On the fractionation of gold and platinoids in aceanic hydrothermal sulfide ores

Element composition of a number of samples of massive seabedhydrothermal sulfide ores of the Mid-Atlantic Ridge at 24 deg 30 min N has been studied. By means of the instrumental neutron activation analysis (INAA) the content of Au, Ir and other elements (chalcophile Zn, As, Se, Ag, Sb; siderophile Fe, Co, Ni; lithophile Sc, Cr, Rb, Cs, Th, U et. al.) have been determined. Median contents of Au and ir were found as 5.3 ppm and 5.2 ppb correspondingly. Possible causes of the fractionation of Au from Ir were considered taking into account the results of factor analysis of the INAA data. The fractionation process likely occurs at the site of ore deposition and is affected by existence of a geochemical barrier formed by the interaction of hot acid reduced solutions with cold weakly alkaline oxidising oceanic water. 22 refs.; 3 figs