John Ayer

Mineral prospectivity maps were produced for gold in two greenstone belts in the Superior geological province in Ontario, Canada, as part of the Metal Earth Project in the Laurentian University, Sudbury, Ontario. These maps, created using the random forest machine learning algorithm, cover the well-endowed Matheson area, which is in the Abitibi sub-province, and the less fertile Dryden area, which is in the Wabigoon sub-province. Newly identified areas for follow-up gold exploration are associated with major faults and 3D geophysical data comprising resistivity, density and susceptibility data. In addition, observations not used in mineral prospectivity mapping based on magnetotelluric, seismic and isotopic data may in part describe why the Matheson greenstone belt is more fertile with respect to gold mineralization than the Dryden greenstone belt. These observations suggest that the Matheson area has major transcurrent faults associated with conductive zones that reach the surface, many of which are associated with deeply penetrating, vertical faults. The isotopic signature of the Matheson crust also suggests it is juvenile, whereas the Dryden area is older.

Recently, there was an increase of costs to explore new economical mineral occurrences, while the success of discovery of new deposits has diminished. Therefore, Metal Earth was conceived with the objective to improve understanding of the processes controlling the distribution of mineral endowment, with a focus on Archean greenstone belts of the Canadian Superior Province as a global representative of these belts. Part of Metal Earth is to study thirteen different transects with a total length of >1000 km associated with Archean greenstone belts with various degrees of mineralisation (from less endowed to well-endowed) using high-resolution multidisciplinary geological and geophysical data. The goal is to reliably identify deeper underlying crustal/mantle conditions controlling mineralisation and also to validate existing ore deposit models by better identifying components contributing to mineral endowment. In this paper, we discuss acquiring, processing and preliminary modelling of multidisciplinary geophysical data (i.e. seismic, magnetotelluric, potential field data and petrophysical characterisations) to reliably model subsurface features along the transects. Across the Swayze transect, seismic sections clearly show sub-horizontal and dipping geological boundaries and magnetotelluric model reveals pathways as narrow upper crustal sub-vertical zones of low resistivity. In addition, joint inversion of gravity and magnetic data on initial models constrained by surface geology, seismic and magnetotelluric models and petrophysical characterisations have improved the models by better detecting at depth the limits of lithological units, low-density batholiths, dykes and fault zones. New models reveal there are significant crustal difference between the well-endowed Abitibi and the less prospective Wabigoon subprovinces. The final models will map the lithospheric architecture and constrain large-scale intracratonic controls on magmatism, crustal and tectonic evolution, and subsequently mineralisation.