visar på en decimeter- till metertjock sulfidhorisont med kraftig impregnation av zinkblände och/eller magnetkis
som lokalt övergår till att bli massiv.
Kartering av borrkärnor längs fyra profiler bekräftar tidigare utförda studier avseende bergartsrelationer. Området
domineras av en gnejsig bergart, Sikträskgranitoiden, som är flankerad av kraftigt regionalmetamorfoserade suprakrustalbergarter
som i sin tur... (More)
Stenbrånet är ett område strax väster om Bastuträsk i utkanten av gruvdistriktet Skelleftefältet i
Västerbotten, norra Sverige. Tidigare undersökningar gjorda av Boliden Mineral AB har visat på förekomst av en
skivformad kropp kraftigt anrikad på Zn, Ag och Pb. Studier av tunnslip och borrkärnor som karterats i detta arbete
visar på en decimeter- till metertjock sulfidhorisont med kraftig impregnation av zinkblände och/eller magnetkis
som lokalt övergår till att bli massiv.
Kartering av borrkärnor längs fyra profiler bekräftar tidigare utförda studier avseende bergartsrelationer. Området
domineras av en gnejsig bergart, Sikträskgranitoiden, som är flankerad av kraftigt regionalmetamorfoserade suprakrustalbergarter
som i sin tur överlagras av postmetamorfa graniter av Revsundstyp. De suprakrustala enheterna består
av kraftigt förgnejsade till migmatiserade vulkaniter och sediment med spår av sulfider (främst magnetkis och
pyrit). Det förekommer även metertjocka granitiska skivor (leukosom) av Skellefte-Härnötyp. Sulfidhorisonten har
antagits finnas i kontakten mellan vulkaniterna och sedimenten, men existensen av en sådan kontakt har inte bekräftats
i denna studie.
De profiler som konstruerats utifrån borrkärnekartering visar att samtliga litologier stupar in mot Sikträskgranitoiden
och bildar en domlik geometri. Sulfidhorisontens lutning stämmer väl överens med den allmänna lagerföljden i
området. Den övergripande stupningen av sulfidhorisonten, gnejsigheten och kontakten mot Revsundsgraniten är
cirka 30º ut från Sikträskdomen.
Mina resultat baserade på kartering och tunnslipsstudier indikerar följande geologiska historia: 1. Avsättning av
sediment och vulkaniter (1.90-1.88 Ga), 2. intrusion av Sikträskgranitoiden (1.88 Ga), 3. regionalmetamorfos (1.88-
1.80 Ga) och slutligen 4. intrusion av Revsundsgranit (1.80-1.78 Ga).
Mineraliseringen har troligen bildats antingen som ett remobilisat av en äldre mineralisering eller som en koncentration
av de metaller som fanns i sedimenten. Metamorfosen har sedan mobiliserat fluider som löst upp metaller
och transporterat dessa till kontakten mellan vulkaniterna och sedimenten, där den kemiska skillnaden mellan bergarterna
har varit tillräcklig för att fälla ut metallerna. (Less)
Abstract
Stenbrånet i situated west of Bastuträsk at the margin of the Skellefte mining district in Västerbotten,
northern Sweden. Previous investigations carried out by Boliden Mineral AB reveal a disc-shaped orebody highly
enriched in Zn, Ag and Pb. Studies of thin sections and mapping of drill cores verify the existence of a dm- to mthick
sulphide horizon with a high impregnation of sphalerite and/or pyrrhotite which locally occurs as massive
sulphide.
Mapping of drill cores along four transects show the relation between various rock units at depth. The area is dominated
by a gneissic rock, the Sikträsk granitoid, which is flanked by highly regional metamorphosed supracrustal
rocks which are stratigrafically covered by postmetamorphic... (More)
Stenbrånet i situated west of Bastuträsk at the margin of the Skellefte mining district in Västerbotten,
northern Sweden. Previous investigations carried out by Boliden Mineral AB reveal a disc-shaped orebody highly
enriched in Zn, Ag and Pb. Studies of thin sections and mapping of drill cores verify the existence of a dm- to mthick
sulphide horizon with a high impregnation of sphalerite and/or pyrrhotite which locally occurs as massive
sulphide.
