The magnetic signature of Neoarchean alkaline intrusions and their related gold deposits: Significance and exploration implications

•3 late Neoarchean alkaline intrusion types are recognized from Abitibi aeromagnetics.•The magnetic characters of plutons are related to their geochemistry.•Pluton’s aeromagnetic signatures typify the style of associated Au mineralization.•Small intrusions with “annular” and “positive–central high” signatures have Au potential.

Exploration for Neoarchean intrusion-related gold deposits in the Abitibi greenstone belt of the Superior Craton, Canada, is of increasing interest as the two most recent Abitibi gold mines are intrusion-related. Late-Archean alkaline intrusions in the Abitibi Subprovince are separated into three groups based on their geophysical and geochemical signatures: (1) large, heterogeneous, unmineralized plutons; (2) small magnetite rich-syenites with magmatic gold, which is often remobilized along fault arrays; (3) small magnetite poor-quartz-syenites to alkali granites with magnetite-rich halos and magmatic gold mineralization. The positive, aeromagnetic high centred signature of some gold-bearing intrusions is related to the high content in magnetite of the more ferromagnesian intrusions resulting from their magmatic evolution. Intrusions with an annular shape record a lower Fe2O3t content in their less magnetite-rich cores and gold mineralization occurs within their magnetite-rich metasomatized host-rocks. If the aeromagnetic signature has an annular-shape, the lower-magnetic zones in the magnetic aureole are the more favourable zones. For those with a positive magnetic signature, the intrusion itself is the target.