Drei typen von Kieslagerstätten om Mofjell-Gebiet, Nordland, und ein neuer vorschlag zur gliederung der kaledonischen kieslager Norwegens

Recent detailed investigations on Palaeozoic sulphide ore bodies in the Mofjell area, south of Mo i Rana (lat. 66°20'N) in northern Norway, revealed three different types of deposits. All these ore bodies lie in highly metamorphosed rocks of the Nordland facies above the Rödingsfjell thrust plane. The Mofjell-type deposits are banded pyritic zinc-lead ores while the Tretthammern- type deposits are less regular and poorly banded pyrrhotitic copperzinc ores. It is believed that the ores of both the above types are pre-metamorphic and have been formed by submarine hydrothermal solutions (initial magmatism of the Caledonian orogenesis) during the deposition of the sediments in the geosyncline. They can thus be regarded as of the exhalative-sedimentary type. The Hauknestind-type deposits are epigenetic pyrrhotitic zinc-lead replacement ores in marble layers and tectonic breccia zones. The ore-forming materials of these deposits probably originated from primary syngenetic sulphide ores, mobilized and emplaced in their present position during the later stage of the orogenesis. Based on this regional division in the Mofjell area, a new non-genetic, descriptive classification of the sulphide ore bodies in the Caledonian mountain chain of Norway is proposed. The pyrite-type, consists dominantly of banded pyritic ores, and the mixed pyrite-pynhotite-type, having a somewhat less distinct banding, consists of pyrite and pyrrhotite in equal amounts. The Cu-pynhotite-type contains irregular pyrrhotite-chalcopyrite ores while finally, the Zn-pyrrhotitetype is made up of pyrrhotite-sphalerite ores, which show a breccia texture. Comparison with the groups introduced by Stanton and Vokes show that the new classification is more comprehensive and does not include the discrepancies of the genetic differences in the Carstens-Foslie classes.