This is not really a guide but just showing how many tombs there might be in each mine level so you know butt i dont know if there random number of tombs in each level or is the same but here is what i managed to get from mining the whole map open.

1 level: 1 tomb
2 level: 9 tombs
3 level: 9 tombs
3 level: 19 tombs
4 level: 19 tombs
5 level: 19 tombs
6 level: 19 tombs
7 level: 15 tombs

Pls comment if you have random or same amount of tombs too.