Despite our reliance on geophysical surveying in mineral exploration, we have a relatively poor understanding of the link between petrophysical properties (at the scale of <1 metre) and geophysical response (at the scale >100 metres). Drilling campaigns is critical because it bridges the two end-member scales and constitutes rocks that can be sampled and from which observations can be made. There are a range of techniques for measuring rock properties in drill holes and on drill core that vary in cost, time, data quality and resolution. A key question for explorers is: What are the optimum data to collect (and at what resolution) to adequately constrain and make geological sense of our geophysical models? A complicating factor is that petrophysical properties are not routinely collected and reconnaissance techniques (e.g., handheld MagSus) provide only part of the picture. This study sets out to define a methodology for petrophysical sampling of mineralised rocks using three mineralised drill holes from separate deposits in the Cobar Province. The inspected core are from the structurally controlled New Cobar deposit and two skarn-type deposits, Nymagee and Hera. New Cobar sits nearby to the magnetic high of the Great Cobar deposit. It contains both magnetite and pyrrhotite; however, not all the pyrrhotite is magnetic, which results in a relatively small geophysical signal. The Nymagee anomaly is a strong dipole and holds a remanence component. The deposit preserves both magnetite and pyrrhotite. At Hera, magnetite is completely absent and the deposits is often described as non-magnetic. As shown in this study, all three deposits do have some magnetic susceptibility associated with, or in the vicinity of, mineralisation. Natural gamma radiation response varies and conductivity responses are locally observed (scale <0.5 metre) across mineralisation for the three deposits. Results of this study are used to develop a methodology that uses core logging tools to support building integrated high-density datasets in drill core analysis. Logging can be assisted by Hylogger data and shows potential as a reference when extrapolating vector data, from laboratory petrophysics, back to the core scale and beyond.

Open-Access Online Publication: May 31, 2023