Lithium is a critical metal and is widely used in new energy industry. The newly discovered carbonate -hosted clay -type lithium deposit has the characteristics of large reserves and low mining cost, which make it to be another potential lithium exploration direction in our country. However, its occurrence state and enrichment mechanism are still unclear, which hinders the evaluation, prediction and comprehensive utilization of this type of lithium deposit. In this study, carbonate -hosted clay -type lithium deposit in Central Yunnan, Southwest China was selected as research object. Samples were analyzed using X-ray diffraction ( XRD) and scanning electron microscopy equipped with energy dispersive X-ray analysis ( SEM-EDX) to investigate the composition and morphology of minerals in Li -rich clay rocks. In addition, focused -ion -beam ( FIB) and time -of-flight secondary ion mass spectrometry (TOF-SIMS) were employed to characterize elemental distribution at micron -scale. Analysis results show that Li has a strong positive correlation with Si and Mg, indicating that the carrier of Li is Mg -rich clay mineral. FIB cross sections were analyzed using a transmission electron microscope ( TEM) equipped with EDX to assess the elemental distribution and mineral composition at nano -scale in Li -rich clay rocks. As a result, smectite and/or cookeite were identified as the carrier of Li. We propose that smectite formed during weathering depositional processes could incorporate a large amount of Li and then transformed into cookeite during burial diagenesis. New insights gained from this study will improve the mineralization model of carbonate -hosted clay -type lithium deposit.