Deep‐Sea Electric and Magnetic Surveys Over Active and Inactive Basalt‐Hosted Hydrothermal Sites of the TAG Segment (26°, MAR): An Optimal Combination for Seafloor Massive Sulfide Exploration

Szitkar, Florent; Hölz, Sebastian; Tarits, Pascal; Petersen, Sven

doi:10.1029/2021jb022082

Cited by 7 publications

(6 citation statements)

References 34 publications

(78 reference statements)

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“…More efforts, including but not limited to combined laboratory simulations and field observations, are needed to delineate how others affect the oxidation of SMS deposits. As SMS deposits are considered potential targets for mining (Szitkar et al., 2021; Van Dover, 2019), such knowledge is instructive for understanding the complicated physicochemical properties of SMS deposits, which may ultimately contribute to designing future exploitation strategies.…”

Section: Discussionmentioning

confidence: 99%

“…Migrating electrons produce current in SMS deposits, creating spontaneous "geobattery" (Sato & Mooney, 1960). Seafloor self-potential surveys have shown that SMS deposits in inactive hydrothermal have strong electric anomalies (Szitkar et al, 2021;Zhu et al, 2020) and therefore confirm the existence of galvanic reactions in SMS deposits. Laboratory simulations have verified that galvanic reactions can accelerate the oxidation rates of sulfides (Knight et al, 2018).…”

Section: 1029/2022gc010368mentioning

confidence: 94%

“…However, detailed magnetomineralogy and magnetic property variations among different hydrothermal products in TAG were not established by Zhao et al (1998). Consequently, although the low concentration of magnetic minerals within the stockwork explains the reduced crustal magnetization in the TAG active mound (e.g., Gehrmann et al, 2019;Tivey et al, 1993), utilizing magnetic surveying data for sophisticated subsurface stockwork geometry inversion and tonnage estimation of SMS deposits remain challenging (e.g., Galley et al, 2021;Szitkar et al, 2021).…”

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confidence: 99%

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Rock Magnetic Signatures of Hydrothermal Mineralization in the Trans‐Atlantic Geotraverse (TAG) Hydrothermal Field

Wang

Chang

2022

Geochem Geophys Geosyst

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The Ocean Drilling Program Leg 158 drill holes from the Trans‐Atlantic Geotraverse hydrothermal field are investigated to understand the rock magnetic signatures of hydrothermal mineralization. A composite columnar section has been constructed through hole correlation to understand the stratigraphic variation of magnetomineralogy within the stockwork. Isothermal remanent magnetization components unmixing, first‐order reversal curve diagrams, low‐temperature magnetic signatures, and electron microscopic analyses disclose magnetic minerals of disparate occurrences related to predominating hydrothermal mineralization reactions in three broad zones: For basaltic basements, serpentinization of olivine phenocrysts during preliminary hydrothermal alteration produces magnetite, in addition to primary titanomagnetite; Chloritized and silicified zone samples contain relict titanomagnetite and exsolved magnetite that survived hydrothermal dissolution; Anhydrite and sulfide zone samples are dominated by magnetite and hematite, likely from oxidation of polymetallic sulfides due to exposure in oxidative seafloor environments during drilling. Our findings suggest that seafloor oxidation potentially modifies the magnetic properties of polymetallic sulfides in hydrothermal deposits, which applies to magnetic tomography of sophisticated subseafloor vent structures and prospecting seafloor massive sulfides (SMS) deposits therein. Meanwhile, we alert future deep‐sea mining that drilling may promote physicochemical alteration of SMS deposits, causing environmental risks. The established magnetic signatures ultimately contribute to understanding the in situ geological preservation of SMS deposits and optimizing exploitation procedures in the future.

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Section: Discussionmentioning

confidence: 99%

Section: 1029/2022gc010368mentioning

confidence: 94%

mentioning

confidence: 99%

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Rock Magnetic Signatures of Hydrothermal Mineralization in the Trans‐Atlantic Geotraverse (TAG) Hydrothermal Field

Wang

Chang

2022

Geochem Geophys Geosyst

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“…In the last decades, galvanometric and electromagnetic methods have been used for the exploration and assessment of SMS resources. These methods include the controlled source electromagnetic (CSEM) method, the direct current (DC) resistivity imaging method, the transient electromagnetic (TEM) method, and the passive self‐potential (SP) method (see case studies in Cairns et al., 1996; Constable et al., 2018; Galley et al., 2021; Gehrmann et al., 2019; Haroon et al., 2018; Ishizu et al., 2019; Kawada & Kasaya, 2018; Müller et al., 2018; Su, Tao, Shen et al., 2022; Szitkar et al., 2021; Zhu et al., 2020). However, ore bodies and metallic deposits are not always characterized by conductivity contrasts (Mao & Revil, 2016; Mao et al., 2016).…”

Section: Introductionmentioning

confidence: 99%

“…For instance, Kasaya et al (2020) successfully conducted marine DC resistivity and SP surveys in hydrothermal deposit areas using two AUVs. Deep-sea passive electric measurements combined with high-resolution magnetic measurements based on AUV were also used in SMS exploration (Szitkar et al, 2021). However, the above investigations are all used for the delineation of SMS deposits at the seafloor.…”

Section: Introductionmentioning

confidence: 99%

Joint Interpretation of Marine Self‐Potential and Transient Electromagnetic Survey for Seafloor Massive Sulfide (SMS) Deposits: Application at TAG Hydrothermal Mound, Mid‐Atlantic Ridge

