Geophysical approaches to the exploration of lithium pegmatites and a case study in Koktohay

doi:10.13745/j.esf.sf.2023.5.14

Abstract

Abstract:

Lithium is a critical metal widely used in Li-ion batteries for energy storage. The demand for lithium resource in a low-carbon economy is immense and rapidly growing, where a jump between 2015 to 2050 is predicted by Science. Currently more than half of lithium production comes from pegmatite lithium deposits. However, due to similar rock property between pegmatites and granite, lithium pegmatite prospecting by geophysical methods has proven difficult. Nevertheless, with the advancements in instrumentation and method developments, geophysical approaches have become increasingly widely used in lithium exploration. In this paper we briefly review the status of lithium resource as strategic raw material, and discuss and summarize the art of geophysical exploration for pegmatite lithium deposits, including rock physics, space remote sensing, gravity and magnetic prospecting, and geoelectrical exploration. A case study of the Koktokay rare-metal pegmatite by audio-frequency magnetotelluric (AMT) method is presented. Pegmatites and leucogranites are characterized by low magnetic susceptibility, low density, low polarizability and high velocity, and the electrical resistivity of pegmatites is affected by hydrophilic minerals and can vary by several orders of magnitude. As the host schist and gneiss in comparison have higher magnetic susceptibility and density, regional gravity and magnetic data are often used to delineate granite bodies. Recent reports show that micro-gravity in some cases can be used to identify pegmatite in host granite. With relatively high resolution and penetration depth, geoelectrical exploration plays an important role in the exploration of concealed pegmatite lithium deposits. In Koktokay, the rock formation and rock mass in the mining district are generally characterized by high resistivity by AMT method, but many low resistivity anomalies are detected. Based on the known ore deposits and geological survey results, the low-resistivity anomalies most likely reflect hidden pegmatites and indicate a good rare-metal resource prospect in the southern Koktokay mining district.

Key words: lithium deposit, pegmatite, geophysical approaches, geo-electical prospecting, Koktkay, rock physics

CLC Number:

HE Lanfang, LI Liang, SHEN Ping, WANG Sihao, LI Zhiyuan, ZHOU Nannan, CHEN Rujun, QIN Kezhang. Geophysical approaches to the exploration of lithium pegmatites and a case study in Koktohay[J]. Earth Science Frontiers, 2023, 30(5): 244-254.

Figures/Tables 7

Table 1 Geophysical approaches typically used for pegmatite exploration in selected countries

数据来源	各类地球物理探测方法的使用情况
数据来源	重力	磁法	遥感	电法	放射性
GreenPeg			○	○
芬兰	○	○	○	○
津巴布韦		○		○
莫桑比克		○			○
尼日利亚		○	○	○	○
阿富汗		○	○
印度	○(微重力)
巴西				○(雷达)
美国	○	○	○	○
中国	○	○	○	○	○

Table 2 Statistics of density and magnetic susceptibility values of pegmatites from different regions

数据来源	岩石	密度/(g·cm^-3)		磁化率/(10^-6 SI)
数据来源	岩石	变化范围	均值	变化范围	均值
甲基卡^[26]	锂辉石伟晶岩	2.60~4.25	2.605
	花岗岩	2.623~2.692	2.646	73.99~24.14	47.64
	伟晶岩	2.593~2.699	2.630	50.90~28.60	40.33
	二长花岗岩	2.554~2.772	2.629
喜马拉雅淡色花岗岩	花岗岩、淡色花岗岩			10~280	73.4
欧洲(EuroPeg)	伟晶岩	2.55~3.19	2.67

Fig.1 Microgravity survey results on pegmatites in western Dharwar, India. Adapted from [22].

Fig.2 Time-lapse complex resistivity of pegmatite samples before and after water absorption

Fig.3 (a) Geological sketch map of the Koktokay mining district and AMT layout and (b) typical geological cross-sections. Adapted from [61].

Fig.4 Typical 2D inversion cross-section of AMT data (L09) along W-E direction in Koktohay

Fig.5 Typical 2D inversion cross-section of AMT data (L01) along S-N direction in Koktohay

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