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Transcript of Sediment-Hosted Copper
cross-bedding Textures conglomerate- / sandstone-filled channels
scour and fill
ripple marks AGE no Archean deposits known Characteristics 1. Disseminated deposits in reduced rocks in continental redbed sequences.
2. Evaporites, caliche, calcrete, mudcracks and other features record arid and semi-arid continental environments of sedimentation.
3.Cu is generally the dominant metal, some deposits may contain significant Ag Depositional Environment permeable sediments
epicontinental shallow-marine basins
high evapration rate Associated Deposit Types halite, sylvite, gypum, anhydrite within same sedimentary sequences sandstone U unconformity U IOCG ORE MINERALOGY chalcocite bornite chalcopyrite pyrite (galena) (sphalerite) native Ag native Cu, where difficient in S Mineral Textures Disseminated stratabound (locally stratiform) framboidal / colloform pyrite common Cu minerals replace pyrite Common Alteration Green, white or grey rocks Reducing Fluids Oxidizing Fluids rich in Fe-calcite & chlorite albitic, hematite rocks depleted in base metals, calcium & potassium Ore Control reducing environments marine black shale
pyritic sediments permeable footwall sediments GENETIC MODEL 2 fluids oxidized brine reduced fluid carries copper as a chloride complex 1. oxidized source rock hematite stable contains ferromagnesian minerals, or mafic rock fragments continental red sandstone
subaerial volcanics 2. brine to mobilize copper evaporites often interbedded with red beds evaporation > rainfall evaporation of seawater 3. reduced fluid to precipitate Cu organic-rich shales hydrocarbons fluids interacting with pyrite chalcocite 4. conditions favourable for fluid mixing permeable faults porous sediments