Bleikvassli Gru ber A/S in Nordland fylke, some 50 kilometres south of Mo i Rana, (Fig. 1) is at the present mining about 100,000 tons per year of pyritic lead-zinc ore. Economic products are lead, zinc and pyrite concentrates. During the course of a systematic mineralogical examination of samples of the ore, the writer detected the presence of small, rounded to euhedral grains of a brown mineral in the heaviest, non-magnetic fractions. Optical and x-ray powder determinations proved this mineral to be cassiterite (SnO₂). Following this, cassiterite was observed and studied in thin sections of the Bleikvassli ore. Colorimetric determinations of the Sn02 content of the ore were also made on more than 30 samples. At the same time, a large sample of the mine tailings was examined mineralogically and chemically. Cassiterite, being non-flotable or nearly so, would not be recovered in any of the concentrates being produced at the mine and would therefore report in the tailings. These are at the present time being allowed to fill up a small lake and thus would be available for re-treatment if the amount of tin in them should prove to be economically recoverable.