No abstract

No abstract

Rationale:Measurements of the multiple sulfur isotopic composition (δ 34 S, δ 33 S and δ 36 S values) of ancient sedimentary sulfide are useful for clarifying and reconstructing the picture of the global sulfur cycle on the early Earth. The methods used for these measurements should provide a high level of precision for the determination of sulfur isotope mass-independent anomalies (Δ 33 S and Δ 36 S values). Here we propose some improvements to the earlier published femtosecond laser-ablation fluorination method to make it suitable for measuring both Δ 33 S and Δ 36 S values in the Archean sedimentary sulfides with acceptable precision. Methods:A new gas purification system for the laser-ablation fluorination method has been developed. The design of this system is based on temperature-controlled flow traps for cryogenic separation of SF 6 gas from other fluorinated products produced by fluorination of sulfide minerals. Compared with the previous version of the purification system, the efficiency of SF 6 purification was significantly improved, which in turn improved the precision of the method for in situ GC/IRMS measurements of 36 S/ 32 S ratios (and determination of Δ 36 S values). Results:The improved method was tested using IAEA reference materials, as well as samples of natural pyrite with zero and non-zero sulfur isotope anomalies. For samples of~12-13 nmol SF 6 (optimal size), the overall precision of the method is ±0.03‰ for Δ 33 S values and ±0.27‰ for Δ 36 S values. This level of precision is satisfactory to examine the sulfur isotope anomalies in the rock. Conclusions:The improved femtosecond laser-ablation fluorination method is applicable for in situ measurements of δ 34 S, Δ 33 S and Δ 36 S values in sulfide minerals.