The distribution of Au has been investigated under tropical rainforest conditions in an Au-rich tributary of the Sungai Kuamut, Sabah, Malaysia. Paired high- and low-energy sediment samples were collected, before disturbance by logging, from gravel and cobble sites on bars and riffles. Gold content of five size fractions finer than 212 μm was determined by fire-assay atomic absorption spectrometry (FA-AAS). Use of a bulk leach cyanidation (BLC) procedure for Au was also tested. A strong, but extremely erratic, Au anomaly is present in the sand-size fractions. The highest Au values are found in gravel environments and concentrations decrease with decreasing grain size to a minimum in the −53 μm fraction. To maintain anomaly contrast while minimizing the chance of missing the erratic Au anomalies, use of the −105 μm fraction is recommended for stream sediment exploration surveys in the region. Because of the abundance and low Au content of the −53 μm fraction, increased erosion and additional inputs of this fraction into the stream after logging activity could significantly dilute the Au anomaly.