Insights to magmatic–hydrothermal processes in the Manus back-arc basin as recorded by anhydrite

Craddock, Paul R.; Bach, Wolfgang

doi:10.1016/j.gca.2010.07.004

Cited by 45 publications

(12 citation statements)

References 53 publications

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“…This linear departure from the initial δ 34 S value could represent an array of isotopic signatures attained at high temperature and those altered during non-equilibrium (enzymatic) reactions, such as microbial sulfate reduction in the low temperature sediments. Inorganic disproportionation of magmatic SO 2 is another potential isotope fractionation mechanism that can produce 34 S-enriched sulfate (by 16 to 21‰) and a residual H 2 S with low δ 34 S [ 28 ]; however, SO 2 has not been detected in Milos vents e.g. [ 41 ] and vent H 2 S is not exceptionally depleted in 34 S.…”

Section: Discussionmentioning

confidence: 99%

“…While stable isotope investigations of deep-sea hydrothermal systems (>1600 m water depth) have garnered much attention [ 12 ]–[ 14 ],[ 21 ],[ 28 ],[ 29 ], their shallow-sea analogs have been largely overlooked [ 30 ]–[ 32 ]. Volcanic arcs often produce shallow-sea vent systems, and their geochemical cycles can differ demonstrably from those found in mid-ocean ridges.…”

Section: Introductionmentioning

confidence: 99%

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Sulfur and oxygen isotope insights into sulfur cycling in shallow-sea hydrothermal vents, Milos, Greece

et al. 2014

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Shallow-sea (5 m depth) hydrothermal venting off Milos Island provides an ideal opportunity to target transitions between igneous abiogenic sulfide inputs and biogenic sulfide production during microbial sulfate reduction. Seafloor vent features include large (>1 m2) white patches containing hydrothermal minerals (elemental sulfur and orange/yellow patches of arsenic-sulfides) and cells of sulfur oxidizing and reducing microorganisms. Sulfide-sensitive film deployed in the vent and non-vent sediments captured strong geochemical spatial patterns that varied from advective to diffusive sulfide transport from the subsurface. Despite clear visual evidence for the close association of vent organisms and hydrothermalism, the sulfur and oxygen isotope composition of pore fluids did not permit delineation of a biotic signal separate from an abiotic signal. Hydrogen sulfide (H2S) in the free gas had uniform δ34S values (2.5 ± 0.28‰, n = 4) that were nearly identical to pore water H2S (2.7 ± 0.36‰, n = 21). In pore water sulfate, there were no paired increases in δ34SSO4 and δ18OSO4 as expected of microbial sulfate reduction. Instead, pore water δ34SSO4 values decreased (from approximately 21‰ to 17‰) as temperature increased (up to 97.4°C) across each hydrothermal feature. We interpret the inverse relationship between temperature and δ34SSO4 as a mixing process between oxic seawater and 34S-depleted hydrothermal inputs that are oxidized during seawater entrainment. An isotope mass balance model suggests secondary sulfate from sulfide oxidation provides at least 15% of the bulk sulfate pool. Coincident with this trend in δ34SSO4, the oxygen isotope composition of sulfate tended to be 18O-enriched in low pH (<5), high temperature (>75°C) pore waters. The shift toward high δ18OSO4 is consistent with equilibrium isotope exchange under acidic and high temperature conditions. The source of H2S contained in hydrothermal fluids could not be determined with the present dataset; however, the end-member δ34S value of H2S discharged to the seafloor is consistent with equilibrium isotope exchange with subsurface anhydrite veins at a temperature of ~300°C. Any biological sulfur cycling within these hydrothermal systems is masked by abiotic chemical reactions driven by mixing between low-sulfate, H2S-rich hydrothermal fluids and oxic, sulfate-rich seawater.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sulfur and oxygen isotope insights into sulfur cycling in shallow-sea hydrothermal vents, Milos, Greece

et al. 2014

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“…Sulfur sources in ancient (volcanic-hosted massive sulfide, VHMS; sedimentary-exhalative, SEDEX) massive sulfide deposits and modern hydrothermal sites at ocean floor are interpreted to have included seawater (e.g., SEDEX, Large 1980; Goodfellow et al 1993), leached magmatic rocks or magmas (e.g., VHMS, Huston 1999), mixing between seawater, leached magmatic rocks and/or magma (e.g., ocean floor hydrothermal sites, Gemmell et al 2004;Kakegawa et al 2008;Peters et al 2010;Craddock and Bach 2010), and metamorphic rocks (e.g., Sangster 1992). The S isotope compositions of many VHMS and SEDEX Zn-Pb-Cu deposits (Goodfellow et al 1993;Huston 1999) and orogenic sediment-hosted deposits (Sangster 1968;Chang et al 2008) positively vary with the seawater sulfate through geologic time, indicating that the S in the deposits was derived by reduction of seawater sulfate.…”

Section: Discussionmentioning

confidence: 99%

Involvement of magmatic fluids at the Laloki and Federal Flag massive sulfide Cu–Zn–Au–Ag deposits, Astrolabe mineral district, Papua New Guinea: sulfur isotope evidence

