Accurate Inversion in Queensland's East Isa Region

Accurate subsurface imaging is critical for successful mineral exploration. In this article, we examine how our advanced 2.5D inversion software outperforms CDI methods using Line 15701 from the publicly available East Isa VTEMplus dataset. This case study not only highlights the limitations of CDI but also demonstrates how our technology provides geologically realistic and actionable models, helping explorers pinpoint potential mineral deposits with confidence.

Background

The East Isa VTEMplus survey was conducted over the Quamby/Dugald River region of Queensland in 2016. Known for its complex folded and steeply dipping geological structures, the area represents a challenging environment for geophysical imaging. CDI methods, which assume horizontal layering beneath each survey sounding, struggle to accurately capture the subsurface complexities. This leads to oversimplified models and artifacts, such as false dipping conductors or incorrect resistivity values over steep topographies. Our 2.5D inversion approach, leveraging finite-volume modeling, bridges this gap by incorporating the three-dimensional effects of geology along the survey line while maintaining computational efficiency.

The Challenge

Line 15701 from the East Isa dataset is representative of the region's challenging geological setting, characterized by folded shale packages and discrete steeply dipping features. CDI data produced conductivity-depth sections that exhibited several anomalies:

Apparent artifacts over regions with steep topography.
Poor lateral resolution of dipping features, leading to inaccuracies in geological interpretation.

These shortcomings underscore the need for an inversion method capable of resolving complex subsurface structures while minimizing misfits between observed and modeled data.

Our Solution

Our 2.5D inversion software offers the following advantages:

Improved Resolution: It accurately captures lateral variations in conductivity, essential for steeply dipping and folded geologies.
Artifact Mitigation: By avoiding the oversimplifications inherent in CDI , our method reduces artifacts caused by topographic effects and lateral inhomogeneities.

The inversion of Line 15701 data showed a significant reduction in artifacts. Key features, including synclinal folds and steeply dipping conductive zones associated with the Dugald River deposit, were resolved with greater clarity and accuracy.

Results and Interpretation

The results from our 2.5D inversion showed:

Clear delineation of conductive anomalies wrapping around resistive quartzite cores.
Enhanced depth and lateral resolution of the synclinal shale package hosting the Pb/Zn mineralization.

In contrast, the CDI exhibited unrealistic conductivity gradients and poorly defined geological boundaries. The CDI model’s oversimplifications introduced substantial errors, particularly in areas of steep geological dip.

Conclusion

This case study underscores the transformative impact of our 2.5D inversion technology. By providing geologically accurate models with reduced artifacts, our software equips exploration teams with the insights they need to make informed drilling decisions. In the East Isa region, where subtle geological features define the difference between discovery and oversight, our approach delivers unparalleled value.