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Geochemical Evolution of the Banded Iron Formation-hosted high-grade iron ore system in the koolyanobbing greenstone belt, western Australia / Thomas Angerer in Economic geology, Vol. 107 N° 4 (Juin/Juillet 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 4 (Juin/Juillet 2012) . - pp. 599-644 Titre : Geochemical Evolution of the Banded Iron Formation-hosted high-grade iron ore system in the koolyanobbing greenstone belt, western Australia Type de document : texte imprimé Auteurs : Thomas Angerer, Auteur ; Steffen G. Hagemann, Auteur ; Leonid V. Danyushevsky, Auteur Année de publication : 2012 Article en page(s) : pp. 599-644 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : BIF-hosted  iron  ore  deposits  Geochemical  evolution  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The banded iron formation (BIF)-hosted iron ore deposits in the lower greenstone succession of the Koolyanobbing greenstone belt, 50 km north of Southern Cross in Western Australia, are a ~200 Mt high-grade Fe (>58%) pre-mining resource and represents one of the most important iron ore districts in the Yilgarn craton. Four hypogene alteration (ore-forming) stages and one supergene upgrading event took place: (1) During ore stage 1, LREE-depleted, transition metal-enriched, Mg-Fe (±Ca) carbonates replaced quartz in BIFs. The deposit-scale alteration was most likely induced by devolatilization of sea-floor–altered, Ca-Si–depleted mafic rocks in the vicinity of the BIF during early regional (syn-D1), very low to low-grade metamorphism and was most strongly developed on reactivated BIF-basalt contacts. (2) Ore stage 2 involved the formation of patchy magnetite ore by a syn-D2 to -D4 dissolution of early carbonate. Enrichment of Fe2O3total in magnetite iron ore was by a factor of 2 to 2.4, and compatible trace elements in magnetite, such as Ga, V, and Al, were immobile. A subdeposit-scale ferroan talc-footprint proximal to magnetite iron ore in the largest deposit (K deposit) was associated with ore stage 2 and resulted from dissolution of magnesite due to reaction with silica in the BIF under greenschist facies conditions and potentially high fluid/rock ratio. (3) Magnetite growth, during ore stage 3, forming granular magnetite-martite ore is related to a subsequent hydrothermal event, occurring locally throughout the belt, especially in D2b faults. (4) Ore stage 4 was associated with Fe-Ca-P-(L)REE-Y–enriched hydrothermal fluids, possibly from a magmatic source such as the postmetamorphic Lake Seabrook granite that crops out about 10 km west of the Koolyanobbing deposits and at the southern margin of the greenstone belt. These Ca-enriched fluids interacted with distal metamorphosed mafic rock and influenced the BIF-ore system in a small number of deposits. They were channelled through regional D4 faults and caused specularite-dolomite-quartz alteration, resulting in Fe grades of up to 68%. (5) Supergene upgrade (ore stage 5) by (further) gangue leaching in the weathering zone was most effective in carbonate-altered BIFs and magnetite ore. This process, together with supergene martitization and goethite replacement of magnetite, led to the formation of high-grade, locally (at K deposit) high P goethite-martite ore. At Koolyanobbing, the two geochemically distinct stages of Archean carbonate alteration clearly controlled the formation of hypogene magnetite-specularite-martite–rich ore and recent supergene modification, including the further upgrade of Fe ore. DEWEY : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/4/599.short [article] Geochemical Evolution of the Banded Iron Formation-hosted high-grade iron ore system in the koolyanobbing greenstone belt, western Australia [texte imprimé] / Thomas Angerer, Auteur ; Steffen G. Hagemann, Auteur ; Leonid V. Danyushevsky, Auteur . - 2012 . - pp. 599-644. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 4 (Juin/Juillet 2012) . - pp. 599-644 Mots-clés : BIF-hosted  iron  ore  deposits  Geochemical  evolution  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The banded iron formation (BIF)-hosted iron ore deposits in the lower greenstone succession of the Koolyanobbing greenstone belt, 50 km north of Southern Cross in Western Australia, are a ~200 Mt high-grade Fe (>58%) pre-mining resource and represents one of the most important iron ore districts in the Yilgarn craton. Four hypogene alteration (ore-forming) stages and one supergene upgrading event took place: (1) During ore stage 1, LREE-depleted, transition metal-enriched, Mg-Fe (±Ca) carbonates replaced quartz in BIFs. The deposit-scale alteration was most likely induced by devolatilization of sea-floor–altered, Ca-Si–depleted mafic rocks in the vicinity of the BIF during early regional (syn-D1), very low to low-grade metamorphism and was most strongly developed on reactivated BIF-basalt contacts. (2) Ore stage 2 involved the formation of patchy magnetite ore by a syn-D2 to -D4 dissolution of early carbonate. Enrichment of Fe2O3total in magnetite iron ore was by a factor of 2 to 2.4, and compatible trace elements in magnetite, such as Ga, V, and Al, were immobile. A subdeposit-scale ferroan talc-footprint proximal to magnetite iron ore in the largest deposit (K deposit) was associated with ore stage 2 and resulted from dissolution of magnesite due to reaction with silica in the BIF under greenschist facies conditions and potentially high fluid/rock ratio. (3) Magnetite growth, during ore stage 3, forming granular magnetite-martite ore is related to a subsequent hydrothermal event, occurring locally throughout the belt, especially in D2b faults. (4) Ore stage 4 was associated with Fe-Ca-P-(L)REE-Y–enriched hydrothermal fluids, possibly from a magmatic source such as the postmetamorphic Lake Seabrook granite that crops out about 10 km west of the Koolyanobbing deposits and at the southern margin of the greenstone belt. These Ca-enriched fluids interacted with distal metamorphosed mafic rock and influenced the BIF-ore system in a small number of deposits. They were channelled through regional D4 faults and caused specularite-dolomite-quartz alteration, resulting in Fe grades of up to 68%. (5) Supergene upgrade (ore stage 5) by (further) gangue leaching in the weathering zone was most effective in carbonate-altered BIFs and magnetite ore. This process, together with supergene martitization and goethite replacement of magnetite, led to the formation of high-grade, locally (at K deposit) high P goethite-martite ore. At Koolyanobbing, the two geochemically distinct stages of Archean carbonate alteration clearly controlled the formation of hypogene magnetite-specularite-martite–rich ore and recent supergene modification, including the further upgrade of Fe ore. DEWEY : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/4/599.short