Harnessing Legacy Geophysical Data and Potential Pitfalls

Legacy data may hold the key to the next big mineral discovery. Now that we have your attention, what is legacy data? Legacy data is information that was created years ago and may not be actively used by an organization anymore. Locating and being aware of what legacy data a company possesses is complicated due to the nature of the mining industry; mineral rights change hands and exploration can take decades before the economics are right. In the meantime, computer power and the sophistication of interpretation methods has grown immensely. Much of the data collected before computer power expanded to allow for full high-resolution 3D geophysical inversion models, remains archived with valuable information waiting to be extracted by modern tools. This article argues that there is much legacy data that would be given new life by inverting it for 3D physical property models; however, some potential pitfalls need to be discussed.

The Possible Pit Falls

Data collected decades ago often suffers from higher noise and less signal strength compared to modern datasets. This is mostly a function of how electronics, GPS locations and computers have become significantly better.  These sources of noise/error can be significant enough that no amount of modern technological wizardry will add value. Determining how much noise is too much is not an exact science, and it can be a time sink. Experience working with older datasets significantly reduces the effort and cost in determining whether allocating resources for further inversions is reasonable. Survey metadata can also be vitally important. Base station information, data recording parameters and other basic information about the survey can be of paramount importance to conducting data quality control and inversions. This information is often misplaced as it is often recorded separately from the dataset in a subsequent report. To summarize, it is easy to spend too much effort attempting to reinvert old datasets that are not ideal candidates due to noise or missing metadata.

Besides the mentioned noise and missing metadata, there is also the possibility that adding more effort will not add significantly more information. In many cases, historical processing and inversions may be sufficient to describe how the geophysical property in question varies over the area of interest. The more complex or 3D the geologic features are, the more information a high-resolution inversion will add. This is a judgment call on the exploration and geophysical teams conducting the inversions to balance the potential costs and benefits of re-processing and inverting legacy data.

The Benefits

The benefits of inverting old data with newer inversion techniques extend beyond increased model resolution. These techniques can highlight three-dimensional structures and contribute to the development of a holistic model of the subsurface. These stated benefits are often enough justification to spend the effort on the legacy data; however, the advantages merely scratch the surface of what is possible. Legacy geophysical data often coexists with other valuable datasets, such as geologic models, drill results, and multiple geophysical surveys. Incorporating the coexisting data into constraints will help the inversion process produce better and more accurate models. While adding constraints increases the required effort and cost, the results can be significant.

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The last advanced technique to mention is joint inversion. Where two distinct geophysical datasets are inverted together, or “jointly”, producing consistent results with both datasets.   This workflow, shown above, is particularly effective when inverting datasets that measure linked properties. However, any combination of datasets covering the same ground can be used. ZTEM and ATEM surveys are examples of linked datasets as both are inverted to obtain conductivity. The interaction between unlinked properties can be challenging, however; the result is a holistic 3D model consistent with all data.

Summary

There are potential issues in allocating resources and effort to legacy data due to noise and missing metadata, which may limit the ability to get new information from the data. However, in areas with complex geology, the information provided by a 3D approach might be just what the project needs. Furthermore, using advanced techniques to bring new life to legacy data will be less expensive than conducting a new survey, while providing a holistic 3D model consistent with all data collected on a property. By utilizing legacy data, mining companies can gain deeper insights and make more informed decisions.

We have extensive experience working with legacy data here at Computational Geosciences Inc. With our proprietary inversion software and cutting-edge techniques, we will help you get the most out of this resource. If you want to find out more about how we can improve the use of your legacy data reach out to us!

Author: Jeffrey Zurek