PT, PD AND OTHER TRACE-ELEMENTS IN SULFIDES OF THE MAIN SULFIDE ZONE,GREAT DYKE, ZIMBABWE - A RECONNAISSANCE STUDY

Three ore samples from the Main Sulfide Zone (MSZ) of the Great Dyke, in Zimbabwe, were investigated by a combination of mineralogical and m icro-analytical techniques including optical microscopy, electron, pro ton, and ion microprobes. The sulfide mineralogy mainly comprises pyrr hotite + pentlandite + chalcopyrite +/- pyrite. Other opaque minerals present are rutile, ilmenite, chromite, loveringite, and rare platinum -group minerals (PGM), such as sperrylite, cooperite, moncheite, and m erenskyite. The micro-analytical methods employed demonstrate the pres ence of variable concentrations of the platinum-group elements (PGE) i n pyrrhotite, pentlandite, chalcopyrite, and pyrite. The following max imum values were obtained by PIXE analysis: 64 ppmw Pt and 35 ppmw Ru in pyrrhotite, 300 ppmw Pd and 182 ppmw Ph in pentlandite, Pd, Ru and Ph below MDL in chalcopyrite, and 233 ppmw Pt and 40 ppmw Ru in pyrite . SIMS analyses confirmed the presence of Pt in pentlandite (range <0. 2 to 47, mean = 8.5 ppmw), in pyrrhotite (<0.25 to 2 ppmw), in chalcop yrite (<0.15 to 3 ppmw), and consistently at elevated levels in pyrite (range 0.48-244, mean = 35.5 ppmw). These analyses are the first to r eport Pt concentrations in pyrite, a sulfide not previously known to b e a carrier of Pt. SIMS imaging revealed a relatively homogeneous dist ribution of Pt in pentlandite, in contrast to its rather inhomogeneous distribution in pyrite. The integrated analytical approach has demons trated the capability of the methods employed to unravel patterns of d istribution of the PGE in the Main Sulfide Zone. Systematic investigat ions of profiles will be necessary to shed light on PGE metallogenesis in the Great Dyke.