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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

Postmagmatic variability in ore composition and mineralogy in the T4 and T5 ore shoots at the high-grade flying fox Ni-Cu-PGE deposit, yilgarn craton, western Australia / Jane E. Collins in Economic geology, Vol. 107 N° 5 (Août 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 859-879 Titre : Postmagmatic variability in ore composition and mineralogy in the T4 and T5 ore shoots at the high-grade flying fox Ni-Cu-PGE deposit, yilgarn craton, western Australia Type de document : texte imprimé Auteurs : Jane E. Collins, Auteur ; Stephen J. Barnes, Auteur ; Steffen G. Hagemann, Auteur Année de publication : 2012 Article en page(s) : pp. 859-879 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : PGE;  high-grade  Flying  Fox  komatiite-hosted  Ni  sulfide  deposit;  Mineralogy;  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The high-grade Flying Fox komatiite-hosted Ni sulfide deposit, located in the Forrestania greenstone belt of the Archean Yilgarn Craton, Western Australia, is hosted in a deformed and metamorphosed volcano-metasedimentary succession. Postmineralization events have sheared and modified the texture and composition of the original massive sulfide ore, creating up to 11 distinct ore shoots including massive, stringer/vein, and breccia sulfides composed of pyrrhotite, pentlandite, chalcopyrite, and variable abundances of pyrite ranging up to 40 vol %. Nickel and platinum group elements (PGE) tenor variations were investigated in two ore shoots, T4 and T5. All mineralization styles show considerable variability in Ni tenor. PGEs show strong linear correlations between Ir, Os, Ru, and Rh, but poor correlation between Pt, Pd, and Cu. The normalized molar proportions of Fe, Ni, and S, projected into the Fe-Ni-S ternary system, show a distinct linear trend of pyrite addition to a typical primary magmatic composition and no correlation with mineralization style. The high pyrite content present throughout the Flying Fox ore is also associated with elevated Cu and As contents and is interpreted to be primarily due to the addition of pyrite from circulating Fe-, S-, Cu-, and As-enriched fluids creating pyrite-pentlandite intergrowths. Localized mechanical segregation of pyrite, sulfidation of pyrrhotite to pyrite, and oxidation of pyrrhotite to pyrite + magnetite has also contributed to these increased pyrite contents, although to a lesser extent. The addition and segregation of pyrite has diluted the Ni tenor, with no evidence to suggest chemical mobilization of Ni. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/859.short [article] Postmagmatic variability in ore composition and mineralogy in the T4 and T5 ore shoots at the high-grade flying fox Ni-Cu-PGE deposit, yilgarn craton, western Australia [texte imprimé] / Jane E. Collins, Auteur ; Stephen J. Barnes, Auteur ; Steffen G. Hagemann, Auteur . - 2012 . - pp. 859-879. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 5 (Août 2012) . - pp. 859-879 Mots-clés : PGE;  high-grade  Flying  Fox  komatiite-hosted  Ni  sulfide  deposit;  Mineralogy;  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The high-grade Flying Fox komatiite-hosted Ni sulfide deposit, located in the Forrestania greenstone belt of the Archean Yilgarn Craton, Western Australia, is hosted in a deformed and metamorphosed volcano-metasedimentary succession. Postmineralization events have sheared and modified the texture and composition of the original massive sulfide ore, creating up to 11 distinct ore shoots including massive, stringer/vein, and breccia sulfides composed of pyrrhotite, pentlandite, chalcopyrite, and variable abundances of pyrite ranging up to 40 vol %. Nickel and platinum group elements (PGE) tenor variations were investigated in two ore shoots, T4 and T5. All mineralization styles show considerable variability in Ni tenor. PGEs show strong linear correlations between Ir, Os, Ru, and Rh, but poor correlation between Pt, Pd, and Cu. The normalized molar proportions of Fe, Ni, and S, projected into the Fe-Ni-S ternary system, show a distinct linear trend of pyrite addition to a typical primary magmatic composition and no correlation with mineralization style. The high pyrite content present throughout the Flying Fox ore is also associated with elevated Cu and As contents and is interpreted to be primarily due to the addition of pyrite from circulating Fe-, S-, Cu-, and As-enriched fluids creating pyrite-pentlandite intergrowths. Localized mechanical segregation of pyrite, sulfidation of pyrrhotite to pyrite, and oxidation of pyrrhotite to pyrite + magnetite has also contributed to these increased pyrite contents, although to a lesser extent. The addition and segregation of pyrite has diluted the Ni tenor, with no evidence to suggest chemical mobilization of Ni. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/5/859.short

