MAGMATIC ORES IN HIGH-TEMPERATURE ALPINE-TYPE LHERZOLITE MASSIFS (RONDA, SPAIN, AND BENI-BOUSERA, MOROCCO)

The alpine lherzolite massifs of southern Spain (Serrania de Ronda) and northern Morocco (Beni Bousera) are mantle intrusions emplaced at high temperature in the continental crust. Three types of mineralization occur in the lherzolites: 1) chromite-Ni arsenide ores (Cr-Ni ores) with orthopyroxene and/or cordierite, 2) chromite ores (Cr ores) with clinopyroxene and/or orthopyroxene, 3) Ni-Fe-(Cu) sulfide-graphite ores (S-G ores) with chromite, plagioclase, and phlogopite. The chromite ores are located in the plagioclase lherzolite core of lherzolite massifs, whereas the two other ore types are distributed in the outer spinel and garnet lherzolite zones. The proposed metallogenic model comprises: 1) crystallization of chromite and pyroxene between 1500° and 950°C; 2) segregation of an immiscible As-S-rich liquid (following the hypothesis of Oen, 1973) that accumulated downward and started crystallization between 800° and 400°C, with the formation of an arsenide matrix among chromite grains; and 3) later crystallization of an S-rich residual liquid in graphite-rich assemblages. -from Authors