Geophysical Signature of the NICO Au-Co-Bi-Cu Deposit and Its Iron Oxide-Alkali Alteration System, Northwest Territories, Canada

Models of the three-dimensional physical property variation of the NICO Au-Co-Bi-Cu deposit, Northwest Territories, and the Southern Breccia albitite-hosted uranium occurrences and their iron oxide-alkali alteration envelopes, were derived from inversion of high-resolution aeromagnetic, gravity, and magnetotelluric (MT) data at deposit to regional scales. In turn, integration of the geophysical results with physical property measurements and geologic observations leads to a new understanding of the geometry of the deposit, adjacent mineralized and altered zones, and potential cogenetic links within the host metasomatic system. NICO, which is a variant of the magnetite group iron oxide copper-gold (IOCG) class of deposit, is spatially associated with a discrete zone of lower electrical resistivity occurring within a broader, NE-dipping zone of higher density. The high-density zone overlaps a NE-dipping zone of higher magnetic susceptibility and is truncated to the southwest by a NW-striking geophysical discontinuity interpreted as a major fault zone. This inferred fault divides the magnetite-altered metasedimentary rocks hosting the NICO deposit from the albite-altered rocks within the Southern Breccia corridor to the southwest that host the uranium mineralization. Having been active during development of the metasomatic system, this fault influenced the formation of these distinct but complementary deposit types.