Geology and metallogenic potential of the northwesternmost Norrbotten Province around Altevatn in Troms, northern Norway
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The Altevatn area constitutes the northwesternmost part of the Archaean to Palaeoproterozoic Norrbotten Province in north-central Scandinavia, making it strategically located with respect to correlations between Fennoscandia proper and apparently similar units to the west, outboard of the Caledonian nappes. Low-grade, c. 1.9 Ga, supracrustal rocks in the Norrbotten Province in Sweden host numerous economical mineralisations, including the world-class Kirunavaara apatite iron deposit. However, the relative inaccessibility of the Altevatn area has rendered it virtually unmapped, and thus leaving open the possibility of similar mineralisations on the Norwegian side. Bedrock and geophysical mapping and geochronological investigations, presented here, show that the Altevatn area consists of Neoarchaean migmatitic ortho- and paragneisses, intruded by c. 1.8 Ga granitoids, ranging in composition from gabbro and monzonite to granite. No rocks similar to the c. 1.9 Ga supracrustal rocks in the Norrbotten Province have been identified, suggesting that such mineralisations are unlikely to be found in the Altevatn area. However, a poorly exposed, high-magnetic gabbro shows relatively high concentrations of Fe, P, Ti and V, providing the most interesting target for follow-up prospecting. Although structural evidence may be interpreted to reflect Svecofennian deformation, we have not found clear geochronological evidence of the Late Palaeoproterozoic accretionary processes that characterise much of Fennoscandia.

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