首页|Magnetotelluric imaging of an iron-oxide copper gold (IOCG) deposit under thick cover

Magnetotelluric imaging of an iron-oxide copper gold (IOCG) deposit under thick cover

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The presence of thick (>100 m) and electrically conductive (< 10Ω.m) ground cover is a majorimpediment in mineral exploration of deep resources. Iron-oxide copper gold (IOCG) systems inAustralia are often associated with a pronounced potential field anomaly, depending on the oxidationstate of iron, but the gravity and magnetic field signatures have little vertical resolutionunless constrained by drill hole petrophysics. Additionally, IOCG systems have deep magmaticsources, with their conductivity anomalies extending at least to the lithospheric mantle. The VulcanIOCG prospect lies about 30 km northeast of the Olympic Dam IOCG mine and is defined by asignificant gravity anomaly associated with brecciated haematite beneath 850mof sedimentarycover sequences. To image the physical properties and structural geometry of the Vulcan IOCGprospect, a 100-site broadband MT and passive seismic array was deployed in a 1 kmgrid over a9 by 9 km area. Three-dimensional inversion of MT responses resolve structure in three distinctdomains. Firstly, broad limestone-quartzite-shale stratigraphy (1–30 Ω.m) in the 850 m cover isdelineated in resistivity and corresponds well with changes in shear-wave velocity. Secondly, theregion of brecciated haematite below the cover sequences is shown to have lower resistivity (<60 Ω.m) than surrounding country rock (> 100 Ω.m). Thirdly, a more electrically conductive (<30 Ω.m) vertical zone that extends > 5 km is imaged a few kilometers to the northeast of theVulcan haematite breccia, and appears to be linked by a region of low shear-wave velocity in thedepth range 1–2 km. Two-dimensional inversion of more regional MT responses along a 200-km line passing through the Vulcan prospect suggest this vertical region of low resistivity linksto the lower-crust with anomalous resistivity of < 60 Ω.m in a similar way as imaged beneaththe Olympic Dam mine. It is suggested that this conductive region is associated with graphiteprecipitated from magmatically derived CO_2-rich fluids cooling in a reducing environment.

MagnetotelluricsIOCGmineral explorationambient noise tomography

Ben Kay、Graham Heinson、Goran Boren、Ying Liu、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 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 Resources and Environmental Engineering,Wuhan University ofScience and Technology,Wuhan, People’s Republic of China

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

Fleet Space Technologies, Adelaide, Australia

Fortescue Metals Group, Perth, Australia

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2024

10.1080/08123985.2024.2378132

Exploration geophysics

Exploration geophysics

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