A rhenium-molybdenum-copper sulfide from the Lukkulaisvaara layered intrusion, northern Karelia, Russia

The average of three EPMA results for a rhenium sulphide found as small inclusions in chalcopyrite associated with PGM, hessite, Ag- Au alloys and Re-bearing molybdenite in pegmatitic plagioclase pyroxenite in basic sills of the Oulanka complex gave Re 55.81, Mo 10.17, Cu 5.73, Fe 1.18, S 26.17, = 99.06, corresponding with the formula (Cu (sub 0.88) Fe (sub 0.21) )- (Re (sub 2.94) Mo (sub 1.04) )S (sub 8) . This mineral is grey in reflected light; reflectance approx 37%. It is similar to an unnamed Re-Mo-Cu sulphide described from the Stillwater complex, Montana. A model is proposed in which the formation of Cu-Ni-PGE- Re-bearing pyroxenite is due to an increase in fluid P during crystallization of the sills.