Mavromatice and co-authors conducted an experiment to reveal zinc isotopic fractionations during the precipitation of calcite.
They found that the isotopic fractionations vary depending of pH with the range of 6.1 to 8.5.
Heavier isotope species enriches in calcite, and with pH increase up to 9, the isotopic fractionation decreases.
This is the first finding that heavy isotope enriches in calcite for either major elements or trace elements, they mentioned.
The mechanism of the enrichment is likely due to initial adsorption of isotopically heavy zinc on the precipitating calcite as a tetrahedral zinc species that is isotopically heavy.
The result of this study indicates that negative excursion of zinc isotope at the P-Tr interpreted as an isotopically light zinc input from volcanic activity might need to be reconsidered.
Article from GCA published in 2018 titled “Zinc isotope fractionation during the inorganic precipitation of calcite – Towards a new pH proxy”