Stream water, an ideal medium for rapidly locating polymetallic mineralization in forest-swamp terrain: a case study in the Da Hinggan Mts., northern Heilongjiang, China

A forest-bog landscape is developed in an area of moderate to low topography in northeastern China. Bogs are widespread along U- and V-shaped valleys (200–2000 m wide) and in depressions. Due to the cold climate, it was initially thought that chemical weathering would be slight in the area. However, a study of the geochemistry of surface water showed that, although most elements occur in relatively low concentrations compared to average contents in world river water, a number of mobile elements are dispersed over long distances. Marked Cu, Zn, Fe, Mn, and SO²⁻₄ anomalies, and relatively weak Ni, Co, Be, Pb and F anomalies form in stream water in the vicinity of known mineralization. Concentrations of Cu, Pb, Zn, Fe, and Mn in suspensates show no marked variations between background and anomalous streams whereas Ag exhibits a marked increase in suspensates near the mineralization. The pH of stream water near the mineralization is considerably lower than the 5 to 6.5 values recorded for background water. It can be concluded that water plays an important role in transporting elements chemically and stream water is a useful medium to sample in follow-up geochemical surveys for base and precious metals (Ag) in this landscape.