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

Abstract

The company La Alquimia Compañía Anónima rock collection comprises a wide range of samples from karstic bauxites to kaolin deposits across the Iberian Peninsula. Collected during mid-20th-century prospecting efforts, aimed to identify bauxites for exploitation and aluminum oxide production, this rock collection offers an unprecedented opportunity to perform a systematic study of some of the most important Iberian karstic bauxite and kaolin deposits. The major-element data from the samples were obtained through handheld X-ray fluorescence (XRF) and analyzed using Principal Components Analysis (PCA), revealing SiO2 and Al2O3 as the key components that explain the most variance. The XRF data confirmed that the samples mostly consist of karstic bauxites and kaolin, with minor amounts of gibbsite and alunite deposits. The calculated Index Of Laterization/Index Of Bauxitization (IOL/IOB) and Chemical Index of Alteration (CIA), and the SiO2 – Al2O3 – Fe2O3 and Al2O3 – CaO*+Na2O – K2O ternary diagrams have facilitated the categorization of karstic bauxites into 'bauxitic' and 'lateritic' types, and the kaolin deposits into 'gabbro' and 'granite' derived types with an intermediate to extreme degrees of weathering. The data highlights potential differences in formation settings possibly influenced by regional factors such as volcanism and tectonics, as well as global factors like eustasy and climate, which could explain the compositional disparities observed in the Iberian karstic bauxites and kaolin deposits.