New insights into the genesis of volcanic-hosted massive sulfide deposits on the seafloor from numerical modeling studies

Schardt, Christian; Large, Ross R.

doi:10.1016/j.oregeorev.2008.11.008

Cited by 33 publications

(15 citation statements)

References 104 publications

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“…Previous models including seafloor topography have generally studied seamounts on ridge flanks in Pacific crust, although some topographic models of black smoker systems have been made (Schardt et al . ; Schardt & Large ). Harris et al .…”

Section: Discussionmentioning

confidence: 99%

Modelling the Lost City hydrothermal field: influence of topography and permeability structure

Titarenko

McCaig

2015

Geofluids

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The Lost City hydrothermal field (LCHF) is hosted in serpentinite at the crest of the Atlantis Massif, an oceanic core complex close to the mid-Atlantic Ridge. It is remarkable for its longevity and for venting low-temperature (40-91°C) alkaline fluids rich in hydrogen and methane. IODP Hole U1309D, 5 km north of the LCHF, penetrated 1415 m of gabbroic rocks and contains a near-conductive thermal gradient close to 100°C km À1 . This is remarkable so close to an active hydrothermal field. We present hydrothermal modelling using a topographic profile through the vent field and IODP site U1309. Long-lived circulation with vent temperatures similar to the LCHF can be sustained at moderate permeabilities of 10 À14 to 10 À15 m 2 with a basal heatflow of 0.22 W m À2 .Seafloor topography is an important control, with vents tending to form and remain in higher topography. Models with a uniform permeability throughout the Massif cannot simultaneously maintain circulation at the LCHF and the near-conductive gradient in the borehole, where permeabilities <10 À16 m 2 are required. A steeply dipping permeability discontinuity between the LCHF and the drill hole is required to stabilize venting at the summit of the massif by creating a lateral conductive boundary layer. The discontinuity needs to be close to the vent site, supporting previous inferences that high permeability is most likely produced by faulting related to the transform fault. Rapid increases in modelled fluid temperatures with depth beneath the vent agree with previous estimates of reaction temperature based on geochemical modelling.

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Section: Discussionmentioning

confidence: 99%

Modelling the Lost City hydrothermal field: influence of topography and permeability structure

Titarenko

McCaig

2015

Geofluids

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“…Early formed Zn-Pb-Fe replacement-type sulfides can act as a semipermeable cap, allowing for successively higher temperature Cu-rich fluids to refine the mound (Figs. 2, 3; Eldridge et al, 1983;Large, 1992;Ohmoto, 1996;Schardt and Large, 2009). This would allow for the dissolution of earlier formed Zn-Pb mineralization and subsequent reprecipitation of the Zn-Pb material closer to the seawater-vent interface, coupled with precipitation of Cu-(Fe)-rich sulfides at the base of the sulfide zone, leading to increases in both zonation and metal tenor ( Fig.…”

Section: Semipermeable Interface Modelmentioning

confidence: 99%

“…This would allow for the dissolution of earlier formed Zn-Pb mineralization and subsequent reprecipitation of the Zn-Pb material closer to the seawater-vent interface, coupled with precipitation of Cu-(Fe)-rich sulfides at the base of the sulfide zone, leading to increases in both zonation and metal tenor ( Fig. 3; Eldridge et al, 1983;Large, 1992;Ohmoto, 1996;Schardt and Large, 2009). …”

Section: Semipermeable Interface Modelmentioning

confidence: 99%

“…The thermal, redox, and chemical interface between the seawater and impermeable seafloor provides an ideal environment to enhance and increase the amount of metal precipitated during hydrothermal venting and partly explains why many large ancient VMS deposits are associated with subseafloor replacement (e.g., Doyle and Allen, 2003). Replacement processes also lead to creation of a semipermeable cap, which enhances zone refining of the sulfide deposit, leading to upgrading of existing mineral assemblages and their grades, which can increase the contained metal of a deposit (Eldridge et al, 1983;Ohmoto, 1996;Schardt and Large, 2009). Replacement is also important in other mineral deposit types, including sediment-hosted Zn-Pb deposits (e.g., Kelley et al, 2004;Gleeson et al, 2013) and Irish-type Zn-Pb deposits (e.g., Wilkinson et al, 2005).…”

Section: Implications and Testable Consequencesmentioning

confidence: 99%

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A Semipermeable Interface Model for the Genesis of Subseafloor Replacement-Type Volcanogenic Massive Sulfide (Vms) Deposits

