Abstract:

Nine cobalt-rich crusts sampled from CL and CM seamounts have been analyzed for noble metals such as Ag, Au, Ru, Rh, Pd, Pt,and so on by using ICP-MS after chemical process. This paper also discussed the noble metals composition distribution, their enrichment indices, normalization modes, and their sources. The results indicate that the average contents of Ag, Au, Ru, Rh, Pd and Pt in cobalt-rich crusts are 1.05×10^-6, 2.3×10^-6, 15.6×10^-9, 22.3×10^-9, 2.39×10^-9 and 432×10^-9,respectively. Enrichment indices such as Pd/(Pt+Pd), Pt/(Pt+Pd) and Pd/Pt ratios in cobalt-rich crusts show distinctive features compared with that of ferromanganese nodules, ocean crusts and terrestrial ores. The average Pd/(Pt+Pd)ratio in cobalt-rich crusts is 0.006 which is the lowest value, followed by 0.06 in nodules, and 0.08 in ocean crust. But the  Pd/(Pt+Pd)  ratio in terrestrial ores is relatively high, and varies between 0.35 and 0.65. The Pt/(Pt+Pd)ratio in cobalt-rich crusts is the highest value, up to 0.99, followed by 0.95 of nodules, and 0.93 of ocean crust. However, the Pt/(Pt+Pd)ratio in terrestrial ores is relatively low, and varies between 0.33 and 0.65. It shows the variations of  characteristic values of  noble metal elements in different areas and environments from the statistical analysis. Moreover, the enrichment of Pt, Au, Ru, Rh, and lack of Pd in cobalt-rich crusts is the typical features of noble metals in cobalt-rich crusts. The chondrite-normalized patterns of  noble metal elements reveal that there exist positive Pt and Au anomalies, and negative Pd anomaly in cobalt-rich crusts of seamounts, among which anomaly extent of Au is in accordant with that of nodules.

Key words: cobalt-rich crust, noble metal element, variation characteristics, enrichment index, normalization