Aragonite mineralization was observed in serpentinized peridotites from the Romanche and Vema Fracture Zones in the Atlantic and the Owen Fracture Zone in the Indian Ocean, either in veins or as radial aggregates in cavities within the serpentinites. Evidence of incipient dissolution of the aragonite crystals was observed in one case. The aragonites tend to have lower Mg content ( 0.95%) relative to other marine aragonites. Their 18O16O, 13C12C and 87Sr86Sr isotopic ratios suggest the aragonite was deposited at ocean floor temperatures from solutions derived from sea water circulating in fissures and fractures within the ultramafic rocks. The 18O16O ratios of the serpentines indicate serpentinization occurred at higher temperatures, probably deeper in the crust. Low-T reactions between circulating seawater and Mg-silicates (primarily serpentine and pyroxenes) caused high pH and enrichment of Mg and Ca in the solution, conditions favoring carbonate precipitation. Aragonite was formed rather than calcite presumably because the high Mg2+ concentration in the solution inhibited calcite precipitation. The high Sr content of the aragonites is probably related, at least in part, to their low temperature of formation. Opaque mineral grains containing over 8% NiO and over 40% MnO were observed concentrated along the margins of some of the aragonite veins, suggesting that Ni is one of the elements mobilized during reactions between ultramafic rocks and circulating seawater.

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1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions.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: Bonatti, Enrico; Lawrence, James R; Hamlyn, P R; Breger, Dee (1980): Aragonite from deep sea ultramafic rocks. Geochimica et Cosmochimica Acta, 44(8), 1207-1214