Minecraft wiki entry for Mining, associated text: If we assume that all ores spawn in 2×2×2 cubes or larger, then there is no need to reveal every block. Mining three spaces wide, with four blocks between each shaft will be completely thorough. If we assume that 90% of ores are 2×2×2, but 10% are 1×1×1; while obtaining 100% unitary thoroughness then requires a spacing of 3 and a tiering distance of 2, the original mine (the 3-space 4-tiering) maintains a thoroughness of 98%. The 100% thorough mine requires mining twice as much stone while only increasing the total yield by 2%, resulting in half the efficiency.