首页|Natural source-field induced polarisation exploration of an iron-oxide copper-gold (IOCG) deposit under thick cover

Natural source-field induced polarisation exploration of an iron-oxide copper-gold (IOCG) deposit under thick cover

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Induced polarisation (IP) is a common geophysical method of exploration for disseminated sulphides.However, in areas with deep (>200 m) and conductive (10 Ωm or less) cover, thetechnique is less successful as it requires a significant transmitter source and large-offset dipoles.An alternative approach is to use natural-variations in Earth’s external magnetic field as the polarisingsource of the signal, known as natural-field IP. This paper presents a study of extracting IPinformation from electrical dipole observations during a broadband magnetotelluric (MT) programwith a 9 km by 9 km grid of 100 sites above the Vulcan IOCG deposit beneath 750 m ofcover, ∼40 km north of the Olympic Dam IOCG mine in South Australia. Inter-site transfer functionsbetween 95 sites and five reference sites at the southeast and southwest corners of the gridwere computed to determine a phase shift between horizontal electric fields in the bandwidth of1–100 s period. Phase shifts of up to – 5 degrees were centred on a region of brecciated hematitewhere drill holes intersected pyrite, and an inferred fault-zone from passive seismics that marksthe boundary between upper crust that is resistive (>100 .m) with high magnetic susceptibilityto the south of the fault, and a region of conductive crust (<10 .m) which is low magneticsusceptibility. Our study suggests that the natural-field IP method can identify regions of polarizableminerals beneath deep cover where artificial power sources cannot be feasibly deployed.Such surveys are cheaper, safer, and easier to deploy as only receivers are required, and 3D coveragecan be obtained as the source-field is of much larger dimension than the survey array. Inaddition, the natural-field IP signals are observed as part of theMTprogram so that both electricalresistivity and polarisation parameters can be determined.

Induced polarisationmagnetotelluricsambient noise tomographyIOCG

Ying Liu、Graham Heinson、Ben Kay、Goran Boren、Simon Carter、Gerrit Olivier、Tim Jones、Rebecca Abel、Lisa Vella、Louise McAllister

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School of Physics, Chemistry and Earth Sciences, University of Adelaide, Adelaide, Australia||School of Geophysics and Geomatics, ChinaUniversity of Geosciences,Wuhan, People’s Republic of China

School of Physics, Chemistry and Earth Sciences, University of Adelaide, Adelaide, Australia

School of Physics, Chemistry and Earth Sciences, University of Adelaide, Adelaide, Australia||Wuhan University of Science and Technology,Wuhan, People’s Republic ofChina

Centre for Ore Deposits and Earth Sciences, University of Tasmania, Hobart, Australia||Fleet Space Technologies, Adelaide,Australia

Fleet Space Technologies, Adelaide,Australia

Fortescue Minerals Group, Perth, Australia

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2024

10.1080/08123985.2024.2354209

Exploration geophysics

Exploration geophysics

EISCI
ISSN：0812-3985
年,卷(期)：2024.55(6)
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