Geophysics of the Voisey's Bay Ni‐Cu‐Co deposits

Balch, S.J.; King, Alice; Crebs, T.J.; Verbiski, M.

doi:10.1190/1.1820594

Cited by 22 publications

(13 citation statements)

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“…AMT is now being used extensively for mineral exploration, with over 30 000 sites measured over the last decade in Canada alone, and particularly 3-D modelling and inversion are being employed. The method is gaining particular importance in settings for which deposits are located near or beyond the limits of controlled-source electromagnetic studies, for example, deep nickel deposits in the Sudbury basin as part of Abitibi-Grenville transect studies (Livelybrooks et al 1996;Stevens and McNeice 1998;Boerner et al 2000a), within the Chibougamau camp in Quebec (Chouteau et al 1997), the world-class Voisey's Bay massive sulphide deposit in Labrador (Balch et al 1998;Watts and Balch 2000), modelling and resolution appraisal of the Bathurst No. 9 body (Queralt et al 2007) and of an enigmatic body in northern Labrador on Okak Bay (Jones and Garcia 2003b), the lithospheric-scale geometry of the gold-bearing Yellowknife Fault as part of SNORCLE , and unconformity uranium deposits in the Athabasca basin as part of EXTECH-IV (Tuncer et al 2006;Tuncer 2007;Farquharson and Craven 2009).…”

Section: Mt Technique Developmentmentioning

confidence: 99%

The electrical resistivity of Canada’s lithosphere and correlation with other parameters: contributions from Lithoprobe and other programmes

et al. 2014

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Over the last 30 years, through Lithoprobe and other programmes, modern, high-quality magnetotelluric (MT) measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across Canada in all provinces and territories, except Nova Scotia. Some regions are well covered, particularly Alberta, southern British Columbia, and western Ontario, whereas others remain poorly covered, such as Quebec and large swaths of Nunavut. Prior publications from individual studies have added significantly to the wealth of Canada's geoscience knowledge, and have demonstrated that MT can contribute significantly to understanding of the tectonic processes that have shaped Canada. However, to date no continent-scale maps of lithospheric electrical parameters have been constructed from the extensive MT database. Herein we review the contributions made by the MT components of Lithoprobe, and present new continental-scale maps of various electrical parameters at crustal and upper mantle depths for the whole of Canada. From those maps, combined with regional estimates of temperature, we develop derivative information on petrological-geophysical properties, including predictions of temperature and water content. We find that at 100 km depth the Canadian Shield is cold and dry, and the Cordillera is warmer but mostly dry, i.e., little water is present in the peridotite. Exceptions are beneath the Prairies, the Wopmay Orogen, and northeast Nunavut where there does appear to be water in the nominally anhydrous minerals. Also, southwest British Columbia appears colder than the rest of the Cordillera due to the subducting Juan de Fuca plate. In contrast, at 200 km depth almost all of Canada is dry.Résumé : Au cours des trente dernières années, grâce à Lithoprobe et à d'autres programmes, des mesures magnétotelluriques (MT), modernes et de grande qualité, ont été prises à plus de 6000 sites à travers le Canada, dans toutes les provinces et territoires sauf en Nouvelle-Écosse; ces mesures sondaient profondément dans la lithosphère et l'asthénosphère sous-jacente. Certaines régions sont bien couvertes, surtout l'Alberta, le sud de la Colombie-Britannique et l'ouest de l'Ontario, alors que d'autres sont mal couvertes, par exemple le Québec et de grandes parties du Nunavut. Des publications antérieures, basées sur des études individuelles, ont grandement contribué à enrichir les connaissances géoscientifiques canadiennes et elles ont démontré que les mesures MT peuvent grandement contribuer à la compréhension des processus tectoniques qui ont formé le Canada. Toutefois, à ce jour, aucune carte des paramètres électriques lithosphériques, à l'échelle du continent, n'a été construite à partir de la vaste base de données MT. Dans le présent article, nous revoyons les contributions des composantes MT de Lithoprobe et nous présentons de nouvelles cartes à l'échelle du continent de divers paramètres électriques aux profondeurs de la croûte et du manteau supérieur pour l'ensemble du Canada. À partir de ces cartes, ...

