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Sediment-Hosted Copper

An introduction of the geology of Red Bed Copper deposits.

Micheal Moroskat

on 10 May 2011

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Transcript of Sediment-Hosted Copper

GTN 456 Sediment-Hosted Copper Deposits restricted to a narrow range of layers within a sedimentary sequence after deposition of the host rock prior to or during lithification marine and lucustrine Host Rocks low-energy calcareous or dolomitic siltstones, shales and carbonate rocks high-energy sandstones and conglomerates continental REDUCED FACIES RED BED stratabound epigenetic diagenetic Textures thin-bedded to finely laminated
bacterial mats/stromatolites
cross-bedding Textures conglomerate- / sandstone-filled channels
scour and fill
rip-up clasts
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
near paleo-equator
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
fossil wood
algal mats
biogenic sulphides
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
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