[en] The relationships between uranium and thorium and among iron, manganese and other minor metal contents of many manganese nodules are investigated. Some interesting correlations are recognized between the concentration of those chemical elements and localities of nodules. Samples collected from the ordinary Pacific Ocean floor are generally rich in thorium and are distributed around the center of Fe-Mn-(Ni+Co+Cu) diagram. In contrast, ferro-manganese nodules from the specific geological regions, where the activity of hydrothermal solution is high, are poor in thorium and extremely rich in iron compared with other heavy metals. Manganese-iron deposits on the continental shelf are thought to have been considerably influenced by diagenesis. At least, two sources of heavy metals would be suggested from this study, that is, the sea water and hydrothermal solution. (auth.)