Targeting iron ore in banded iron formations using ASTER data / Paul Duuring in Economic geology, Vol. 107 N° 4 (Juin/Juillet 2012) 

Public ISBD [article]  in Economic geology > Vol. 107 N° 4 (Juin/Juillet 2012) . - pp. 585-597 Titre : Targeting iron ore in banded iron formations using ASTER data : weld range greenstone belt, Yilgarn Craton, western Australia Type de document : texte imprimé Auteurs : Paul Duuring, Auteur ; Steffen G. Hagemann, Auteur ; Yulia Novikova, Auteur Année de publication : 2012 Article en page(s) : pp. 585-597 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : ASTER  image  analysis  Fe  ore  deposits  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image analysis is a proven method for mapping mineral and geochemical zonation associated with a variety of ore types, including orogenic Au, porphyry Cu-(Mo), porphyry-skarn, Pb-Zn-Au, and Mn systems. Only recently has this technique been applied, in a general sense, to mineral alteration mapping and exploration for Fe ore deposits hosted by banded iron formations (BIFs). For this reason, the Archean Weld Range greenstone belt that hosts the Beebyn and Madoonga Fe ore deposits has been chosen as a case study area to test the effectiveness of ASTER imaging techniques for the identification of Fe orebodies. Banded iron formations in the Weld Range district crop out as a series of parallel, 10- to 500-m-wide, <150-m-high, ENE-trending ridges that continue along strike for up to 70 km. Individual ridges of BIFs are surrounded by mafic igneous rocks, whereas felsic volcanic and volcaniclastic rocks and granitoid intrusions are exposed as rounded low-lying mounds in the northern and eastern areas of the district. All outcrop is at least moderately weathered. Thick layers of unconsolidated alluvial and colluvial sediments dominate low-lying areas. The Beebyn and Madoonga high-grade (>55 wt % Fe) iron ore deposits host Archean hypogene magnetite and specular hematite orebodies that are locally replaced by more recently formed, supergene goethite-hematite ore within several hundred meters of the present erosion surface. A common feature of all ore types hosted by BIFs is a high Fe content relative to SiO2. Consequently, all types of Fe ore in the Weld Range district are best identified by the ferric iron to silica index and the opaques to silica index, for the reason that these ASTER image products detect surfaces that are rich in (opaque) Fe oxide minerals and have a low silica abundance. Gabbro, dolerite, and basalt country rocks located within 20 m of high-grade Fe ore zones in BIFs are altered to hypogene Fe-rich chlorite and, more rarely, are altered by Fe-rich talc. These hypogene alteration zones are best detected by the ferrous iron content in MgOH minerals and carbonates and the FeOH group abundance products, which identify hypogene Fe chlorite and Fe talc. This study demonstrates that integrated remote spectral sensing techniques (ASTER, airborne hyperspectral, and radiometric) used in conjunction with geophysical surveys (aeromagnetic and gravity) are useful for district-scale exploration for Fe orebodies hosted by BIFs. The spectral sensing techniques are a rapid, cost-effective, and efficient means for generating and ranking exploration targets that are located in areas with restricted physical access. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/4/585.short [article] Targeting iron ore in banded iron formations using ASTER data : weld range greenstone belt, Yilgarn Craton, western Australia [texte imprimé] / Paul Duuring, Auteur ; Steffen G. Hagemann, Auteur ; Yulia Novikova, Auteur . - 2012 . - pp. 585-597. