Chemical weathering progress and whole-rock mineral assemblage changes associated with slope geo-hazards in Guangdong, China

The geochemical and mineralogical processes underlying the mechanical weakening of rock and soil in subtropical South China remain insufficiently quantified. We evaluated lithology-dependent chemical weathering as an intrinsic background for collapses and landslides in northern and eastern Guangdong, China, coupling 6,841 mapped hazard sites with X-ray fluorescence and whole-rock X-ray diffraction (XRD) analyses of 40 samples from 11 sites. Igneous-rock areas show higher total hazard density (13.58 vs. 9.49 sites/100 km²) and 1.9-fold higher collapse density than sedimentary-rock areas. After correction for silicate CaO (CaO*) using measured P₂O₅, igneous products have site-balanced means (site means averaged equally) of 88.3 for the chemical index of alteration (CIA) and 71.9 for parent-rock-normalized CIA-rate, versus 85.0 and 21.7 for sedimentary products. CIA distributions overlap despite a modest sample-level difference (exact p = 0.043), whereas CIA-rate separates the product groups completely (exact p = 1.0 × 10⁻⁷). Whole-rock assemblages show feldspar depletion, quartz persistence and kaolinite enrichment in igneous products. Sedimentary products, with each subtype represented by one site, remain heterogeneous because of inherited 2:1 clay minerals and framework grains. Mineral-ratio differences within the conservative XRD sensitivity envelopes are not interpreted. These patterns characterize lithology-specific weathered materials associated with regional hazards; the observational design does not establish independent causal contributions. CIA-rate expresses normalized differences from selected lithology-specific parent-material baselines. Mineral ratios support interpretation of relative weathering intensity in the sampled igneous rocks. In sedimentary rocks, they serve only as lithology-sensitive descriptors of mineral assemblages.