Let R be the total ore output of the company.
Of Big Dig’s output, 100 - 10 - 60 = <<100-10-60=30>>30% is nickel.
Since 720 is 60% of 100% of their output, 720 / R = 60 / 100.
Thus, Big Dig mines R = 100 * 720 / 60 = <<100*720/60=1200>>1200 tons of ore daily.
Therefore, Big Dig mines 1200 * 30 / 100 = <<1200*30/100=360>>360 tons of copper daily.
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