by grapefruitv » Sat Mar 31, 2018 4:41 pm
Iron spawns in nodes, not by separate boulders. Where those nodes will be is defined at the moment insides of your map were initially generated. Your tunnels are too close, this way you are actually decreasing your chance at finding anything. Try bigger gaps, 10 tiles or so.
Overall you spent very little time working on your mine so far, 20x10 + 3x20 is not that much and one can't say you are being unlucky just yet.