By A. Strasheim
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Additional info for Analytical Chemistry in the Exploration, Mining and Processing of Materials. Plenary Lectures Presented at the International Symposium on Analytical Chemistry in the Exploration, Mining and Processing of Materials, Johannesburg, RSA, 23–27 August 1976
The problems of cost-effective interpretation can often be formidable. Stream sediment surveys Stream sediment represents nature's closest approximation to a composite sample of the clastic products of weathering upstream from the sampling site. For this reason, stream sediment surveys are commonly employed for reconnaissance purposes. km. and (b) secondary reconnaissance to detect stream sediment anomalies related to individual mineral deposits by sampling tributary streams at intervals of 500m to 2km or more, depending on the length of the dispersion train which can extend for as much as several kilometres downstream from the deposit.
To compensate for losses, a chemical yield approach is usually employed. There was a tendency, particularly in early work, for researchers to use analytical separations and other manipulations which are of questionable usefulness on the assumption that chemical yield would cor rect for errors encountered. For example it is not uncommon to find the isolation of a final precipitate accomplished using a Zn or Mg reductant. This practice, even when controlled by a chemical yield determination, is unacceptable.
Osmium and to some extent Ru may be lost by volatillization during this step. Osmium is particularly susceptible to this prob lem. Evaporations of Os solutions should be done in the absence of oxidiz ing agents eg traces of oxides of N even in trace amounts. Prolonged heat ing of the evaporated residue should be avoided. Insoluble residues, includ ing trichlorides of Ir and Rh and metallic Au may be produced. In evapor ating chloride solutions it is useful to add a small amount of NaCl to minimize the latter problem with Au.