Mapping of drill cores along four transects show the relation between various rock units at depth. The area is dominated
by a gneissic rock, the Sikträsk granitoid, which is flanked by highly regional metamorphosed supracrustal
rocks which are stratigrafically covered by postmetamorphic granites of Revsund type. The supracrustal rocks are
composed of highly gneissic to migmatitic volcanics and sediments with traces of sulphides (mainly pyrrhotite and
pyrite). There are also abundant metre-thick granitic layers (leucosome) of the Skellefte-Härnö suite in the supracrustals.
The sulphide horizon has been assumed to exist along the contact zone between the volcanics and the
sediments, but the existence of this contact has not been found in this work.
The profiles based on drill core mapping show that all lithologies dip towards the Sikträsk granitoid forming a
dome-like geometry. The dip of the sulphide horizon agrees well with the general structural layering in the area.
The dip of the sulphide horizon, the gneissosity and the contact to the Revsund suite is approximately 30º out from
the Sikträsk dome.
My results from drill-core mapping and studies of thin sections indicate the following geologic history: 1. Deposition
of sediments and volcanics (1.90-1.88 Ga), 2. the intrusion of the Sikträsk granitoid (1.88 Ga), 3. regional
metamorphism (1.88 Ga) and, finally, 4. intrusion of the Revsund suite (1.80-1.78 Ga).
The mineralization has probably been formed either by a remobilized older mineralization or as a concentration of
the metals already in the sediments. The metamorphosis have then mobilized fluids which have soluted the metals
and transported them to the contact between the volcanics and the sediments, where the chemical difference between
the units has been enough to deposit the metals. (Less)
Please use this url to cite or link to this publication:
author
Åkerman, Jonas
supervisor
organization
alternative title
Mapping of drill cores in a Zn-Ag-Pb-mineralization in Stenbrånet, Västerbotten
year
type
H1 - Master's Degree (One Year)
subject
keywords
Zn, Stenbrånet, Sikträsk, migmatit, Revsundsgranit, borrkärnskartering, migmatite, Revsund granite, drill core mapping
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
213
funder
Boliden Mineral AB
language
Swedish
id
2335534
date added to LUP
2012-01-31 16:17:12
date last changed
2012-01-31 16:17:12
@misc{2335534,
  abstract     = {Stenbrånet i situated west of Bastuträsk at the margin of the Skellefte mining district in Västerbotten,
northern Sweden. Previous investigations carried out by Boliden Mineral AB reveal a disc-shaped orebody highly
enriched in Zn, Ag and Pb. Studies of thin sections and mapping of drill cores verify the existence of a dm- to mthick
sulphide horizon with a high impregnation of sphalerite and/or pyrrhotite which locally occurs as massive
sulphide.
Mapping of drill cores along four transects show the relation between various rock units at depth. The area is dominated
by a gneissic rock, the Sikträsk granitoid, which is flanked by highly regional metamorphosed supracrustal
rocks which are stratigrafically covered by postmetamorphic granites of Revsund type. The supracrustal rocks are
composed of highly gneissic to migmatitic volcanics and sediments with traces of sulphides (mainly pyrrhotite and
pyrite). There are also abundant metre-thick granitic layers (leucosome) of the Skellefte-Härnö suite in the supracrustals.
The sulphide horizon has been assumed to exist along the contact zone between the volcanics and the
sediments, but the existence of this contact has not been found in this work.
The profiles based on drill core mapping show that all lithologies dip towards the Sikträsk granitoid forming a
dome-like geometry. The dip of the sulphide horizon agrees well with the general structural layering in the area.
The dip of the sulphide horizon, the gneissosity and the contact to the Revsund suite is approximately 30º out from
the Sikträsk dome.
My results from drill-core mapping and studies of thin sections indicate the following geologic history: 1. Deposition
of sediments and volcanics (1.90-1.88 Ga), 2. the intrusion of the Sikträsk granitoid (1.88 Ga), 3. regional
metamorphism (1.88 Ga) and, finally, 4. intrusion of the Revsund suite (1.80-1.78 Ga).
The mineralization has probably been formed either by a remobilized older mineralization or as a concentration of
the metals already in the sediments. The metamorphosis have then mobilized fluids which have soluted the metals
and transported them to the contact between the volcanics and the sediments, where the chemical difference between
the units has been enough to deposit the metals.},
  author       = {Åkerman, Jonas},
  keyword      = {Zn,Stenbrånet,Sikträsk,migmatit,Revsundsgranit,borrkärnskartering,migmatite,Revsund granite,drill core mapping},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {Borrkärnekartering av en Zn-Ag-Pb-mineralisering vid Stenbrånet, Västerbotten},
  year         = {2007},
}