Noble-metal mineralization in the Semenov-2 hydrothermal field (13°31′N), mid-atlantic ridge

Melekestseva, I. Yu.; Kotlyarov, V. A.; Хворов, П.В.; Ivanov, V.N.; Bel’tenev, V. E.; Dobretsova, I. G.

doi:10.1134/s1075701510080118

Cited by 13 publications

(15 citation statements)

References 14 publications

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“…The Cu-Au-Bi-Te association may reflect a felsic magmatic source for the metals, similar to that observed in subaerial magmatic hydrothermal systems (Hannington et al 2005). Discrete Bi telluride minerals also have been documented in massive sulfides at Brothers, Palinuro Seamount, and in deposits on the Izu-Bonin arc (Dekov and Savelli 2004;Törmänen and Koski 2005;Melekestseva et al 2010Melekestseva et al , 2017Berkenbosch et al 2012;Iizasa et al 2018). The most Au-rich samples also include complex mineral assemblages including abundant bornite, tennantite, or other sulfosalts.…”

Section: Precious Metal Associations and Processes Of Enrichmentmentioning

confidence: 52%

“…The concentrations of Au are orders of magnitude higher than in similarly Cu-rich black smokers from the mid-ocean ridges, suggesting that Au concentrations in the vent fluids must be much higher. The most common interpretation is that the Au is sourced from magmatic volatiles and deposited mostly in high-temperature Cu-rich chimneys, but there may be relatively little accumulation of massive sulfide (Dekov and Savelli 2004;Törmänen and Koski 2005;Melekestseva et al 2010Melekestseva et al , 2017Berkenbosch et al 2012;Iizasa et al 2018). Other trace elements, such as Bi and Te, show covariations with Au enrichment in these chimneys, reaching concentrations of up to 200 ppm Bi and 150 ppm Te (Watanabe and Kajimura 1994;.…”

Section: Precious Metal Associations and Processes Of Enrichmentmentioning

confidence: 99%

“…The most Au-rich samples also include complex mineral assemblages including abundant bornite, tennantite, or other sulfosalts. The latter commonly include distinctive high-sulfidation minerals, such as the enargiteluzonite in the Eastern Manus Basin (Petersen et al 2002; Dekov and Savelli 2004;Törmänen and Koski 2005;Melekestseva et al 2010Melekestseva et al , 2017Berkenbosch et al 2012;Iizasa et al 2018). However, normal mid-ocean ridge black smokers, which can also be Au-rich, typically do not show any of these trace element enrichments or high-sulfidation minerals, implying that other processes may also account for the Cu-Au association.…”

Section: Precious Metal Associations and Processes Of Enrichmentmentioning

confidence: 99%

“…In the ultramafichosted Logatchev deposit, native gold has been found in association with chalcopyrite, bornite, and covellite (Murphy and Meyer 1998;, whereas in the Beebe hydrothermal field, native gold has been found with pyrrhotite and iron oxides but rarely with chalcopyrite (Webber et al 2017). Native gold has also been reported in opaline silica from the basalt-hosted Semyenov-2 hydrothermal field (Melekestseva et al 2010(Melekestseva et al , 2017. Abundant Au-rich electrum has been found in hydrothermally reworked sulfides from the TAG hydrothermal field from the Mid-Atlantic Ridge (Hannington et al 1995).…”

Section: Precious Metal Mineralogymentioning

confidence: 99%

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Divining gold in seafloor polymetallic massive sulfide systems

2019

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Hydrothermal fluids on the modern seafloor are important carriers of base and precious metals in a wide range of volcanic and tectonic settings. The concentrations and distribution, especially of gold and silver, in associated seafloor massive sulfide (SMS) deposits are strongly influenced by variable source rocks, fluid chemistry, and precipitation mechanisms. Compositional data of 130 SMS deposits around the world show a large range of gold and silver grades, in part reflecting strong buffering of the hydrothermal fluids by their host rocks. Geochemical reaction-path modeling shows that in most cases the investigated hydrothermal fluids are undersaturated with gold and silver, and solubilities can be orders of magnitude higher than the Au and Ag concentrations measured in the corresponding fluids. Precipitation of gold during conductive cooling of mid-ocean ridge black smoker (MOR) fluids occurs at low temperatures but can be very rapid, with > 90% of the gold deposited in the first 25°C of cooling below~150°C. The result is a Zn-Au polymetallic assemblage with Au and Ag deposited at the same time together with Pb and sulfosalts. In ultramafic-dominated (UM) systems, the strongly reduced hydrothermal fluids promote the deposition of gold at higher temperatures and explain the correlation between gold and copper in these deposits. In this case, the lower stability of the AuHS°complex at low ƒO 2 (buffered by fayalite, magnetite, and quartz) results in gold deposition at > 250°C with early bornite and chalcopyrite and before sphalerite and silver, producing a high-temperature Cu-Au assemblage. In sediment-hosted (SED) systems, the much higher pH stabilizes Au(HS) 2 − and keeps gold in solution to very low temperatures, after the precipitation of chalcopyrite, sphalerite, and galena, resulting in Au-poor polymetallic sulfides and very late-stage deposition of gold, commonly with amorphous silica. In arc-related (ARC) systems, gold deposition occurs at somewhat higher temperatures than in the MOR case, in part because the fluids start with higher gold concentrations. This can be explained by probable direct magmatic contributions, and the high ƒO 2 of the fluids, which promotes the solubility of gold at the source. During cooling, gold precipitates at about 160°C with sphalerite, tennantite, silver, and galena, resulting in an Au-rich polymetallic sulfide assemblage. The mixing of hydrothermal fluids with seawater generally causes oxidation and eventually a decrease in the pH at a mixing ratio of 1:1, causing an initial increase in the solubility of gold and silver. This can delay gold deposition from aqueous species to very low temperatures. These complex systematics make prediction of Au and Ag grades difficult. However, important new data are coming to light on the actual concentrations of the precious metals in hydrothermal fluids. In particular, the input of magmatic volatiles and leaching of pre-existing gold can lead to significant increases in the Au and Ag concentrations of the venting fluids and earlier d...

