Tutorials/Mining – Official Minecraft Wiki
Quarry Mining. For reference, 20×20 quarries (down to bedrock) typically yield 3 10 stacks of coal, 1 7 stacks of iron ore, up to half a stack of gold ore, perhaps 50 redstone dust (lower down), and a few Lapis Lazuli and diamond gems, though these results vary with the width, depth and location of your quarry.