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Nalunaq |
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Greenland |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Nalunaq gold deposit is located in the Nanortalik district near the southern tip of Greenland.
It is a Palaeoproterozoic age, mesothermal vein deposit, hosted by mafic rocks which ave been metamorphosed to amphibolite-facies . Gold mineralisation is associated with sheeted quartz veins which outcrop sporadically over an interval of more than 2 km and lie within a large-scale shear structure, which is apparently related to regional thrusts. The shear zone is slightly discordant to layering of the metapillows and metadolerites in the volcanic package.
The most pronounced mineralised structures are zones of intense deformation with evidence of ductile shearing surrounded by brittle margins. The Main Vein is hosted in a narrow ductile shear zone with a constant orientation, having an overall strike of 45 to 50° and an average dip of 36° SE. Locally, the structure undulates somewhat, and dips measured in the face of the adits vary between 22 and 45°.
The bulk of the gold mineralisation is hosted by quartz veins, occurring principally as sheeted veins with stripes and bands of included calcsilicates. These quartz veins range in width from 0ˇ05 to 1ˇ8 m and form a relatively continuous structure, often with pinch and swell structures, with clear evidence of both compressive and dilational post-mineralisation deformation within the mineralised structure. There is no simple relationship between gold grade and thickness of the quartz veins, possibly due to post-mineralisation deformation.
The main mineralised quartz vein is almost always associated with a pronounced calcsilicate alteration zone of between 0ˇ2 and 0ˇ5 m in width, on one or both sides of the vein. The alteration selvage is normally only poorly mineralised, although where very high grade gold is present in the vein, the alteration zone may also sporadically carry significant amounts of gold. A very low sulphide content characterises the mineralised quartz vein and the immediate country rock, generally comprising less than 1% as pyrite, pyrrhotite, arsenopyrite, lollingite and chalcopyrite (roughly in order of abundance) with gold and electrum, scarce Bi-sulphosalts, covellite and galena. The gangue mineralogy is dominated by amphibole, plagioclase feldspars, quartz and clinopyroxene.
Gold is primarily (97%) present as free gold and is more prolific at the contacts between the quartz and the calcsilicate altered host rock, or included slivers of it, although there it displays a high nugget effect. The gold grains occur predominantly as inclusions in silicate minerals (7299ˇ9%), interstitial to silicates (027ˇ5%), inclusions in sulphides that are locked in silicates (06ˇ7%), and inclusions in sulphides (02ˇ9%). The deposit is characterised by high grades (up to 5240 g/t Au over 0ˇ8 m).
Drilling by 2004 had defined defined a resource 0.484 Mt @ 25ˇ5 g/t gold in measured and indicated
resources, equivalent to 12.3 t of contained gold. In addition, 0.281 Mt with 20ˇ3 g/t of inferred
resources were identified in areas immediately adjacent to the developed mineralised zones at Nalunaq.
The most recent source geological information used to prepare this decription was dated: 2004.
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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Bell, R.-M., Kolb, J., Waight, T.E., Bagas, L. and Thomsen, T.B., 2017 - A Palaeoproterozoic multi-stage hydrothermal alteration system at Nalunaq gold deposit, South Greenland: in Mineralium Deposita v.52, pp. 383-404.
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Grammatikopoulos T A, Porritt L, Petersen J S and Christensen K, 2004 - Mineralogical characterisation and process mineralogy of gold-bearing rocks from the Nalunaq gold deposit, Greenland: in Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc. v113 pp B197-203
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