AEM‐constrained 2D inversion of AMT data over the Voisey's Bay massive sulfide body, Labrador

Abstract

The Voisey's Bay area, in northern Labrador, presents unusual problems in the interpretation of audiofrequency magnetotelluric data. The survey area is located between two east-oriented fjords; the sea-water filling these is assumed to have a resistivity of about 0.3 ohm.m. This is in strong contrast toi the resistive Proterozoic metamorphics underlying the survey area, which have resistivities in the range 10,000 to 100,000 ohm.m. Thus, the sea-water interface can be expected to have a major impact on measurements. In addition, recent sediments occur in minor pods along drainages and near lakes, and these again cause significant AMT responses. Previous work (e.g. Mackie and Watts, 1999) has modeled the gross effect of the sea, and Balch et al. (1998) presented a comparison between AMT and AEM surveys over the same area. In this paper, we show how the use of AEM data to quantify the resistivity and extent of shallow conductors improves the numerical interpretation of AMT data.

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

“…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).…”

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

“…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;…”

Electromagnetic imaging of a complex ore body: 3D forward modeling, sensitivity tests, and down-mine measurements

“…Over the last decade, these factors have proved MT to be a reliable method of EM imaging ͑Garcia and Jones, 2001͒, particularly when coupled with modern 24-bit acquisition systems, and continuous-profiling systems such as Mount Isa Mines ' MIMDAS ͑Sheard, 2001͒ or Quantec's TITAN-24 ͑White andGordon, 2003͒. As a direct consequence of these advances, the application of audio-MT ͑AMT͒ ͑i.e., MT at frequencies of 10 Hz to 10 kHz͒ for mineral exploration has increased significantly over the last decade, particularly for base and precious metals in Canada where it has been used at more than 25,000 sites, principally in Voisey's Bay, the Sudbury Basin, and the Thompson Nickel Belt ͑e.g., Balch et al, 1998;Stevens and McNeice, 1998;Zhang et al, 1998;Watts and Balch, 2000;Jones and Garcia, 2003͒. The aim of our research was to study the capability of AMT not only to detect, but also to delineate complex conductive ore bodies at minable depths. Previous model-based studies have been undertaken in the Sudbury Basin ͑e.g., Livelybrooks et al, 1996͒; however, further work is required to achieve a better understanding of the applicability of AMT for mine-scale problems.…”