Structural analysis of aeromagnetic data from the Rainy River Block, Wabigoon subprovince, Minnesota, USA and Ontario, Canada: Strain partitioning along a Neoarchean terrane boundary and implications for mineral exploration

Abstract

High-resolution aeromagnetic data are used to constrain the structural architecture and mineral potential of the Neoarchean Rainy River Block (RRB)—a sigma-shaped wedge of till-covered volcano-plutonic rocks that form the southern margin the Wabigoon subprovince and span the international border between northern Minnesota, USA and western Ontario, Canada. Reduced-to-pole transformed, upward continued and derivative enhanced aeromagnetic data show that the RRB can be divided into three structural domains: the Rainy Lake wrench zone (RLWZ), Border zone (BZ), and Oaks belt (OB). Strain intensity decreased from east (strongly deformed RLWZ) to west (moderately deformed OB). The RLWZ experienced superimposed folding that resulted in complex rock geometries and sigmoidal patterns in the aeromagnetic data. A large northeast trending syncline, partially represented by an aeromagnetic low that is cut by similarly oriented shear zones and faults, comprises the BZ. The OB is interpreted to occupy a regional-scale strain shadow and is composed of a relatively well preserved and magnetically heterogeneous volcanic pile and subvolcanic intrusion that have been overturned and are steeply north dipping. As the RRB is fault-bounded terrane boundary and hosts numerous mafic intrusions, it was a regional zone of synvolcanic and syntectonic paleo-permeability and, therefore, has potential for hosting orogenic gold and volcanogenic massive sulfide (VMS) deposits. However, linear fault geometries throughout most of the RRB were not conducive to formation of large orogenic gold deposits and pervasive deformation in the RLWZ may have compromised preservation of hypogene VMS mineralized zones. Thus, the structurally preserved OB is the most prospective area for hosting VMS deposits in the RRB, whereas the BZ and surrounding rocks are prospective for hosting orogenic gold deposits near a ∼30km long restraining bend in the Quetico Fault.