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 4 (Juin/Juillet 2012) . - pp. 585-597 Mots-clés : ASTER  image  analysis  Fe  ore  deposits  Australia Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image analysis is a proven method for mapping mineral and geochemical zonation associated with a variety of ore types, including orogenic Au, porphyry Cu-(Mo), porphyry-skarn, Pb-Zn-Au, and Mn systems. Only recently has this technique been applied, in a general sense, to mineral alteration mapping and exploration for Fe ore deposits hosted by banded iron formations (BIFs). For this reason, the Archean Weld Range greenstone belt that hosts the Beebyn and Madoonga Fe ore deposits has been chosen as a case study area to test the effectiveness of ASTER imaging techniques for the identification of Fe orebodies. Banded iron formations in the Weld Range district crop out as a series of parallel, 10- to 500-m-wide, <150-m-high, ENE-trending ridges that continue along strike for up to 70 km. Individual ridges of BIFs are surrounded by mafic igneous rocks, whereas felsic volcanic and volcaniclastic rocks and granitoid intrusions are exposed as rounded low-lying mounds in the northern and eastern areas of the district. All outcrop is at least moderately weathered. Thick layers of unconsolidated alluvial and colluvial sediments dominate low-lying areas. The Beebyn and Madoonga high-grade (>55 wt % Fe) iron ore deposits host Archean hypogene magnetite and specular hematite orebodies that are locally replaced by more recently formed, supergene goethite-hematite ore within several hundred meters of the present erosion surface. A common feature of all ore types hosted by BIFs is a high Fe content relative to SiO2. Consequently, all types of Fe ore in the Weld Range district are best identified by the ferric iron to silica index and the opaques to silica index, for the reason that these ASTER image products detect surfaces that are rich in (opaque) Fe oxide minerals and have a low silica abundance. Gabbro, dolerite, and basalt country rocks located within 20 m of high-grade Fe ore zones in BIFs are altered to hypogene Fe-rich chlorite and, more rarely, are altered by Fe-rich talc. These hypogene alteration zones are best detected by the ferrous iron content in MgOH minerals and carbonates and the FeOH group abundance products, which identify hypogene Fe chlorite and Fe talc. This study demonstrates that integrated remote spectral sensing techniques (ASTER, airborne hyperspectral, and radiometric) used in conjunction with geophysical surveys (aeromagnetic and gravity) are useful for district-scale exploration for Fe orebodies hosted by BIFs. The spectral sensing techniques are a rapid, cost-effective, and efficient means for generating and ranking exploration targets that are located in areas with restricted physical access. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/107/4/585.short

The BIF-hosted high-grade iron ore deposits in the archean koolyanobbing greenstone belt, western Australia / Thomas Angerer in Economic geology, Vol. 105 N° 5 (Août 2010) 

Public ISBD [article]  in Economic geology > Vol. 105 N° 5 (Août 2010) . - pp. 917-945 Titre : The BIF-hosted high-grade iron ore deposits in the archean koolyanobbing greenstone belt, western Australia : structural control on synorogenic- and weathering-related magnetite-, hematite-, and goethite-rich iron ore Type de document : texte imprimé Auteurs : Thomas Angerer, Auteur ; Steffen G. Hagemann, Auteur Année de publication : 2011 Article en page(s) : pp. 917-945 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Australia  Archean  Iron  Ore Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Koolyanobbing banded iron formation (BIF)-hosted iron ore deposits (total premining resources ~150 million metric tons (Mt), indicated reserves ~32 Mt) are located in the Mesoarchean lower succession BIF of the Koolyanobbing greenstone belt, Younami terrane, Yilgarn craton in Western Australia. In the Koolyanobbing greenstone belt a deformation sequence that broadly correlates with the proposed deformation history of most greenstones belts within the Southern Cross domain includes: D1 structures (mainly small-scale F1a and F1b folds, formed in a north-south to northwest-southeast compressional regime), a ductile to brittle deformation sequence, D2 to D4 (generated during east-west compression) and, a late-stage brittle segmentation of BIF and reactivation of faults, attributed to D5. The formation of the seven known medium- (45–58 wt % Fe) to high-grade (58–68 wt % Fe) magnetite-, martite-, specularite-, and goethite-bearing orebodies can be subdivided into four Archean stages and one weathering-related upgrade from the Permian and/or Mesozoic to recent times. The Archean ore-forming stages comprise: (1) early Fe-Mg ± Ca metasomatism causing local ferroan carbonate and ferroan talc alteration of the metamorphosed quartz-magnetite BIF protolith; (2) sequential syn-D2a (coaxial) to syn-D4 (transpressional) tight folding-driven removal of carbonate, quartz and minor ferroan talc by solution and mechanical transfer, producing residual enrichment of medium- to high-grade magnetite ore; (3) magnetite mineralization in syn-D2b and syn-D4 breccias and fractures, forming medium-grade ore zones, or overprint magnetite in BIF and first-stage magnetite ore; and (4) mineralization of hydrothermal specularite and locally associated ferroan dolomite-quartz alteration, and local oxidation of magnetite in and near brittle D4 faults, fractures, and reactivated F1 and F2a fold cores. Modern weathering-related leaching of carbonate (and minor quartz), pseudomorphic goethite replacement of existing iron oxides and gangue, and coeval or subsequent to oxidation in the vadose zone formed goethite-martite ore with local relics of specularite or magnetite and/or kenomagnetite. The intensity and localization of this supergene modification is, in most deposits at Koolyanobbing, controlled by existing hypogene magnetite, specularite-rich medium- to high-grade ore zones and/or carbonate-altered BIF at depth. The existence of high-grade ore below the weathering horizons suggests the possibility of further concealed magnetite- and/or specularite-rich orebodies within the deposits and region. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/5/917.abstract [article] The BIF-hosted high-grade iron ore deposits in the archean koolyanobbing greenstone belt, western Australia : structural control on synorogenic- and weathering-related magnetite-, hematite-, and goethite-rich iron ore [texte imprimé] / Thomas Angerer, Auteur ; Steffen G. Hagemann, Auteur . - 2011 . - pp. 917-945. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 105 N° 5 (Août 2010) . - pp. 917-945 Mots-clés : Australia  Archean  Iron  Ore Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Koolyanobbing banded iron formation (BIF)-hosted iron ore deposits (total premining resources ~150 million metric tons (Mt), indicated reserves ~32 Mt) are located in the Mesoarchean lower succession BIF of the Koolyanobbing greenstone belt, Younami terrane, Yilgarn craton in Western Australia. In the Koolyanobbing greenstone belt a deformation sequence that broadly correlates with the proposed deformation history of most greenstones belts within the Southern Cross domain includes: D1 structures (mainly small-scale F1a and F1b folds, formed in a north-south to northwest-southeast compressional regime), a ductile to brittle deformation sequence, D2 to D4 (generated during east-west compression) and, a late-stage brittle segmentation of BIF and reactivation of faults, attributed to D5. The formation of the seven known medium- (45–58 wt % Fe) to high-grade (58–68 wt % Fe) magnetite-, martite-, specularite-, and goethite-bearing orebodies can be subdivided into four Archean stages and one weathering-related upgrade from the Permian and/or Mesozoic to recent times. The Archean ore-forming stages comprise: (1) early Fe-Mg ± Ca metasomatism causing local ferroan carbonate and ferroan talc alteration of the metamorphosed quartz-magnetite BIF protolith; (2) sequential syn-D2a (coaxial) to syn-D4 (transpressional) tight folding-driven removal of carbonate, quartz and minor ferroan talc by solution and mechanical transfer, producing residual enrichment of medium- to high-grade magnetite ore; (3) magnetite mineralization in syn-D2b and syn-D4 breccias and fractures, forming medium-grade ore zones, or overprint magnetite in BIF and first-stage magnetite ore; and (4) mineralization of hydrothermal specularite and locally associated ferroan dolomite-quartz alteration, and local oxidation of magnetite in and near brittle D4 faults, fractures, and reactivated F1 and F2a fold cores. Modern weathering-related leaching of carbonate (and minor quartz), pseudomorphic goethite replacement of existing iron oxides and gangue, and coeval or subsequent to oxidation in the vadose zone formed goethite-martite ore with local relics of specularite or magnetite and/or kenomagnetite. The intensity and localization of this supergene modification is, in most deposits at Koolyanobbing, controlled by existing hypogene magnetite, specularite-rich medium- to high-grade ore zones and/or carbonate-altered BIF at depth. The existence of high-grade ore below the weathering horizons suggests the possibility of further concealed magnetite- and/or specularite-rich orebodies within the deposits and region. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/105/5/917.abstract