Keynote Speech - Mapping Seafloor Massive Sulfides at the Central Indian Ridge with a Novel Central Loop Electromagnetic Profiler

Mueller, H.; Schwalenberg, Katrin; Hilgenfeldt, Christian; Dobeneck, Tilo von

doi:10.3997/2214-4609.201602118

Cited by 5 publications

(3 citation statements)

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“…Recently, several loop transmitter/receiver systems have been developed and successfully applied that measure either in the time domain (Hölz et al 2015), frequency domain (Müller et al 2015;Müller et al 2016), or use an ROV to navigate close to the seafloor (Kowalczyk 2008(Kowalczyk , 2011(Kowalczyk , 2013Asakawa et al 2016;Nakayama & Saito 2016). Our study focuses on the MARTEMIS system developed by Hölz et al (2015), which is towed in the immediate proximity of the seafloor behind the vessel (Figs 1b and c).…”

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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“…In offshore marine settings, either with a basin-scale controlled-source electromagnetic survey 2,7 or an ocean-bottom shallow inductive method 56,57 , it is possible to acquire induced polarization or complex conductivity information 7 . In these scenarios, the real part of the subsurface conductivity can be acquired through an inversion algorithm with proper constraints 58 , which provides a map of the effective conductivity σ m of the porous media (without conductive grains) in the subsurface.…”

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confidence: 99%

Quantifying Induced Polarization of Conductive Inclusions in Porous Media and Implications for Geophysical Measurements

Feng

Cameron

et al. 2020

Sci Rep

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induced polarization (ip) mapping has gained increasing attention in the past decades, as electrical induced polarization has been shown to provide interesting signatures for detecting the presence of geological materials such as clay, ore, pyrite, and potentially, hydrocarbons. However, efforts to relate complex conductivities associated with ip to intrinsic physical properties of the corresponding materials have been largely empirical. Here we present a quantitative interpretation of induced polarization signatures from brine-filled rock formations with conductive inclusions and show that new opportunities in geophysical exploration and characterization could arise. initially tested with model systems with solid conductive inclusions, this theory is then extended and experimentally tested with nanoporous conductors that are shown to have a distinctive spectral ip response. Several of the tests were conducted with nano-porous sulfides (pyrite) produced by sulfate-reducing bacteria grown in the lab in the presence of a hydrocarbon source, as well as with field samples from sapropel formations. Our discoveries and fundamental understanding of the electrode polarization mechanism with solid and porous conductive inclusions suggest a rigorous new approach in geophysical exploration for mineral deposits. Moreover, we show how induced polarization of biologically generated mineral deposits can yield a new paradigm for basin scale hydrocarbon exploration.

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“…In a marine setting, electromagnetic systems have been applied successfully in exploring for oil and gas reserves (see Constable 2010 for a review), gas hydrates (Yuan and Edwards, 2000;Weitemeyer et al, 2006;Schwalenberg et al, 2010a,b;Constable et al, 2016), and submarine massive sulfide (SMS) deposits (Cairns et al, 1996;Kowalczyk, 2008;Lipton, 2008;Kowalczyk et al, 2015;Hölz et al, 2015;Mueller et al, 2016). SMS deposits contain valuable resources of Cu, Pb, Zn, Au, and Ag (Herzig, 1999), and some of these deposits, such as the Solwara 1 deposit in the Bismark Sea (Lipton, 2008), may have potential to be economically mined.…”

Section: Introductionmentioning

confidence: 99%

On electric fields produced by inductive sources on the seafloor

et al. 2017

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The transient electromagnetic (TEM) method has recently been proposed as a tool for mineral exploration on the seafloor. Similar to airborne TEM surveys conducted on land, marine TEM systems can use a concentric or coincident wire loop transmitter and receiver towed behind a ship. Such towed-loop TEM surveys could be further augmented by placing additional stationary receivers on the seafloor throughout the survey area. We examine the electric fields measured by remote receivers from an inductive source transmitter within a 1D layered earth model. At sea, it is conceivable to deploy either a horizontal transmitter (like the analogous standard airborne configuration), or a more exotic vertical transmitter. Therefore we study and compare the sensitivity of both the vertical and horizontal towed-loop systems to a variety of seafloor conductivity structures.Our results show that the horizontal loop system is more sensitive to the thickness of a buried conductive layer and would be advantageous over the vertical loop system in characterizing the size of a shallowly buried mineralized zone. The vertical loop system is more sensitive to a resistive layer than the horizontal loop system. The vertical electric field produced by the vertical loop transmitter is sensitive to greater depths than the horizontal fields, and measuring the vertical field at the receivers would therefore be advantageous.We also conducted a novel test of a towed horizontal loop system with remote dipole receivers in a marine setting. The system was tested at the Palinuro volcanic complex in the Tyrrhenian Sea, a site of known massive sulfide mineralization. Preliminary results are consistent with shallowly buried material in the seafloor of conductivities > 1 S/m.

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Keynote Speech - Mapping Seafloor Massive Sulfides at the Central Indian Ridge with a Novel Central Loop Electromagnetic Profiler

Cited by 5 publications

References 0 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

Quantifying Induced Polarization of Conductive Inclusions in Porous Media and Implications for Geophysical Measurements

On electric fields produced by inductive sources on the seafloor

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