Evidence of Lithium Enrichment in a Continental Red-Bed Succession: The Cahuasas Formation, Molango Rift, Mexico

Lithium has become a critical raw material, and research interest has expanded beyond pegmatites and brines toward unconventional sedimentary environments, although continental red-bed successions remain largely underexplored. This study presents a preliminary mineralogical and geochemical characterization of the basal interval of the Middle Jurassic Cahuasas Formation, Molango Rift System, Hidalgo, Mexico. Polarized-light microscopy, ICP–OES, XRF, XRD, Raman spectroscopy, FTIR, XPS, and SEM–EDS were combined. ICP–OES yielded a mean lithium concentration of 115.00±4.58 ppm, approximately 4.8 times the upper continental crust average of 24 ppm, but only 1.7 times the average shale concentration. XRD indicates a mineral assemblage dominated by quartz and chlorite, with diffraction matches to the reference pattern (Al0.05Li0.05Si0.95O2; PDF 96-900-2384). The Raman spectra contain a band at 707 cm−1, reproduced in all analyzed spectra, consistent with a possible α-spodumene-type contribution. FTIR, SEM–EDS, and XRF indicate a silicate–aluminosilicate matrix, while a weak XPS signal at 54.50 eV is compatible with Li 1s. The basal interval of the Cahuasas Formation is documented as hosting previously unreported lithium enrichment. These results provide preliminary evidence of a localized lithium anomaly, with diffraction matches to the reference pattern of a Li–Al-bearing phase. Given its preliminary nature, this study is limited to characterizing the anomaly and clarifying the mineralogical species present, without addressing genetic processes or economic aspects.