The Campo Felice and Monte Orsello bauxite occurrences (Abruzzi, Italy)

Bauxite deposits were largely exploited in Italy at the beginning of the 20th century up to the 2nd World War. The most productive districts were located in the Gargano peninsula, in the Murge and Salento (Apulia), in Campania and in the Abruzzi region. The Abruzzi bauxite district comprises several deposits, which are currently uneconomic, in the Campo Felice, Monte Orsello and Monti D’Ocre areas (Apennine Mts.). Similarly to other mineralizations of southern Italy, the Abruzzi occurrences belong to the karst-type bauxites located along a Late Cretaceous hiatus within a Bahamian-type carbonate platform succession (Bárdossy et al. 1977). Two main bauxite horizons can be recognized: a first corresponding to a Late Albian-Early Cenomanian stratigraphic gap and a second bounded by Late Cenomanian-Early Turonian limestones (Chiocchini et al. 1994). The most prominent deposits occur in the Campo Felice and Monte Orsello areas, in the first of the mentioned gaps. These bauxites (which are the object of this study) form large 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. Boehmite is the main mineral, but gibbsite has been detected in trace. The most abundant Fe-mineral is hematite, followed by goethite and lepidocrocite (rare). Kaolinite is also widespread in all the deposits, and is particularly concentrated in the matrix between ooids. The Ti-minerals anatase and rutile are ubiquitous, as well as the 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 Ca-fluorocarbonates have been observed. Major, minor and trace element analyses have shown that these bauxites are not only mineralogically, but also geochemically similar to those of the Matese Mts. and Caserta district, being characterized by: ~ 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 ΣREE ~ 640 ppm. The textures, mineralogy and geochemistry of the Abruzzi deposits suggest a continuous reworking of evolved lateritic soils, which were progressively mechanically concentrated in karstic depressions where they were further subjected to local chemical weathering. Bárdossy G., Boni M., Dall’Aglio M., D’Argenio B. & Pantó G. 1977. Bauxites of peninsular Italy. Composition, origin and geotectonic significance. Stuttgart, Schweizerbart’sche Verlagsbuchhandlung, Gebr. Borntraeger, Monograph Series on Mineral Deposits, 15, 61 p. Chiocchini M, Farinacci A., Mancinelli A., Molinari V. & Protetti M. 1994. Biostratigrafia a foraminiferi, dasicladali e calpionelle delle successioni carbonatiche mesozoiche dell’Appennino centrale (Italia). Studi Geologici Camerti Volume Speciale “Biostratigrafia dell’Italia centrale”, 9-129.