Morphology of framboidal pyrite and its textural evolution: Evidence from the Logatchev area, Mid-Atlantic Ridge

Abstract The Rainbow hydrothermal field (36°14′N) and the Saldanha seamount (36°34′N), in the Mid-Atlantic Ridge (MAR), are tectonic exposures of serpentinized upper mantle peridotites, both associated with significant hydrothermal activity. On the basis of detailed mineralogical and geochemical characterization of serpentinites from both sites, several serpentinization-related issues are discussed in the present work. As expected in oceanic environments, most of the sampled rocks are lizardite-chrysotile serpentinites exhibiting a variety of pseudomorphic through non-pseudomorphic textures, such textural evolution probably being related to changing water/rock ratios during this retrograde process. Oxygen isotope temperatures indicate that the serpentinization took place at 300–200 °C; on the other hand, isotopic data suggest that replacement of early pseudomorphic lizardite by lizardite ± chrysotile non-pseudomorphic textures requires that temperatures and/or water/rock ratios are high enough to promote the necessary dissolution–recrystallization processes. Mass-balance calculations for olivine-serpentine and orthopyroxene-serpentine pairs provided a basis for establishing serpentinization reactions likely to have produced the present rocks. Moreover, these calculations also showed that, notwithstanding some noticeable loss of MgO from olivine and of SiO2 from orthopyroxene, serpentinization of both minerals implies volume increases on the order of 26–27%, therefore potentially promoting the overall expansion of the rock. The geochemical and isotopic features of the studied rocks indicate that unmodified seawater was responsible for the serpentinization of the MAR peridotites. However, the mineralogy and REE patterns of some of these serpentinites indicate occasional subsequent interaction of the serpentinized rocks with seawater at much lower temperatures (seafloor alteration, characterized by carbonate deposition and negative Ce anomalies), or with high-temperature ore-forming hydrothermal fluids (ore-forming alteration, characterized by sulfide precipitation and steep positive Eu anomalies).

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Pyrite Varieties at Pobeda Hydrothermal Fields, Mid-Atlantic Ridge 17°07′–17°08′ N: LA-ICP-MS Data Deciphering

Minerals ◽

10.3390/min10070622 ◽

2020 ◽

Vol 10 (7) ◽

pp. 622

Author(s):

Valeriy Maslennikov ◽

Georgy Cherkashov ◽

Dmitry Artemyev ◽

Anna Firstova ◽

Ross Large ◽

...

Keyword(s):

Low Temperature ◽

Massive Sulfide ◽

Black Smoker ◽

Fine Grained ◽

Framboidal Pyrite ◽

Icp Ms ◽

Mid Atlantic Ridge ◽

Seafloor Massive Sulfide ◽

Hydrothermal Fields ◽

Feeder Zone

The massive sulfide ores of the Pobeda hydrothermal fields are grouped into five main mineral microfacies: (1) isocubanite-pyrite, (2) pyrite-wurtzite-isocubanite, (3) pyrite with minor isocubanite and wurtzite-sphalerite microinclusions, (4) pyrite-rich with framboidal pyrite, and (5) marcasite-pyrite. This sequence reflects the transition from feeder zone facies to seafloor diffuser facies. Spongy, framboidal, and fine-grained pyrite varieties replaced pyrrhotite, greigite, and mackinawite “precursors”. The later coarse and fine banding oscillatory-zoned pyrite and marcasite crystals are overgrown or replaced by unzoned subhedral and euhedral pyrite. In the microfacies range, the amount of isocubanite, wurtzite, unzoned euhedral pyrite decreases versus an increasing portion of framboidal, fine-grained, and spongy pyrite and also marcasite and its colloform and radial varieties. The trace element characteristics of massive sulfides of Pobeda seafloor massive sulfide (SMS) deposit are subdivided into four associations: (1) high temperature—Cu, Se, Te, Bi, Co, and Ni; (2) mid temperature—Zn, As, Sb, and Sn; (3) low temperature—Pb, Sb, Ag, Bi, Au, Tl, and Mn; and (4) seawater—U, V, Mo, and Ni. The high contents of Cu, Co, Se, Bi, Te, and values of Co/Ni ratios decrease in the range from unzoned euhedral pyrite to oscillatory-zoned and framboidal pyrite, as well as to colloform and crystalline marcasite. The trend of Co/Ni values indicates a change from hydrothermal to hydrothermal-diagenetic crystallization of the pyrite. The concentrations of Zn, As, Sb, Pb, Ag, and Tl, as commonly observed in pyrite formed from mid- and low-temperature fluids, decline with increasing crystal size of pyrite and marcasite. Coarse oscillatory-zoned pyrite crystals contain elevated Mn compared to unzoned euhedral varieties. Framboidal pyrite hosts maximum concentrations of Mo, U, and V probably derived from ocean water mixed with hydrothermal fluids. In the Pobeda SMS deposit, the position of microfacies changes from the black smoker feeder zone at the base of the ore body, to seafloor marcasite-pyrite from diffuser fragments in sulfide breccias. We suggest that the temperatures of mineralization decreased in the same direction and determined the zonal character of deposit.

