The Hällefors sulfide ores are located in the westernmost part of Bergslagen Ore Province, south central Sweden. The ore-bearing rock sequence consists of K-rich felsic metavolcanics. In the eastern part of the field, stratiform ore occurs in the upper part of a 30–40 m thick limestone. This ore consists of carbonate-bearing manganiferous skarn rock with conformable sulfide- and/or magnetite-rich beds. In the ore there are interlaycred beds of limestone, dolomite and tuffite. The sulfide skarn ironoxide ore is interpreted as a product of regional metamorphism of pre-existing strata. It comprises four chemical components, which are suggested to represent tuff materials (Si, Al, K), and chemically precipitated oxides (Fe, Mn), carbonates (Ca, Mg) and sulfides (S, Zn, Pb, As, Ag). The precipitates are considered to be products of submarine hydrothermal activity. The absence of wallrock alteration and channelways for ore-bearing solutions indicates that the ore was deposited on the sea floor distally to the outlet vents of the solutions. The ore and the wallrock are intensely faulted; the sulfides, especially galena, have been partly remobilized into faults and fissures. The Zn-Pb vein mineralizations in the western and middle parts of the field may be remobilization products of older stratiform ores.