Geochemistry and potential industrial use of Numidian sandstones from Southern Apennines (Italy)

ABSTRACT Forty-nine samples of quartz-rich sandstones collected in the Numidian Flysch of Southern Apennines (Italy) have been studied to highlight their geochemical characteristics and to check their potential industrial use. Sampling was performed from five different depositional sequences along a NW-SE traverse: Monteverde (MV, n=8), Aquilonia (AQ, n=8), Pietragalla (PQZ, n=16), Rotondella (RO, n=6) and Valsinni (VAL, n=8). The sandstones derived from NW successions (MV, AQ and PQZ) show a major compositional maturity with higher contents in SiO2 (93% wt in average), K2O (around 1% wt) and Rb (25 ppm), connected with the presence of K-feldspar and micas; they show lower contents of CaO (0,1% wt), Sr, MgO (0,10% wt) and Fe2O3 (0,9% wt) owing to the absence of carbonatic and clay-ferruginous cements. The sandstones from SE sequences (RO and VAL) show lower contents of SiO2 (88% wt in average), K2O (0.3% wt in average) and Rb (9 ppm) and higher contents of CaO, MgO and Fe2O3. According to Herron (1988) classification, the sandstones from NW are subarkoses and sublitharenites, whereas those from SE fall mainly in the Fe-sand field. The sandstones from NW area show a potential vocation to use in the glass industry; to test this capability, four samples from these sequences were analysed considering different granulometric fractions. Chemical analyses were performed on four granulometric fractions (A250μm). The C and D fractions represent the most suitable for a vitrifiable mix because they are the most rich-SiO2 (around 96% wt) and the poorest in contaminant elements (Fe2O3=1,25-0,30%, Al2O3=3,63-1,97%, MgO=0,14-0%, CaO=0,1-0,02%). However, C and D fractions fall outside the granulometric range required by the glass industry, this problem can be easily solved subjecting them to further grinding. A and B fractions result less suitable for glass industry owing to their chemical characteristics (SiO2=93,7–77,2%, Fe2O3=3,35-0,44%, Al2O3=10,7-3,5%, MgO=0,41-0,03%, CaO=0,4-0,03%), on the other hand, these fractions are the most abundant (A+B≈ 80% in weight against C+D ≈20% in weight). We suggest that after additional treatments (ultrasound washing, magnetic and electrostatic separation, and chemical dissolution) even these fractions could be used in glass industry. Overall the Numidian sandstones from Southern Italy seem suitable for glass industrial uses