Boron circulation and recharge pattern in Zabuye drainage basin, Tibetan plateau

Abstract

Zabuye salt lake is famous for abundance of B and Li resource, especially for natural product of lithium carbonate mineral. Based on systematic measurement of chemical compositions and boron isotope, the fractionation mechanisms of boron were discussed to constrain possible boron cycle among different reservoirs. The excellent consistency of borax isotopic composition on the basis of fractionation between hydroboracite and borax and basicboron structure indicates that boron isotopic fractionation occurred during lake water evolution, such as crystallization, adsorption, and alteration processes. The increase of δ11B values in brine with corresponding pH varying from 9.86 to 9.01 suggests that pH has predominent control over the separation because 11B will preferentially concentrated in trigonal (B(OH)3) species. Very low δ11B values of brine in Zabuye salt lake imply a negative origin as almost all natural geochemical processes will result in positive values without any other extra boron input. Similar fractionation factor between carbonate-rich clay and brine to that between sediment and brine in other salt lakes in Tibetan Plateau also strongly support the accumulation of boron from the input of carbonate-rich clay. Unlike the consecutive evaporation in Bange salt lake with relatively positive δ11B values, Zabuye salt lake has experienced crystallization from initial brine and subsequent redissolution of carbonate-rich clay processes and the extracted boron is carried into the lake by river water and rising springs.