Comparison between Manual and Automated Targeting for Nolans Bore-Style Rare Earth Element (REE) Deposits

Abstract

A manual litho-structural interpretation of airborne magnetic, radiometric and digital elevation model (DEM) data over the Nolans Bore rare earth element (REE) deposit, in northern Australia, has identified additional REE targets in the area. These targets were compared to automated targets generated using a Levenberg-Marquardt neural network (LMNN) analysis of the data. A number of different quantitative analyses were performed: one with only the geophysical data as an input and one that included the structural interpretation. The geophysical data needed modification for use in the LMNN algorithm, as the known deposit is anomalous in its absence of magnetite and a corresponding magnetic anomaly. Therefore, a shallow depth slice was extracted from a 3D inversion model of the magnetic data and the magnetic susceptibility values were inverted to form anomalies over non-magnetic regions. A Th/U ratio was calculated from the measured single radioelement responses. The structural interpretation was modified to incorporate only those faults oriented in the direction of the controlling structures at the known deposit. DEM data were used as a mask to ensure that targets were found in low-lying areas where the radiometric data is influenced less by topography or masks the underlying bedrock. It was found that the interpreted targets closely match the predicted targets, but that the predicted targets yielded smaller, more specific locations for follow-up work.