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Metamorphosed and partially molten hydrothermal alteration zones of the Akulleq glacier area, Paamut gold province, South-West Greenland

Tebi, Magnus Asiboh LU (2011) In Dissertations in Geology at Lund University GEOR02 20112
Department of Geology
Abstract (Swedish)
Området kring akulleqglaciären ligger i närheten av bosättningen Paamiut, sydvästra Grönland.
Tonalit- trondhjemit och granodioritgnejser (TTG) utgör huvudlitologin i området. Inom TTG-gnejserna återfinns
ett cirka 1 km brett hästskoformat bälte av suprakrustala bergarter. Ultramafiska metamorfa bergarter utgör linser i
det suprakrustala bältet och pegamtiter intruderar de olika litologierna (Kolb, 2011). Kvartsådror förekommer i de
ovan beskrivna linserna samt i kontakter mellan dessa och TTG-gnejserna (Kolb, 2011). De metamorfa mafiska
bergarterna (metagabbro och amfibolit) har medelkornstorlek och innehåller hornblende, plagioklas och kvarts.
Kvartshalten är högre i metagabbron än amfiboliten och relikt klinopyroxen är... (More)
Området kring akulleqglaciären ligger i närheten av bosättningen Paamiut, sydvästra Grönland.
Tonalit- trondhjemit och granodioritgnejser (TTG) utgör huvudlitologin i området. Inom TTG-gnejserna återfinns
ett cirka 1 km brett hästskoformat bälte av suprakrustala bergarter. Ultramafiska metamorfa bergarter utgör linser i
det suprakrustala bältet och pegamtiter intruderar de olika litologierna (Kolb, 2011). Kvartsådror förekommer i de
ovan beskrivna linserna samt i kontakter mellan dessa och TTG-gnejserna (Kolb, 2011). De metamorfa mafiska
bergarterna (metagabbro och amfibolit) har medelkornstorlek och innehåller hornblende, plagioklas och kvarts.
Kvartshalten är högre i metagabbron än amfiboliten och relikt klinopyroxen är förekommande. Bergarterna
innehåller cm-stora, grovkorniga, leukokratiska fickor som består av plagioklas, kvarts, ± ortopyroxen samt
klinopryoxen. Dessa fickor tolkas vara bildade in situ.
Kvartsådrorna är vanligtvis omgivna av hydrotermala omvandlingshaloer. Mineralsammansättningen i de
omvandlade zonerna varierar mellan olika bergarter. Omvandlad metagabbro uppvisar epidot-serisit-kvarts-titanit ± biotit ± klinozoisit ± kalifältspat-amfibol-pyrit-kalkopyrit-pentlandit-arsenopyrit-pyrrhotit-sammansättning.
Omvandlade felsiska bergarter uppvisar en sammansättning bestående av kvarts, kalcit, klorit, kalifältspat,
saussurit, pyrit, kalkopyrit samt pyrrhotit. Partiell uppsmältning kan i vissa fall observeras i de omvandlade
zonerna, där de tidigare nämnda mineralsammansättningarna bildar granoblastiska kvartsfältspatiska, åderlika
morfologier. Sulfider är i huvudsak spridda inom mesosomen, med under 1 % inom det kvartsfältspatiska lagret. De
hydrotermala omvandlingszonerna är anrikade vad gäller hydratmineral. Därav kan det antagas att dessa lager har
varit utsatta för uppsmältning i en högre utsträckning under progradmetamorfos, jämfört icke omvandlade bergarter
i området. (Less)
Abstract
The Akulleq glacier area is located to the east of Paamiut settlement, South-West Greenland. Tonalite- trondhjemite- granodiorite (TTG ) gneiss constitute the main rock type with an approximately 1 km wide, horseshoe shaped supracrustal belt situated within the TTG gneiss. Meta- ultramafic rocks form lenses in the supracrustal belt and pegmatites intrude the different lithologies (Kolb, 2011). Quartz veins occur in the lenses of meta-gabbro, meta-ultramafic rock and supracrustal rocks and at their contacts with TTG gneiss (Kolb, 2011). The meta-mafic rocks (meta-gabbro and amphibolite) are medium-grained, comprising hornblende, plagioclase and quartz. The abundance of quartz in meta-gabbro is higher and relic clinopyroxene is observed in... (More)
The Akulleq glacier area is located to the east of Paamiut settlement, South-West Greenland. Tonalite- trondhjemite- granodiorite (TTG ) gneiss constitute the main rock type with an approximately 1 km wide, horseshoe shaped supracrustal belt situated within the TTG gneiss. Meta- ultramafic rocks form lenses in the supracrustal belt and pegmatites intrude the different lithologies (Kolb, 2011). Quartz veins occur in the lenses of meta-gabbro, meta-ultramafic rock and supracrustal rocks and at their contacts with TTG gneiss (Kolb, 2011). The meta-mafic rocks (meta-gabbro and amphibolite) are medium-grained, comprising hornblende, plagioclase and quartz. The abundance of quartz in meta-gabbro is higher and relic clinopyroxene is observed in places. The rocks contain cm-scale, coarse-grained leucocratic pockets that are composed of plagioclase, quartz, ±orthopyroxene and clinopyroxene that are interpreted as in situ melt pockets.
