Local variability of gold in active stream sediments

Abstract

The distribution of gold in a short 120 m reach of an upland stream in Scotland has been investigated using an established freeze-core sampling method that avoids problems of elutriation. Thirty cores were taken from six sites chosen to represent the variety of geomorphological settings. Bed sediments varied between sites(24.3> D 50>9.2 mm). Gold distribution is described in terms of concentration, mass and number of grains. Data are erratic in coarse fractions (>500 μm) because of the low number of individual gold grains and the high frequency of barren samples. The < 63 μm fraction gave the most consistent results, especially for gold loads (g · kg −1) reflecting the high number of individual grains. The distribution of gold is discussed in relation to the geomorphological controls and sediment transport processes that lead to enrichment and dilution of gold deposits. The sampling method is shown to provide a practical approach for obtaining representative and quantitative data on fine-grained gold distributions.