The high grade crabodies and the jaspilites of the Middleback Group Archaean (?) in the Middleback Ranges (Loc. 1) are the largest reserves if iron ore in South Australia. Most of the numerous deposits elsewhere in the State, especially the high grade ones, are small. Exploration by the South Australian Mines Department outside the Middleback Ranges has assessed all the known deposits, resulting in new opinions as to their origin, age, reserves and benefication characteristics. The term "iron ore" is used here to describe material which can be fed directly to a furnace or can be beneficiated to produce a furnace feed.' "Iron formation" is used as a general term for a sequence containing iron rich members usually interlayered with shale, quartzite, carbonate rocks etc. or their metamorphosed equivalents. Pyritic slate is included in this term. "Jaspilite" refers to a rock consisting essentially of interbedded layers containing widely varying proportions of iron oxide and silica, both chemically precipitated. "Martite" is used to describe oxidized magnetite, to distinguish it from hematite of primary or unknown origin. Modern blast furnace practice requires extremely high grade feeds and no appraisal of an iron ore today is complete without some assessment of its beneficiation. The comments on beneficiation are based on work carried out by the Australian Mineral Development Laboratories for the South Australian Department of Mines. A.M.D.L. also carried out the Petrological examination.