Usually, a hydrothermal alteration halo surrounds the quartz vein and the alteration assemblages vary with rocktype. The hydrothermal alteration assemblage in meta-gabbro contains epidote-sericite-quartz-titanite ± muscovite± biotite ± clinozoisite±K-feldspar-amphibole-pyrite-chalcopyrite-pentlandite-arsenopyrite-pyrrhotite. A quartz-calcite-chlorite-K feldspar-saussurite-pyrite-chalcopyrite-pyrrhotite alteration assemblage is developed in felsic rocks. These mineral assemblages are partially molten to form granoblastic quartzo-feldspathic veinlike morphology in places. Sulfides are mainly disseminated within the mesosome with less than 1% observed within the quartzo-feldspathic layer. The hydrothermal alteration zones show enrichment in hydrous minerals, thus, favour preferential melting in this domain compared to the unaltered rocks during prograde metamorphism as would be expected. (Less)
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author
Tebi, Magnus Asiboh LU
supervisor
organization
alternative title
Metamorfa och delvis smälta hydrotermala omvandlingszoner i området kring glaciären Akulleq, guldprovinsen Paamiut, sydvästra Grönland
course
GEOR02 20112
year
type
H2 - Master's Degree (Two Years)
subject
keywords
remobilized gold, South-West Greenland, Paamiut gold province, hydrothermal alteration, sulfide, Paamiut guldprovins, sydvästra Grönland, hydrotermal omvandling, sulfid
publication/series
Dissertations in Geology at Lund University
report number
292
language
English
additional info
External supervisor Jochen Kolb, forskningsprofessor, De Nationale Geologiske Undersøgelser for Danmark og Grønland - GEUS, Ø. Voldgade 10, 1350 Kbh. K, Danmark.
id
3021561
date added to LUP
2012-08-22 11:33:55
date last changed
2012-08-22 11:49:13
@misc{3021561,
  abstract     = {The Akulleq glacier area is located to the east of Paamiut settlement, South-West Greenland. Tonalite- trondhjemite- granodiorite (TTG ) gneiss constitute the main rock type with an approximately 1 km wide, horseshoe shaped supracrustal belt situated within the TTG gneiss. Meta- ultramafic rocks form lenses in the supracrustal belt and pegmatites intrude the different lithologies (Kolb, 2011). Quartz veins occur in the lenses of meta-gabbro, meta-ultramafic rock and supracrustal rocks and at their contacts with TTG gneiss (Kolb, 2011). The meta-mafic rocks (meta-gabbro and amphibolite) are medium-grained, comprising hornblende, plagioclase and quartz. The abundance of quartz in meta-gabbro is higher and relic clinopyroxene is observed in places. The rocks contain cm-scale, coarse-grained leucocratic pockets that are composed of plagioclase, quartz, ±orthopyroxene and clinopyroxene that are interpreted as [i]in situ[/i] melt pockets.
Usually, a hydrothermal alteration halo surrounds the quartz vein and the alteration assemblages vary with rocktype. The hydrothermal alteration assemblage in meta-gabbro contains epidote-sericite-quartz-titanite ± muscovite± biotite ± clinozoisite±K-feldspar-amphibole-pyrite-chalcopyrite-pentlandite-arsenopyrite-pyrrhotite. A quartz-calcite-chlorite-K feldspar-saussurite-pyrite-chalcopyrite-pyrrhotite alteration assemblage is developed in felsic rocks. These mineral assemblages are partially molten to form granoblastic quartzo-feldspathic veinlike morphology in places. Sulfides are mainly disseminated within the mesosome with less than 1% observed within the quartzo-feldspathic layer. The hydrothermal alteration zones show enrichment in hydrous minerals, thus, favour preferential melting in this domain compared to the unaltered rocks during prograde metamorphism as would be expected.},
  author       = {Tebi, Magnus Asiboh},
  keyword      = {remobilized gold,South-West Greenland,Paamiut gold province,hydrothermal alteration,sulfide,Paamiut guldprovins,sydvästra Grönland,hydrotermal omvandling,sulfid},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Metamorphosed and partially molten hydrothermal alteration zones of the Akulleq glacier area, Paamut gold province, South-West Greenland},
  year         = {2011},
}