Palaeomagnetism of Australian Hematite Ore Bodies-I The Middleback Ranges of South Australia

The results of a palaeomagnetic study on high-grade hematite ore bodies of South Australia are reported. The two major ore bodies, Iron Monarch and Iron Prince, gave consistent directions of magnetization with either steep to moderate negative and positive inclinations. The positive and negative groups of Iron Monarch are not antiparallel. Because of the presumably long time interval represented by the sampling, this is interpreted as being due to polar wandering with a superimposed reversal of the Earth's field. The remanent magnetization is carried by hematite and is extremely stable against alternating field and thermal demagnetization. The intensity of the NRM is very weak compared to the TRM, which suggests it to be a CRM in origin. Lack of a detailed polar wandering curve for the Pre-Cambrian of Australia prevents precise palaeomagnetic dating of the ores, but the results clearly suggest a Pre-Cambrian age. The magnetic anisotropy of the ores is low and the distribution of the principal susceptibility axes reflects in part the structure of the host rock. The Iron Duke orebody did not yield a reliable palaeomagnetic result.