Trans-Crustal Geophysical Responses Beneath the Supergiant Timmins-Porcupine Orogenic Gold Camp, Canada

Abstract

A new 80-site magnetotelluric (MT) survey, integrated with reprocessed seismic reflection profiles, across the supergiant Timmins-Porcupine gold camp of the Abitibi greenstone belt (AGB) was conducted to investigate the architecture of crustal-scale structures. Resistivity sections derived from 3-D MT inversions reveal a significant 600 S conductor north of the Porcupine-Destor fault zone at 3–5 km depth striking east-west parallel to the Pipestone fault zone. It is attributed to a deeply buried >2687 Ma graphitic argillaceous unit at the base of Porcupine assemblage. A second conductor at 8–10 km depth strikes northwest-southeast parallel to the Buskegau River fault. The margin of this conductor correlates spatially with lateral breaks in seismic reflectors and velocity models in the upper, middle, and lower crust, and adds to evidence of a crustal-scale suture which also resulted in imbrication of <2698 Ma metasedimentary rocks onto the southern AGB. Enhanced conductivity and spatially complex electrical structure of the crust to the north of the Porcupine-Destor fault zone reflect the asymmetric distribution of metasedimentary packages, second- and third-order bounding structures, and gold mineralization. The MT resistivity models also resolve an upper crustal conductor located 10 km south of the surface trace of the Porcupine-Destor fault zone, providing support for a south-dipping crustal fault. The Timmins results suggest middle crustal signatures of the extensional stage of the fault system have been overprinted by orogen-parallel ductile flow at ∼2660–2590 Ma and narrow (2–5 km wide) breaks in seismic reflectors are more likely associated with late strike-slip deformation.