## 3 Results and Discussion
### Influence Factors during the Dissolution Process for Re-Os Dating  
The Os signal was different when 1 g of pyrite was dissolved using two methods (Figure 1A). The intensity was \(3.0\times 10^{4}\) cps for the inverse aqua regia conditions, and the Os signal increased 1.7 times when 1 mL of HCl\({}_{4}\) was added to the inverse aqua regia. The Os signal was unchanged as the volume of HCl\({}_{4}\) increased. There are two possible explanations for this result: one is that the sample could not be totally dissolved with inverse aqua regia. The other is that the oxidizing power of inverse aqua regia was too weak to completely oxidize Os. To further investigate this reaction, 1 g of pyrite mixed with 0.1 g of HLP was analyzed (Table 3). Since the concentrations of Re and Os in HLP were too high for the low level of Os in metal sulfides, an unknown sample (pyrite) was also analyzed (Table 4). Under inverse aqua regia conditions, the Re, \({}^{187}\)Os, and common Os concentrations in pyrite were 26.60 ppb, 4.3 ppt, and 62.49 ppt, respectively. After the addition of 1 mL HCl\({}_{4}\) to inverse aqua regia, the Re, \({}^{187}\)Os, and common Os concentrations in pyrite were 26.67 ppb, 4.3 ppt, and 62.29 ppt, respectively. As the volume of HCl\({}_{4}\) increased to 3 mL, the concentrations of Re and Os in pyrite were nearly unchanged. Simultaneously, the results for HLP were also in fairly good agreement with certified values. The results from the HCl\({}_{4}\)-inverse aqua regia method were almost identical to the inverse aqua regia method, which suggest that the sample was totally dissolved and Re and Os in the sulfides were equilibrated with the spike by these two methods. We inferred that the oxidation of the acids may have been the reason for the large gap in the detected signal between these two methods. The oxidizing power of inverse aqua regia acids was not strong enough to completely oxidize Os to OsO\({}_{4}\). Therefore, the concentration of OsO\({}_{4}\) in the trapping solution was significantly lower than that obtained upon addition of HCl\({}_{4}\). Thus, we suggest that the oxidizing power of acids did not influence the equilibrium of isotope exchange between \({}^{185}\)Re and \({}^{190}\)Os spikes within the Re and Os in the sample, but the Os signal was obviously affected. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample Name** & **Re (ng)** & **\({}^{187}\)Os (ng)** & **Common Os (ng)** & **Total Os** \\ \hline Blank & 0.0067 & 0.0002 & 0.0008 & 0.0010 \\ Blank & 0.0032 & 0.0001 & 0.0008 & 0.0009 \\ Blank & 0.0033 & 0.0001 & 0.0010 & 0.0010 \\ Blank & 0.0043 & 0.0001 & 0.0013 & 0.0014 \\ AV(ng) & 0.0044 & 0.0001 & 0.0010 & 0.0011 \\ \hline \end{tabular}  
* AV: mean values. The mean values and uncertainties (2 s) were calculated using ISOPLOT weighted average.  
\end{table} 
Table 2: Blank level. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample Name** & **Re \(\upmu\)g/g\({}^{-1}\)** & **\({}^{187}\)Os ng/g** & **Age (Ma)** \\ \hline HLP & 283.0 \(\pm\) 3.0 & 658.5 \(\pm\) 4.7 & 221.8 \(\pm\) 3.6 \\ HLP & 288.3 \(\pm\) 2.5 & 667.3 \(\pm\) 6.7 & 220.7 \(\pm\) 3.6 \\ HLP & 279.5 \(\pm\) 3.3 & 641.5 \(\pm\) 6.1 & 218.8 \(\pm\) 4.0 \\ HLP & 289.0 \(\pm\) 2.8 & 668.6 \(\pm\) 4.8 & 220.5 \(\pm\) 3.4 \\ AV & 284.9 \(\pm\) 4.5 & 659.0 \(\pm\) 12.5 & 220.5 \(\pm\) 1.2 \\ CV & 283.8 \(\pm\) 6.2 & 659.0 \(\pm\) 14.0 & 221.4 \(\pm\) 5.6 \\ \hline JDC & 17.26 \(\pm\) 0.22 & 25.21 \(\pm\) 0.20 & 139.3 \(\pm\) 2.5 \\ JDC & 17.54 \(\pm\) 0.31 & 25.78 \(\pm\) 0.27 & 140.2 \(\pm\) 3.2 \\ JDC & 17.23 \(\pm\) 0.20 & 24.93 \(\pm\) 0.24 & 138.0 \(\pm\) 2.5 \\ JDC & 17.92 \(\pm\) 0.42 & 26.49 \(\pm\) 0.27 & 141.0 \(\pm\) 3.9 \\ AV & 17.49 \(\pm\) 0.32 & 25.60 \(\pm\) 0.69 & 139.6 \(\pm\) 1.3 \\ CV & 17.39 \(\pm\) 0.32 & 25.46 \(\pm\) 0.60 & 139.6 \(\pm\) 3.8 \\ \hline \end{tabular}  
* CV: certified values. AV: mean values. The mean values and uncertainties (2 s) were calculated using ISOPLOT weighted average.  
\end{table} 
Table 1: Analytical results for molybden RMI, HLP, and JDC mixed with 3 g of pyrite.