Evaluation of Banded Iron Formation using Magnetic Susceptibility

Abstract

In a banded magnetite deposit where assays gave no indication of concentrate yield, information required for process plant design was derived from downhole magnetic susceptibility logs. Early analysis showed poor correlation between Davis Tube Recovery (DTR) and downhole magnetic susceptibility. The role of anisotropy in this relationship was identified and a correction factor applied to bring all data to an equivalent core to bedding angle. The result was a very high definition measure of in-situ magnetite distribution from which product yield estimates could be made. The definition of ore type according to magnetic susceptibility profile enabled the content of potential Run of Mine ore to be characterised. Information required for front end plant design relating to economic cut-off grade, magnetic separator configuration and waste rock volumes could be estimated at an early stage of project development. The use of geophysical data has now been applied successfully to other banded formations where conventional mining block models fail to deliver the resolution of data required by process engineers.