First row transition metals deportment in Cretaceous karst bauxite: the case of the southern Italy and Sardinia Island deposits

In the last decade an increasing interest has been paid to the distribution of critical metals and critical raw materials in karst bauxite deposits. Great interest has been devoted to Rare Earth Elements although some deposits show remarkable enrichment in other critical metals including, for instance, W, Ta , and some first row transition metals such as V, Cr, Co, and Ni. Here we explore the deportment of V, Cr, Co, and Ni in five karst bauxite deposits in southern Italy (Apulia and Campania Districts) and Sardinia Island. These areas are located in the converging zone between the African and Eurasian plates since Cretaceous. Sardinia is a microplate which was part of the southern margin of the European plate whereas Adria is considered a single plate separated from the African plate by the Ionian basin . According to the Al2O3-SiO2-Fe2O3 diagram the karst bauxite of the Campania and Apulia district are mostly Fe-rich bauxites and bauxites. The Sardinian ores are bauxites and Fe-poor bauxites, although several samples fall in the clayey bauxite field. The ores show larger median values of first row transition metals with respect to the average Upper Continental Crust. Sardinian ore is enriched in V (median value 623 ppm) whereas in the Apulia District are observed the highest median values for Cr (Otranto site: median value 1005 ppm) and Ni (Spinazzola site: median value 470 ppm). Further, the distribution of both Co and Ni is characterized by the presence of several outliers. R-mode Factor Analysis was performed on each of the five datasets including SiO2, Al2O3, Fe2O3 TiO2, V, Cr, Co, and Ni, devoid of the outliers and after Varimax rotation. Multivariate statistics indicate that three factors always explain more than 84% of total variance. In some deposits Co and Ni share significant weights in the same factor suggesting common fate. In the ores from the Apulian district, Fe2O3 and V share significant weights in the same factor indicating Fe-oxyhydroxides play a role in controlling V. Al2O3 and TiO2 in four deposits show significant weights in the same factor confirming Al-hydroxides and Ti oxide accumulate during bauxitization. In several cases Al2O3 and TiO2 share significant weights with transition metals such as Cr and Co suggesting that Al-hydroxides and Ti oxide may also play a role in distributing these elements.