Some aspects of the skarn ore problems in Central Sweden. According to the interpretation of the non-manganiferous skarn-bearing iron ores of Central Sweden that was given by Magnusson and the present writer 15 years ago and has later been repeated (Geijer and Magnusson 1944, 1952 a, 1952 b), this group is not genetically homogeneous. It contains >primary skarn ores>, of pyrometasomatic origin, and more numerous >reaction skarn ores> that were originally formed by sedimentation or by replacement at low or moderate temperatures, and later changed through interior reactions caused by regional heating. This metamorphism, like the development of primary skarn ores, took place during the epoch when the containing leptite formation was folded and invaded by the Earlier group of Svionian granites. Further, the >magnesia metasomatism> that accompanied these events has wrought great chemical changes in many of the earlier formed deposits. In a textbook (Magnusson 1953), however, these views have been presented in a somewhat modified form, the possibility being indicated that the deposits interpreted as such with primary skarn may all be reaction skarn deposits altered by the magnesia metasomatism.