We present new mineral chemistry, fluid inclusion, stable carbon and oxygen, as well as Pb, Sr, and Nd isotope data of Ca-Mg-silicate-rich ejecta (skarns) and associated cognate and xenolithic nodules from the Mt. Somma-Vesuvius volcanic complex, Italy. The typically zoned skarn ejecta consist mainly of diopsidic and hedenbergitic, sometimes “fassaitic” clinopyroxene, Mg-rich and Ti-poor phlogopite, F-bearing vesuvianite, wollastonite, gehlenite, meionite, forsterite, clinohumite, anorthite and Mg-poor calcite with accessory apatite, spinell, magnetite, perovskite, baddeleyite, and various REE-, U-, Th-, Zr- and Ti-rich minerals. Four major types of fluid inclusions were observed in wollastonite, vesuvianite, gehlenite, clinopyroxene and calcite: a) primary silicate melt inclusions (T_HOM = 1000–1050 °C), b) CO₂ ± H₂S-rich fluid inclusions (T_HOM = 20–31.3 °C into the vapor phase), c) multiphase aqueous brine inclusions (T_HOM = 720–820 °C) with mainly sylvite and halite daughter minerals, and d) complex chloride-carbonate-sulfate-fluoride-silicate-bearing saline-melt inclusions (T_HOM = 870–890 °C). The last inclusion type shows evidence for immiscibility between several fluids (silicate melt – aqueous chloride-rich liquid – carbonate/sulfate melt?) during heating and cooling below 870 °C. There is no evidence for fluid circulation below 700 °C and participation of externally derived meteoric fluids in skarn formation. Skarns have considerably variable ²⁰⁶Pb/²⁰⁴Pb (19.047–19.202), ²⁰⁷Pb/²⁰⁴Pb (15.655–15.670), and ²⁰⁸Pb/²⁰⁴Pb (38.915–39.069) and relatively low ¹⁴³Nd/¹⁴⁴Nd (0.51211–0.51244) ratios. The carbon and oxygen isotope compositions of skarn calcites (δ¹³C_V-PDB = −5.4 to −1.1‰; δ18O_V-SMOW = 11.7 to 16.4‰) indicate formation from a ¹⁸O- and ¹³C-enriched fluid. The isotope composition of skarns and the presence of silicate melt inclusion-bearing wollastonite nodules suggests assimilation of carbonate wall rocks by the alkaline magma at moderate depths (< 5 km) and consequent exsolution of CO₂-rich vapor and complex saline melts from the contaminated magma that reacted with the carbonate rocks to form skarns.