Mineralogical and Geochemical Characteristics of Triassic Lithium-Rich K-Bentonite Deposits in Xiejiacao Section, South China

Abstract

Widespread alteration in the Early–Middle Triassic volcanic ash of the Xiejiacao section, south China, has resulted in significant occurrences of lithium-rich K-bentonite deposits with economic potential. Detailed mineralogical and geochemical investigations of Li-rich K-bentonite deposits from the Xiejiacao section of Guangan city, South China, are presented here. The X-ray diffraction (XRD) data and major element chemistry indicates that the Li-rich K-bentonite deposits contain quartz, clay minerals, feldspar, calcite and dolomite, and the clay minerals are dominated by illite and ordered (R3) illite/smectite (I/S). The concentrations of major and trace elements in Li-rich K-bentonite deposits altered from volcanic ashes are most likely derived from felsic magmas, associated with intense volcanic arc activity. The composition of the clay components suggests that the Li-rich K-bentonite deposits are probably altered from the smectite during diagenesis, whereas smectite is mainly formed by submarine alterations of volcanic materials and subsequently the I/S derived from the volcanogenic smectite illitization. Moreover, accurate determination of the structure in I/S reveals that the temperatures reached by the sedimentary series are around 180 °C with a burial depth of ~6000 m. The widely distributed lithium-rich clay deposits strongly indicate widespread eruptions of volcanic ashes in the Early–Middle Triassic, which released huge amounts of volcanic ash. Lithium fixed in the illite and I/S is considered to have leached from the volcanogenic products by a mixed fluid source (i.e., meteoric, porewater and hydrothermal fluids). These Li-rich clay minerals in the marine basin contain economically extractable levels of metal and are a promising new target for lithium exploration.

Volcanic activity during the Early–Middle Triassic transition in the Sichuan Basin, South China: Duration, evolution and implications

“…GBR formed mainly around the boundary between Early and Middle Triassic period (Z. Chen et al, 1999;Lehrmann, Payne, et al, 2007;Y. J. Lin et al, 2020;Sun et al, 2017;Xiang et al, 2019; Z. F. Zhu & Wang, 1986).…”

“…Marine layers from the Early to Middle Triassic periods in the Yangtze Block are well‐preserved and accessible, providing a useful record of the biostratigraphy and sedimentary events of this era, as well as the biotic resurgence after the end‐Permian mass extinction. GBR formed mainly around the boundary between Early and Middle Triassic period (Z. Chen et al, 1999; Lehrmann, Payne, et al, 2007; Y. J. Lin et al, 2020; Sun et al, 2017; Xiang et al, 2019; Z. F. Zhu & Wang, 1986). However, the distribution of GBR tuff layers varies between regions.…”

“…Previous studies have largely focused on the mineralogy, protoliths and depositional environment of the lithium‐rich GBR (Z. Chen et al, 1999; A. Q. Chen et al, 2015; Ma et al, 2019; Wu et al, 1994; Xiang et al, 2019; L. J. Zhu, 1994; Z. F. Zhu & Wang, 1986). Y. J. Lin et al (2020) suggest that the high lithium content of these tuff layers may be related to their magmatic source. However, detailed cross‐sectional comparisons between different lithologies are lacking, and there are conflicting explanations for the enriched potassium and lithium content of GBR.…”

“…Y. J. Lin et al (2020) suggest that the high lithium content of these tuff layers may be related to their magmatic source. However, detailed cross-sectional comparisons between different lithologies are lacking, and there are conflicting explanations for the enriched potassium and lithium content of GBR.…”