Yttrium, lanthanum and manganese geochemistry in fluorite deposits from Sardinia (Italy)

Yttrium, lanthanum and manganese have been analyzed in 71 fluorite and in 66 calcite samples from 19 mineral deposits of Sardinia and in 48 Paleozoic country rocks. Fluorite from karst deposits does not contain detectable amounts of Y and La. Comparison of the Y/La ratio of the hydrothermal fluorite, country rocks and the corresponding data reported in the literature suggests no participation of late-magmatic fluids in the ore processes. A genetic correlation between the amounts of these elements in the mineral and the alteration of the metamorphic Paleozoic wall rocks is inferred. The Y/La ratio does not show any significant differences among the hydrothermal calcites. As for the karstic calcite, only the samples from the Orbai and Su Benatzu deposits have detectable Y and La contents (Orbai, Y ? = 52 ppm, L ?a = 45 ppm; Su Benatzu, Y ? = 15 ppm, La = 18 ppm). Mn, not detectable in fluorite, shows significantly different values between karstic (Mn ranging from 800 to 2750 ppm) and hydrothermal calcites (Mn ranging from 3837 to 7083 ppm). This difference, along with the Y/La ratio, allows a prevalent hydrothermal genetic process to be recognized for Mt. Ega, Orbai and Su Benatzu deposits, in spite of their karstic occurrence. © 1983.