Genesis of cookeite, the primary lithium mineral in the Late Carboniferous strata of the North China Craton

Lithium (Li) is essential for advancing the global green energy transition. As demand for this critical element grows, identifying new and unconventional Li resources has become increasingly important. Here we investigate a bauxitic sedimentary Li deposit in the Late Carboniferous strata of the North China Craton (NCC), where Li-enriched phyllosilicate layers contain up to 6782 ppm Li. Mineralogical and geochemical analyses show that Li is mainly hosted in cookeite, with significant contributions from Muscovite II and minor amounts from elbaite. Cookeite was identified by characteristic X-ray diffraction (XRD) peaks (14.03, 7.03, 3.51, and 1.49 Å), supported by spatial correlations between Li-enriched domains revealed by Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) mapping, and by Fourier Transform Infrared Spectroscopy (FTIR) signatures. Broad FTIR bands at 3532–3516 and 3355–3335 cm⁻¹ in Li-rich domains reflect OH stretching in Li–Al brucite-like layers, confirming cookeite. TESCAN Integrated Mineral Analyzer (TIMA) provided textural context, showing cookeite as discrete grains and intergrowths with kaolinite and muscovite, commonly forming starburst aggregates of authigenic origin. Lithium enrichment in the NCC bauxites reflects a three-stage evolution: weathering release from detrital silicates, diagenetic crystallization of cookeite and K-deficient Muscovite II, and late hydrothermal overprint that upgraded Li along fractures and pisolitic/oolitic structures with Ti oxides. This sequence underscores the combined roles of weathering, diagenesis, and hydrothermal processes in concentrating Li. These findings emphasize the significance of cookeite as the primary Li-bearing mineral in Late Carboniferous bauxitic deposits of the NCC. More broadly, this study provides a framework for exploring similar karst-hosted deposits worldwide, where cookeite, Li-muscovite, and Ti oxides may serve as key exploration indicators. LIBS and FTIR are shown to be efficient tools for identifying Li-bearing phases in fine-grained samples, offering rapid and cost-effective support for targeted Li exploration.