Garnet chemistry to constrain ore processes and establish exploration methodologies for orthomagmatic systems in high temperature metamorphic settings

Lower-crustal, high-grade metamorphic terranes have typically been recognised as unprospective for orthomagmatic sulfide mineralisation. However, recent work in volatiles and their role in aiding typically dense sulfide liquid across the mantle-crust boundary have increasingly recognised the role the lower-crust has as a potential zone for exploration. Thus, the unusual lower-crustal orthomagmatic Nova-Bollinger Ni-Cu deposit, hosted within high-grade metamorphic rocks and marbles of the Fraser Zone, represent an ideal opportunity to understand these processes on the deposit-scale.

Previous work on the Nova-Bollinger Ni-Cu deposit has shown that its sulfide-laden magma was emplaced into its host country rocks during peak regional metamorphism. These country rocks are comprised of garnetiferous gneisses and local marbles that were intruded by hot sulfide liquid. This study will present new petrological, geochemical, and isotopic data through the lens of garnet and carbonate systematics while modelling fine-resolution metamorphic conditions at the Nova-Bollinger deposit. Preliminary data display geochemical relationships between garnet and sulfide through internal zoning of slow-diffusing elements in garnet. Modelling of the metamorphic P-T-t conditions is ongoing and will inform of the deposit-scale metamorphic conditions during emplacement and place the data within the context of the Mesoproterozoic Albany-Fraser Orogen. Continuing work on C-and O stable isotopes in carbonate associated with sulfide will look to define the role of volatile exsolved carbon, which may have acted as a density aid for dense sulfide liquid.

Understanding the petrological and geochemical interplays sulfide has with garnet and carbonate and its relationship with its host country rocks are critical to expanding the search-space for metal exploration in lower-crustal, high-grade metamorphic terranes.

Involvement

Project Coordinator:

• Marco Fiorentini

Collaborators:

• Joshua Chong
• Laure Martin
• Naomi Tucker

Additional Information

Funding Agencies: ARC (DP190102422)

Industry Participants: IGO