Weathering of clay minerals in terra rossa and the provenance of karstic bauxite revealed by geochemical big data and mineralogical analysis

Provenance research has always been a critical topic in the study of karstic bauxites. In this field, whether carbonate rocks can serve as the parent rock of karstic bauxites has been a subject of debate for the past century, substantially hindering our understanding of the metallogenic mechanism of karstic bauxites. The critical issue in this controversy is whether clay minerals in the weathering residues of carbonate rocks (i.e., terra rossa) can be transformed into gibbsite, which serves as the original ore mineral of karstic bauxites. To address this issue, we conducted a comprehensive analysis of a large dataset by extensively sampling karstic weathering residues in the Guangxi region of China. It was found that the degree of desilicification and allitization in the weathering residues could not meet the requirements for a bauxite source, even at the peak of natural weathering. Remarkably, investigations into the mineral composition and the mechanisms of mineral-phase transformation demonstrate that clay minerals in terra rossa rarely transform into gibbsite. Conclusively, terra rossa cannot directly serve as the source material for karstic bauxites. On a global scale, the trace element characteristics indicate that the primary source material of karstic bauxites derives from the final weathering products of aluminosilicate rocks, represented by lateritic bauxites, which provide an adequate supply of gibbsite as the original ore-mineral source. Our research enhances understanding of the metallogenic mechanisms associated with karstic bauxites and supports future exploration.