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Trans-crustal geophysical responses beneath the supergiant Timmins-Porcupine orogenic gold camp, Canada
  • +4
  • Ademola Q Adetunji,
  • Ian J. Ferguson,
  • Jack M Simmons,
  • Chong Ma,
  • Saeid Cheraghi,
  • David B Snyder,
  • John A Ayer
Ademola Q Adetunji
Laurentian University

Corresponding Author:[email protected]

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Ian J. Ferguson
University of Manitoba
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Jack M Simmons
Laurentian University
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Chong Ma
Laurentian University
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Saeid Cheraghi
Laurentian University
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David B Snyder
Laurentian University
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John A Ayer
Harquail School of Earth Sciences, Laurentian University
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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 major 40 km by 20 km sub-horizontal 500-1000 S conductor north of the Porcupine Destor fault zone at 5–10 km depth. A horizontal component of this conductor, attributed to a deeply buried >2687 Ma graphitic argillaceous unit at the base of Porcupine assemblage, strikes east-west parallel to the Pipestone fault zone. A second steeply-dipping component strikes northwest-southeast parallel to the Buskegau River fault. This conductor correlates spatially with lateral breaks in seismic reflectors and velocity models in the upper, middle, and lower crust, and provides 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 reflects 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. Breaks in seismic reflectors underlying this conductor provide additional evidence of sub-vertical structures extending through the middle crust, postdating post-tectonic collapse or orogen-parallel ductile flow at ∼2660-2590 Ma, and consistent with late strike-slip deformation.