Detectability of pegmatite lithium deposits by controlled-source electromagnetic methods

doi:10.13745/j.esf.sf.2023.5.21

Abstract

Abstract:

Lithium-bearing minerals are used as raw materials for rechargeable lithium batteries on electric cars, cell phone, etc., while pegmatite lithium deposits account for about a quarter of the world’s lithium resources. However, the effectiveness of electromagnetic exploration methods for high-resistivity pegmatite Li-Be deposits has not been systematically studied. Pegmatite dikes generally have high resistivity—it is close to 10000 ohms for ore-bearing pegmatites, and higher for common pegmatites. Whilst the resistivity of the host rock is generally up to several thousand ohms. Thus how to effectively identify high-resistivity ore-bearing pegmatites under resistive background has become an urgent technical problem. Here, we use transverse magnetic field to solve the detection problem for high-resistivity targets, and the effectiveness of the newly developed detection method is evaluated over the traditional single-line controlled-source method. We systematically compare different components of electromagnetic response from different configurations in terms of response characteristics and resolution, and calculate the root mean square misfit. We find the horizontal electric field component from double-line source shows higher resolution for high-resistivity targets over the traditional single-line source.

Key words: controlled-source electromagnetic method, pegmatite lithium deposit, root mean square error, transverse magnetic field

CLC Number:

WEI Xinhao, ZHOU Nannan, ZHANG Shun. Detectability of pegmatite lithium deposits by controlled-source electromagnetic methods[J]. Earth Science Frontiers, 2023, 30(5): 265-274.

Figures/Tables 11

Fig.1 Layout of double-line (a) and traditional single-line (b) configurations

Table 1 Resistivity and thickness parameters in model 1

模型	第一层信息	第二层信息	第三层信息
高阻模型1	$ρ 1 = 2 000 Ω · m$ $d 1 = 100 m$	$ρ 2 = 2 000 ~ 100 000 Ω · m$ $d 2 = 1 ~ 500 m$	$ρ 3 = 2 000 Ω · m$

Table 1 Resistivity and thickness parameters in model 1

模型	第一层信息	第二层信息	第三层信息
高阻模型1	$ρ 1 = 2 000 Ω · m$ $d 1 = 100 m$	$ρ 2 = 2 000 ~ 100 000 Ω · m$ $d 2 = 1 ~ 500 m$	$ρ 3 = 2 000 Ω · m$

Table 2 Resistivity and thickness parameters in model 2

模型	第一层信息	第二层信息	第三层信息
高阻模型2	$ρ 1 = 3 000 Ω · m$ $d 1 = 1 ~ 500 m$	$ρ 2 = 12 000 Ω · m$ $d 2 = 1 ~ 100 m$	$ρ 3 = 3 000 Ω · m$

Table 2 Resistivity and thickness parameters in model 2

模型	第一层信息	第二层信息	第三层信息
高阻模型2	$ρ 1 = 3 000 Ω · m$ $d 1 = 1 ~ 500 m$	$ρ 2 = 12 000 Ω · m$ $d 2 = 1 ~ 100 m$	$ρ 3 = 3 000 Ω · m$

Fig.2 Attenuation curves of the horizontal electric field excited by double-line and traditional single-line sources at different locations. (a) Model 1. (b) Model 2.

Fig.3 RMS misfit of horizontal electric field component of transient electromagnetic (TEM) response (with 5% background response (BGR)) from different sources in model 1. (a) At near-source point for single-line configuration. (b) At near-source point for double-line configuration. (c) At far-source point for single-line configuration. (d) At far-source point for double-line configuration. Gray areas indicate RMS values less than 1.

Fig.4 RMS misfit of vertical magnetic field component of TEM response (BGR, 5%) from different sources in model 1. See Fig.3 for more caption detail.

Fig.5 RMS misfit of horizontal electric field component of TEM response (BGR, 3%) from different sources in model 1. See Fig.3 for more caption detail.

Fig.6 RMS misfit of vertical magnetic field component of TEM response (BGR, 3%) from different sources in model 1. See Fig.3 for more caption detail.

Fig.7 RMS misfit of horizontal electric field components of TEM response (BGR, 5%) from different sources in model 2. See Fig.3 for more caption detail.

Fig.8 RMS misfit of horizontal electric field component of frequency domain electromagnetic (FDEM) response (BGR, 5%) from different sources in model 1. See Fig.3 for more caption detail.

Fig.9 RMS misfit of horizontal electric field component of FDEM response (BGR, 5%) from different sources in model 2. See Fig.3 for more caption detail.

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