Abstract

The application of highly sensitive (<1ppm) mineralogical methods (see details at www.natires.com) during geochemical exploration and environmental studies has revealed a wide range of native metals grains (NMG) and alloys in almost all samples of soils and natural deposits. Variable amounts of NMG have been observed in areas affected by industrial pollution, within city boundaries and also in areas remote (200-400km) from any obvious sources of pollution.

The observed NMG include Si, Cr, Fe, Co, Ni, Cu, Zn, Pd, Cd, Sn, Sb, W, Pb, Bi, which were present as pure phases and also, in some cases as alloys of two or more elements.

Mineralogy

Qualitative and quantitative determinations of the compositions of the NMG have shown that these depend on the locations of the samples. In some cases a precise correlation between the amount and chemical composition of the NMG and the composition of underlying host rocks has been established. The NMG and alloys generally vary in size from n*1 to n*10µm, rarely reaching 200µm. Four morphological types of grains have been observed: spherical grains (are the most abundant), relatively isometric-angular grains, grains with irregular form and minor grains as peels. Textural evidence of dissolution or supergene alteration of the NMG has not been observed, indicating that they form and exist stably under supergene conditions. The genesis of NMG requires further investigation, however the occurrence of these reduced native elements indicates that electro-chemical processes have been important in their formation under supergene conditions. Detailed mineralogical studies of NMG and alloys in natural deposits and soils appears to be important in the evaluation of the influence natural and industrial objects on the environment, especially given that NMG can include toxic elements such as Cd, Pb etc (V. Cappuyns, et al., 2006).

Acknowledgments

Special thanks go to Anthony J. Naldrett, suggested many improvements on the manuscript.

References

V. Cappuyns, R. Swennen, A. Vandamme and M. Niclaes. Environmental impact of the former Pb-Zn mining and smelting in East Belgium. Journal of Geochemical Exploration Volume 88, Issues 1-3, 2006, pp. 6-9 (Extended Abstracts presented at the 7th Symp. on the Geochemistry of the Earth's Surface (GES-7)