3 Copper-Ore + 1 Tin-Ore = 2 Bronze-Dust
Bronze is a rather old material used way before iron. I guess they had a way to create it without macerating their Tin and Copper-Ores. The recipe is only half as efficient as creating Bronze out of dust, but it would make Bronze-Tools a better choice before using the mining-drill. Actually at the time you are able to create a Bronze Pick you are most likely also able to create a Mining-Drill, which is the better choice.