The altered tuffs in the Late Permian coal- bearing basement of the southwest region exhibit significant enrichment in rare earth elements and other critical metals. Low- temperature hydrothermal fluids have made an important contribution in this enrichment and mineralization. Western Guizhou, located in a globally significant region of low- temperature hydrothermal activity, provides an exceptional natural laboratory to unravel the mechanisms driving REE enrichment in coal- bearing strata under such conditions. The geochemical and mineralogical composition of altered tuffs can provide insights into fluid evolution, thermal history, and mineralization processes during alteration. However, a lack of under standing persists regarding the composition of altered mineral assemblages and their coexistence in the tuffs, which limits our comprehension of critical metal enrichment processes. This study reveals that the tuffs have geochemical properties consistent with high- titanium basalts; volcanic glass and secondary minerals formed by metasomatic alteration, such as feldspar and pyroxene, may have formed in the supergene weathering or early diagenetic stage; the vein- like distribution of monazite indicates the origin of late hydrothermal fluids. The proposed enrichment pattern of REEs in these tuffs is as follows: shortly after volcanic ash deposition, the tuff underwent supergene weathering. Surface water and periodic seawater incursions leached REEs from the upper tuff layers, causing downward migration. Subsequently, exfiltration hydrothermal fluids interacted with the tuff, leaching REEs from the lower layers and transporting them upwards, ultimately leading to enrichment in the overlying rock strata.