Abstract. Coarse-grained pyroxenite cumulates occurring within an olivine leucogabbro/pyroxenite gabbro rhythmic suite host a new sulphide mineralization type in the Beja Layered Gabbroic Sequence, Portugal. The sulphides formed in an intercummulus phase as a re- sult of the coalescence of disseminated blebs of pyrrhotite with abundant pentlandite and chalcopyrite exsolutions, gradually dis- rupting the silicate matrix. Intra- and inter-granular veinlets are sealed by Ni-rich minerals of the linnaeite group, with decreasing Co content from earlier to later generations. The deposition of Ni (± Co)-rich pyrite represents the late mineral infill in the linnaeite veins. Pyrite veinlets and subhedral grains in the pyrrhotite groundmass display gradually lower Ni contents with time. Chalcopyrite is the latest sulphide phase, sealing micro-fractures and replacing pre- existing sulphides. EPMA data revealed concentrations up to 1500 ppm of Pt, Pd, Au, Ag Cd and Bi in pentlandite, chalcopyrite and in minerals of the linnaeite group. Keywords. Layered gabbros, pyroxenite, intercummulus, massive sulphides 1 Introduction The Beja Igneous Complex is an intrusive belt that can be followed for ca. 100 km along the southwestern bor- der of the Ossa Morena Zone in Portugal (Fig. 1). The Beja Igneous Complex records syn-orogenic Variscan magmatic activity, extending from Upper Devonian to Late Visean (Dallmeyer et al. 1993). Three units are classically defined within the Beja Igneous Complex: 1) the Beja Layered Gabbroic Sequence (LGS), mainly consisting of olivine-bearing gabbroic rocks, rimmed by heterogeneous diorites resulting from variable extents of magma mix- ing and crustal assimilation; 2) the Cuba-Alvito Complex comprising granodioritic and gabbroic rocks; and 3) the Baleizão Porphyry Complex, a late, shallow intrusion con- sisting of porphyritic granitoids (Andrade 1983; Santos et al. 1990; Silva et al. 1970). In order to assess the metallogenic potential of the Beja Layered Gabbroic Sequence, significant efforts were made to determine its internal architecture and related ore-form- ing systems. Two main styles of mineralization have been recognized previously (Jesus 2002; Jesus et al., 2003b): 1) massive Fe-Ti-V oxide accumulations within ultramafic cumulate lenses; and 2) anastomosing (locally stockwork) Cu(-Ni) sulphide vein arrays within strongly developed metasomatic halos. This paper is the first documenta- tion of a new type of mineralization: intercummulus mas- sive Ni-Cu-Co sulphides hosted by a pyroxenitic cumu- late facies. 2 Geological framework Detailed mapping of the Beja Layered Gabbroic Sequence (inset, Fig. 1) has revealed NW-trending magmatic layer- ing that dips approximately 30ºSW, typically associated with a magmatic lamination. Field and geochemical cri- Chapter 4-14 Intercummulus massive Ni-Cu-Co and PGE-bearing sulphides in pyroxenite: a new mineralization type in the layered gabbroic sequence of the Beja Igneous Complex (Portugal) Ana P. Jesus, António Mateus, José Munhá, Álvaro Pinto CREMINER/Centro Geologia/Dep. Geologia, U. Lisboa, Ed. C6, Campo Grande, 1749-016,Lisboa, Portugal 4-14