Alteration and mineralisation at the Island Copper deposit is related to the intrusion of Early Jurassic quartz feldspar porphyry
dykes into surrounding comagmatic Bonanza volcanic rocks. The pyrophyllite alteration zone forms an upward flaring cone,
largely hosted within a breccia body that c ross-cuts the Cu, Mo, and Au-rich ore shell. This alteration zone contains
pyrophyllite, dumortierite and diaspore and resembles alteration occurring in some high-sulfidation deposits, but which is barren.
Fluid mineral equilibria and fluid inclusion studies indicate formation at approximately 300 C from fluids dominated by steam
and gases. These fluids appear highly acidic, but sulfur poor, leading to extreme base leaching within the breccia body and
surrounding rocks.