THE METHOD FOR ESTIMATING THE LIMITS OF GOLD INCORPORATION INTO MINERAL STRUCTURES

Data on the limits of Au incorporation into minerals are necessary for quantitative study of gold behavior in mineral systems. The proposed method for estimating these limits applies to the general case when se veral forms of Au are present in crystals. It is based on using so-cal led <<gold-guide>> elements (GGEs), which increase the activities of A u-containing species in the fluid phase and give rise to cocrystalliza tion of Au with the mineral by the mechanism of formation of unstable but really existing intermediate phases. These phases fulfill the role of virtual edge-member phases of the type AuR (R=S, O, etc.), limitin g the solubility of Au in the mineral. The influence of the third comp onent (GGE) on Au incorporation is taken into account by extrapolating the content of uniformly distributed Au form to the zero GEE content. The method was realized on a CdS-based mineral greenokite, with Se an d As used as GGEs. It is estimated that the limit of gold incorporatio n is (5+/-1)10(-3) wt. % Au at 500 degrees C and 100 MPa. The results obtained give grounds for reconsidering the previously established lim iting contents of Au in mineral phases. For this purpose, it is propos ed to study Au distribution between a mineral under investigation and a <<reference>> mineral (RM). The latter must have a sufficiently high limit of Au incorporation and regular Au distribution throughout the crystals, with its quantitative characteristics corresponding to isomo rphic mixtures. Greenokite may be used as a RM in the study of sulfide minerals. In the case of oxides, magnetite may be a proper RM.