Palladium, Iridium and Gold in Deep-Sea Cores

Abstract

<p> Wet chemical neutron activation analysis procedures for Au., Pd and Ir together with a non-destructive gamma-counting procedure for Mn are described and applied to the determination of these metals in three Antarctic (E21 -17, E13-3 and E 17-10) and one Caribbean (P63 04-9) deep-sea cores. A total of 49 samples were analyzed. The average values of Au, Pd, Ir in ppb and Mn in Wt.% (together with standard deviations of the mean are: (see table in theses) No large differences exist between Au, Pd and Ir concentrations in different types of deep-sea sediments nor in cores from different areas and their values are within the general concentration range found in most crustal rocks. A general discussion of the sources of precious metals in deep-sea sediments is given. The most important precious metal source in the cores studied in this work is detrital material from land. The contribution of extraterrestrial material to the Au and Pd content of deep-sea sediments is not important but in cores with depositional rates as low as a few tenths of a mm per thousand years, extraterrestrial material may account for more than half of the total Ir content. From the non-detrital Ir content of deep-sea manganese nodules the accretion rate of extraterrestrial material over the. entire surface of the earth is calculated to be about 200 tons per day with an upper limit of 310 tons per day. The constancy of Ir content in deep-sea cores as a function of depth suggests that the influx of extraterrestrial material during the past 3 to 4 million years was probably fairly constant. </p>