The distribution of Au in a Au-rich tributary of the Sungai Kuamut, Sabah, Malaysia, was studied initially by the authors in 1999 prior to disturbance of the tropical rain forest by logging. That study found: (i) a strong but extremely erratic Au anomaly with median values of 230 to 690 ppb in the fine and medium sand sized fractions from both cobble and gravel sites; and (ii) Au values typically <15 ppb in the −53 μm fraction. It was suggested that increased input of fine sediment into the stream after logging might substantially dilute and modify the Au anomaly. Logging of the drainage basin in 2000–2001 provided an opportunity to test this possibility.
Results from sampling at gravel sites in 2001 show no dilution of Au values after logging. This is attributed to the occurrence of rainfall and flood events that counteracted dilution of the anomaly by releasing deeply buried Au and/or flushing excess fine sediment from the stream channel. It is concluded that the strength of Au anomalies in stream sediments is likely to fluctuate as a result of the interactions of rainfall events, stream discharge, and the effects of land disturbance on erosion.
- © 2005 AAG/The Geological Society of London