Delineating mineralization and imaging the regional structure with magnetotellurics in the region of Chibougamau (Canada)

Abstract

Tensor magnetotelluric (MT) soundings were carried out to delineate the geometry of an extended shallow conductor detected by airborne electromagnetic method in the mining camp of Chibougamau (Canada). Careful distortion analysis of the impedance tensors from eleven sites indicate that the subsurface is reasonably 2-D within the 0.0025–10s range. The recovered regional impedances are corrected for static shifts employing 2-D inversion for minimum structure. The modeled resistivity cross‐sections show a far more complex conductivity structure than anticipated. The sheet‐like shallow conductor lies near the boundary between the conductive southern section located in the Abitibi subprovince and the resistive northern section located in the Opatica subprovince. It extends to a depth of 250 m. Two other limited conductive zones are imaged respectively between 0.4 km and 3 km and between 1.5 km and 4 km. We propose that the conductors are associated with sulfide mineralization and graphite in shear zones. They are delimited by steeply south dipping thrust faults. The northern resistive section does not show clear resistivity changes up to a depth of 15 km. Gravity data collected along the MT profile have provided additional constraints. Both MT and gravity models are consistent with one another and with the known regional geologic structure. They indicate that the Abitibi greenstone belt is 3.5–4.4 km thick in the survey area and that the steeply dipping geology at the surface is flattening at depths of 4 km approximately.

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

“…The former used the property that the vertical magnetic field tipper response is far more sensitive to non-uniform fields than is the MT response, whereas the latter approach was more mathematical in nature using a frequency domain principal component method. • The application of high-frequency AMT for mineral exploration was advanced by Lithoprobe scientists on a number of fronts (Garcia and Jones 2000), from instrumentation (Phoenix Geophysics' V5A and MTU-5A developments), understanding of AMT source fields (Garcia and Jones 2002a), acquisition methodologies (Jones and McNeice 2002), including a proposed novel telluric-telluric-magnetotelluric (TT-MT) method , down-mine measurements (Queralt et al 2007), specialized wavelet processing (Garcia and Jones 2008), distortion of controlled-source AMT data , 3-D distortion analysis (Garcia and Jones 2002c), and implementation and interpretation (Zhang and Chouteau 1992;Livelybrooks et al 1996;Chouteau et al 1997;Jones and Garcia 2006), including a cautionary tale resulting from regional current systems (Jones and Garcia 2003b). 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.…”

Application of 2D magnetotelluric methods in a geological complex area, Xinjiang, China

“…The present magnetotelluric equipments make it convenient to record large number of digital signals and produce tensor impedance of high frequencies (about 10 4 Hz). The development of remote reference and robust approaches in data processing, distortion correction, and multidimensional modeling and inversion methods since the late 80's has made the interpretation of magnetotelluric data more reasonable (Bahr and Simpson, 2005;Berdichevsky and Dmitriev, 2008;Chouteau et al, 1997;Nabighian and Asten, 2002;Queralt et al, 2007). For example, the two-dimensional rapid relaxation inversion (namely, RRI, Booker, 1988, 1991) was used to outline the massive (Ni-Cu) sulfide ore bodies (Chouteau et al, 1997;Livelybrooks et al, 1996;Stevens and McNeice, 1998); the nonlinear conjugate gradient inversion (as NLCG, Rodi and Mackie, 2001) was used to interpret magnetotelluric data in Okay Bay deposit and McArthur River mine in Canada (Jones and Garcia, 2003;Tuncer et al, 2006).…”

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;…”