2D and 3D resistivity and IP inversion at the Cluny (Mt. Isa) deposit

Summary

A total of twenty line kilometres of IP, DC resistivity and MT data have been acquired using MIMDAS (MIM’s Distributed Acquisition System) over the Cluny prospect, south of Mt. Isa (shown in the figure on the right) in Queensland, Australia. The utilisation of two-dimensional and three-dimensional inversion programmes has provided a significant advantage in the interpretation of these data. The integration of geology and geophysics through the use of inversion, particularly three-dimensional inversions, has greatly improved the geological understanding of the Cluny region. It has enabled the identification of variations along linear conductors, and anomalous chargeable zones. This has implications for the ability of geophysics to provide discrimination for mineralisation along linearly extensive stratigraphy.

The first figure below shows the topography and the line positions where data were collected. Also shown is a "fence diagram" showing 2D inversion results for all lines. This result is useful but does not show the three dimensional configuration easily. Three dimensional inversion is advisable, and will produce acceptable results because the survey lines are sufficiently close together. If the 2D survey lines were further apart, then the data would not constrain model values between the lines, and a fully 3D inversion would fail to produce acceptable results.

Left: Survey site topography. Right: The series of stacked 2D IP inversions of the Cluny survey. Horizontal and vertical scaling is identical.

Two DC resistivity data sets shown as pseudosections, gathered along the survey lines.

The small figure to the right shows the full 3D chargeability model recovered by inversion. Isosurface versions of the resistivity and chargeability models showing linear structures are displayed next. Movies (AVI format) showing these models can also be displayed. There is one primary conductive structure but it is an un-interesting black shale unit. This is chargeable, but there is also a western chargeable structure, which is the economic ore. This image is from the AVI movie files of resistivity structure. Click links here to display the resistivity model or chargeability movies.

Isosurface depictions of the 3D models of chargeability (left) and resistivity (right) recovered by full 3D inversions of corresponding data sets.

See the UBC-GIF website (Resources => Publications) for a published summary of this case history.