SummaryThe Sierras de San Luis, a part of the Sierras de Pampeanas, are located in central Argentina. The crystalline basementexperienced its main metamorphic overprint during the Famatinian cycle in Precambrian to Paleozoic time. The basement is mostly built up of amphibolite facies garnet-mica-schist and gneiss as well as granulites. The quartz textures in gneisses show bulging and grain boundary migration. The intercalated mafic-ultramafic rock lenses which are found at the surface are part of a 120km long NNE-SSW striking intrusion. This intrusion heated up the basement locally to granulite facies metamorphic conditions. The P-T conditions of the amphibolite facies metamorphism are according to Hauzenberger et al. (2001) between 550C and 650C and 4 to 6.5 kbar. The granulite facies conditions are between 700C and 800C at a pressure of 4 to 6.5kbar. The mafic-ultramafic rocks are mostly built up of anorthosite, orthopyroxenite, norite, metagabbro and dunite. The ultramafic rocks show a MgO rich chemistry with Xmg in Olivine ranging from 0.80 to 0.84. These rocks are characterized by a moderate to massive base metal sulfide (BMS) mineralization. The sulfides show primary magmatic textures as well as secondary mineralization textures. The platinum group minerals (PGM) such as merensyite-melonite group minerals and cobaltite group minerals which are found in some samples are related to enrichment in BMS and Cr-spinel. A detailed mineralogical and petrological investigation of samples from drill core LAS 5/3 (with 258.95 meters depth) has been documented in this work. The presented study documents the presence of PGM`s such as merenskyite, melonite and cobaltite which occur as primary and secondary mineralization, associated with pyrrhotite, pentlandite, chalcopyritein orthopyroxenite samples. A plot of the Pd-Bi-Te data of the PGM`s shows a crystallization temperature of about 500C.