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TitleSulfur isotope evidence for magmatic contributions to submarine and subaerial gold mineralization: conical sea mount and Ladolam gold deposit, Papua New Guinea
AuthorGemmell, J B; Sharpe, R; Jonasson, I R; Herzig, P M
SourceEconomic geology and the bulletin of the Society of Economic Geologists vol. 99, no. 8, 2004 p. 1711-1725, https://doi.org/10.2113/99.8.1711
Year2004
Alt SeriesEarth Sciences Sector, Contribution Series 2005033
PublisherSociety of Economic Geologists
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
AreaLihir Island area; Manus Basin; Papua New Guinea
Lat/Long WENS 152.0000 153.0000 -3.0000 -4.0000
Subjectseconomic geology; igneous and metamorphic petrology; metallic minerals; seamounts; gold; mineralization; magmatism; isotopic studies; isotope geochemistry; sulphur; sulphides; volcanoes; basalts; polymetallic ores; zinc; lead; silver; arsenic; antimony; veins; stockworks; pyrite; hydrothermal systems; hydrothermal alteration; hydrothermal deposits; epithermal deposits; groundwater; meteoric waters; sulphate; submarine hydrothermal vents; mineralogical analyses; chemical analyses; textural analyses; leaching; precipitation; Ladolam gold deposit; Luise caldera; magmatic volatiles; seawater; fumaroles
Illustrationslocation maps; geological sketch maps; tables; photomicrographs; histograms; bar graphs
AbstractConical seamount is a submarine alkali basalt volcano situated 10 km south of Lihir Island in the Tabar-Feni island chain, Papua New Guinea. Polymetallic (Zn-Pb-Ag-Au-As-Sb) veins, pyritic stockwork, and hydrothermally altered rocks discovered on the summit of Conical seamount represent a unique example of submarine gold mineralization with mineralogical, chemical, and textural characteristics common to some subaerial epithermal systems. The giant Ladolam epithermal gold deposit (42 Moz Au) is situated in the crater of an alkali stratovolcano on Lihir Island. Portions of the epithermal mineralization and alteration assemblages at Ladolam are similar to those observed on Conical seamount. Conical seamount has the lightest, hydrothermal (i.e., nondiagenetic) sulfide d34S values (-17.5 to +6.1 per thousand) measured to date from modern sea-floor hydrothermal systems. A previous model for the Conical seamount hydrothermal system suggested a contribution of magmatic volatiles in the earliest stages of mineralization (stage 1), followed by a combination of sulfur leached from the underlying volcanic rocks and reduced seawater sulfate during the main base and precious metal precipitating event (stage 2). New sulfur isotope data allow a reinterpretation of this model that suggests a greater input of magmatic volatiles, plus boiling, throughout both stage 1 and 2 mineralization. Sulfides from the Ladolam gold deposit have a range of sulfur isotope values (-12.9 to +3.6 per thousand) similar to that of Conical seamount. These sulfur isotope data have previously been interpreted as the result of magmatic volatiles escaping from a crystallizing magma and mixing with dilute meteoric ground water. Anhydrite associated with the gold mineralization has two populations of d34S values (8-14 and 20-22 per thousand), which indicate the interaction of magmatic volatiles with seawater that has previously been discounted. The range of sulfide and sulfate d34S values at Ladolam is reinterpreted to be due to a complex interaction of magmatic hydrothermal fluids, meteoric ground water, and seawater. Native sulfur in thermal areas in Luise caldera and pyrite in offshore hyd rothermal vents in Luise harbor have similar d34S values to the Ladolam epithermal mineralization, indicating that fluids similar to the young Ladolam ore-forming event are still reaching the floor of Luise caldera. Sulfur isotope data from Conical seamount and the Ladolam deposit suggest that magmatic volatiles have contributed a significant amount of sulfur to both these gold-rich hydrothermal systems.
GEOSCAN ID220504