Progress of in situ U-Th/He Isotopic Dating Technique and Its Application to Low Temperature Deposits

The traditional single-grain U-Th/He isotopic dating method a uses time-consuming acid dissolution, correction for α-ejection and more requirements on target minerals (euhedral, transparent, no cracks or inclusions). in situ U-Th/He isotopic dating is a newly developed dating technique, which uses extracted ⁴He from target mineral by laser ablation system and analyzes the ⁴He and U, Th and other parent isotopes via the Noble Gas Mass Spectrum (Alphachron) coupled with laser system and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The U-Th/He age of the deposits can be acquired by an age calculation formula using the analytical results of ⁴He, U, and Th isotopes. The principles, analytical processes, and minerals suitable for dating, technique difficulty and application prospect in low-temperature mineral deposits, are presented in this paper. In situ U-Th/He dating technique solved two key problems compared to traditional single-grain method: (1) Correction of α-ejection is unnecessary, improving the reliability and accuracy of dating results, and (2) Overcoming the bias from heterogeneous distribution of parent isotopes (U, Th), enlarging the range of U-Th/He isotopic dating. Although the in situ U-Th/He isotopic dating technique still needs to address issues such as collateral heating, precise measurement of pit volume and standard materials, it has shown itself to be a promising prospect for silicates, phosphates and Fe-Ti oxides. With the improvement of the in situ U-Th/He isotopic dating technique, particularly the U-Th/He isotopic dating of hydrothermal sulfides, this technique will provide a better way to date low-temperature mineralization.