Several small sulphide disseminations and vein fillings, characterized by the presence of Ni and Co minerals, occur in a greenstone area around the community of Los, Hälsingland. The largest vein filling, i.e. the Los cobalt deposit, was mined during the 18th century and contains a gangue of calcite, quartz, small amounts of baryte, fluorite and tourmaline in which the ore minerals cobaltite, gersdorffite, pyrrhotite, chalcopyrite, pitchblende, pyrite, arsenopyrite, bismuthinite and marcasite, are found. The wall rock is altered and minerals of the ore paragenesis are deposited in it. These disseminations contain euhedral uraninite and granular pitchblende which apparently represent two generations, the uraninite being older than the main deposition of the sulphides. The genetic relationship of the Co-Ni-Cu-Bi-U-paragenesis is discussed. One age determination by the U/Pb method on pitchblende gives an almost concordant age of 1,690 m.y. which coincides with the age of the rapakivi granites in Finland regarded as contemporaneous with the sub-Jotnian granites (Dala-granites) in the Los area.