Geology, hydrothermal activity, and sea-floor massive sulfide mineralization at the rumble II west mafic Caldera / Matthew I. Leybourne in Economic geology, Vol. 107 N° 8 (Décembre 2012)  

Public ISBD [article]  inEconomic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1649-1668 Titre : Geology, hydrothermal activity, and sea-floor massive sulfide mineralization at the rumble II west mafic Caldera Type de document : texte imprimé Auteurs : Matthew I. Leybourne, Auteur ; Cornel E. J. de Ronde, Auteur ; Richard J. Wysoczanski, Auteur Année de publication : 2013 Article en page(s) : pp. 1649-1668 Note générale : economic geology Langues : Anglais (eng) Mots-clés : sea-floor  massive sulfide mineralization  Caldera Résumé : Sea-floor imagery, volcanic rock, massive sulfide, and hydrothermal plume samples (δ3He, pH, dissolved Fe and Mn, and particulate chemistry) have been collected from the Rumble II West volcano, southern Kermadec arc, New Zealand. Rumble II West is a caldera volcano with an ∼3-km-diameter summit depression bounded by ring faults with a resurgent central cone. Rocks recovered to date are predominantly mafic in composition (i.e., basalt to basaltic andesite) with volumetrically lesser intermediate rocks (i.e., andesite). On the basis of its size, geometry, volcanic products, and composition, Rumble II West can be classified as a mafic caldera volcano. Rumble II West has a weak hydrothermal plume signature characterized by a small but detectable δ3He anomaly (25%). Time-series light scattering data though, obtained from vertical casts and tow-yos, do show that hydrothermal activity has increased in intensity between 1999 and 2011. Massive sulfides recovered from the eastern caldera wall and eastern flank of the central cone are primarily comprised of barite and chalcopyrite, with lesser sphalerite, pyrite, and traces of galena. The weak hydrothermal plume signal indicates that the volcano is in a volcanic-hydrothermal quiescent stage compared to other volcanoes along the southern Kermadec arc, although the preponderance of barite with massive sulfide mineralization indicates higher temperature venting in the past. Of the volcanoes along the Kermadec-Tonga arc known to host massive sulfides (i.e., Clark, Rumble II West, Brothers, Monowai, Volcano 19, and Volcano 1), the majority (five out of six) are dominantly mafic in composition and all but one of these mafic volcanoes form moderate-size to large calderas. To date, mafic calderas have been largely ignored as hosts to sea-floor massive sulfide deposits. That 75% of the presently known massive sulfide-bearing calderas along the arc are mafic in composition (the dacitic Brothers volcano is the exception) has important implications for sea-floor massive sulfide mineral exploration in the modern oceans and ancient rock record on land. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1649.short [article] Geology, hydrothermal activity, and sea-floor massive sulfide mineralization at the rumble II west mafic Caldera [texte imprimé] / Matthew I. Leybourne, Auteur ; Cornel E. J. de Ronde, Auteur ; Richard J. Wysoczanski, Auteur . - 2013 . - pp. 1649-1668. economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1649-1668 Mots-clés : sea-floor  massive sulfide mineralization  Caldera Résumé : Sea-floor imagery, volcanic rock, massive sulfide, and hydrothermal plume samples (δ3He, pH, dissolved Fe and Mn, and particulate chemistry) have been collected from the Rumble II West volcano, southern Kermadec arc, New Zealand. Rumble II West is a caldera volcano with an ∼3-km-diameter summit depression bounded by ring faults with a resurgent central cone. Rocks recovered to date are predominantly mafic in composition (i.e., basalt to basaltic andesite) with volumetrically lesser intermediate rocks (i.e., andesite). On the basis of its size, geometry, volcanic products, and composition, Rumble II West can be classified as a mafic caldera volcano. Rumble II West has a weak hydrothermal plume signature characterized by a small but detectable δ3He anomaly (25%). Time-series light scattering data though, obtained from vertical casts and tow-yos, do show that hydrothermal activity has increased in intensity between 1999 and 2011. Massive sulfides recovered from the eastern caldera wall and eastern flank of the central cone are primarily comprised of barite and chalcopyrite, with lesser sphalerite, pyrite, and traces of galena. The weak hydrothermal plume signal indicates that the volcano is in a volcanic-hydrothermal quiescent stage compared to other volcanoes along the southern Kermadec arc, although the preponderance of barite with massive sulfide mineralization indicates higher temperature venting in the past. Of the volcanoes along the Kermadec-Tonga arc known to host massive sulfides (i.e., Clark, Rumble II West, Brothers, Monowai, Volcano 19, and Volcano 1), the majority (five out of six) are dominantly mafic in composition and all but one of these mafic volcanoes form moderate-size to large calderas. To date, mafic calderas have been largely ignored as hosts to sea-floor massive sulfide deposits. That 75% of the presently known massive sulfide-bearing calderas along the arc are mafic in composition (the dacitic Brothers volcano is the exception) has important implications for sea-floor massive sulfide mineral exploration in the modern oceans and ancient rock record on land. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1649.short

