Summary
This report presents preliminary results of regional fieldwork in the Okstind- ene Area, the Rödingfjäll Nappe Complex (RNC), Uppermost Allochthon, Nordland, Norway. The area hosts the Bleikvassli sedimentary-exhalative Pb-Zn deposit, and the main objective with this work is to establish a geological basis for prospecting after new Pb-Zn deposits in the area. The area comprises four lithological units; the Kjerringfjellet(?), Anders Larsa/Lifjell and Kongs- fjell Groups and the Målvatn Unit. All units are dominated by metasediments, mainly garnet-mica and calcareous mica schists. Calcite and dolomite marbles are abundant in the Anders Larsa and Lifjell Groups, whereas various quartz- feldspathic schists are typical of the Målvatn Unit. Amphiboles, which are metabasalts and andesites of probable transitional MORB to island arc affinity according to geochemistry, are present in all units. They are particularly abundant in the Kongsfjell Group close to the contacts to the Anders Larsa/ Lifjell Groups and between calcareous mica schists and garnet-mica schists. Isolated bodies of ultramafics, partly chromite-bearing, are present within the Målvatn Unit, close to Kongsfjell Group. Taking into account the geo- chemistry of the amphibolites and the association with mainly continent- derived sediments, the Okstindene lithologies have most probably formed in a spreading regime behind an ensialic arc. Sr-isotope analysis of the marbles, show that the sediments have an age of 590-600 Ma, in accordance with ages obtained elsewhere in the RNC. The area has been subjected to five major deformation phases, of which the first three have been very intense. The rock units have been folded into one megascale, recumbent fold, bounded by major thrusts. This structure has a major impact on prospecting after new deposits, meaning that the contact between the Lifjell and Kongsfjell Group I
