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Although the enrichment of arsenic (As) and boron (B) has been extensively observed in the major river basin within the Tibetan Plateau, little is known about the hydrogeochemical processes regulating the enrichment and mobility of As and B within river sediments. The present study conducted geochemical investigations of river sediments along the river flow path of the Singe Tsangpo River (STR) basin, and examined the mobility of As and B within river sediments under various environmental conditions through incubation experiments. The results suggested that the weathering of Cs-bearing silicate minerals could be a potential origin for As in the river sediments, which was evidenced by the corresponding variations between Cs and As (R = 0.60, P < 0.01). In contrast, carbonate weathering has contributed to the B enrichment, supported by the correlation between CaO and B concentrations (R = 0.60, P < 0.01). The incubation experiments showed intense mobilizations of As and B (∼12 mg/kg) under varying environmental conditions, where the increases in HCO 3 − concentration and temperature could enhance both As and B mobilization. Additionally, the As mobilization was enhanced by the anaerobic and alkaline conditions. These scenarios are relevant to the hydrogeochemical processes that regulate the As and B enrichment in both river water and groundwater from the STR basin, including the redox fluctuations that resulted from flood and draught cycling and the variations in the water/sediment particle ratios. The present study thus provided new insights into the hydrogeochemical control on the enrichment and mobility of As and B in the river sediments from the STR basin, which is also applicable in other riverine systems under similar conditions. • Geochemical characteristics in river sediments indicate different origins between As and B. • Geothermal water discharge contributes to As and B enrichment in river sediments. • Hydrologic disturbances could potentially regulate sediment As and B mobility. [ABSTRACT FROM AUTHOR]

[Display omitted] • Systematic mineralogical and B isotope studies were carried out along the JSD-1 drill core. • Tourmalines in host rocks from 200 m to 2800 m depths in JSD-1 are a magmatic origin. • The δ11B of tourmalines in granite and pegmatite in JSD-1 suggests an S-type granite. • Magma differentiation accompanied by fluid exsolution facilitates the lithium enrichment. • Fluids exsolved from the late-stage magmas could reach the crystallization of spodumene. The Jiajika pegmatite-type Li deposit located in the southeastern Songpan-Ganze terrane of the eastern Tibetan Plateau is one of the largest hard-rock Li deposit in China, and its ore-genetic mechanism is still controversial. To understand the Li concentration of potentially economic levels in the Jiajika pegmatite-type Li deposit, the association between Li enrichment and granitic magma evolution is investigated using B isotope in tourmaline grains along the entire 3211-m-depth of the JSD-1 drill core in this work. Tourmalines hosted in granite, pegmatite, barrovian-type metamorphic rock and calc-magnesium-silicate metamorphic rock are being plotted in the fields of Li-poor granitoids and associated pegmatites and aplites on the Al-Fe-Mg and Ca-Fe-Mg ternary diagrams. These characteristics, along with their high Fe/Mg ratios and high Al cation numbers in Y position, are indicative of a magmatic origin. The B isotope (δ11B) of tourmalines in granite and pegmatite in Jiajika granitic pegmatite type Li deposits vary from −9.49 to −7.06‰, in line with the range observed in 90 % of worldwide granites and pegmatites. In comparison of the measured data of δ11B vs. Li to the modeled curves indicates that the differentiation process of granitic magma follows an equilibrium crystallization model better than a fractional crystallization model. The compiled evidence proves that magma differentiation accompanied by fluid exsolution facilitates the enrichment of Li during granitic magmatic evolution. The formation of the domal structure of granitic sheets due to the decompressing effect of magma ascent favors massive fluid exsolution at the late-stage granitic magma, which contributes to the deposition of spodumene dominated ore body at the shallower depth of 5–150 m. [ABSTRACT FROM AUTHOR]