The grain size distribution and fraction composition of bottom sediments (BS) in the Amur River are studied. The total composition of sediments, their clay subfractions—water-peptizable (WPC) and aggregated (AC) clays—and residue after clay elutriation were analyzed. It has been established that contents of Fe, Mn, Zn, and Cu in the clay subfractions are 2–4 times higher than in common bottom sediments and their residue left after the extraction of clay subfractions, confirming a significant role of clay minerals in the accumulation of elements mentioned above. It is shown that diatom algae participate in the accumulation and transport of Fe, Mn, Zn, and Cu in the river water-suspended matter-bottom sediments (clay minerals) system. It has been established that high Zr concentrations in bottom sediments are related to the presence of zircon therein.
The mineralogy and chemistry of the fine fractions separated from the bottom sediments (aquasols) in the Amur River were studied in the subfractions of the fractional peptization differing in the binding strength between the water-peptized and aggregated components. Detritus of quartz, field spars, and strongly degraded layered silicates mainly passes into the water-peptized state. Interstratified layered silicates with different combinations of chlorite and mica layers prevail in the aggregate subfraction. The distribution of the microelements in the bottom sediments, the water-peptized and aggregated clays, and the residues after their separation was determined. The content of iron, manganese, zinc, and copper in the clay subfractions was higher than in the bottom sediments and in the residue after the separation of the clay subfractions by 2–4 times, which confirmed the functional significance of the clay minerals. The presence of diatomic algae in the components of the bottom sediments was revealed by scanning electron microscopy. The contribution of the diatoms to the accumulation of iron, manganese, zinc, and copper was shown.