Tao

Zhu

et al. 2022

JGR Solid Earth

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The self-potential (SP) method is expected to play an important role in the exploration of seafloor massive sulfide (SMS) resources. Since the redox potential changes with depth below the seafloor, SMS deposits are the source of an electrical (source) current density, generating in turn a recordable electrical field. This electrical field can be remotely measured at and above the seafloor. By integrating this electrical field, we obtained a so-called SP profile or map. The electrical conductivity distribution of SMS deposits is an important ingredient in the inversion of these SP data in order to distinguish between causative primary sources (i.e., associated with the SMS deposits themselves) and secondary current sources associated with conductivity contrasts below the seafloor. Such ingredient is therefore necessary to properly localize SMS deposits and eliminating ghosts associated with high conductivity contrasts. The conductivity structure of the seafloor is however unknown in most SP surveys. This study presents the first joint interpretation of transient electromagnetic and SP surveys. The field data were acquired at the Trans-Atlantic Geotraverse (TAG) hydrothermal mound. The conductivity structure of TAG mound was obtained by inverting transient electromagnetic data. This electrical conductivity distribution is then used to invert the SP data. The obtained (primary) source current distribution delineates the geometry of the SMS deposits. The deposits are located in the center of the mound as well as at its edges, in a way that is consistent with water column data. Combining the two geophysical methods improves our ability to better decipher the fine geometry of SMS deposits below the seafloor.Plain Language Summary Seafloor massive sulfide (SMS) deposits contain abundant amounts of Cu, Zn, Au, and Ag, which are of growing economic interest for our civilization. In recent years, the exploration of SMS deposits has entered into a new era with the goal of better assess and characterize these resources. In this perspective, geophysical methods are in high demand to localize SMS deposits and obtain their three-dimensional geometry. The self-potential (SP) method provides an efficient non-intrusive and cost-effective approach to image SMS deposits. Previous surveys have documented the existence of recordable negative SP anomalies above the seafloor in association with SMS deposits. SP tomography can be used to assess the 3D geometry of SMS deposits. That said, the conductivity pattern below the seafloor is unknown in previous SP surveys while it is an important ingredient in the inversion of the SP data. Active source measurements like the transient electromagnetic (TEM) method can be used to obtain the electrical conductivity distribution below the seafloor. So, we propose to combine SP and TEM data to improve our ability to image SMS deposits. We apply the new methodology to a famous submarine hydrothermal field located in the Atlantic mid-oceanic ridge Trans-Atlantic Geotraverse and investigated in the past...

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Redox Sensitive Mineral Magnetic Signatures of Seafloor Massive Sulfide Deposits

Wang,

Tao,

Liao

et al. 2024

JGR Solid Earth

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Seafloor massive sulfide (SMS) deposits in different geological settings can have variable magnetic mineralogy, but the mechanism and implications of their spatiotemporal diversity are poorly understood. Based on seabed shallow drilling and surficial sampling of the Yuhuang hydrothermal field, Southwest Indian Ridge, we investigate here whether ubiquitous oxidative weathering affects the magnetic properties of SMS deposits. Microscopic observation and ferrous iron concentrations reveal that seafloor SMS deposits are extensively oxidized; subseafloor SMS deposits are relatively fresh, but oxidation initiates immediately after sample recovery. Negative frequency dependence of magnetic susceptibility likely due to measurement eddy currents is observed for fresh samples but not for oxidized ones, which suggests that oxidative weathering reduces the electromagnetic detectability of SMS deposits in geophysical investigations. Pyrrhotite (and probably other magnetic iron sulfide minerals), magnetite, and hematite are recognized as dominating magnetic (ferromagnetic, sensu lato) minerals in SMS deposits. Electron and quantum diamond microscope observations reveal pyrrhotite mineralization from high‐temperature reducing hydrothermal fluids, while iron‐oxides are mostly oxidation products of primary sulfides. Oxidative weathering modifies paleomagnetic records of SMS deposits. Bulk magnetic parameters vary systematically with enhanced oxidation degree. Temperature‐dependent magnetic measurements are useful tools for distinguishing the oxidation state of SMS deposits. Overall, these findings explain magnetic mineral variability in SMS deposits, linking mineral magnetic properties with seafloor geophysical investigations. Mineral magnetism can also be a redox state proxy for tracing natural and artificial environmental fluctuations in seafloor hydrothermal fields, inspiring novel interdisciplinary research to understand interactions in the dynamic Earth System.

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Deep‐Sea Electric and Magnetic Surveys Over Active and Inactive Basalt‐Hosted Hydrothermal Sites of the TAG Segment (26°, MAR): An Optimal Combination for Seafloor Massive Sulfide Exploration

Cited by 7 publications

References 34 publications

Rock Magnetic Signatures of Hydrothermal Mineralization in the Trans‐Atlantic Geotraverse (TAG) Hydrothermal Field

Rock Magnetic Signatures of Hydrothermal Mineralization in the Trans‐Atlantic Geotraverse (TAG) Hydrothermal Field

Joint Interpretation of Marine Self‐Potential and Transient Electromagnetic Survey for Seafloor Massive Sulfide (SMS) Deposits: Application at TAG Hydrothermal Mound, Mid‐Atlantic Ridge

Redox Sensitive Mineral Magnetic Signatures of Seafloor Massive Sulfide Deposits

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