Geochemical Research for Heavy Metal Contents and Leaching Ability of Hydrothermal Alteration Zone in Osaru River Basin, Hokkaido

Abstract

 Some of the natural origin heavy metal is sourced from alteration region accompanied by ore deposits and mineral vein. In this research, we investigate heavy metal contents and leaching ability of hydrothermal alteration zone, targeted on Osaru River basin located in southern part of Hokkaido, Japan. Several hydrothermal alteration zone and ore deposits are distributed in the tributary of Osaru River. A lots of Zn, As, Pb, Cu, Ni-enriched rock samples are observed in hydrothermal alteration region. Although especially high heavy metal contents are observed near hydrothermal alteration area, subsurface soils near alteration region does not reflect on metal-rich chemical composition of hydrothermal alteration zone. High leaching arsenic subsurface soils are detected only downstream part of main Osaru River basin composed of fluvial sediments. The arsenic transport from alteration zone is controlled by secondary adsorption to the metal-oxides, -hydroxides, or the other clay minerals in hydrothermal alteration zone. The arsenic leaching potential from alteration zone to the river depends on alteration aspect and environment, and especially, subsurface alteration zone including ferrihydrite and goethite distributed near riverside have high leaching potential.