## 1 Introduction  
Re-Os isotopes are an important part of isotopic geochronology. Re and Os are highly siderophile elements (HSE) indicating a strong preference for a metal or sulfide phase over forming silicate minerals [1; 2; 3]. Therefore, the Re and Os could be enriched in metal sulfides such as molybden, pyrite, chalcopyrite, and arsenopyrite. Some minerals have economic value (e.g., molybden and chalcopyrite) while others coexist with minerals of economic value (e.g., pyrite and arsenopyrite). Therefore, the application of Re-Os isotope systems on a metal sulfide can be a powerful tool for directly dating the metallogenic epoch [4; 5; 6; 7; 8].  
The most successful application of the Re-Os isotopic system for dating metal sulfides is molybden: the mineralization epoch of deposits is easily dated if molybden develops in a mining area [9; 10; 11]. However, besides molybden, other sulfide metals have lower probabilities of success on Re-Os dating because sulfide metals have low levels of Re and Os. For example, the content of Re and Os in pyrite is distributed between ppb to sub-ppb [12], and these minerals are denoted as low-content Re-Os metal sulfides including pyrite, chalcopyrite, and arsenopyrite. In the case of molybden, the application of the Re-Os isotopic system on low-content Re-Os metal sulfides can be used to date many more types of deposits [13; 14; 15; 16; 17; 18]. Unfortunately, low-content Re-Os metal sulfideshave a low probability of success when using Re-Os dating, and the inability to guarantee the stability of the measured signal is one of the reasons that leads to an inaccurate determination of the Re and Os content in metal sulfides.  
Generally, 0.4 g of metal sulfide can be completely digested with 11 mL of inverse aqua regia [18; 19]. In order to increase the Os signal, some researchers have dissolved larger samples (~1 g) in larger Carius tubes with nearly 20 mL of inverse aqua regia [20; 21]. However, with low levels of Os in metal sulfides, this sample weight is not sufficient for Re-Os dating. For sample weights greater than 1 g, the dissolving capacity of acids might not be sufficiently strong to oxidize Os to OsO\({}_{4}\). OsO\({}_{4}\) plays an important role in Os separation techniques. For ICP-MS analysis, the sensitivity of Os (VIII) is much higher than other valence states of Os [22]. All Os separation techniques, including distillation, micro-distillation, and solvent extraction methods are based on the volatility and non-polarity of OsO\({}_{4}\)[23; 24]. Furthermore, [PERSON] and [PERSON] [25] indicated that the oxidation of acids leads to the oxidation of Re and Os to their highest valence states and promotes the complete chemical equilibration of \({}^{185}\)Re and \({}^{190}\)Os in a sample. [PERSON] et al. [26] improved the Carius method in that the samples were first dissolved with HNO\({}_{3}\) in a 120 mL Carius tube to release gas with a small portion of volatile Os released at the same time (6% of total Os). They then collected Os using HCl and transferred these back to the Carius tube after the sulfides were reacted with HNO\({}_{3}\). This method allowed the sample mass to be increased to 3 g using nearly 30 mL of acids, but the procedure appeared to be very complex.  
[PERSON] et al. [27] demonstrated that the HClO\({}_{4}\)-inverse aqua regia method could dissolve 0.8 g of sample with only 9 mL of acids (8 mL of inverse aqua regia and 1 mL of HClO\({}_{4}\)). In this paper, we focused on the effectiveness of the HClO\({}_{4}\)-inverse aqua regia method for sample weights greater than 1 g. The conditions were optimized to maximize the amount of sample tested. The influencing factors during the dissolution process for Re-Os dating are also discussed in this paper. This refined method was verified using several standard reference samples.