Do you realize this thread is almost a year old? Though I was looking for a motherload clone and would like to play I dig it. Also, the last post before yours was on my birthday! Yay!
Motherload exist on iOS Mother load on the ios is " i dig it " everything is the same except the graphics are better.
Spice Miner is similar, although it doesn't play the same. Terracore Adventures is almost exactly the same as Motherload, although without the physics that Motherload has. *space miner woops correcting a typo from months in the past
Found it! It's kinda expencive for iPad but for iPod and iPhone it's 0.99$ http://www.google.com/url?sa=t&rct=j&q=i%20dig%20it&source=web&cd=1&sqi=2&ved=0CDUQFjAA&url=http%3A%2F%2Fitunes.apple.com%2Fus%2Fapp%2Fi-dig-it%2Fid314864297%3Fmt%3D8&ei=hU06UIeTM6OpiALDiIDYBQ&usg=AFQjCNHs4vUEbBZUQXdxqelWfAnvLNWZ1g -- iPhone http://itunes.apple.com/us/app/i-dig-it-hd/id362087496?mt=8