Using radiochemical methods, the authors have measured the distribution of uranium, thorium, radium, polonium and protactinium isotopes from the top and bottom sides of the a manganese nodule from Station 20 of the PLEIADES Mn7601 campaign. This "apple" shaped nodule (6.5x3.0 cm) was laying on a bed of siliceous ooze (see illustrations). Successive thin layers of the nodule were carefully scraped from the surface of the measured area with a sharp surgical blade. All samples reduced to powder were air-dried at 110°C for at least two hours before analysis. The relative gross alpha activities from each layer were assayed by Alpha spectrometry using a thick-source counting in a scintillation counter.

The authors have selected for analysis a manganese nodule from Station 20 of the PLEIADES Mn7601 campaign. This "apple" shaped nodule (6.5x3.0 cm) was laying on a bed of siliceous ooze (see illustrations). Electron microprobe measurements were made on the same section as that used in the alpha-track studies. Prior to the microprobe analyses, however, the nodule slab was highly polished to reduce surface relief A MAC electron microprobe was employed and the electron beam was focused to a dmmeter of about 2 micrometers using 15 kV and 300 mA.

The authors have selected for analysis a manganese nodule from Station 20 of the PLEIADES Mn7601 campaign. This "apple" shaped nodule (6.5x3.0 cm) was laying on a bed of siliceous ooze (see illustrations). Successive thin layers of the nodule were carefully scraped from the surface of the measured area with a sharp surgical blade. All samples reduced to powder were air-dried at 110°C for at least two hours before analysis. The chemical composition of (1) the top 3-5 mm, (2) the bottom 3-5 mm, and (3) the bulk nodule from a section of Mn7601-20-2 adjacent to the portion used for the radiochemical studies was determined by atomic absorption and neutron activation analysis.

Manganese nodules have attracted considerable attention in recent years as a potential source of Mn, Fe, Co, Ni, Cu and other minor elements. These elements are enriched in manganese nodules relative to igneous rocks, sea-water, and deep-sea clays. The present paper describes methods by which element correlations may be determined with the electron-probe, and summarizes the results obtained by electron-beam scanning and specimen traversing. The results obtained in the present electron-probe investigation of manganese nodules may be summarized as follows: (l) The iron concentration fluctuates whereas the manganese concentration is relatively uniform throughout a manganese nodule, hbing slightly higher where iron is low. (2) There is a distinct correlation between Fe, Co, Ti, and Ca. (3) There is pronounced element coherence between Xi, Cu, Zn, and Mg, and between K and Ba. These elements are enriched with Mn and Al in regions of a nodule where the iron concentration is low. (4) The pronounced inter element relationships suggest that isomorphic substitution is an important factor controlling minor element distribution in manganese nodules. The ions Ni2+. Cu2+, Zn2+, Mg2+, K+ and Ba2+ substitute for Mn2+ in the "manganite" phases, Co(III) occurs with Fe(III) in hydrated iron oxide phases and Ti(IV) in delta-MnO2.