Magnetite deposits with distinctive actinolite apatite -bearing gangue and spatially-extensive sodic-calcic wall rock
alteration occur in both Proterozoic metamorphic terrains and Mesozoic-Tertiary magmatic arcs. Examples from both
settings constitute significant sources of iron ore (e.g. Kiruna, Sweden; El Romeral, Chile) and some host major Cu-Au
deposits that have a local association with K-silicate alteration (e.g. Cloncurry district, NW Queensland; Copiapo district,
Chile). A growing body of evidence points to a hydrothermal origin for these systems involving high temperature, low S
oxidized fluids. The Cloncurry magnetite-Cu-Au deposits are products of the local structurally channelized influx of a
specialized high salinity ore fluid into larger-scale alteration systems developed during pluton emplacement at greater depths
than those associated with subvolcanic (porphyry) Cu-Au deposits. The geological characteristics of deposits in magmatic
arcs are consistent with a similar mode of origin albeit in rather different tectonic settings.