Major-element analysis of the La Alquimia Compañía Anónima rock collection: Establishing a geochemical repository for the systematic classification of Iberian karstic bauxite and kaolin deposits

The La Alquimia Compañía Anónima rock collection comprises a diverse range of rock samples collected across the Iberian Peninsula to identify bauxites suitable for aluminum oxide production. In this study, the major-element compositions of the rock samples were analysed using non-destructive portable X-Ray Fluorescence (XRF). The data were processed through Principal Component Analysis (PCA), calibrated and used to calculate the Index of Laterisation/Index of Bauxitisation (IOL/IOB) and the Chemical Index of Alteration (CIA). The PCA results revealed SiO₂, Al₂O₃ and Fe₂O₃ as the key components explaining most of the rock samples compositional variance. The calibrated data provided the major element compositions, confirming that the rock samples predominantly correspond to karstic bauxites and kaolin deposits. For the karstic bauxite samples, the calculated IOL/IOB values, combined with the SiO₂–Al₂O₃–Fe₂O₃ ternary diagram, facilitated their classification. The samples were categorised into bauxitic types associated with regions of moderate uplift and karst development and near-lateritic types indicative of advanced weathering processes typical of more stable continental terrains under warm and humid climates. Besides, the calculated CIA values and the Al₂O₃–CaO*+Na₂O–K₂O ternary diagram were applied to classify the kaolin deposits. This approach also identified compositional variations among the kaolin rock samples, reflecting differences in their formation. The rock collection serves as a repository for advancing the regional understanding of the formation, distribution and geochemical trends of Iberian karstic bauxite and kaolin deposits. Moreover, these deposits hold significance as potential sources of Al, Li and REE, emphasising the value of the La Alquímia Compañía Anónima collection as a geochemical repository, particularly considering the growing demand for these critical resources.