Abstract: Manganiferous deep sea nodules containing non-ferrous metal values are selectively reduced to reduce manganic oxides to manganous oxide (MnO) and the non-ferrous metal values to the metallic state, and the selectively reduced nodules are then smelted to produce a molten metallic alloy containing the non-ferrous metal values and a slag containing most of the manganese. The molten alloy is blown with a free-oxygen-containing gas to eliminate most of the manganese, and the substantially manganese-free metal is then sulfided to produce a matte suitable for separation and recovery of the non-ferrous metal values. After sulfiding the matte can be blown with a free-oxygen-containing gas to lower the iron content thereof. Not all the iron is removed if it is advantageous to keep a high proportion of cobalt in the matte.