Petrological Mapping and Chemical Discrimination of Alteration Facies as Vectors to IOA, IOCG, and Affiliated Deposits within Laurentia and Beyond
Résumé
Recent research on iron oxide and alkali-calcic alteration systems of the Great Bear magmatic zone, Romanet Horst, Central Mineral Belt, Bondy Gneiss Complex (Canada) and southeast Missouri (USA) districts highlights the potential for Laurentia to host undiscovered iron oxide-apatite (IOA), iron oxide copper–gold (IOCG), and affiliated deposits. The metasomatic footprints are vertically zoned from deeper Na (albite), through Ca-Fe (amphibole-magnetite-apatite), K-Fe (magnetite-biotite-K-feldspar to shallower hematite-sericite-chlorite-carbonate), and epithermal alteration facies. The facies can be discriminated by Na-Ca-Fe-K-Mg mineral assemblages and cation proportions, and from other ore systems by cation contents and Al-Si proportions. Each facies has distinct paragenetic, chemical, and geophysical characteristics and their metasomatic reaction paths vector to specific deposit types (IOA, IOCG, skarn, albitite-hosted U or Au-Co-U, and polymetallic vein deposits). Exploration in Laurentia can be focused by considering: (1) distribution of IOA, IOCG, and affiliated deposits in mineral belts up to 1500 km long; (2) pan-Laurentia distribution of fertile Paleoproterozoic and Mesoproterozoic terranes; and (3) diagnostic metasomatic signatures that can be used as vectors to ore.
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