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Abstract
Magnetite and sphalerite in the non-apatitic iron ores and sulphide ores of central Sweden, which are considered to be of volcanogene, syngenetic origin, have been investigated chemically. Microprobe analyses show a pure magnetite, which besides iron, only contains small amounts of additional elements. This concerns also magnetite occurring in iron ore deposits with magnesia-rich alterations, previously attributed to a pyrometasomatic origin, but here considered as para-contemporaneous with the volcanism. The uniform composition of magnetite points to a common source of the iron in the different types of ore. The small contents of manganese (around 1 wt% MnO) in the magnetite of the manganiferous skarn iron ores are due to a higher manganese activity in the ore-bearing solutions. The iron content of sphalerite in the manganiferous skarn iron ores and the sulphide ores varies between 12.8 and 18.6 mole % FeS. The sphalerite in the manganiferous skarn iron ores contains up to 2 wt % Mn. The variations in the iron and manganese contents of the sphalerite are attributed to primary compositional variations during the formation.