Home – Home – Jornals – Russian Geology and Geophysics 2002 number 1

It is shown on the basis of experimental data that, to define a structural component of Au impurity, it must be isolated from the total concentration of uniformly distributed Au, chiefly in its sorption form. For this purpose the curve "content of the uniformly distributed Au form vs. mean specific surface of crystal" is to be extrapolated to the domain of such values at which the effect of the surface is negligibly small. In studying gold impurity in pyrite the optimal specific surface is 6 cm²/g. This approach can also be applied to natural minerals. By the example of pyrites from Au-Ag deposits in northeastern Russia the problem of "invisible" gold has certainly been solved: Its appearance in pyrite is exclusively due to sorption rather than to Au incorporation into mineral structure. Comparison of experimental and natural data shows that the mechanism of impurity absorption is the same in both cases and it is involved with the active role of the crystal surface and surficial defects. The high concentrations of "invisible" gold in pyrite are caused by its sorption of intermediate compounds and complexes containing Au and its accessory elements (first of all, As). On decomposition they leave Au0 micro particles and, possibly, more complicated metastable Au-bearing micro phases on the surface.