Rare earth elements in standard samples of ocean Fe-Mn nodules and crusts

Contents of rare earth elements (REE) in standard samples of Fe-Mn nodules (SDO-5, 6), Fe-Mn crust (SDO-7), and red clay (SDO-9) have been determined by ICP-MS and instrumental neutron activation analysis. Reproducibility of ICP-MS was 5-6%. These results are discussed and compared with other data. It has been found that distribution of REE in the standard samples of ocean Fe-Mn ores and red clay is highly homogenous.

Composition of standard reference samples of Fe-Mn nodules and bottom sediments

The first series of Soviet standard reference samples of composition of ore materials and ocean pelagic sediments has been created. It includes iron-manganese nodules (SDO-4, SDO-5 and SDO-6), ore crusts (SDO-7) diatomaceous ooze (SDO-8), and deep-sea red clays (SDO-9). The standards are intended to serve as a metrologic basis for physical, physicochemical and chemical analyses of iron-manganese minerals and ocean sediments. The standards are provided with certified analyses of rock-forming components and certain trace elements. Certified characteristics are based on statistical analysis of data obtained from an inter-laboratory experiment involving analysis of the standard reference samples by a variety of methods.

(Table 1) Mean grain sizes and standard deviations of gas hydrate samples

Methane hydrates are present in marine seep systems and occur within the gas hydrate stability zone. Very little is known about their crystallite sizes and size distributions because they are notoriously difficult to measure. Crystal size distributions are usually considered as one of the key petrophysical parameters because they influence mechanical properties and possible compositional changes, which may occur with changing environmental conditions. Variations in grain size are relevant for gas substitution in natural hydrates by replacing CH4 with CO2 for the purpose of carbon dioxide sequestration. Here we show that crystallite sizes of gas hydrates from some locations in the Indian Ocean, Gulf of Mexico and Black Sea are in the range of 200-400 µm; larger values were obtained for deeper-buried samples from ODP Leg 204. The crystallite sizes show generally a log-normal distribution and appear to vary sometimes rapidly with location.