1st Order Streams Research Articles

Tungsten exploration in the Valnesfjord region, Nordland, Northern Norway

A tungsten exploration programme in the Valnesfjord region was carried out during two short summers by drainage and follow-up investigations. At each sampling site a heavy-mineral concentrate and a stream sediment sample were collected in either 1st or 2nd order streams. Soil samples were collected from the C horizon at a depth of 30–120 cm, in most cases at the top of the bedrock. Five litres of soil were sampled, 200 g for chemical analysis and the rest was preconcentrated by panning and the scheelite grains counted. The raw data from the stream sediments were all normalized to one litre of the −1-mm fraction of the panned sediment. The threshold value is 30 grains of scheelite in the normalized samples and the peak value from the regional survey was 131 grains of scheelite. The majority of the anomalous samples (8) were related to a “shear zone”. A detailed follow-up survey revealed that the scheelite mineralization is associated with a zone in the lowermost part of the shear zone in a dolomite-limestone sequence and/or a calcareous biotite schist. The peak anomaly in the stream sediments was 1000 grains of scheelite, while the soil samples gave a peak value of 2500 grains of scheelite. Three types of mineralization were found by UV investigations in the field: (a) tourmalinites with large scheelite crystals in vugs; (b) small crystals of scheelite in quartz pegmatites; and (c) disseminated scheelite in calcareous biotite schists. The latter is the most interesting from an economical point of view.