(Page 579) Average chemical composition of a manganese nodule from DOWNWIND (R/V Spencer Baird) DWHD16 station in the Pacific Ocean

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.