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Paper Number: 1906 Metallogeny of Arctic Norway Sandstad, J.S.1, Bjerkgård, T.1, Ihlen, P.M.1, Henderson, I.H.C.1, Melezhik, V.A.1, Torgersen, E.1 and Viola, G.1,2

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Paper Number: 1906 Metallogeny of Arctic Norway Sandstad, J.S.1, Bjerkgård, T.1, Ihlen, P.M.1, Henderson, I.H.C.1, Melezhik, V.A.1, Torgersen, E.1 and Viola, G.1,2 Paper Number: 1906 Metallogeny of Arctic Norway Sandstad, J.S.1, Bjerkgård, T.1, Ihlen, P.M.1, Henderson, I.H.C.1, Melezhik, V.A.1, Torgersen, E.1 and Viola, G.1,2 1Geological Survey of Norway, N-7491 Trondheim, Norway. [email protected] 2Department of Geology and Mineral Resources, Norwegian University of Science and Technology, N-7491 Trondheim, Norway ___________________________________________________________________________ The Geological Survey of Norway has over the last five years carried out a mapping programme; "Mineral Resources in North Norway" (MINN). The programme is aimed at improving the basic geological information relevant to the assessment of the mineral potential in the three northernmost counties. The metallogeny of the area is discussed with emphasis on the new results from MINN. The bedrock geology of Northern Norway comprises Archaean to Palaeoproterozoic basement rocks of the Fennoscandian Shield overthrusted by Caledonian nappes in the Silurian. The nappe units comprise Archaean to Palaeozoic metasedimentary and meta-igneous rocks derived from Baltica, micro- continents outboard of Baltica, and from Laurentia. Neoarchaean (ca. 2.8 Ga) banded iron formations have been mined for over 100 years in the northeastern part of Norway, in the Bjørnevatn area, close to the Russian border. More than 200 Mt of ores grading ca. 30 % Fe (magnetic) have been mined, while the total resources are estimated to be over 500 Mt. The mines are currently under care and maintenance. The quartz-magnetite banded formations (BIF) are interpreted as exhalative sedimentary ores hosted by a basaltic sequence. Following the rifting of the Archaean craton, Palaeoproterozoic volcano-sedimentary belts were formed. They contain the most prolific metallogenic provinces in the Fennoscandian Shield. Prospects of Ni-Cu- (PGE) mineralisation in gabbro and pyroxenite complexes may represent magmatic formations during the initial phase of rifting. Sediment-hosted Cu-deposits were formed during further rifting and sagging in sandstone and conglomerate, as well as in dolostone and dol-arenite. The characteristic ore mineral paragenesis is bornite+chalcopyrite+chalcocite (±neodigenite), which is commonly enriched in Ag and locally also has elevated contents of Au, PGE and Co. The mineralisation exhibits textural features indicative of syn-diagenetic and epigenetic mineral precipitation with localized structural reworking. The largest of these, the Nussir deposit, comprises 66 Mt @ 1.15 % Cu, and operation is planned to start in the near future. Palaeoproterozoic orogenic gold deposits and occurrences are common in the greenstone belts , and are associated with major regional structures formed during the Svecofennian Orogeny (c. 1.9 Ga). The Bidjovagge Au-(Cu) deposit was mined in the periods 1972-75 and 1985-91; about 1.95 Mt of ore with average grades of 4 g/t Au and 1.2 % Cu was mined in the last period. Host rocks include strongly sheared albite felsite and graphitic schist. The Transscandinavian Igneous Belt (1.8-1.63 Ga) comprises the western part of Fennoscandia in North Norway. It includes major monzonite (mangerite), anorthosite, gabbro/norite and granite (charnockite) intrusives with potential for Fe-Ti -(P) and Ni-Cu deposits. Rifting of the Proterozoic Rodinia mega-continent and opening of the Iapetus Ocean in the Neoproterozoic to Palaeozoic resulted in the development of passive margins. Deposition of stratiform iron formations (IFs) and SEDEX Zn-Pb-Cu deposits on the Laurentian side and orthomagmatic Ni-Cu- (PGE) deposits on the Baltic side can be related to this phase. The IFs occur within mica schist-marble sequences and can be traced for over 500 km in the Caledonides of northern Norway. The banded, haematite+magnetite ore has been mined for over 100 years in the Rana area (production > 100 Mt @ 33-37 % Fe). They are assumed to have been deposited in Middle Cryogenian time (800–730 Ma) on a glacially influenced carbonate-siliciclastic shelf. Subsequent arcs and marginal basins, formed either outboard Fennoscandia (Baltic plate) or on the Laurentian side of Iapetus, host abundant Zn-Cu and Cu- Zn VMS deposits. During plate convergence and ocean closure/initial collision phase intraorogenic Ni-Cu and VMS Cu-Zn ores were formed. The final collisional stage is characterised by various vein type deposits, including Au, Ag and Pb deposits. .
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