Rare natural polycomponent alloys based on gold and copper from a platinumplacer in the Konder alkaline-ultrabasic massif, southeastern Aldan Shield, Russia

Gold occurring in the platinum placer of the Konder alkaline-ultrabasic mas sif is represented by the following varieties: copper gold (6.9-25.0 wt % C u; single grain with 44.3 wt % Cu)-Au3Cu (cuproauride), AuCu (tetraauricupr ide), and rare AuCu3 (auricupride); copper-platinum (up to 11.8 wt % Pt)-(A u, Pt)Cu; and copper-palladium (up to 10.3 wt % Pd)-(Au, Pd)Cu; as well as silver alloys (up to 62.7 wt % Ag and 4.8 wt % Cu)-from Au, Au-3(Ag, Cu) to electrum and kustelite. Together with individual grains, gold also forms r ims and microinclusions at the margins of cubic crystals of low-impurity hi gh-Fe isoferroplatinum (9.5-11.5 wt % Fe) derived from phlogopite-magnetite clinopyroxenites (Nekrasov et al., 1994). This gold variety was not found in association with other types of the Konder nuggets genetically related t o dunites, i.e., with those (a) of irregular shape with a significant admix ture of chromite crystals and (b) rounded with rare chromite inclusions. Ti le gold minerals and alloys are accompanied by various minerals of platinum -group elements (PGE), e.g., tetraferroplatinum, tulameenite, Pd-hongshiite , complex sulfides and arsenides of Pd and Pt, as well as antimonides, bism uthides, tellurides, stannides, plumbides, palladium germanide, ctc. Accord ing to experimental and geochemical data (Nekrasov et al., 1994; this paper ), the Ag-Cu-Ag alloys of the Konder massif were formed at 200-450'C and lo w f(O2) (10(-15) to 10(-25)) and f(S2) (Up to 10(-25)). According to X-ray diffraction data, the silver gold is disordered and has a face-centered cub ic lattice. The copper cold has a tetragonal cell with the degree of orderi ng decreasing from CuAu to CuAu3 and Au.