Chemical Pre-treatment Methods for Measurement of Ge Isotopic Ratio on Sphalerite in Lead-Zinc Deposits

Up to the present, main research of Ge isotopes has been carried out on organic, magmatic and meteoritic samples. Pb-Zn deposits are one of the most important reservoirs of Ge; however, there are few studies on Ge isotopes for these samples. Ge separation and purification for samples collected from Pb-Zn deposits are the basis of Ge isotope research. Therefore, the suitability for Pb-Zn ores of the Ge isotopic purification method established for meteoritic samples in details has been investigated. The results demonstrate that anion exchange resins single-column method for Pb-Zn ores can eliminate the potential interferences efficiently (including Fe, Se and other interfering matrix elements), but does not work for Zn as Zn/Ge>3, indicating that further separation and purification by ion-exchange column are needed to eliminate Zn. Conditional experiments of standard samples (ores and sphalerite) and three sphalerite samples from the Fule deposits showed that adjusting the volume of anion exchange resin elution acid (1.4 mol/L, HNO₃) from 6 mL to 10 mL and maintaining the method of cation exchange resin is suitable for Ge isotope purification. The results of anion/cation exchange resin two-column procedure indicate that the recovery of Ge was better than 99%, and the potential interferences on Ge isotopes (including Fe, Se, Zn and other interfering matrix elements) were almost 100% eliminated. Although the previous method has a good recovery of Ge (97.3%) and the potential interferences on Ge isotopes (including Fe, Se, Zn and other interfering matrix elements) were reduced to the negligible levels, the recovery is lower than the recommended method in this paper. Furthermore, the Ge isotopic composition of three sphalerite samples from the Fule deposit show that there are no signals coming from interfering elements and matrix elements, and the mass fractionation of Ge isotope followed the rule of mass-dependent fractionation. Overall, this modified method for Ge isotope measurement is suitable for sphalerite samples.