Noku¹,

Espi

Matsueda

2014

Miner Deposita

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We present the first sulfur (S) isotope data of sulfides, sulfates, pyrite in host mudstone, and bulk sulfur of gabbroic rocks from the Laloki and Federal Flag massive CuZn-Au-Ag deposits in the Astrolabe mineral district, Papua New Guinea. Early-stage pyrite-marcasite, chalcopyrite, and sphalerite from Laloki display wide range of δ 34 S values from −4.5 to +7.0‰ (n=16). Late-stage pyrite, chalcopyrite, and sphalerite have restricted δ 34 S values of −1.9 to +4.7‰ (n = 16). The mineralizing stage these correspond to had moderately saline (5.9-8.4 NaCl eq. wt%) mineralizing fluids of possible magmatic origin. A single analysis of late-stage barite has a value of δ 34 S +17.9‰, which is likely similar to coexisting seawater sulfate. Pyrite from the foot-wall mudstone at Laloki has very light δ 34 S values of −36.1 to −33.8‰ (n=2), which suggest an organic source for S. Pyrite-marcasite and chalcopyrite from Federal Flag show δ 34 S values of −2.4 to −1.9‰ (n=2), consistent with a magmatic origin, either leached from intrusive magmatic rocks or derived from magmatic-hydrothermal fluids. The very narrow range and near-zero δ 34 S values (−1.0 to +0.6‰) of bulk gabbroic samples is consistent with mantle-derived magmatic S. Sulfur isotope characteristics of sulfides and sulfates are, however, very similar to base metal sulfide accumulations associated with modern volcanic arcs and sedimented midocean ridges. The most reasonable interpretation is that the range of the sulfide and sulfate δ 34 S values from both Laloki and Federal Flag massive sulfide deposits is indicative of the complex interaction of magmatic fluids, seawater, gabbroic rocks, and mudstone.

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“…The analyses were done by combustion of the samples and oxidation of the sulfur released to SO 2 (Grassineau et al, 2000(Grassineau et al, , 2001a. Sulfur isotope compositions of sulfides of mineralized veins were also analyzed by MC-ICPMS Thermo Scientific Neptune at the PSO (Pôle Spectrométrie Océan, Brest, France) following the analytical method described in Craddock and Bach (2010) and Craddock et al (2008). For sulfur isotope analysis of pyrite, nineteen samples were crushed in a small agate mortar and 1 g of sample was weighed into a 15 ml PTFE (polytetrafluoroethylene) digestion vessel.…”

Section: Sample Preparationmentioning

confidence: 99%

Sulfur and strontium isotopic study of epithermal mineralization: A case study from the SE Afar Rift, Djibouti

Moussa

Rouxel

Grassineau

et al. 2017

Ore Geology Reviews

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Epithermal mineralization was recently described in synrift volcanic rocks from the SE Afar Rift in Djibouti. To infer fluid sources in this system, coupled sulfur and strontium isotopic analyses were performed on mineralized samples from hydrothermal veins and stockwork zones. Mineralization includes gypsum and chalcedony, and/or quartz ± carbonate containing gold and sulfides. Sulfur isotopic compositions of sulfides and sulfates were determined using Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC ICPMS); Laser Ablation MC ICPMS; and Continuous Flow Elemental Analyzer-Isotope Ratio Mass Spectrometry while strontium isotopes were determined by Thermal Ionisation Mass Spectrometry (TIMS) methods. Sulfur isotopic composition of sulfides (mainly pyrite) varies from − 9.2 to + 6.6‰. These values are classically reported for hydrothermal sulfides resulting from the mixing of variable S sources such as seawater sulfate and magmatic source. In addition, individual pyrite grains within the same sample show both positive and negative δ34S values suggesting multi-phase mineralization processes. Coupled sulfur and strontium isotopic compositions of seven sulfate samples hosted in (i) gypsum mound, (ii) evaporites, (iii) stockwork veins in sediments or in volcanic rocks were also investigated to characterize the sources of Sr and S. The δ34S values of the sulfate ranged from − 0.8 to + 14.3‰ while the 87Sr/86Sr ranged from 0.70389 to 0.70639 consistent with variable mixing ratios of Sr and S derived from volcanic sources and seawater-derived sulfate. This study shows that, although precious-metal deposition is related to low-sulfidation epithermal environment, both acidic fluid of magmatic and saline origins contributed to the hydrothermal system in the SE Afar Rift. Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.

show abstract

Insights to magmatic–hydrothermal processes in the Manus back-arc basin as recorded by anhydrite

Cited by 45 publications

References 53 publications

Sulfur and oxygen isotope insights into sulfur cycling in shallow-sea hydrothermal vents, Milos, Greece

Sulfur and oxygen isotope insights into sulfur cycling in shallow-sea hydrothermal vents, Milos, Greece

Involvement of magmatic fluids at the Laloki and Federal Flag massive sulfide Cu–Zn–Au–Ag deposits, Astrolabe mineral district, Papua New Guinea: sulfur isotope evidence

Sulfur and strontium isotopic study of epithermal mineralization: A case study from the SE Afar Rift, Djibouti

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