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This is a type of fractal known as a space-filling tree, and it ensures that every mine in the grid is exactly the same distance away from the destination. With normal belts at the edges (which are actually crinkled around into the inside as well), and higher-speed belts in the center, this has the maximum possible output capacity. I haven't been able to use the ore fast enough that it doesn't back up, but then I haven't really tried very hard. I'm pretty sure that with this many mines it's capable of optimally filling even the triple-speed belts. Now I just need to upgrade my iron mine...