Variation of geochemical risk associated with the use of ophiolitic washing muds as refilling material in a basalt quarry of the Northern Appennine (Italy).

Ophiolitic sequences in Northern Apenninesare usually exploited as source of raw materialfor civil engineering works. Grinding procedures ofbasalts imply the production of dusts with relativelyhigh concentration of PHES. This paper studied theincrease of geochemical risk when washing mud producedat Sasso di Castro quarry site (Tuscany) is reusedas rock keeper in a near dismissed quarry andhighlighted geochemical fractionation produced on thebase of different mineral hardness. Co, Cr, Ni and Vconcentration measured in washing mud were higherthan the limits fixed by the Italian law but compatiblewith background values. The mobility of these fourelements during future weathering processes wereestimated by considering the element transfer coefficientsand assuming weathered rocks and soils as twodifferent natural analogues of the future state ofwashing mud. The future concentration was estimatedby considering the average lifetime of mineral grainscalculated through their dissolution rate, molar volumeand grain diameter. The variations of geochemicalconcentrations were used to estimate the percentageincrease of the geochemical risk at the displacementplace. After 50 years the associated geochemical risk isstill considerably lower than the probability to bedamaged by a single landslide event.