Destabilization of Titanite in the Roxby Downs Granite Surrounding the Olympic Dam Fe-Oxide Cu-U-Au-Ag Deposit in South Australia - 2019

Rare Earth Deposits & Mining

Kontonikas-Charos and two co-authors reported in 2019 that titanite textures and geochemistry have been investigated from the Roxby Downs Granite, host to the Olympic Dam Fe-oxide Cu-U-Au-Ag deposit, South Australia. Three textural subtypes of titanite are documented:

1. primary magmatic (cores and rims);
2. late/interstitial; and
3. secondary (low T recrystallisation).

Magmatic cores are defined by enrichment in LREE (~3 wt%), Nb (up to 1 wt%) and Zr relative to rims, which typically contain <1 wt% LREE and Nb, as well as greater concentrations of Al, Ca, Fe and F. Secondary titanite forms as a low temperature hydrothermal overprint on primary titanite, as well as an alteration product of chloritised phlogopite.

Titanite breakdown is a ubiquitous feature of the RDG, and occurs through interaction with CO₂^- and F-rich fluids, forming REEfluorocarbonates, which are subsequently overprinted by REE-phosphates with increased proximity to the Olympic Dam Breccia Complex. This change is related to interaction with fluids containing appreciable free PO₄²-, liberated from local fluorapatite dissolution, and represents later/retrograde stages in the formation of the Olympic Dam deposit.