Electromagnetic experiments for the detection and characterization of seafloor massive sulfides: two case studies from the Mediterranean and Northern Mid-Atlantic Ridge

Seafloor massive sulfides (SMS) are regarded as a potential future resource to satisfy the growing global demand of strategic metals. Aside from mining and retrieving profitable amounts of massive sulfides from the seafloor, the present challenge is to detect and delineate significant SMS accumulations, which are generally located near mid-ocean ridges and along submarine volcanic arc and backarc spreading centers.In the past years we have used the marine transient electromagnetic induction system MARTEMIS, a coincident-loop TEM system developed at GEOMAR (Kiel, Germany), in various marine geological settings for the detection and characterization of SMS in the shallow seafloor down to a depth of ~30m. The system was also used in combination with remote EM receivers (Coil2Dipole experiment) to allow for investigations of conductive structures, which are covered by up to ~100m of sediments.We present experiments from two locations, one at an inactive site in the Mediterranean (Palinuro, Tyrrhenian Sea) where the occurrence of SMS had previously been confirmed by drilling, and one active site on the Northern Mid-Atlantic Ridge (Grimsey Hydrothermal Field, offshore Northern Iceland) where no SMS have been found in gravity cores up to now. The results demonstrate the suitability of the system to detect, delineate and characterize SMS even in scenarios, where the mineralizations are no longer connected to any hydrothermal activity or are buried under a sedimentary cover.

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Serpentinization at the Rainbow and Saldanha sites, Mid-Atlantic Ridge: Mineralogical, geochemical, and isotopic features

The Canadian Mineralogist ◽

10.3749/canmin.1900010 ◽

2019 ◽

Vol 57 (5) ◽

pp. 677-706

Author(s):

Isabel Ribeiro da Costa ◽

Frederick Joseph Wicks ◽

Fernando J.A.S. Barriga

Keyword(s):

Upper Mantle ◽

Hydrothermal Activity ◽

Isotopic Data ◽

Geochemical Characterization ◽

Textural Evolution ◽

Mantle Peridotites ◽

Carbonate Deposition ◽

Mid Atlantic Ridge ◽

Ree Patterns

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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The oldest seafloor massive sulfide deposits at the Mid-Atlantic Ridge: 230Th/U chronology and composition

Geochronometria ◽

10.1515/geochr-2015-0009 ◽

2015 ◽

Vol 42 (1) ◽

Cited By ~ 7

Author(s):

Vladislav Kuznetsov ◽

Eriks Tabuns ◽

Kathrine Kuksa ◽

Georgy Cherkashov ◽

Fedor Maksimov ◽

...

Keyword(s):

Massive Sulfide ◽

Hydrothermal Activity ◽

Ocean Floor ◽

Hydrothermal Field ◽

Sulfide Deposits ◽

Massive Sulfides ◽

Geochemical Properties ◽

Geochemical Study ◽

Mid Atlantic Ridge ◽

Seafloor Massive Sulfide

Abstract A geochronological and geochemical study on 10 samples of seafloor massive sulfides (SMS) from the inactive Peterburgskoye hydrothermal field at the Mid-Atlantic Ridge (MAR) was carried out. The 230Th/U ages of the SMS are the oldest for the Quaternary hydrothermal ores ever found at the ocean floor. According to them the hydrothermal activity at Peterburgskoye field started at least 170 ka and continued down to 63 ka. The oldest hydrothermal ores from this field consist mainly of pyrite and chalcopyrite and have geochemical properties typical for SMS associated with basalts.

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Geological mapping of the Menez Gwen segment at 37°50′N on the Mid-Atlantic Ridge: Implications for accretion mechanisms and associated hydrothermal activity at slow-spreading mid-ocean ridges

Marine Geology ◽

10.1016/j.margeo.2019.03.012 ◽

2019 ◽

Vol 412 ◽

pp. 107-122 ◽

Cited By ~ 1

Author(s):

M. Klischies ◽

S. Petersen ◽

C.W. Devey

Keyword(s):

Hydrothermal Activity ◽

Geological Mapping ◽

Ocean Ridges ◽

Mid Atlantic Ridge ◽

Slow Spreading ◽

Menez Gwen

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Chronology of seafloor massive sulfides formation within the Pobeda hydrothermal cluster (Mid-Atlantic Ridge)

Geochronometria ◽

10.2478/geochr-2020-0019 ◽

2020 ◽

Vol 47 (1) ◽

pp. 63-70

Author(s):

V. Kuznetsov ◽

G. Cherkashov ◽

K. Kuksa ◽

A. Firstova ◽

F. Maksimov ◽

...

Keyword(s):

Hydrothermal Activity ◽

Geochronological Data ◽

Massive Sulfides ◽

Mineralogical Study ◽

Mid Atlantic Ridge

AbstractA geochronological and mineralogical study on the seafloor massive sulfides from the Pobeda hydrothermal cluster at the Mid-Atlantic Ridge was carried out. To improve the reliability of geochronological data, the 230Th/U ages were measured for both the bulk samples and monomineral separates. The oldest age ca. 52 kyr within Pobeda-1 and ca. 107 kyr within Pobeda–2 fields have been obtained. Then, several episodes of hydrothermal activity were identified within both fields up to ca. 0.3 kyr ago and up to ca. 4.3 kyr ago, respectively.

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230Th/U chronology of ore formation within the semyenov hydrothermal district (13°31′ N) at the Mid-Atlantic ridge

Geochronometria ◽

10.2478/s13386-011-0001-1 ◽

2011 ◽

Vol 38 (1) ◽

pp. 72-76 ◽

Cited By ~ 16

Author(s):

V. Kuznetsov ◽

F. Maksimov ◽

A. Zheleznov ◽

G. Cherkashov ◽

V. Bel’Tenev ◽

...

Keyword(s):

Hydrothermal Activity ◽

The West ◽

Ore Formation ◽

Sulfide Deposits ◽

Massive Sulfides ◽

North West ◽

North East ◽

Radiochemical Study ◽

Mid Atlantic Ridge

AbstractA radiochemical study was carried out on massive sulfides from Semyenov hydrothermal district at the Mid-Atlantic Ridge. New and published results provide evidence that 230Th/U ages obtained for massive sulfides are reliable. The sulfide deposits from the West, North-West, North-East, and East hydrothermal sites at the Semyenov hydrothermal district were formed between ∼124 ka and ∼37 ka ago. The hydrothermal activity might have started in the eastern part of the district and moved to the west by episodic ore formation.

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