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Section: Precious Metal Associations and Processes Of Enrichmentmentioning

confidence: 52%

Section: Precious Metal Associations and Processes Of Enrichmentmentioning

confidence: 99%

Section: Precious Metal Associations and Processes Of Enrichmentmentioning

confidence: 99%

Section: Precious Metal Mineralogymentioning

confidence: 99%

See 2 more Smart Citations

Divining gold in seafloor polymetallic massive sulfide systems

2019

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“…SMS samples were recovered by dredge (Station 287) and TV-grab (Stations 240, 277, 275, 293) during cruises 30 and 32 of RV Professor Logatchev [29,30]. In total, 29 sulphide samples were studied.…”

Section: Methodsmentioning

confidence: 99%

Au and Te Minerals in Seafloor Massive Sulphides from Semyenov-2 Hydrothermal Field, Mid-Atlantic Ridge

et al. 2019

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The Semyenov-2 hydrothermal field located at 13°31′N of the Mid-Atlantic Ridge (MAR) is associated with an oceanic core complex (OCC) and hosted by peridotites and basalts with minor amounts of gabbro and plagiogranites. Seafloor massive sulphides (SMS) are represented by chimneys with zonality, massive sulphides without zonality and sulphide breccia cemented by opal and aragonite. The mean value of Au (20.6 ppm) and Te (40 ppm) is much higher than average for the MAR SMS deposits (3.2 ppm and 8.0 ppm, respectively). Generally, these high concentrations reflect the presence of a wide diversity of Au and Te minerals associated with major mineral paragenesis: primary native gold, melonite (NiTe2) and tellurobismuthite (Bi2Te3) are related to high-temperature chalcopyrite (~350 °C); electrum (AuAg)1, hessite (Ag2Te) and altaite (PbTe) are related to medium- and low-temperature Zn-sulphide and opal assemblages (260–230 °C). Calaverite (AuTe2) and Te-rich “fahlore” Cu12(Sb,As,Te)4S13 are texturally related to the chalcopyrite-bornite-covellite. Enrichment of Au in sulphide breccia with opal and aragonite cement is driven by the re-deposition and the process of hydrothermal reworking of sulphide. The low-temperature fluid mobilizes gold from primary sulphide, along with Au and Te minerals. As a result, the secondary gold re-precipitate in cement of sulphide breccia. An additional contribution of Au enrichment is the presence of aragonite in the Cu-Zn breccia where the maximal Au content (188 ppm) is reached.

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Gold and tin mineralisation in the ultramafic-hosted Cheoeum vent field, Central Indian Ridge

et al. 2020

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The Cheoeum vent field (CVF) is the first example of an inactive ultramafic-hosted seafloor massive sulphide (SMS) deposit identified in the middle part of the Central Indian Ridge. Here, we report on the detailed mineralogy and geochemistry of ultramafic-hosted sulphide sample atop a chimney, together with a few small fragments. Hydrothermal chimneys are characterised by high concentrations of Au (up to 17.8 ppm) and Sn (up to 1720 ppm). The sulphide mineralisation in the CVF shows (1) early precipitation of anhedral sphalerite and pyrite–marcasite aggregates under relatively low-temperature (< 250 °C) fluid conditions; (2) intensive deposition of subhedral pyrrhotite, isocubanite, chalcopyrite, Fe-rich sphalerite (Sp-III), and electrum from high-temperature (250–365 °C) and reduced fluids in the main mineralisation stage; and (3) a seawater alteration stage distinguished by the mineral assemblage of marcasite pseudomorphs, altered isocubanite phase, covellite, amorphous silica, and Fe-oxyhydroxides. Electrum (< 2 μm in size) is the principal form of Au mineralisation and is mainly associated with the main mineralisation stage. The consistently high fineness of electrum (801 to 909‰) is indicative of the selective saturation of Au over Ag in the fluid during high-temperature mineralisation, which differs from the Au mineralisation associated with typical basaltic-hosted hydrothermal systems on mid-ocean ridges. Tin is mainly substituted in structures of sphalerite, isocubanite, and chalcopyrite as a solid solution, and not as mineral inclusions. The continuously ascending hydrothermal fluids enable the early formed Sn-bearing sulphide to be dissolved and reprecipitated, producing significantly Sn-enriched replacement boundaries between isocubanite and Sp-III. This study suggests that Au–Sn mineralisation could be facilitated by the low redox potential of ultramafic-hosted hydrothermal systems such as in the CVF, which may be a common occurrence along slow-spreading mid-ocean ridges.

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Noble-metal mineralization in the Semenov-2 hydrothermal field (13°31′N), mid-atlantic ridge

Cited by 13 publications

References 14 publications

Divining gold in seafloor polymetallic massive sulfide systems

Divining gold in seafloor polymetallic massive sulfide systems

Au and Te Minerals in Seafloor Massive Sulphides from Semyenov-2 Hydrothermal Field, Mid-Atlantic Ridge

Gold and tin mineralisation in the ultramafic-hosted Cheoeum vent field, Central Indian Ridge

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