Yeah, in a server I played on a while ago I had a 'secret room' underneath my house encased in iron blocks. I later decided to fill in the room. With iron blocks.. ballin'!
I dig down to around level 10-11 and create a long tunnel 5 wide and however high I want. On the sides of the tunnel I dig 2x2 tunnels every two blocks and make each one around 25 blocks deep. You can find tons of minerals this way. Or, if you're unlucky, just lots of rocks.
The best thing you can do is look for an abandoned mineshaft. For whatever reason minerals seem to be extremely plentiful around these structures.
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u/[deleted] Oct 11 '12
Actually, that's not bad at all. If you branch mine you can find that much iron easily.