P-wave velocity measurements for preliminary assessments of the mineralization in seafloor massive sulfide mini-cores during drilling operations

Spagnoli, Giovanni; Weymer, Bradley A.; Jegen, Marion; Spangenberg, Erik; Petersen, Sven

doi:10.1016/j.enggeo.2017.07.003

Cited by 7 publications

(2 citation statements)

References 29 publications

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“…In comparison to the surrounding host rock, SMS typically exhibit substantial contrasts in their physical parameters, i.e. magnetic susceptibility (Spagnoli et al 2017a), acoustic velocity (Spagnoli et al 2017b) and electrical conductivity (Morgan 2012;Spagnoli et al 2016). Thus, making them ideal targets for geophysical exploration.…”

Section: Introductionmentioning

confidence: 99%

Marine dipole–dipole controlled source electromagnetic and coincident-loop transient electromagnetic experiments to detect seafloor massive sulphides: effects of three-dimensional bathymetry

Haroon

Hölz

Gehrmann

et al. 2018

Geophysical Journal International

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Seafloor massive sulphides (SMSs) are regarded as a potential future resource to satisfy the growing global demand of metals including copper, zinc and gold. Aside from mining and retrieving profitable amounts of massive sulphides 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 centres. Currently, several geophysical technologies are being developed to detect and quantify SMS occurrences that often exhibit measurable contrasts in their physical parameters compared to the surrounding host rock. Here, we use a short, fixed-offset controlled source electromagnetic (CSEM) system and a coincident-loop transient electromagnetic (TEM) system, which in theory allow the detection of SMS in the shallow seafloor due to a significant electrical conductivity contrast to their surroundings. In 2016, CSEM and TEM experiments were carried out at several locations near the TransAtlantic Geotraverse hydrothermal field to investigate shallow occurrences of massive sulphides below the seafloor. Measurements were conducted in an area that contains distinct SMS sites located several kilometres off-axis from the Mid-Atlantic ridge, some of which are still connected to hydrothermal activity and others where hydrothermal activity has ceased. Based on the quality of the acquired data, both experiments were operationally successful. However, the data analysis indicates bias caused by three-dimensional (3D) effects of the rough bathymetry in the study area and, thus, data interpretation remains challenging. Therefore, we study the influence of 3D bathymetry for marine CSEM and TEM experiments, focusing on shallow 3D conductors located beneath mound-like structures. We analyse synthetic inversion models for attributes associated with 3D distortions of CSEM and TEM data that are not sufficiently accounted for in conventional 1D (TEM) and 2D (CSEM) interpretation schemes. Before an adequate quantification of SMS in the region is feasible, these 3D effects need to be studied to avoid over/underestimation of SMS using the acquired EM data. The sensitivity of CSEM and TEM to bathymetry is investigated by means of 3D forward modelling, followed by 1D (TEM) and 2D (CSEM) inversion of the synthetic data using realistic error conditions. Subsequently, inversion models of the synthetic 3D data are analysed and compared to models derived from the measured data to illustrate that 3D distortions are evident in the recorded data sets.

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Section: Introductionmentioning

confidence: 99%

Marine dipole–dipole controlled source electromagnetic and coincident-loop transient electromagnetic experiments to detect seafloor massive sulphides: effects of three-dimensional bathymetry

Haroon

Hölz

Gehrmann

et al. 2018

Geophysical Journal International

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“…By comparison, for the case of electrolytic conduction, the conductivity is directly related to the porosity of the sample (e.g., Archie's Law, Archie, ). This relationship does not hold for SMS deposits, which act as semiconductors causing the conductivities to be orders of magnitude higher and display complex behavior due to their frequency‐dependent chargeability (Spagnoli et al, , ). Samples from the Central Indian Ridge show similar behavior with a clear frequency dependence, for example, larger conductivities at higher frequencies (Müller et al, ).…”

Section: Resultsmentioning

confidence: 99%

Marine Mineral Exploration With Controlled Source Electromagnetics at the TAG Hydrothermal Field, 26°N Mid‐Atlantic Ridge

Gehrmann

North

Graber

et al. 2019

Geophysical Research Letters

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Seafloor massive sulfide (SMS) deposits are of increasing economic interest in order to satisfy the relentless growth in worldwide metal demand. The Trans‐Atlantic Geotraverse (TAG) hydrothermal field at 26°N on the Mid‐Atlantic Ridge hosts several such deposits. This study presents new controlled source electromagnetic, bathymetric, and magnetic results from the TAG field. Potential SMS targets were selected based on their surface expressions in high‐resolution bathymetric data. High‐resolution reduced‐to‐the‐pole magnetic data show negative anomalies beneath and surrounding the SMS deposits, revealing large areas of hydrothermal alteration. Controlled source electromagnetic data, sensitive to the electrical conductivity of SMS mineralization, further reveal a maximum thickness of up to 80 m and conductivities of up to 5 S/m. SMS samples have conductivities of up to a few thousand Siemens per meter, suggesting that remotely inferred conductivities represent an average of metal sulfide ores combined with silicified and altered host basalt that likely dominates at greater depths.

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Joint Frequency in the Rock Mass Rating 2014 Classification System Based on Field P-wave Propagation Velocity Tests: A New Rating Method

2021

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P-wave velocity measurements for preliminary assessments of the mineralization in seafloor massive sulfide mini-cores during drilling operations

Abstract: P-wave velocity measurements for preliminary assessments of the mineralization in seafloor massive sulfide mini-cores during drilling operations

Cited by 7 publications

References 29 publications

Marine dipole–dipole controlled source electromagnetic and coincident-loop transient electromagnetic experiments to detect seafloor massive sulphides: effects of three-dimensional bathymetry

Marine dipole–dipole controlled source electromagnetic and coincident-loop transient electromagnetic experiments to detect seafloor massive sulphides: effects of three-dimensional bathymetry

Marine Mineral Exploration With Controlled Source Electromagnetics at the TAG Hydrothermal Field, 26°N Mid‐Atlantic Ridge

Joint Frequency in the Rock Mass Rating 2014 Classification System Based on Field P-wave Propagation Velocity Tests: A New Rating Method

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