## 3 Results and Discussion
### Influence Factors during the Dissolution Process for Re-Os Dating
During the digestion process, a yellow precipitate was observed when the sample weights were more than 2 g. A previous study suggested that the oxidation of the acids would dissipate as the precipitate appeared [12]. This effect was observed under inverse aqua regia conditions, and the \({}^{187}\)Os signal decreased significantly as the sample weight increased beyond 2 g. However, the precipitate still appeared after the addition of 3 mL HClO\({}_{4}\) but the \({}^{187}\)Os signal increased with increasing sample weight. The yellow precipitate was formed as the volume of inverse aqua regia decreased from 17 mL to 9 mL; however, the \({}^{187}\)Os signal remained unchanged (Figure 2). These results suggest that there was no obvious relationship between the yellow precipitate and the oxidation of the acids. The reason for the formation of the yellow precipitate remains unclear, but the precipitate did not influence the equilibrium of isotope exchange between \({}^{185}\)Re and \({}^{190}\)Os spikes within the Re and Os in the sample. [PERSON] and [PERSON] [33] indicated that the Os released from some matrices can be difficult to equilibrate with spikes at low temperatures (<200 \({}^{\circ}\)C); therefore, the tube is always heated to high temperatures (220 \({}^{\circ}\)C-240 \({}^{\circ}\)C). However, the risk of Carius tube explosion increases significantly as the heating temperature increases. For personal safety reasons, it is necessary to find the lowest temperature to ensure the equilibrium of isotope exchange between spikes and the sample. Before starting this experiment, the temperature of the oven was monitored to ensure that the temperature was stable during the heating period. The temperature of the oven was monitored every 2 h for 24 h, and the temperature was set at 200 \({}^{\circ}\)C, 190 \({}^{\circ}\)C, and 180 \({}^{\circ}\)C, respectively (Table 5). The results suggested that the actual temperature (AT) of the oven was consistent with set temperature (ST) during the heating period, which means that it can be used to research the relationship between the heating temperature and the equilibrium of isotope exchange. The JDC was dissolved using the HClO\({}_{4}\)-inverse aqua regia method at different temperatures (Table 6). As the heating temperature decreased from 210 \({}^{\circ}\)C to 190 \({}^{\circ}\)C, the results for JDC were in fairly good agreement with the certified value. These data indicate that the Re and Os in sulfides were equilibrated with the spike. However, there was a large degree of inconsistency with the results of JDC and the certified value when the heating temperature was 180 \({}^{\circ}\)C. The results of the Re concentration agreed well with the certified value while the Os values did not. This explains the large gap in the final results between the certified values. All of these data suggest that the Os released from the sample has difficulty equilibrating with spikes if the heating temperature is lower than 190 \({}^{\circ}\)C. We concurrently found that the Re in the sample more easily equilibrated with the spike than Os. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Re ng/g** & **Common Os pg/g** & \({}^{187}\)**Os pg/g** & **Dissolution Medium** \\ \hline
26.20 \(\pm\) 0.21 & 7.586 \(\pm\) 0.144 & 63.37 \(\pm\) 0.44 & 20 mL of inverse aqua regia \\
26.56 \(\pm\) 0.18 & 2.062 \(\pm\) 0.089 & 63.88 \(\pm\) 0.45 & 1 mL of HClO\({}_{4}\), 19 mL of inverse aqua regia \\
26.20 \(\pm\) 0.23 & 2.582 \(\pm\) 0.037 & 63.29 \(\pm\) 0.39 & 2 mL of HClO\({}_{4}\), 18 mL of inverse aqua regia \\
26.49 \(\pm\) 0.23 & 2.621 \(\pm\) 0.142 & 63.70 \(\pm\) 0.38 & 3 mL of HClO\({}_{4}\), 17 mL of inverse aqua regia \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Analytical results for 1 g of unknown pyrite in 20 mL of combined acids.