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The sedimentary hematite-magnetite ores of marine origin, occurring within the crystalline mica schists of the caledonian mountain of Northern Norway, belong to a characteristic type of iron ore deposits, internationally known as the Dunderland ore type. Such deposits are known from latitude 65 degrees 20' to 69 degrees 40' N, thus covering a distance along the mountain chain of about 550 km. Transversely to this direction, they are known for at most 90 km, but generally much less. It is significant, that they do not occur farther southwards along the mountain chain, nor in its eastern part. The reason seems to be, taht they are connected with the so-called western development or the mountain chain formations, which disappear below the ocean in the Trondheim district. Compared with the eastern development, it is characterized by greater thickness of the sedimentary series, a far more considerable part of crystalline limestones and - so faar as now known - absence of the basic lavas (greenstone formation), which are important in the east and south. It belongs to a more central part of the geosyncline. The southern and greater part of the ore-bearing district is so strongly folded, that it has been difficult to establish the stratigraphic relation between the different deposits or their proper place within the formations. |
