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GEOLOGY and ORE 8 / 2007 1960S and Was Related to a Suite of Disko Norites in West Greenland

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GEOLOGY and ORE 8 / 2007 1960S and Was Related to a Suite of Disko Norites in West Greenland GO_08.qxp 23/02/07 13:16 Page 1 The PGE potential in Greenland No. 8 - February 2007 GO_08.qxp 23/02/07 13:16 Page 2 The PGE potential in Greenland The potential for Platinum Group Elem- ent (PGE) resources in Greenland is clear and encompasses mineralisation in Precambrian to Palaeogene envi- ronments. The PGE potential in Green- land attracted interest already in the 1960s and has been part of the Survey’s considerations since the 1970s . The corporate interest in PGE tar- gets in Greenland was initiated by Hammer Dal Kryolitselskabet Øresund in the early GEOLOGY AND ORE 8 / 2007 1960s and was related to a suite of Disko norites in West Greenland. Platinomino A/S was established in 1968 to search Kangerlussuaq/ Skaergaard for Merensky Reef type deposits in SSillisissanguitillisissanguit the Fiskenæsset Complex. In the late Fiskefjord NunaatNunaat 1980s, Platinova Resources prospected Tasiilaq known PGE indications in Amitsoq peri- Qeqertarsuatsiaat dotites in southern Greenland. Since (Fiskenæsset) Index map of localities on Greenland. 1995 norites in the Tasiilaq region, East Greenland have been the target Amitsoq for Cu-Ni-PGE exploration by several companies. In 2005 NunaMinerals ini- tiated PGE exploration in the mafic intrusions of the Fiskefjord area. In Belt; a suite of leuconorite and gabbro rocks the 1980s GEUS and university groups in irregular bodies with traces of PGEs re- Archaean and Palaeo- focused on the formation of massive lated to Ni-Cu-sulphide mineralisation. proterozoic settings sulphides in the Palaeogene basalts of Within the same region, large ultramafic Disko Island, which has led to contin- bodies and mafic layered complexes locally Fiskenæsset anorthosite complex: ued exploration for Noril´sk type min- show traces of PGE-mineralisation. The Chromitite layered anorthosite intrusion. eralisations. Renewed academic stud- Proteroizoic Ammassalik Belt on the East ies and exploration by Platinova coast of Greenland hosts a suite of norites The Archaean Fiskenæsset anorthosite com- Resources in the classic Skaergaard to which are related massive sulphide oc- plex, with a strike length of > 200 km, is intrusion (East Greenland) resulted in currences, potentially PGE-bearing. hosted in high grade tonalitic gneiss. The 1987 in the discovery of a reef-type, Palaeogene Ni-sulphide occurrences with complex is named after the village Fiske- world class PGE deposit. potential PGE concentrations are known in næsset/Qeqertarsuatsiaat. The floor of the the West Greenland Basalt Province. Ex- intrusion has not been identified, but the ploration has been carried out for more roof found immediately below flows of than a century in the Disko Bay region. mafic pillow lava. A detailed stratigraphy Geological environment Known occurrences are mainly hosted in shows a succession with a lower gabbro for PGEs presumably contaminated lavas, and in unit followed by an ultramafic unit with dykes at the base of the volcanic succes- mineral-graded dunites, peridotites and Traces and showings of PGE mineralisation sion. Only reconnaissance investigations hornblendites. These are followed by a are numerous in the Precambrian terrains have been performed in similar environ- lower leucograbbro unit with minor ultra- of Greenland. The Archaean of south-west ments in East Greenland. mafic layers and a middle gabbro unit Greenland hosts anorthositic suites, like The main focus of PGE exploration in with minor layers of anorthosite and ultra- the reworked Fiskenæsset complex (south the Palaeogene of East Greenland has been mafics and peridotites (hornblende-ortho- of Nuuk). The complex hosts accumulation the layered mafic intrusions in which many pyroxene-spinel). Above these units follow of chromite in anorthosite, and traces of mineralisations have been located, includ- the upper leucogabbro unit with abundant PGE mineralisation in Ni-sulphide segrega- ing the Kap Edvard Holm complex and the chromitite bands, an anorthosite unit and tions in amphibolite. The Archaean shield world class Platinova Reef within the Skaer- the upper gabbro unit. The complex has north of Nuuk hosts the Maniitsoq Norite gaard intrusion. been repeatedly deformed and metamor- 2 GO_08.qxp 23/02/07 13:16 Page 3 THE PGE POTENTIAL IN GREENLAND Chromitite banded anorthosites from the Fiskenæsset anorthosites complex, southern West Greenland. Photo: GEUS. phosed under amphibolite – and locally granulite facies conditions. Exploration PGE exploration has been limited. In the 1970s Platinomino A/S searched for Meren- sky type platinum deposits. The impetus was the discovery of an approx. 