Abstract

The Great Bear magmatic zone in northern Canada hosts large iron oxide and alkali-altered systems that developed within a 10-m.y. period during the Paleoproterozoic. In the Eastern Treasure Lake and Duke sectors, and at the NICO deposit, early albitization associated with magmatism was followed by tungsten mineralization that was spatially associated with extensive skarn and Fe skarn alteration. Subsequent fluid-rock reactions led to substantial iron enrichment that culminated in iron oxide-apatite mineralization. At the transition from compressional/transpressional to extensional/transtensional stress regimes, changes in magma composition increased the metal budget of exsolved magmatic-hydrothermal fluids and played a key role in the formation of Au-Co-Bi mineralization at the NICO deposit and its satellite showings in the Duke zone. This process happened as the systems regionally transitioned to magnetite-bearing, potassic-iron alteration. The continued evolution of magmatism and fluid chemistry then contributed to the formation of iron oxide-copper-gold (IOCG) and variant mineralized zones in the Sue-Dianne and NICO deposits and other showings, and albite-hosted uranium mineralized zones elsewhere. The Great Bear magmatic zone illustrates that the evolution of magmatically derived fluids during a transition between different stress regimes can play a significant role in metal endowment and the ability of metasomatic systems to form skarn, iron oxide-apatite, IOCG, and albitite-hosted uranium mineralization.

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