Brownfield exploration poses many challenges to the geologist: large amounts of data are usually available but often difficult to integrate and use effectively; at the same time old ideas and exploration models often hamper new interpretations and the development of new targets. Traditional interpretation involves a time-consuming and subjective 2D section analysis. In contrast, 3D targeting adds a new approach to the brownfield exploration rebus.
Excalibur Mining Ltd is currently exploring for gold in the Tennant Creek region of Australia’s Northern Territory. The company’s main focus is the redevelopment of the Juno and Nobles Nob gold deposit (2Moz of mined ore) and the discovery of new deposits in the vicinity of the historical mines. The area has more than 80 years of prospecting and exploration history and a very large quantity of data is available to guide exploration. SRK has applied state-of-the-art 3D targeting to identify new exploration targets in the area.
3D targeting is a new technique that uses all available geological information to build a 3D block model of the site of interest. The model is interrogated and the most prospective volumes identified. To minimise modelling times rapid 3D modelling software such as GOCAD™, Leapfrog™ and Geomodeller™ are used.
The Excalibur study started with a brain-storming session to identify the characterising features of the Juno and Nobles Nob deposits and define a Mineral System model to be used as the geological framework. All available geological information was then integrated in the model, including lithologies, assays, structures, geophysics (magnetic, EM), mineralised trends, etc. The final 3D model included several million cells, each containing information for the nine geological properties considered.
Three main results were achieved:
• Nine exploration targets were identified, ready to be assessed and potentially drilled by Excalibur
• A rigorous review of the mineralisation model improved the geological understanding of the deposits
• A step-by-step analysis allowed a critical assessment of the quality of the information available and the identification of areas of improvement, where additional or better data could be collected. This new information could possibly be integrated in a revised 3D targeting model allowing the definition of better targets
SRK believes 3D targeting can be successfully applied as an advanced exploration tool when sufficient data are available. The flexibility of this approach allows its application to all deposit styles and geological contexts with a high potential for structurally complex areas. The geological understanding required to perform the analysis helps improve the geological model itself and ensure that all targets identified have strong geological support.
