Oxides of the Pd-Sb-Bi system from the Chiney Massif (Aldan Shield, Russia)

Pd-Sb-Bi oxides occur in the exocontact sulphide ores of the Chiney anortho site-gabbronorite massif. Three types of oxides have been distinguished: Pb -Sb, Pd-Sb-Bi, and Pd-Bi oxides. Pd-Sb oxides are complete pseudomorphs aft er stibiopalladinite. Pd-Sb oxide has a grey-brown colour and is weakly to moderately anisotropic. In some cases there is an optical zonality which co rresponds to the heterogeneity of the the composition. Reflectance in diffe rent grains varies from 14.8 to 21.6 % at 380 nm and from 26.0 to 33.7 % at 589 nm. The average VHN20 is 124 kg/mm(2). The formula of the Pd-Sb oxide exhibiting the highest degree of oxidation is close to Pd5Sb2O4. Pd-Sb-Bi o xide occurs as grey rims, formed on Bi-bearing sudburyite. It is weakly ani sotropic. In comparison with Pd-Sb oxide it has a lower reflectance. Its av erage VHN5 is 81 kg/mm(2). The oxide composition varies from Pd-0.49(Sb,Bi) (0.28) O(0.24)to Pd-0.33(Sb,Bi)(0.24)O-0.43. Pd-Bi oxide, formed after froo dite, is grey and weakly anisotropic, heterogeneous in most cases, and has emulsion-like inclusions of a high-reflecting phase. Reflectance spectra ar e lower than for the other oxides. VHN5 is on average 156 kg/mm(2). Composi tional points in the Pd-Bi-O diagram lie along the Bi2O3-Pd line, which sug gests that the studied oxide is a solid solution of Pd in Bi2O3 (or a decom position structure of Bi2O3 and Pd). The composition with the lowest concen tration of Pd (5.62 wt. %) is similar to that of bismite Bi2O3 and the oxid e with the lowest concentration of Pd is close to the provisional formula P d3Bi3O4 The formation of Pd-Sb-Bi-O minerals may have been due to a high-te mperature fluid influencing the host sandstones of the exocontact ores.