Genesis and growth of internal microstructures of manganese nodule

Abstract

Microscopic and microprobe studies of manganese nodule from the Somali basin indicate that the reflectance of Fe-Mn oxyhydroxide varies with Mn and Fe concentrations. The non-oxyhydroxide components (detrital, biogenic debris, organic matter, etc.) appear to have a substantial control in the growth of different microstructures and show tendency to align their longest axes in the growth direction of structural units. This alignment appears to be due to the inward forces associated with surface tension of the 2 adjacent colloidal precipitate surfaces which have a tendency to grow into a spheroid, probably similar to phenomenon of drop formation. Detrital components within the nodule material identified include heavy titanium minerals, viz. titanomagnetite, ilmenite and rutile which may be the erosional products of precambrian granites of the Seychelles group of islands. The microprobe point analyses indicate that the studied nodule structures have accreted mainly by hydrogenous precipitation with less than 15% detrital influence. The alkali and alkaline earth metals (Na, K, Ca and Ba) appear to exist in the Mn mineral phase as charge balancing cations or result from the adsorption of seawater cations on the large surface areas for delta-MnO sub(2).