Allochthonous native gold in piedmont alluvium in the southern West Siberia

The paper presents the results of our investigations carried out to examine the behavior of native gold in the southern West Siberia during the fluvial transport of an auriferous terrigenous material at the mountain-to-plain transition geomorphological zone. The piedmont alluvium accumulates the small- and, to a lesser extent, fine-grained gold transported from the denudation zones by the main mountain-lowland rivers. The background Au content varies from n to 10n mg/m3. High contents (100n mg/m3 to n g/m3) are recorded in some sectors in the upper zones of channel alluvium (spit and shoal facies). Flatness coefficient of particles is an important characteristic of allochthonous native gold in the piedmont alluvium. This property shows direct correlation with the lateral dimension of particles. Composition is an essential typomorphic property of the small- and fine-grained gold in the studied sediments. This statement is primarily valid for the degree of fineness commonly related to the Ag content in gold. In some cases, a significant indicator role can be played by traces of Hg and Cu. For example, Hg is an important indicator for the gold-mercury mineralization, whereas Cu is an essential indicator in the case of gold mineralization associated with rhodingites and high-temperature Cu-Au mineralization. Abundance of the allochthonous native gold in different-age terrigenous sediments testifies to its high stability during the continental sedimentation.