The occurrence of high-temperature skarns from Oraviţa (Banat, Romania): A mineralogical overview
Résumé
A shallow-level dioritic pluton of Upper Cretaceous age caused extensive contact metamorphism of a Mesozoic calcareous sequence at Oraviţa-Ciclova in Romania. The peak metamorphic assemblage (stage I) includes wollastonite, åkermanite-rich melilite, Ti-rich calcic garnet, and pyrrhotite. A second, subsequent paragenesis (stage II) is due to local decreases in fluid pressure and includes gehlenite, Ti-poor calcic garnet, monticellite, Al-rich diopside, magnetite, perovskite, and probably a Ca-Si mineral (kilchoanite?). An early hydrothermal stage (stage III) produced retrogression of the first two stages and a paragenesis including vesuvianite, clintonite, fukalite, katoite, and hydroxylellestadite. A second, late hydrothermal event (stage IV) resulted in the formation of clinochlore, talc, epidote, zeolites (scolecite and thomsonite-Ca), thaumasite, and tobermorite. A last, weathering, paragenesis corresponding to stage V includes allophane (C-S-H gels) and probably portlandite, unpreserved because of its transformation to aragonite, then calcite. The peak metamorphic conditions during the prograde evolution are estimated to have been 750–800 °C for a fluid pressure of up to 0.5 kbar. The main constants determined from chemical, optical, and X-ray powder analyses of these mineral species are reported here. This work documents the first occurrence of katoite and the second occurrences of perovskite, fukalite, and hydroxylellestadite in the Romanian skarns.