Um... yes?
Iron is around 155 if I remember correctly. Mining tin will stay green until that point easily, and 10-20 points beyond it. Every node works this way; before you get to the next type, the mining you are on will stay green.
You never NEED to smelt or mine rare deposits to skill up. They can help, but they aren't necessary; and in the case of smelting, rarely do you get skill points for it past the tin/bronze stage.