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The deposit is hosted by a maar-diatreme system that cuts Late Cretaceous sedimentary rocks and spilites. It is characterised by two stages of advanced argillic alteration: stage I fluids produced deep alunite + quartz and shallower kaolinite + quartz, both associated with disseminated pyrite; stage II fluids overprinted them with deep pyrophyllite and an overlying silica cap, at temperatures that had risen from around 250 to between 250 and 300 degrees C, as indicated by mineral stabilities and sulphur isotope geothermometry. H, O and S isotope analysis indicates that stage I alteration and disseminated Au-Ag mineralisation occurred at equilibrium with magmatic discharge fluids with only minor (up to 25%) dilution by meteoric water. Stage II advanced alteration resulted from a renewed influx of essentially pure magmatic fluid, whose significant dilution by groundwater generated the shallow silica cap.The acid sulphate mineralisation was sealed from groundwater and seawater infiltration by deposition of an adjacent carbonate-sulphate zone, itself due to circulation of heated seawater. The results suggest that the dominant proportion of metals and fluids in acid sulphate systems are derived from bulk condensates of magmatic vapours, though small proportions of other fluids may cause precipitation., The deposit is hosted by a maar-diatreme system that cuts Late Cretaceous sedimentary rocks and spilites. It is characterised by two stages of advanced argillic alteration: stage I fluids produced deep alunite + quartz and shallower kaolinite + quartz, both associated with disseminated pyrite; stage II fluids overprinted them with deep pyrophyllite and an overlying silica cap, at temperatures that had risen from around 250 to between 250 and 300 degrees C, as indicated by mineral stabilities and sulphur isotope geothermometry. H, O and S isotope analysis indicates that stage I alteration and disseminated Au-Ag mineralisation occurred at equilibrium with magmatic discharge fluids with only minor (up to 25%) dilution by meteoric water. Stage II advanced alteration resulted from a renewed influx of essentially pure magmatic fluid, whose significant dilution by groundwater generated the shallow silica cap.The acid sulphate mineralisation was sealed from groundwater and seawater infiltration by deposition of an adjacent carbonate-sulphate zone, itself due to circulation of heated seawater. The results suggest that the dominant proportion of metals and fluids in acid sulphate systems are derived from bulk condensates of magmatic vapours, though small proportions of other fluids may cause precipitation.

The Late Cretaceous to Eocene rocks form part of an accretionary prism complex and host more than 600 known massive sulphide deposits and prospects. Fluid inclusion, stable isotope and whole-rock data all support sea-floor volcanogenesis in both sediment-starved and sedimented mid-ocean ridge settings. Deposits hosted by pillow lavas, massive basalts and mafic tuffs are analagous to Cyprus-type deposits. Those hosted by intercalated slates and greywackes are analagous to Besshi-type deposits. Both types are similar morphologically and are characteristically stratiform to stratabound. They vary in size from under 1 000 000 t to over 5 000 000 t ore, with the largest mostly Besshi-type. Dominant minerals are pyrite, pyrrhotite, chalcopyrite and sphalerite, with minor cubanite, arsenopyrite, tetrahedrite and secondary marcasite. Gangue is mainly quartz and chlorite. Sedimentary features and ubiquitous. The sediment-hosted ores give lower temperature values and higher sulphur and oxygen levels than volcanic-hosted ores, reflecting mixing of hydrothermal fluids with seawater in the sediment pile. Geochemical analyses suggest normal and enriched mid-ocean ridge basalts and low-K arc tholeiites., The Late Cretaceous to Eocene rocks form part of an accretionary prism complex and host more than 600 known massive sulphide deposits and prospects. Fluid inclusion, stable isotope and whole-rock data all support sea-floor volcanogenesis in both sediment-starved and sedimented mid-ocean ridge settings. Deposits hosted by pillow lavas, massive basalts and mafic tuffs are analagous to Cyprus-type deposits. Those hosted by intercalated slates and greywackes are analagous to Besshi-type deposits. Both types are similar morphologically and are characteristically stratiform to stratabound. They vary in size from under 1 000 000 t to over 5 000 000 t ore, with the largest mostly Besshi-type. Dominant minerals are pyrite, pyrrhotite, chalcopyrite and sphalerite, with minor cubanite, arsenopyrite, tetrahedrite and secondary marcasite. Gangue is mainly quartz and chlorite. Sedimentary features and ubiquitous. The sediment-hosted ores give lower temperature values and higher sulphur and oxygen levels than volcanic-hosted ores, reflecting mixing of hydrothermal fluids with seawater in the sediment pile. Geochemical analyses suggest normal and enriched mid-ocean ridge basalts and low-K arc tholeiites.