The system Ag-Pd-Te; phase relations and mineral assemblages
The system Ag-Pd-Te; phase relations and mineral assemblages
Mineralogical Magazine (December 2015) 79 (7): 1813-1832
The phase equilibria in the system Ag-Pd-Te were studied by the technique of using an evacuated silica glass tube at 350 degrees and 450 degrees C. Five ternary phases were synthesized: sopcheite (Pd (sub 3) Ag (sub 4) Te (sub 4) ), lukkulaisvaaraite (Pd (sub 14) Ag (sub 2) Te (sub 9) ), telargpalite (Pd (sub 2-x) Ag (sub 1+x) Te) and the previously unknown phases Pd (sub 7.5-x) Ag (sub 0.5+x) Te (sub 3) and Pd (sub 2+x) Ag (sub 2-x) Te. The synthetic telargpalite has a compositional range from 26 to 29 wt.% Ag, with the formula Pd (sub 2-x) Ag (sub 1+x) Te, where x varies from 0.09 to 0.22. The phase Pd (sub 2+x) Ag (sub 2-x) Te has a compositional range from 34 to 35 wt.% Ag, where x varies from 0.18 to 0.24. The phase Pd (sub 7.5-x) Ag (sub 0.5+x) Te (sub 3) forms a solid solution from 4 to 11 wt.% Ag, where x varies from 0.02 to 0.83. Phases Pd (sub 20) Te (sub 7) and Pd (sub 13) Te (sub 3) dissolve up to 3.5 and 2 wt.% Ag, respectively. Other binary palladium tellurides do not dissolve Ag. The phase Pd (sub 3) Ag (sub 4) Te (sub 4) , an analogue of the mineral sopcheite, forms a stable association with hessite and kotulskite it also coexists with lukkulaisvaaraite. Sopcheite is stable up to 383 degrees C. Natural occurrences of hessite, kotulskite and lukkulaisvaaraite together in equilibrium indicate formation above this temperature. Phase relations defined the mineral assemblages that can be expected to occur in nature. The phase Pd (sub 7.5-x) Ag (sub 0.5+x) Te (sub 3) potentially represents a new mineral; it will probably be found in association with lukkulaisvaaraite and telargpalite or telluropalladinite, among other platinum-group minerals. The phase Pd (sub 2+x) Ag (sub 2-x) Te can be found in association with telargpalite. Mineral assemblages defined in this study can be expected in Cu-Ni-PGE mineral deposits, associated with mafic and ultramafic igneous rocks, particularly in mineralized zones with known silver-palladium tellurides.