2004 Volume 38 Issue 4 Pages 203-222
We created geochemical maps of the Chugoku region, Japan by chemical analysis of 265 stream sediments and examined the background distribution of elemental concentrations. The geochemical maps strongly reflect the surface geology and mineral deposits. Factor analysis applied for our geochemical data suggests that granite, felsic volcanic, and mafic-ultramafic rocks mainly control the spatial distribution of elemental concentrations in stream sediments. The correspondence of elemental concentrations to respective surface geology is clearly revealed by a multiple comparison. The spatial distributions of Be, Na2O, Nb, rare earth elements, Ta, Th, and U contents correspond to granite distribution. Felsic volcanic rock contributes to high concentrations of Rb, Cs, Ba, and Tl. The distributions of MgO, Al2O3, P2O5, CaO, 3d transition metals (except Cu), and Sr concentrations are controlled by mafic and ultramafic rocks. The ultramafic rock has very strong influence to the spatial distributions of MgO, Cr, Ni, and Co concentrations, although they crop out in a small area. However, limestone in accretionary complexes has no positive effect on CaO and Sr abundances in stream sediments. The distribution patterns of some elements (Cu, Zn, As, Mo, Cd, Sn, Sb, Hg, Pb, and Bi) have close relationships to the distributions of mineral deposits such as Cu, Zn-Pb, As-Sb, W-Sn-Mo, and Hg deposits. Especially, Akenobe and Ikuno mines (the largest hydrothermal deposits in the study area), and Yoshioka, Mihara, and Koizumi mines (hydrothermal and skarn deposits) contribute to highly enrichments of these elements. However, not all geochemical anomalies for these elements correspond to the distributions of mineral deposits. The active erosion and heterogeneity of ores in stream sediments probably hide their influence to elemental distribution.
