Mineralogical and chemical analysis of an Eastern Pacific core has been conducted in the context of a study of mineralisations in pelagic sediments; the data point out the relations between thin (2-100 m) manganese oxyhydroxide concretions and volcano-sedimentary environments. Between Clarion and Clipperton Islands, the polymetallic precipitates are precocious and they are due to the submarine volcanic activity of this spreading zone; in spite of their small size, all the elements are concentrated in the precipitates: Mn (9-46%), Fe (0.2-11%), Ni (0.1-3.4%), Cu (0.1-1.7%), Co (0.1-0.8%). The high internal structuration of micromineralisations, the splitting up of the elements in the laminations, the variability of contents according to the state of crystallinity can be explained by diagenetic processes at the scale of the grain. The contrast between the degree of evolution of these mineralisations and the situation of the area, that was submitted to important terrigenous and volcanic sedimentary inputs, lead to consideration of the micronodules as 'blocked structures', precursors of nodules, developed from diagenetic reactions of the micro-environment.

From 1983 until 1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions. At the time it was the most extended data compilation on ferromanganese deposits world wide. Initially published in a proprietary format incompatible with present day standards it was jointly decided by AWI and NOAA to transcribe this legacy data into PANGAEA. This transfer is augmented by a careful checking of the original sources when available and the encoding of ancillary information (sample description, method of analysis...) not present in the NOAA-MMS database.

Supplement to: Monaco, Andre (1979): Les microminéralisations polymétalliques: Structures bloquées des sédiments pélagiques. Chemical Geology, 27(1-2), 125-142