Fe-rich magmatic volatiles in the Ridgeway Au-Cu porphyries: evidence from magnetite-quartz comb-layered textures

Magnetite (± quartz) comb-layered textures occur in intrusions intimately associated with ore-bearing hydrothermal alteration assemblages at the Ridgeway alkalic porphyry Au-Cu deposit. These magnetite-rich textures imply that extremely Fe-rich magmatic volatiles accumulated within these silicic intrusions. Our micro-textural and micro-analytical study suggests that these Fe-rich magmatic volatiles transported and deposited ore-forming metals (including Cu, Zn, Mo, Pb, and Au). The occurrence of thickly stacked magnetite-quartz comb-layered textures implies that large volumes of these volatiles streamed through the Ridgeway intrusions. Their recognition highlights the specialized nature of the magma suite associated with the formation of an extremely highgrade Au porphyry deposit.