Bauxite in Abruzzi (Italy): the Campo Felice and Monte Orsello occurrences

Bauxite deposits were largely exploited in Italy at the beginning of the twentieth century up to the 2nd World War. The most productive districts were located in the Apulia, Campania and Abruzzi region. The Abruzzi bauxite district comprises several deposits, which are currently uneconomic, at Campo Felice, Monte Orsello and in the Ocre Mts. (Apennine chain). Two main bauxite horizons occur: a first corresponding to a Late Albian-Early Cenomanian stratigraphic gap, and a second bounded by Late Cenomanian-Early Turonian limestones (Bárdossy et al. 1977; Chiocchini et al. 1994). The largest deposits are located in the Campo Felice and Monte Orsello areas, along the first of the mentioned gaps. The bauxites occur here as almost continuous horizons and/or lenses up to 10 m thick and more than 50 m wide. The textures of the Abruzzi bauxites range from oolitic-pisolitic to arenitic-conglomeratic, this suggesting a continuous reworking of evolved lateritic soils (Bárdossy et al. 1977). Boehmite is the main mineral, and gibbsite has been detected only in traces. The most abundant Fe-mineral is haematite, followed by goethite and rare lepidocrocite. Kaolinite is also widespread, and is particularly concentrated in the bauxite matrix. Anatase and rutile are ubiquitous, as well as several detrital trace minerals: monazite, xenotime, zircon, baddeleyite and ilmenite. Pyrite has been detected in the nuclei of some ooids. In few samples, cavity-filling autigenic REE-fluorocarbonates (i.e. bastnäsite and parisite) have been observed. Major, minor and trace element analyses have shown that the Abruzzi bauxites are not only mineralogically, but also geochemically similar to those of the Campania mineralised district. They are characterised by the following mean values: ∼55 wt-% Al2O3, ∼20 wt-% Fe2O3, ∼10 wt-% SiO2, ∼2 wt-% TiO2, Sc ∼60 ppm, V ∼270 ppm, Cr ∼240 ppm, Ni ∼200 ppm, Co ∼35 ppm, Zr ∼500 ppm, Ga ∼60 ppm, Y ∼80 ppm and ΣREEs ∼670 ppm. REEs have variable concentrations along the deposit profile, showing the highest values in correspondence of the bastnäsite/parisite-bearing layers. The REEs concentrations are also positively correlated with Ce/Ce* values. This correspondence indicates that REE autigenic mineral precipitation could be associated with oxidative events related to the uprise of the paleogroundwater table within the deposit, as also observed for the bauxites of the Apulia district by Mongelli et al. (2014). Due to the rapid rise in world demand of ‘critical elements’, our future work will be mainly dedicated to monitor the behaviour of REEs during the bauxitisation process in the Abruzzi deposits, and to their relationship with the supergene mineral phases.