Oral Presentation Sub22 Conference

Geophysical results after five years of the Metal Earth project (17160)

Richard S Smith 1 , Mostafa Naghizadeh 1 2 , Saeid Cheraghi 1 , Ademola Adetunji 1 , Rajesh Vayavur 1 , Esmaeil Eshaghi 3 , Graham J Hill 4 , David Snyder 1 , Eric A Roots 1 , Fabiano Della Justina 1 , Hossein Jodeiri Akbari Fam 1 , Christopher Mancuso 1 , William McNeice 5 , Amir Maleki 6 , Rasmus Haugaard 1 , Taus R C Jørgensen 1 , Philip Wannamaker 7 , Virginie Maris 7
  1. Laurentian University, Ottawa, ONTARIO, Canada
  2. OptiSeis Solutions Ltd, Calgary, Canada
  3. Fortesque Metals Group, East Perth, Australia
  4. Czech Academy of Sciences, Prague, Czech Republic
  5. Discovery Geophysics International, Vancouver, Canada
  6. Wallbridge Mining Company, Sudbury, Canada
  7. Energy and Geoscience Institute, Salt Lake City, USA

The Metal Earth project attempts to improve the understanding of controls on mineralization in Precambrian terranes by utilizing a multidisciplinary approach involving geology, geophysics, geochemistry and geochronology. The geophysics excel in elucidating the structure of the shallow, mid and deeper crust, with the primary tools being magnetic, gravity, magnetotelluric and reflection seismic data, primarily collected along crooked 2D profiles.  Magnetic data is generally used to help map the geology away from the profiles; while the gravity data is useful for extending the near-surface geology to greater depths, as deep as 10 km, particularly when constrained by physical properties or seismic data.

The magnetotelluric data shows the upper crust to about 10 km as highly resistive, except for subvertical conductive zones that correspond to major deformation zones, many of which are metalliferous. These zones connect to larger horizontal conductive zones in the mid-to-lower crust, and could represent mineralizing fluid pathways feeding the deposits in the upper crust.   

The reflection seismic data show the upper crust is primarily non-reflective, except for small and isolated horizontal reflectors.  However, the mid crust shows many horizontal reflectors, usually with a ‘constant’ dip, often to the north.  The deeper crust, below about 20 km is typically subtly different from the mid crust. 

Passive seismic data have also been collected.  Surface-wave tomography can be used to infer broad zones of similar seismic velocity between major reflectors.  Receiver function analysis has been used to identify deeper structures such as a horizontal feature at or below the Moho and a dipping structure evident to about 70 km depth.

Processing crooked-line reflection seismic data is technically challenging so this has necessitated development of analysis techniques such as multifocussing, 3D processing, full-waveform inversion, and cross-dip move-out methods, which reduce the noise and provide valuable cross-dip information. 

 

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  • Caption:: Comparing the stack sections and migrated images obtained by different flows including a) conventional NMO+DMO stack and b) poststack phase-shift time migration of the stack section along a straight CMP line, c) 2.5D MF stack and d) poststack Kirchhoff time migration of 2.5D MF stack section along a slalom CMP line. All sections are plotted within the same northing coordinate.
  • Acknowledgements: Financial support was provided by the Canada First Research Excellence Fund. The reflection seismic data were collected by SAExploration and processed by Absolute Imaging. Moombarriga Geoscience and Complete Magnetotelluric Solutions acquired the MT data. The passive seismic data were acquired and processed by Sisprobe. Specialty geophysics software was provided by Mira Geoscience, Seequent and Aspentech Paradigm. This is Metal Earth contribution number MERC-ME-2022-30