Metamorphic and metasomatic processes in the Loma Marcelo skarn, Neoproterozoic basement of the Sierras Australes of Buenos Aires Province In the area of the Pan de Azúcar-del Corral Hills, western edge of the Sierra de Curamalal, the Neoproterozoic basement of the Sierras Australes of Buenos Aires Province crops out. In the same sector, specifically in the Loma Marcelo, cataclastic and mylonitic granites and small skarn bodies (Loma Marcelo skarn) crop out. The mineralogical composition of the skarn allows distinguishing two zones: a calcic zone composed by garnet, clinopyroxene, wollastonite, vesuvianite, scapolite, plagioclase, calcite, and other minerals, and a magnesian one mainly constituted by calcite, dolomite, chondrodite and spinel. The existence of interstitial fluorite together with electron microprobe chemical analysis conducted in vesuvianite and chondrodite crystals show the presence of high F content in the skarn. According to measurements of stable isotopes of C and O performed in the skarn carbonates, metasomatic fluids involved in its formation were mainly of magmatic nature. As well as the granitic rocks, the skarn shows deformational structures such as penetrative foliation and lattice preferred orientation. The geological history of the basement of the Sierras Australes and the study of the Loma Marcelo skarn point out the existence of at least two metasomatic events linked to both igneous and metamorphic processes of different ages. Also, the regional petro-tectonic context and the presence of features of possible igneous origin in the skarn would suggest a protolith of carbonatitic origin. However, mineralogical and structural data would point out a sedimentary origin for the protolith.