Are there any studies about the demographics of the Mongolian Empire's military?

Consider the Mongolian while powerful, make up only a small population of all the people they rule. And there are several major wars from different Mongolian Khanate. So who make the majority of their soldiers? I would guess the Chinese because several Mongolian military actions were against those Chinese dynasties so they should have ruled lots of Chinese. But are there any formal documents or studies about that? Thanks.