Zinc Isotope Fractionation during Early Dissolution of Biotite Granite

Stable metal isotopes show great promise as a novel technique to study fundamental processes underlying micronutrient dynamics in soils and uptake by plants in situ. An important step in the development of these isotope systems is to constrain the extent and mechanisms of the isotopic fractionation in the plant-soil environment. One of the prominent micronutrient sources that needs to be constrained is release from parent material. To this end, we tested the isotopic fractionation of Zn during the very early stages of proton-and ligand-controlled dissolution of a finely powdered, fresh biotite granite using batch experiments. The observed fractionation pattern was similar for both dissolution mechanisms (proton and ligand promoted). Isotope fractionations were highest in the early stages of dissolution and probably kinetically controlled. After a few days, isotope fractionation imparted isotopically light Zn in the soil solution.