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Section: Mt Technique Developmentmentioning

confidence: 99%

The electrical resistivity of Canada’s lithosphere and correlation with other parameters: contributions from Lithoprobe and other programmes

et al. 2014

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“…Watts (1997) describes the importance of on-time measurements in borehole EM for nickel prospecting in Sudbury. Balch et al (1998) conclude that for Ni-Cu systems, on-time measurements are required to discriminate between high-grade high conductance zones and low-grade, uneconomic zones.…”

Section: Introductionmentioning

confidence: 95%

Detection of a perfect conductor with an airborne electromagnetic system: The Gemini Field Test

Smiarowski

Macnae

2013

GEOPHYSICS

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The cores of high-grade nickel and copper sulphides appear as "perfect conductors" to most electromagnetic (EM) and airborne electromagnetic (AEM) systems, because they have bulk electrical conductivities of the order of 100;000 S∕m. The EM response of these highly conductive cores is essentially undetectable with off-time measurements or when using nonrigid towed-bird systems. Compact AEM systems with accurate primary field bucking and on-time or in-phase measurements are sensitive to perfect conductors, but are incapable of detecting deep targets. Using a GPS system to define geometry, calculations suggest that it should be easy for an AEM system to detect "perfect conductors" provided the receiver was several hundred meters distant from the transmitter. A twin (Gemini) aircraft test was undertaken to test this concept in 2005. The field test successfully demonstrated detection of very conductive targets. Errors associated with geometric changes were better than 0.5% of the primary field at 400 m separation, allowing detection and characterization of the 30 Hz, in-phase response of small and extended conductors. The test shows that a 200 × 100 m very-strongly conductive thin-sheet target would be detectable to depths of 200 m below surface using off-the-shelf technology. Larger conductors would be detectable at greater depths.

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“…Where AMT signal levels are low, e.g., in the dead band at $ 800-3000 Hz (Garcia and Jones 2002), the controlled-source audiomagnetotelluric method (CSAMT, f = 1-10000 Hz, Zonge and Hughes 1991) is routinely applied. Consequently, MT methods have a long-standing history in the investigation of mineral deposits (Strangway et al 1973;Meju 2002;Jones 2017) with field cases reported from, for instance, copper, gold, lead, silver and zinc deposits (Kellett et al 1993;Garcia Juanatey et al 2013a, b;Hübert et al 2013;Hu et al 2013), copper, gold and iron deposits (Heinson et al 2006), copper and iron deposits (Chouteau et al 1997;Jones and Garcia 2003), copper, iron and zinc deposits (Basokur et al 1997), copper, lead and zinc deposits (Sasaki et al 1992;Bastani et al 2009), copper and nickel deposits (Lakanen 1986;Livelybrooks et al 1996;Jones et al 1997;Balch et al 1998;Stevens and McNeice 1998;Zhang et al 1998;Watts and Balch 2000;King 2007;Xiao et al 2011;Varentsov et al 2013; Le et al 2016a), copper, silver and zinc deposits (Gordon 2007), gold deposits (Jones et al 1997;Liu et al 2006;Howe et al 2014;Takam Takougang et al 2015;Hübert et al 2016;Le et al 2016b), and uranium deposits (Leppin and Goldak 2005;Tuncer et al 2006;Farquharson and Craven 2009;Goldak et al 2010;…”

Section: Mt Methods In Exploring Deep Ore Depositsmentioning

confidence: 99%

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

Kalscheuer

Juhojuntti

Vaittinen³

2017

Surv Geophys

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A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of $ 300-1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and elect...

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Geophysics of the Voisey's Bay Ni‐Cu‐Co deposits

Cited by 22 publications

References 0 publications

The electrical resistivity of Canada’s lithosphere and correlation with other parameters: contributions from Lithoprobe and other programmes

The electrical resistivity of Canada’s lithosphere and correlation with other parameters: contributions from Lithoprobe and other programmes

Detection of a perfect conductor with an airborne electromagnetic system: The Gemini Field Test

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

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