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Malmbjerg, Mellempas, Flammefjeld |
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Greenland |
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Mo
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Malmbjerg and Mellempas porphyry molybdenum deposits are associated with the alkaline Werner Bjerge Complex at about 72°N, while the Flammefjeld deposit is associated with the large Kangerlussuaq Alkaline Complex at about 68°N, all three of which are on the rifted continental margin of East Greenland, close to the present day coast.
The East Greenland volcanic rifted margin was formed during the Paleogene continental breakup above the ancestral Iceland mantle plume, accompanied by massive outpourings of plateau basalts, intrusion of major gabbroic and felsic plutons, and the emplacement of a huge coast-parallel dyke swarm. This magmatic activity was largely concentrated in three periods: 62 to 59, 57 to 54, and around 50 to 47 Ma although it is now known to have continued with a distinctly youger component also.
The Werner Bjerge Complex represents a large subvolcanic complex composed of alkali gabbros, granites, and both under- and over-saturated syenites, and is one of a line of such complexes trending obliquely both to the continental margin and to the main faults and structural lineaments of the area. This complex was intruded into Carboniferous country rocks. In places it can be seen to be overlain by a preserved volcanic roof of predominantly feldspar porphyries. The Malmbjerg granite stock (dated at between 26.0 ±1.1 to 21.1 ±0.9 Ma) and its mineralised carapace outcrops a few kilometers west of the main Werner Bjerge Complex and thus cannot be directly related to the main complex.
The Malmbjerg deposit contains three lithological units: i). An uppermost perthite granite with a quartz-feldspar porphyry roof, which, along with the adjacent sediments, contains most of the molybdenite mineralization; ii). The perthite granite is intruded by a porphyritic aplite; iii). Lowest is a third porphyry type having two textural varieties distinguished by the nature and form of their phenocrysts. Three types of mineralisation are recognised: i). A network of veins containing molybdenite, forming a zone in the uppermost part of the stock with the shape of an inverted bowl; ii). greisen mineralisation in flat-lying veins; and iii). minor base metal mineralisation in vertical, argillised fracture zones.
The Mellempas molybdenite mineralisation, occurs within the Werner Bjerge Complex, is less well explored and believed to be of lesser economic importance. It is associated with a biotite granite body which cuts other rocks of the complex.
Flammefjeld, about 500 km south of Malmbjerg, comprises volcanic breccias and quartz porphyries that cut the syenites of the 800 sq. km Kangerlussuaq intrusion. The mineralised body is concealed and has not been drilled out. It is represented by up to 1 m size blocks contained within an igneous breccia pipe. These blocks are of various granitic rocks, including quartz-feldspar porphyry and aphanitic granophyre containing an intense stockwork of
quartz and molydenite-bearing fractures. The breccia complex has dimensions of around 500x800 m and includes dykes of aplite, rhyolite and quartz-feldspar porphyry, as well as more mafic rocks. The breccia pipe is interpreted to have transported the molydenite-bearing blocks from an underlying classic porphyry molybdenum deposit.
Dating of mineralisation at Malmbjerg and Flammefjeld has yielded ages of between 25.8 ±0.1 and 39.6 ±0.1 Ma,
Malmbjerg has an estimated mineral resource of 150 Mt @ 0.23% MoS2.
For detail consult the reference(s) listed below.
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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Selected References:
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Brooks C K, Tegner C, Stein H and Thomassen B, 2004 - Re-Os and 40Ar/39Ar Ages of Porphyry Molybdenum Deposits in the East Greenland Volcanic-Rifted Margin: in Econ. Geol. v99 pp 1215-1222
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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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