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The origin of boron in boron-rich salt lakes in the Tibetan Plateau is highly controversial.In this study,we carried out a detailed study on boron geochemistry and isotope composition of lake sediments collected in Zigetang Co,central Tibet.Evaporites had high boron concentrations of 172.3–418.6 lg/g and δ~(11)B values of-8.2%to-3.3%,suggesting a non-marine origin for the saline lake.The boron isotopic fractionation factor,a,between evaporite and brackish water(a_(evaporite–brackish))decreased systematically with depth,from 0.9942 at the top of the drill core to 0.9893 at the bottom;the linear variation between α_(evaporite–brackish)and depth reflects boron isotopic fractionation associated with progressive crystallization.The positive correlation between δ~(11)B versus[B]and δ~(11)B versus depth in the evaporite phase reflects pH and boron speciation in the solution control on the adsorption of boron,and B(OH)_3 species incorporated preferentially into Mg(OH)_2 precipitation at high pH.
The origin of boron in boron-rich salt lakes in the Tibetan Plateau is highly controversial. In this study, we carried out a detailed study on boron geochemistry and isotope composition of lake sediments collected in Zigetang Co, central Tibet. Evaporites had high temperature of 172.3-418.6 lg / g and δ ~ (11) B values of-8.2% to-3.3%, suggesting a non-marine origin for the saline lake. The boron isotopic fractionation factor, a, between evaporite and brackish water (a (evaporite-brackish)) was systematically with depth from 0.9942 at the top of the drill core to 0.9893 at the bottom; the linear variation between α evaporite-brackish and depth bore boron isotopic fractionation associated with progressive crystallization.The positive correlation between δ ~ (11) B versus [B] and δ ~ (11) B versus depth in the evaporite phase habit pH and boron speciation in the solution control on the adsorption of boron, and B (OH) _3 species incorporated preferentially into Mg (OH) _2 precipitation at high pH.