Vol 13, No 2 (2019)

The by-products of the Far East Sn deposits related to Li–F granites include trace elements. The petrography and mineral composition of the Sn-bearing metasomatites of the Verkhneurmiysky ore cluster (VUOC) of the Amur region (feldspatites, greisens, zwitters, turmalinites, and chloritites) and the multistage complex rare-metal (RM) mineralization of the Sn occurrences in area of Li–F granites are studied. The minerals of strategic metals (Nb, Ta, W, Y, REE (from La to Lu), Be, Li, Rb, Zr, Hf, In, Sc, Se, Cd, and Te) are found. The RMs occur as minerals (fergusonite, plumbopyrochlore, allanite, monazite, roquesite, sakuraiite, etc.) and isomorphic substitution in the ore (wolframite; cassiterrite; Cu, Sn, Fe, Mo, Zn, and Pb sulfides; native bismuth; etc.) and rock-forming (fluorite, siderophyllite, muscovite, and epidote) minerals. Some RMs (Y, REEs, Nb, In, and Sc) most frequently occur in Sn-bearing metasomatites. The RM minerals formed during the VUOC evolution (from the premineral feldspatite to the postmineral chloritite stage) with decreasing intensity of RM mineral formation and compositional evolution from lithophile to chalcophile RMs: (LREE, Zr, Hf) → (W, Nb, Ta, Y, HREEs, Sc) → (Sn, In, Cd, Se, Te). The formation of the VUOC RM mineralization was caused by magmatic, metasomatic, and crystal chemical factors. The possible complex exploration of the Far East Sn deposits is shown for areas of Li–F granites.

Changes in mineralogical composition occurring in the course of preparation of drinking water in-situ are studied based on the data from the monitoring wells of the Tunguska groundwater intake. Intensive dissolution of feldspars, pyroxenes, siderite, and, to a lesser extent, quartz with the formation of secondary minerals (amorphous silica, clay minerals, and secondary siderite) occur in the aquifer of the Tunguska intake. In addition, solid products of the destruction are formed, including microfragments of minerals, which together with the primary clay, secondary minerals, and oxides and hydroxides of iron and manganese that originated in the process of intralayer oxidation of water, participate in the colmatation of cracks and the slit space of the well filters. Regeneration actions result only in a partial recovery of the specific flow rate of the wells, since the hydrochloric acid used in them leaches only the oxide–hydroxide part of the colmatant, leaving virtually unchanged its aluminosilicate component.

The results of studies of the macro- and microelement composition of the riverbed sediments of the Bureya River are presented. Analysis of the changes in the distribution of microelements (rare-earth elements), as well as in the values of geochemical indices (WIP, STI, R, CIA, CIW, PIA, and V), shows that the sediments in different parts of the river were formed by various sources. Thus, the values of the mentioned indices, as well as their trends, allow one to assume that the primary matter sources in the upper (mountain) reaches of the Bureya River are granitoids occurring within the bounds of the river valley. This part of the river shows downstream a regular increase in the fraction of more weathered matter in the erosion area. The indices of chemical weathering in the riverbed deposits of the lower reaches of the Bureya River (the river reaching the submountain plain) do not follow the trend appearing in the upper reaches. The riverbed sediments as such in the lower reaches of the Bureya River are similar in chemical composition to the sediments of the Amur River. The author assumes in view of these facts that the riverbed sediments of the lower reaches of the Bureya River are mainly constituted by the substance supplied by the Amur River.