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Submarine magmatic-hydrothermal systems at the Monowai volcanic center, Kermadec arc / Matthew I. Leybourne in Economic geology, Vol. 107 N° 8 (Décembre 2012)  

Public ISBD [article]  inEconomic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1669-1694 Titre : Submarine magmatic-hydrothermal systems at the Monowai volcanic center, Kermadec arc Type de document : texte imprimé Auteurs : Matthew I. Leybourne, Auteur ; Ulrich Schwarz-Schampera, Auteur ; Cornel E. J. de Ronde, Auteur Année de publication : 2013 Article en page(s) : pp. 1669-1694 Note générale : economic geology Langues : Anglais (eng) Mots-clés : Monowai volcanic center  magmatic hydrothermal systems Résumé : The Monowai volcanic center is located at the midpoint along the ∼2,530-km-long Tonga-Kermadec arc system. The Monowai volcanic center is comprised of a large elongate caldera (Monowai caldera area ∼35 km2; depth to caldera floor 1,590 m), which has formed within an older caldera some 84 km2 in area. To the south of this nested caldera system is a large composite volcano, Monowai cone, which rises to within ∼100 m of the sea surface and which has been volcanically active for the past several decades. Mafic volcanic rocks dominate the Monowai volcanic center; basalts are the most common rock type recovered from the cone, whereas basaltic andesites are common within the caldera. Hydrothermal plume mapping has shown at least three major hydrothermal systems associated with the caldera and cone: (1) the summit of the cone, (2) low-temperature venting ( We believe the Monowai volcanic center is host to a robust magmatic-hydrothermal system, with significant differences in the style and composition of venting at the cone and caldera sites. At the cone, the large shifts in pH, very high δ3He% values, elevated TDFe and TDFe/TDMn, and the H2S- and CH4-rich nature of the plume fluids, together with elevated Ti, P, V, S, and Al in hydrothermal particulates, indicates significant magmatic volatile ± metal contributions in the hydrothermal system coupled with aggressive acidic water-rock interaction. By contrast, the caldera has low TDFe/TDMn in hydrothermal plumes; however, elevated Al and Ti contents in caldera particulate samples, combined with the presence of alunite, pyrophyllite, sulfide minerals, and native sulfur in samples from Mussel Ridge suggest past, and perhaps recent, acid volatile-rich venting and active Fe sulfide formation in the subsurface. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1669.short [article] Submarine magmatic-hydrothermal systems at the Monowai volcanic center, Kermadec arc [texte imprimé] / Matthew I. Leybourne, Auteur ; Ulrich Schwarz-Schampera, Auteur ; Cornel E. J. de Ronde, Auteur . - 2013 . - pp. 1669-1694. economic geology Langues : Anglais (eng) in Economic geology > Vol. 107 N° 8 (Décembre 2012) . - pp. 1669-1694 Mots-clés : Monowai volcanic center  magmatic hydrothermal systems Résumé : The Monowai volcanic center is located at the midpoint along the ∼2,530-km-long Tonga-Kermadec arc system. The Monowai volcanic center is comprised of a large elongate caldera (Monowai caldera area ∼35 km2; depth to caldera floor 1,590 m), which has formed within an older caldera some 84 km2 in area. To the south of this nested caldera system is a large composite volcano, Monowai cone, which rises to within ∼100 m of the sea surface and which has been volcanically active for the past several decades. Mafic volcanic rocks dominate the Monowai volcanic center; basalts are the most common rock type recovered from the cone, whereas basaltic andesites are common within the caldera. Hydrothermal plume mapping has shown at least three major hydrothermal systems associated with the caldera and cone: (1) the summit of the cone, (2) low-temperature venting ( We believe the Monowai volcanic center is host to a robust magmatic-hydrothermal system, with significant differences in the style and composition of venting at the cone and caldera sites. At the cone, the large shifts in pH, very high δ3He% values, elevated TDFe and TDFe/TDMn, and the H2S- and CH4-rich nature of the plume fluids, together with elevated Ti, P, V, S, and Al in hydrothermal particulates, indicates significant magmatic volatile ± metal contributions in the hydrothermal system coupled with aggressive acidic water-rock interaction. By contrast, the caldera has low TDFe/TDMn in hydrothermal plumes; however, elevated Al and Ti contents in caldera particulate samples, combined with the presence of alunite, pyrophyllite, sulfide minerals, and native sulfur in samples from Mussel Ridge suggest past, and perhaps recent, acid volatile-rich venting and active Fe sulfide formation in the subsurface. DEWEY : 553 ISSN : 0361-0128 En ligne : http://economicgeology.org/content/107/8/1669.short

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