Piercey¹

2015

Economic Geology

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Subseafloor replacement-style volcanogenic massive sulfide (VMS) deposits are a subset of VMS deposits where sulfides have replaced unconsolidated volcanic, volcano-sedimentary, and sedimentary material. These deposits are anomalously large and are important global sources of metals. They have distinct textures at the sulfide-ore interface, including bed-by-bed replacement of sedimentary layers, and typically fill void space between unconsolidated volcaniclastic detritus or fractures in flows or intrusions. At the microscale, metalbearing sulfides have partially to fully replaced framboidal (bacteriogenic) sulfides, or the framboidal sulfides have acted as nuclei upon which additional metalliferous massive sulfide is deposited.The textures presented are reconciled within a semipermeable interface model for replacement. In this model unconsolidated sediment, volcaniclastic rocks, or fractured coherent volcanic rocks provide a permeable to semipermeable interface that allowed ingress of cold seawater into the pore spaces of the stratigraphic sequence prior to and during lulls in hydrothermal activity. Seawater sulfate in the pore water is partially reduced by bacteria to provide reduced sulfur (H2S) as well as framboidal pyrite in the host sequence(s). The reduced sulfur and framboidal pyrite, as well as the cool pore water, provided a thermal, redox, and chemical gradient in which upwelling hydrothermal fluids interact. In such an environment rising hydrothermal fluids mix with cold water, not only at the seawater interface leading to exhalative sulfide deposition, but also in the subseafloor leading to sulfide precipitation via replacement. The upwelling hydrothermal fluids can also interact with bacterial H2S in the pore spaces of the unconsolidated material, resulting in additional subseafloor precipitation of metal sulfides. The fluids also result in replacement of framboidal pyrite nuclei pseudomorphous after the original framboidal masses. This semipermeable interface also favors enhanced zone refining, assuming the hydrothermal system is sufficiently long lived, leading to upgrading of the tenor of the sulfides with well-developed metal zoning, as observed in many ancient replacement-type deposits. Furthermore, the precipitation of a significant subseafloor sulfide mineralization results in greater trapping of metals from upwelling fluids and larger tonnage deposits with greater contained metal.This model may also be applicable to other replacement-type deposits in broadly similar geologic and hydrothermal environments (e.g., sediment-hosted and Irish-type Zn-Pb deposits). Additional, critical tests are required to validate and refute the model and potential tests are presented herein.

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“…The leaching model requires that both the ore metals and sulfur were extracted from the footwall strata by hydrothermal fluids circulating above a deeper magma chamber (e.g., Franklin et al, 1981Franklin et al, , 2005Schardt and Large, 2009). Experimental studies suggest that both rock type and water/rock ratios have an important influence on the efficiency with which metal and sulfur are leached by such a system (e.g., Seyfried et al, 1999;James et al, 2003).…”

Section: Leaching Model Vs Magmatic Model For the Teutonic Bore And mentioning

confidence: 99%

Multiple Sulfur Isotope Analyses Support a Magmatic Model for the Volcanogenic Massive Sulfide Deposits of the Teutonic Bore Volcanic Complex, Yilgarn Craton, Western Australia

Chen¹,

Campbell²,

Xue³

et al. 2015

Economic Geology

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We report sensitive high mass resolution ion microprobe, stable isotopes (SHRIMP SI) multiple sulfur isotope analyses ( 32 S, 33 S, 34 S) to constrain the sources of sulfur in three Archean VMS deposits-Teutonic Bore, Bentley, and Jaguar-from the Teutonic Bore volcanic complex of the Yilgarn Craton, Western Australia, together with sedimentary pyrites from associated black shales and interpillow pyrites. The pyrites from VMS mineralization are dominated by mantle sulfur but include a small amount of slightly negative mass-independent fractionation (MIF) anomalies, whereas sulfur from the pyrites in the sedimentary rocks has pronounced positive MIF, with ∆ 33 S values that lie between 0.19 and 6.20‰ (with one outlier at -1.62‰). The wall rocks to the mineralization include sedimentary rocks that have contributed no detectable positive MIF sulfur to the VMS deposits, which is difficult to reconcile with the leaching model for the formation of these deposits. The sulfur isotope data are best explained by mixing between sulfur derived from a magmatic-hydrothermal fluid and seawater sulfur as represented by the interpillow pyrites. The massive sulfide lens pyrites have a weighted mean ∆ 33 S value of -0.27 ± 0.05‰ (MSWD = 1.6) nearly identical with -0.31 ± 0.08‰ (MSWD = 2.4) for pyrites from the stringer zone, which requires mixing to have occurred below the sea floor. We employed a twocomponent mixing model to estimate the contribution of seawater sulfur to the total sulfur budget of the two Teutonic Bore volcanic complex VMS deposits. The results are 15 to 18% for both Teutonic Bore and Bentley, much higher than the 3% obtained by Jamieson et al. (2013) for the giant Kidd Creek deposit. Similar calculations, carried out for other Neoarchean VMS deposits give value between 2% and 30%, which are similar to modern hydrothermal VMS deposits. We suggest that multiple sulfur isotope analyses may be used to predict the size of Archean VMS deposits and to provide a vector to ore deposit but further studies are needed to test these suggestions.

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New insights into the genesis of volcanic-hosted massive sulfide deposits on the seafloor from numerical modeling studies

Cited by 33 publications

References 104 publications

Modelling the Lost City hydrothermal field: influence of topography and permeability structure

Modelling the Lost City hydrothermal field: influence of topography and permeability structure

A Semipermeable Interface Model for the Genesis of Subseafloor Replacement-Type Volcanogenic Massive Sulfide (Vms) Deposits

Multiple Sulfur Isotope Analyses Support a Magmatic Model for the Volcanogenic Massive Sulfide Deposits of the Teutonic Bore Volcanic Complex, Yilgarn Craton, Western Australia

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