Rubidium is one of the important rare metals, which has been used in military and science—technological fields and even widely in civil use field. The Shihuiyao rubidium—multi metal deposit in Selenhot， Inner Mongolia was discovered as an ultra large scale rare metal deposit in 2010. Based on detailed field geological investigation, muscovite 40Ar 39Ar isotopic dating was carried out. The results show that the weighted average age of muscovite in greisenization granite is 144.7 ± 1.1 Ma, and the isochron age is 143.3 ± 1.4 Ma. The weighted average age of schistose muscovite in quartz vein is 146.4 ± 1.0 Ma, and the isochron age is 143.9 ± 1.5 Ma. It is shown that the Shihuiyao rubidium—multi metal deposit was formed at late Yanshanian. Shihuiyao area has strong fold , development fracture, frequently and widely distribute magmatic activity. These are major scale amazonitization granite , greisenization granite and parts of greisenization granite. Greisenization is widely distribute. These are all beneficial to rare elements to sediment and assemble such as rubidium, niobium, tantalum, lithium and beryllium etc. So there is great potential for the prospecting of rear metal deposit in the area.