Regional geochemical prospecting in Calabria, Southern Italy

Abstract

A governmental regional drainage survey assessed the mineral potential of Calabria in 1974. The Calabria area of southern Italy is a mineralized region in which Penninic and Austro-Alpine nappes, comprising ophiolites, metasedimentary rocks (phyllites, paragneiss, granulites, amphibolites) and granitic and granodiorite plutons, are overthrusting carbonate Apenninic nappes. Pre-Alpine stratabound and vein-type base-metal sulfide mineralization predominate, tectonically redistributed during the Alpine orogeny. A total of 5518 samples of the original 6999 active stream sediments from an area of 10,000 km 2 were analyzed by X-ray fluorescence and atomic absorption for Cu, Pb, Zn, Hg, Fe, Mn, As, W, Mo, Sn, and Be on the minus 180 μm fraction. Follow-up investigation of a 39-km 2 area around Bivongi-Ferdinandea using 760 soil samples analyzed for Fe, Mn, Zn, Cu, Pb, K, Mo, and Au, investigated molybdenite and chalcopyrite occurrences associated with granodiorite. A five-factor R-mode factor analysis reflected geological and mineralization features in the reconnaissance data. Factor 1 (Fe-Mn-Cu-Zn) is related to the Fe and Mn distribution in the stream sediments. Factor 2 (Be-Sn) reflects presence of pegmatites within metamorphic and magmatic rocks. Factor 5 (Mo) is essentially a single-element factor. Factor 4 (As-Pb-Zn-Hg-Cu) reflects mineralization. Factor 3 (W-Ba) does not cluster in association with any specific lithological unit. Significant metal associations, recognized from R-mode factor analysis, were used as independent variables and regressed against the original metal concentration of each sample. Residuals of multiple regression analysis, differentiated features representing mineralization from those related either to lithologic or geochemical parameters. New prospecting targets were identified and areas of known mineral occurrences were evident in the distinction of residuals. R-mode factor analysis of data from the follow-up investigation identified three factors. Factor 2 (Mo-K) reflects Mo mineralization and associated hydrothermally altered areas but does not suggest additional target areas.