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Skaergaard Intrusion |
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Greenland |
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Au PGE PGM Pt Pd
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Super Porphyry Cu and Au
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The Skaergaard layered gabbroic intrusion is of Tertiary age and is located in Eastern Greenland.
The east coast of Greenland is a volcanic rifted margin characterised by voluminous igneous activity. The progressively younger magmatism has been divided into:
i). Lower Basalts, up to 2 km thick of tholeiites, olivine tholeiites, picrites & ankaramites;
ii). Plateau Basalts - >5 km of olivine tholeiites and tholeiites representing perhaps a volume of 10 million cubic km.;
iii). Layered gabbros and related dykes, which includes the Skaergaard Intrusion; and
iv). Wehrlites and related rocks.
The Skaergaard Intrusion is a layered gabbro. Mineralisation occurs within a 150 m thick layered succession of leucocratic and melanocratic gabbros in the upper part of the Middle Zone of the intrusion. The upper 100 m of the generally olivine free Middle Zone includes three prominent layers of macro-rhythmic leucogabbro known as the "Triple Group", the upper part of which contains large euhedral liquidus olivines.
The precious metal mineralisation is found in a 70 m interval starting 14 m below the lowest leucogabbro band and contains at least 10 levels (each a few tens of centimetres to several metres thick) of significant Pd & Pt enriched layered leucocratic and melanocratic gabbro, separated by PGE and Au poor gabbro. These intervals are concordant with the modal layering of the intrusion. Each has a chemical zonation outwards from the centre of the intrusion with decreasing Pt:Pd ratios (due to the increase in Pd), followed by a strong increase in Au, before both Au and PGE's drop off. The mineralised zones take the form of a series of stacked saucers of PGE mineralisation, with a gold outer annulus. The diameter of these "saucers" decrease upwards.
The main mineralised zone is referred to a s the Platinova Reef.
The gold resource has been quoted at 40 Mt @ 2.38 g/t Au and >100 Mt @ 1.9 g/t Au.
PGE grades of up to 3 g/t Pd (Pt:Pd ratio of around 0.1) have been encountered over widths of 10 m.
In addition to the Skaergaard Intrusion, there are a number of other Palaeogene intrusions in the area related to the same magmatic event, many with associated mineralisation, including the gabbroic Kap Edvard Holm Intrusion, the Kaerven Gabbro Complex, the large syenitic Kangerlussuaq Alkaline Complex, and the dioritic Circe 1320 complex, together with a range of mafic to alkaline dykes (Nielsen 1978). A distinct set of large gabbroic dykes or 'macrodykes', with typical widths of around 100 to 500 m, are exposed in the area around the Skaergaard intrusion, including the Miki Fjord (e.g. Blichert-Toft et al., 1992), Vandfalsdalen (e.g. White et al., 1989), Kraemer Island (Momme and Wilson 2002), Kangerlussuaq (Holm et al., 2006) and the Togeda Macrodykes. Two of these macrodykes, Miki Fjord and Togeda, contain Cu-PGE-Au sulphide mineralisation along their margins. Sulphides occur as disseminated interstitial blebs and rounded globules of chalcopyrite and pyrrhotite with some Fe–Ti oxides and platinum-group minerals, comprising largely Pd bismuthides and tellurides.
The most recent source geological information used to prepare this decription was dated: 1995.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Andersen J C O, 2007 - Postmagmatic sulphur loss in the Skaergaard Intrusion: Implications for the formation of the Platinova Reef: in Lithos v92 pp 198-221
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Andersen J C O, Rasmussen H, Nielsen T F D, Ronsbo J G 1998 - The Triple Group and the Platinova Gold and Palladium Reefs in the Skaergaard intrusion: stratigraphic and petrographic relations: in Econ. Geol. v93 pp 488-509
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Andersen, J.C.O. Rollinson, G.K.,McDonald, I., Tegner, C. and Lesher, C.E., 2017 - Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland: in Mineralium Deposita v.52, pp. 929-942.
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Ernst R.E., Liikane D.A., Jowitt S.M., Buchan K.L. and Blanchard, J.A., 2019 - A new plumbing system framework for mantle plume-related continental Large Igneous Provinces and their mafic-ultramafic intrusions: in Journal of Volcanology and Geothermal Research, v.384, pp. 75-84. doi.org/10.1016/j.jvolgeores.2019.07.007.
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Holwell D A and Keays R R, 2014 - The Formation of Low-Volume, High-Tenor Magmatic PGE-Au Sulfide Mineralization in Closed Systems: Evidence from Precious and Base Metal Geochemistry of the Platinova Reef, Skaergaard Intrusion, East Greenland : in Econ. Geol. v.109 pp. 387-406
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Mungall, J.E., Jenkins, M.C., Robb, S.J., Yao, Z. and Brenan, J.M., 2020 - Upgrading of magmatic sulfides, revisited: in Econ. Geol. v.115, pp. 1827-1833.
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Nielsen T F D 2004 - The Shape and Volume of the Skaergaard Intrusion, Greenland: Implications for Mass Balance and Bulk Composition: in J. of Petrology v45 pp 507-530
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Nielsen T F D, Brooks C K 1995 - Precious metals in magmas of east Greenland: factors important to the mineralization in the Skaergaard intrusion: in Econ. Geol. v 90 pp 1911-1917
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Wernette, B., Li, P. and Boudreau, A., 2020 - Sulfides, native metals, and associated trace minerals of the Skaergaard intrusion, Greenland: evidence for late hydrothermal fluids: in Mineralium Deposita v.55, pp. 1197-1214.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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