1 metre wide bronzitite layer with discrete chromite banding. The bronzitite contains minor nickel sulphides. Assays gave very promis- ing results of up to 0.6 ppm Pt and 3 ppm Pd which, however, could not be confirmed. In 1980 study of one stratigraphical section in the anorthosite complex showed that PGEs are concentrated mainly in ultra- mafic lithologies and chromitites. The lat- ter contain up to 310 ppb Pt, 175 ppb Pd and 220 ppb Rh. Similar concentrations also occur in anorthosites and leucogab- bros rich in disseminated sulphides. In 1991 GEUS resampled the bronzitite and a few other parts of the anorthosite complex. The bronzitite gave 74 ppb Pt and 115 ppb Pd. In other parts of the anortho- Bronzitite layer in anorthosites from the Fiskenæsset anorthosites complex, southern West site complex, several-hundred-metre-thick Greenland. Photo: GEUS. 3 GO_08.qxp 23/02/07 13:16 Page 4 THE PGE POTENTIAL IN GREENLAND Carbonatite 52° Norite Finnefjeld gneis q Gneis undifferentiated to sor S. I Fault Sketch map of the West Greenland Norite Belt. Sukkertoppen suats rs iaq Geotectonic setting e s a T The Norite Belt is located along the east- ia g n ern flank of the dome of the Finnefjeld a K gneiss complex. The structure of the belt GEOLOGY AND ORE 8 / 2007 seems controlled by the 3034 Ma old Finnefjeld gneiss. The norites appear little affected by the high grade retrograde metamorphism observed in the surround- 15 km ing basement. The Norite Belt can be 65° 52° 65° divided in a northern part characterised by few large norite bodies and a southern lenses of ultrabasites with small amounts The bodies vary in size from 2 x 4 km down part of several, but smaller bodies and of sulphide have been found. Some have to 10 x 20 m. They are predominantly com- pods of norite. been chip and channel sampled. The best posed of gabbronorite and leucogabbro, The age of the Norite Belt is uncertain, results so far are 83 ppb Pt and 693 ppb collectively referred to as norite. Primary but is probably around 3.0 Ga. Post-kine- Pd, average over 2 metres. An ultramafic textures, such as igneous layering, are local- matic diorite intrusions in the Niaqunngu- sheet near the bronzitite unit yielded 68 ly preserved. Elevated Ni, Cu and PGE con- naq/Fiskefjord region (south of the Norite ppb Pt and 361 ppb Pd over 1 metre. centrations are found in sulphide showings Belt) are tentatively correlated to the Norite of apparently magmatic origin. The sul- Belt. The diorites are 2975 ± 13 Ma old. phides may show some degree of meta- Sillisissanguit Nunaat - morphic remobilisation. Exploration Maniitsoq Norite Belt: The norite rocks are very homogeneous The norite bodies have been targets for Mafic intrusions and amphibolite layers. bodies with rare igneous banding composed exploration since 1965, but only a few of alternating layers of plagioclase and hyp- PGE analyses are available from the early The Norite Belt (15 x 75 km) is located east ersthene with accessory chromite. Amphi- exploration. Kryolitselskabet Øresund A/S of Maniitsoq and hosts a suite of irregular bolite layers are locally associated to the reported a typical Ni:Pd+Pt ratio in sul- bodies of basic rocks intruding into the norites. phide mineralisation of 50 000:1. New regional gneiss complex of the Akia terrane. analyses from 2001 gave: Igneous layering in a norite body from the West Greenland Norite Belt, Typical weathered surface of a norite boulder from the West Greenland Sillissisanguit nunat. Photo: GEUS. Norite Belt, Sillissisanguit nunat. Photo: GEUS. 4 GO_08.qxp 23/02/07 13:16 Page 5 THE PGE POTENTIAL IN GREENLAND Rustzone enriched in PGE (Σ 2.8 ppm) in an amphibolitic sequence along the eastern flank of the West Greenland Norite Belt. Photo:GEUS. • Peak values for Pd of 0.6 ppm in three No economic deposit has been located, the predominant mineral accompanied by sulphide-bearing samples of norite and despite the common occurrence of sul- chalcopyrite, pyrite and pentlandite in a amphibolite, and of 0.2–0.4 ppm in phide accumulations. The mineral assem- primary texture together with pyrite, lin- five sulphide-bearing samples of norite blage is rather uniform, with pyrrhotite as neaite, bravoite and magnetite in replace- and amphibolite. • A peak value for Pt of 2.2 ppm in one sample and of 0.7 ppm in four sam- ples, all from heavily mineralised and altered gabbro and amphibolite related to the norites. Five samples of miner- alised norite showed concentrations of 0.2–0.6 ppm. • Four mineralised samples show a total PGE (Pd+Pt) of 1.0–2.7 ppm Mineralisation and associated rock types Elevated PGE numbers are found in norites and amphibolites related to zones enriched in sulphides. Rust zones and gos- sans identify zones enriched in sulphides. The sulphides occur as disseminations, veinlets, interstitial fillings and as more massive lenses. The showings are general- ly a few tens of metres long. The sulphide Slope with weathered dunite from the Fiskevandet region, southern West Greenland. Photo: occurrences show an uneven distribution. NunaMinerals A/S. 5 GO_08.qxp 23/02/07 13:16 Page 6 THE PGE POTENTIAL IN GREENLAND GEOLOGY AND ORE 8 / 2007 Drilling in dunite by NunaMinerals A/S in the Fiskevandet region, southern West Greenland.
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