A world-first audio-frequency-magnetic (AFMAG) survey flown by Estrella Resources over its flagship Carr Boyd nickel-copper project near Kalgoorlie in Western Australia’s Goldfields region has zeroed-in on nickel-sulphide drill targets to 600m depth.
The company says the helicopter-borne survey has given it a vastly better understanding of the project’s geology and includes “industry-leading vision” of its highly-prospective host rocks. The geological picture has also been complemented by resistivity depth imaging (RDI) subsequently conducted by leading survey technology group, Expert Geophysics.
The AFMAG geophysical technique measures electrical resistivity differences in rocks and is a particularly useful tool to map locations and orientations of nickel-sulphide–bearing units to 600m depths. RDI is a process where a line of metal electrodes are plugged into topsoil and electrical current is made to flow.
Estrella says RDI cross-sections across the 75-square-kilometre intrusive complex, which contains 16km strike of nickel-sulphide-prospective basal ultra-mafic contacts near the base of Colreavy komatiite and Carr Boyd pyroxenite host-rocks, show enhanced 3D orientation and locational understanding of the bedrock conductors it had identified in an earlier TargetEM (electromagnetic) survey.
The Carr Boyd pyroxenite and Colreavy komatiite were found to show low levels of resistivity relative to other rock-types in the project area. Estrella now interprets the Colreavy komatiite to dip steeply to the east, while the Carr Boyd pyroxenite plunges vertically.
The company is combining the results from both its EM and AFMAG surveys to model and home drilling in on the prospective internal basal contacts of the Carr Boyd intrusion in search of massive and disseminated nickel-sulphide mineralisation.
Estrella Resources managing director Christopher Daws said: “Estrella Resources has now gained further detailed information to develop precise drill targets to unlock further nickel sulphide deposits. The RDI data is a fantastic tool for exploration as the survey is capable of monitoring a greater range of electrical resistivities than other time-domain systems currently in the market. This means we have industry-leading vision of our highly prospective host rocks.”
Daws said the significant contrasts between the low and high-resistance rocks within the project would allow it to map them with “a strong degree of certainty”.
Estrella, which has a market cap of $10.6 million, controls a contiguous 259sq km of tenure in seven exploration licences and three mining licences. It includes the Carr Boyd mine, which has had previous production of 202,100 tonnes at 1.43 per cent nickel and 0.46 per cent copper.
The company has calculated a JORC exploration target of between 5 and 7 million tonnes grading from 0.7 to 1.5 per cent nickel and 0.3 to 0.5 per cent copper. It includes an inferred maiden resource estimate at its T5 target of 860,000 tonnes grading 0.66 per cent nickel and 0.42 per cent copper.
The company has embraced the use of state-of-the-art electromagnetic and resistivity geophysical surveys in its bid to unlock deep drill targets in the largely-unexplored and poorly-understood Carr Boyd ultramafic intrusive complex. Historically, the complex has been a major nickel and copper producer, so it will be worth keeping an eye on whether it can again deliver.
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By Rohan Halfpenny
