Morphological and chemical characteristics of grains of placer gold from the Otinja River

In the Serbo-Macedonian metallogenic province in the Republic of North Macedonia, numerous occurrences of Au have been found in alluvial sediments. Placer gold originates from known genetic types of Cu-Au porphyry deposits (Bučim and Borov Dol) and epithermal Au deposits (Plavica and Allchar). However, in the Otinja river, the primary source of Au still remains unclear. Twenty-three Au grains collected from the river of Otinja alluvion were primarily analyzed on a scanning electron microscope (SEM) to investigate their morphological and chemical characteristics. The gold aggregates that were found range in size from about 120 μm to 2 mm, they have mostly subrounded to rounded shapes, rarely irregular shapes, with microtextures indicating a source at a distance of several km. Chemical composition tests show mainly Au-Ag mixtures, with Au contents ranging from 94.45 to 100%. By chemism, Au grains belong to the group of very high grade gold with high purity (951 to 1000). In general, impurity contents are very low. In order of representation, the following are most present: Ag (0.02–4.89%), Fe (0.02–4,74%), Cu (0.02– 0.54%), Te (0.09–0.55%), and Se (0.29%).