During R/V T. Thompson cruise TT-192 around the the Mariana and Volcano Volcanic Arcs 60% of the dredge recoveries contained ferromanganese deposits. Substrate rocks consisted of intermediate to mafic volcanic rocks, volcaniclastic rocks, volcanic breccia, and minor limestone. Volcaniclastic rocks were dominantly sandstone but ranged from mudstone to conglomerate. Ferromanganese deposits occur in five ways: Yellow-brown to black ferromanganese encrustations on rocks; brown, grey, and black ferromanganese oxides cementing volcaniclastic sandstone; stratiform, stratabound Mn oxide rich layers that are pale to dark grey, rarely brownish-grey, with a submetallic luster; cobbles of dark grey submetallic, irregularly shaped masses of manganese (Mn nodules ?) and weatehered black cobbles rich in magnetite. A selection of these deposits was chemically analysed including major and minor elements, rare earth elements, and platinum-group elements. The chemistry determination was done by Induction Coupled Plasma analyses done by J. G. Crock, and K. Kennedy at the U.S. Geological Survey laboratories in Reston, Denver and Menlo Park respectively. Water and CO2 determinations were done by wet chemical techniques.

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1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions.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.This dataset represents the digitized Tables 5 and 6, pp. 30-33, of the related publication.