Geochemistry and Origin of Layers in Single Manganese Nodule from the Philippine Sea and Manganese Nodules from Offshore Minami-Torishima, Western Pacific

Layers from one manganese nodule dredged from the Philippine Sea（16°56＇N, 129°48＇E; water depth, 5700 m） and 45 bulk nodules from offshore Minami-Torishima Island, Japan（23°3＇N, 153°22＇E; water depth, 1200 m） were analyzed chemically and their origin is discussed based on geochemical constraints. In general, Cu, Ni, Zn and Mo tend to increase with increasing Mn content, while Co, Pb, Ba, V, Sc, Th, and the rare earth elements（REEs） show less variation with increasing Mn content. Nodule 42 H from the Philippine Sea has an average Mn/Fe ratio close to 1 and shows a positive Ce anomaly, suggesting a predominant hydrogenous origin. Profiles of 230Th230 ex and Thex/232 Th ratios in the outer ~0.3 mm of nodule 42 H indicate a steady growth rate of ~1.7 mm/Myr. Nodule E30 from offshore Minami-Torishima is characterized by lower Mn, Fe, Mn/Fe（0.53） and Mo/V（0.2） ratios but higher P and Cu/Ni（0.31） ratio relative to other nodules from that area. The Ce content of E30 is unusually low（82 ppm） when compared with other nodules from the area and it is the only nodule analyzed with a negative Ce anomaly（-0.64）. Based on the geochemical data we suggest that most nodules from offshore Minami-Torishima are primarily of hydrogenous origin except E30, which is dominated by hydrothermal input, and E45, which has about a 35% hydrothermal contribution.