Sources for gold,palladium and iridium in deep-sea sediments

Deep-sea sediment cores, one from the Caribbean (calcareous ooze) and three from the Pacific-Antarctic basin (Globigerina ooze, siliceous ooze and pelagic clay) were analysed for Au, Pd, Ir and Mn by neutron activation. The average noble metal contents for 37 samples are: Au (ppb) Pd (ppb) Ir (ppb) 1.05 ± 0.9 3.5 ± 2.8 0.31 ± 0.14 Biogenic and lithogenic (terrigenous) constituents account for much of the noble metal in these sediments. The average noble metal content, particularly that of Au and Ir, shows little variation over the entire suite of four cores despite large differences in the proportions of biogenic and lithogenic fractions. In general neither component is a markedly more significant noble metal sink than the other. However, a strong correlation between Au and CaCO₃ in the Caribbean calcareous ooze suggests that the biogenic fraction is a significant concentrator in this core.Palladium content is more variable than that of Au or Ir and in two of the Antarctic cores some Pd, probably of hydrogenous origin, is present.The Ir content of all cores is higher than that expected of purely terrigenous sources and there is little suggestion of biogenic concentration of the metal. $\text{Au}\text{Ir}$ ratios differ greatly from average continental crust but are similar to oceanic crust. In one of the Antarctic cores some Ir of hydrogenous and of extraterrestrial origin may be present.