THE GENINA GHARBIA CU-NI-PGE MINERALIZATION, EASTERN DESERT, EGYPT: AN EXTENSIVE LATE-MAGMATIC HISTORY
Platinum group minerals (PGM) are only Pd-bismuthotellurides; i.e., michenerite, merenskyite and Pd-Bi-melonite. PGM are usually associated with hessite, altaite, tsumoite, sylvanite and native-Te. Ninety percent of PGM and tellurides grains are located at sulfide-silicate contacts and as inclusions in altered silicates. The total Cu + Ni locally reaches up to 1.5 wt%, with Cu/Ni ratios <1. Anomalous platinum group elements (PGE) concentrations (maximum 260 ppb Pd, 65 ppb Pt, 9 ppb Rh, 38 ppb Ir, 10 ppb Ru, 7 ppb Os) were detected in sulfide bearing samples. The Pd/Pt ratio increases from the hornblende harzburgite to hornblende gabbro.
The mineralogical and chemical characteristics of the Genina Gharbia mineralization are best explained by a three-stage process: (1) a stage of magmatic crystallization in which, metals were concentrated in a sulfide melt largely in the hornblende harzburgite, (2) a late-magmatic stage in which base and precious metals were concentrated in a volatile-rich fluid, and (3) a post-magmatic faulting and shearing stage which shortly remobilized metals and concentrated them along shear zones. In stage (1) PGE were hosted in base metal sulfides, mainly pentlandite and cobaltite-gersdorfite. The availability of semimetals (Te, Bi) in the late-magmatic fluid deposited PGM in stage (2).