I found the total surface area of the Earth at Wikipedia: 510,072,000 km²
The same page had the land surface area: 148,940,000 km²
And this paper provided the area affected by mining: 240,000 km²
Then calculate:
~0.05% of the total surface of the Earth is affected by mining (0.047052771%)
~0.2% of the land surface of the Earth is affected by mining (0.161139687%)
But to put it in perspective, Utah is 219,887 km² (source)