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Faculty Opinions recommendation of A dual symbiosis shared by two mussel species, Bathymodiolus azoricus and Bathymodiolus puteoserpentis (Bivalvia: Mytilidae), from hydrothermal vents along the northern Mid-Atlantic Ridge.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1033730.388928 ◽

2006 ◽

Author(s):

Jessup Shively

Keyword(s):

Hydrothermal Vents ◽

Mussel Species ◽

Mid Atlantic Ridge

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Acoustic Reverberation at Selected Sites in the Mid-Atlantic Ridge Region,

10.21236/ada298387 ◽

1993 ◽

Author(s):

Jerald W. Caruthers ◽

J. R. Fricke ◽

Ralph A. Stephen

Keyword(s):

Mid Atlantic Ridge ◽

Acoustic Reverberation

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The age of magmatic and metamorphic events in the Mid-Atlantic Ridge: interpretation of K-Ar isotope dating data

Russian Journal of Earth Sciences ◽

10.2205/2000es000044 ◽

2001 ◽

Vol 2 (3) ◽

pp. 269-278

Author(s):

S. A. Silantiev ◽

L. K. Levskiy ◽

M. M. Arakelyants ◽

V. A. Lebedev ◽

A. Bugo ◽

...

Keyword(s):

Mid Atlantic Ridge ◽

Isotope Dating

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PRELIMINARY FORESHOCK ANALYSIS OF SUBMARINE TRANSFORM FAULT EARTHQUAKES ALONG THE EQUATORIAL MID-ATLANTIC RIDGE

10.1130/abs/2016rm-274840 ◽

2016 ◽

Author(s):

Ross P. Meyer ◽

◽

Joe H. Haxel ◽

Robert P. Dziak ◽

Deborah K. Smith

Keyword(s):

Transform Fault ◽

Mid Atlantic Ridge

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Detection of framboidal pyrite size distributions using convolutional neural networks

Marine and Petroleum Geology ◽

10.1016/j.marpetgeo.2021.105159 ◽

2021 ◽

pp. 105159

Author(s):

Artur Davletshin ◽

Lucy Tingwei Ko ◽

Kitty Milliken ◽

Priyanka Periwal ◽

Chung-Che Wang ◽

...

Keyword(s):

Neural Networks ◽

Convolutional Neural Networks ◽

Size Distributions ◽

Framboidal Pyrite

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Geochemical Fractions of Heavy Metals in Bottom Sediments of the Pobeda Hydrothermal Field, Mid-Atlantic Ridge (17°07′–17°08′ N)

Environmental Sciences Proceedings ◽

10.3390/iecms2021-09343 ◽

2021 ◽

Vol 6 (1) ◽

pp. 14

Author(s):

Liudmila Demina ◽

Irina Gablina ◽

Olga Dara ◽

Dmitry Budko ◽

Nina Gorkova ◽

...

Keyword(s):

Total Content ◽

Element Distribution ◽

Hydrothermal Field ◽

Residual Fraction ◽

Carbonate Sediments ◽

Metalliferous Sediments ◽

Geochemical Fractions ◽

Metalliferous Sediment ◽

Fe And Mn ◽

Mid Atlantic Ridge

We examined the distribution of Fe, Mn, Cu, Zn, and Pb in one core of metalliferous, and one core of non-mineralized (background) carbonate sediments (located 69 km northwards), from the Pobeda hydrothermal field. Mechanisms of metal accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including mobile (exchangeable complex, authigenic Fe-Mn hydroxides, and sulfides), and lithogenic (fixed in crystalline lattices) forms. Maps of element distribution in sediment components were obtained using a scanning electron microscope equipped with an energy-dispersive spectrometry detector. In metalliferous sediments, according to X-ray diffraction data, the main Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis). The contents of Fe and Mn reached 31.6 and 0.18%, respectively, whereas concentrations of Cu, Zn and Pb were 0.98, 0.36, and 0.059%. The coefficient of metal enrichment relative to background values varied from 16 to 125 times. The exception was Mn, for which no increased accumulation was recorded. Essential mass of Fe (up to 70% of total content) was represented by the residual fraction composed of crystallized goethite, aluminosilicates, the minerals derived from bedrock destruction processes. Among geochemically mobile fractions, 90–97% of total Fe was found in the form of authigenic oxyhydroxides. The same fraction was the predominant host for Mn in both metalliferous and background sediments (55–85%). A total of 40–96 % of Cd, Cu, Zn, and Pb were associated with these Fe and Mn fractions. The sulfide fraction amounted to roughly 10% of each metal. In metalliferous sediment core, the maximum concentrations of metals and their geochemically mobile fractions were recorded in deeper core intercepts, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that metals are mostly accumulated in carbonate sediments in their contact zone with the underlying serpentinized basalts.

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