Average chemical analyses of ferromanganese deposit samples from dredges taken in the Indian Ocean (Cruise D16, R.R.S. Discovery)

Manganese crusts and nodules were retrieved from dredges and grabs performed during Cruise D16 of R.R.S. Discovery. Samples were analysed by a combination of atomic absorption spectrometry and direct-reading optical emission spectrography. Samples were first crushed in an agate mortarand pestle to pass 300 mesh and stored in sealed Polythene tubes. 'Salting' from previoussamples was minimised by washing the mortar and pestle with HC1, de-ionised water, andacetone, and, in order to minimise the effects of sampling errors, care was taken not toincorporate the nodule nucleus into the sample. Samples were ignited at 420°c for 4 h, cooled in a desiccator. The ignited material was then prepared for analysis. All analytical results except are presented on an air-dried basis.