The tectonics and mineralisation of the Black Angel Pb/Zn deposit, central West Greenland
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Carmichael, Andrew John. 1988. The tectonics and mineralisation of the Black Angel Pb/Zn deposit, central West Greenland. Doctoral thesis, Goldsmiths, University of London [Thesis]
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Text (The tectonics and mineralisation of the black angel Pb/Zn deposit, central west Greenland)
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Abstract or Description
The 13.5 M Tonne Black Angel Zn-Pb-A/J-Fe deposit at Marmorilik, West Greenland (71·10' N, 51· 045' W) consists of six massive, strata bound to discordant sulphide lenses hosted in poly-deformed, poly-metamorphosed evaporite bearing carbonates of the Early Proterozoic Upper Marmorilik Formation. This study is an analysis of the tectonics and mineralisation of the orebodies. The research programmed involved detailed and regional structural and stratigraphic mapping, section measuring, extensive underground mapping and sampling, logging of drill cores, detailed mineralogical and textural studies, and stable and lead isotopic analyses.
The deposits occur within the Karrat Group supracrustal sequence of the Mid-Proterozoic (1860 -1680 ma. )Rinkian mobile belt, an upper greenschist to granulite facies terrain composed of Archean and Early Proterozoic tectono-stratigraphic units. Four deformation phases have been recognised within the supracrustal of the Marmorilik and Nukavsak Formations. Three penetrative phases have been assigned to the polyphase Rinkian event end are namely, D1 - an early recumbent nappe phase, D2 - a south verging fold and slide phase and D3 - a sinistral sheer event. Peak metamorphic conditions of upper greenschist facies in the mine area were attained after this deformation, which was succeeded by an extensional D4 deformation (Late Precambrian) associated with dolerite dyke intrusion.
The mineralisation occurs as folded and boudinage massive sulphide lenses within a narrow, highly deformed. east-west trending mineralised corridor in the Marmorilik Formation carbonates. The ores consist of tectonised, metamorphosed and recrystalised medium to coarse grained sphalerite, galena, pyrite, pyrrhotite and chalcopyrite with subordinate tennantite and arsenopyrite. Primary void-fill (marcasite/early pyrite) textures occur in metamorphic pyrite grains. Intense shearing at the ore host rock contacts has produced discordant relationships and the inclusion of rafted calcites marble and pelitics clasts, quartz eyes and fluorite vein fragments within the sulphides. Ten types of ore tectonites have been recognised and these have been classified, according to their mineralogy and texture, Into four distinct ore facies associations. The ore facies associations are related to particular deformation structures. Those belonging to D1 and D3 are the most significant. D1 produced large ENE-WNW trending recumbent overfolds and thickening of the ore lenses and D3 gave rise to ESE-WNW trending per inclines with substantial ore thickening and remobilisation in the fold hinge regions.
Lead isotope analyses on galenas from the deposits end surrounding carbonate hosted mineralisation indicate strongly homogenised ‘orogen' to upper crustal leads. Minor changes in the ore lead source are possible indicated by a bimodal distribution of the data. Stable carbon, oxygen and sulphur isotope analyses on the sulphides and carbonate host material gave homogenised results indicative of a strong metamorphic over print S-isotope geotherm mometry on sphalerite galena pairs gives a temperature of 470 ℃ for the D3 deformation.
The geological setting, mineralogical associations and primary textural features of the Black Angel deposit indicates that they were probably formed as stratabound Mississippi Valley Type massive sulphdie ores which were subsequently highly deformed and metamorphosed such that primary depositional, textural and isotopic signatures are no longer preserved.
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Item Type: |
Thesis (Doctoral) |
| Identification Number (DOI): |
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| Keywords: |
mineralisation, Black Angel Pb/Zn deposit, orebodies, regional structural and stratigraphic mapping, isotopic analyses |
| Date: |
June 1988 |
| Item ID: |
33732 |
| Date Deposited: |
05 Jul 2023 14:51 |
| Last Modified: |
08 Aug 2023 13:00 |
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URI: |
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