Genetic relationship between granite and pegmatite in the Kaluan lithium deposit, Western China: evidence from the inversion of audio-magnetotelluric data

The Altay Orogenic Belt in Xinjiang, China, is characterized by numerous pegmatite veins, among which Kaluan pegmatite potentially hosts an ultra-large lithium spodumene deposit. Since the discovery of lithium deposits in this region, the formation of pegmatites has been a focal point in mineral deposit studies. Previous research has primarily focused on the geological and geochemical aspects, lacking indirect geophysical evidence regarding the genetic link between the pegmatite veins and the deep-seated granitic basement. This paper utilizes four audio-magnetotelluric (AMT) profile datasets to inverse the electrical structure characteristics of the area. To obtain reliable AMT inversion results, following preprocessing of the raw data, the Bahr decomposition method was employed to estimate the two-dimensional (2D) deviation for all measurement points. In addition, the Groom-Bailey (GB) multisite multifrequency decomposition method was used to estimate the azimuth angle of the electrical axis in the study area. Data processing results indicate that the shallow subsurface in this area exhibits favorable 2D characteristics, making it suitable for 2D inversion studies. Lastly, impedance tensor data were rotated to align with the direction of the electrical axis, and inversion was performed using the transverse magnetic polarization mode data. In the conclusion of this paper, we have integrated the results of resistivity measurements from rock specimens, magnetic anomaly, geological cross-sections, and existing geochemical research findings to comprehensively explore the geological conditions of pegmatite formation in the study area. The research findings of this study indicate that the pegmatite veins of the Kaluan lithium deposit typically develop above the deep-seated granitic basement and are controlled by both surface and subsurface fault structures. Meanwhile, isotopic studies in geochemistry reveal a strong affinity between the granitic rocks and the pegmatites in terms of provenance. Based on this comprehensive analysis, it can be inferred that a close genetic relationship exists between the Kaluan pegmatite veins and the deep-seated granitic basement, as well as the fault structures.