The Sonju Lake intrusion (SLI) is a 1200-m-thick, shallow-dipping, sheet-like intrusion that forms part of the Beaver Bay Complex (RI-58, Chapter 7). Although its exposed strike-length is only about 3 km (Fig. 3-1), the SLI has a distinctive aeromagnetic signature that can be traced for at least 20 km beneath a cover of glacial drift. The nearly constant width of its aeromagnetic anomaly sugges...
