Exploration of Seafloor Massive Sulfide Deposits with Fixed-Offset Marine Controlled Source Electromagnetic Method: Numerical Simulations and the Effects of Electrical Anisotropy

Ronghua Peng,Xiangyun Hu,Bo Han

doi:10.3390/min10050457

Ronghua Peng, Xiangyun Hu + Show 1 more

Open Access

https://doi.org/10.3390/min10050457

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Journal: Minerals	Publication Date: May 19, 2020
Citations: 5	License type: CC BY 4.0

Affiliation: China University of Geosciences

Abstract

Seafloor massive sulfide (SMS) deposits have attracted growing interest and become the focus of current seafloor mineral exploration. One key challenge is to delineate potential SMS accumulations and estimate their quantity and quality for prospective resource mining. Recently, geophysical electromagnetic methods which are routinely used for land-based mineral exploration are being adapted to detect and assess SMS occurrences by imaging their conductivity distributions. However, the rough seafloor topography and electrical anisotropy of the seafloor formations encountered in practical surveys pose challenges for reliable data interpretation, and recent studies have revealed that the rough bathymetry could cause measurable distortions. Here, we consider a fixed-offset marine controlled-source electromagnetic method (CSEM) for SMS exploration, and investigate the effects of electrical anisotropy of sedimentary formations through numerical simulations for marine CSEM surveys aiming at conductive targets in the shallow regions of the seafloor. Numerical results demonstrate that the presence of electrical anisotropy could impose significant influence on fixed-offset marine CSEM data and suggest that the distortions should be sufficiently accounted for reliable data interpretation, thus lending confidence to subsequent quantification of available SMS minerals.

Highlights

The rapid development of a growing number of emerging economies has motivated continuing prospecting and exploration efforts for alternative resources to meet ever-growing global demand for minerals and materials
seafloor massive sulfide (SMS) deposits that have been disconnected to active hydrothermal vents are believed to host a large amount of minerals for prospective mining
These inactive SMS deposits are likely to be masked by sediments and difficult to be identified

Summary

Introduction

The rapid development of a growing number of emerging economies has motivated continuing prospecting and exploration efforts for alternative resources to meet ever-growing global demand for minerals and materials. Since SMS deposits typically accumulate high-grade metalliferous minerals and clays, they usually show significant electrical resistivity anomalies compared to the unmineralized host rocks [5,9,11]. The presence of electrical anisotropy may cause measurable distortions in the acquired EM data and suppress the responses of potential SMS deposits, deteriorating the ability of marine CSEM for SMS exploration, especially aiming at deep-seated SMS deposits. The potentials within a tetrahedral element are tetrahedral element are approximated by a linear combination of vector and scalar basis functions, represented as respectively. Piecewise linear polynomials defined on the edges and nodes are, respectively, used for vector and scalar basis functions. Solved iteratively using the quasi-minimal method incomplete preconditioning residual method (QMR) with an incomplete LU preconditioning [43]

Validation the Modeling

A deep-water layered anisotropic modelmodel with awith conductive

SMS Model Studies

10. The normalized amplituderesponse response of of model to model

Summary and Conclusions