Multiple Solutions of Ore-Forming Fluids of Carbonate Rock-Related Nephrite Deposits Constrained by Hydrogen and Oxygen Isotopes

Hydrogen and oxygen isotopes of ore-forming fluid of nephrite deposits have always been changing due to mixings between different fluids and oxygen isotope exchanges between the ore-forming fluid and country rocks, resulting in that the tremolite (or actinolite) has to constantly re-establish new isotope fractionation equilibriums with the dynamic fluid, which is of great significance to understand the genesis of hydrogen and oxygen isotopes of nephrite. Based on this, Taylor’s closed model and fluid mixing model are used to unravel the control of multi-stage evolution of ore-forming fluid on the δD and δ18O of nephrite. Although Taylor’s closed model is conducive to interpreting the genesis of nephrite with light δD and δ18O, such as Vitim nephrite, Russia, and Chuncheon nephrite, South Korea, it is unable to be effectively used in other nephrite. The fluid mixing model can quantitatively constrain proportions of different fluids during different ore-forming stages. Multiple solutions of ore-forming fluids of carbonate rock-related nephrite result from the absence of external constraints, such as isotope compositions of intrusive rocks, carbonate rocks, and meteoric water. Due to the generally heavy δ18O of country rocks, a small amount of meteoric water that enters the hydrothermal system in the later ore-forming stage is insufficient to offset the δ18O increment of nephrite caused by the oxygen isotope exchange between country rocks and water, which should be responsible for the abnormal heavy δ18O of Luodian nephrite, Dahua nephrite, Sanchakou nephrite, Xiaomeiling nephrite, etc., and not metamorphic water dominating their formation.