Was are typical electrical power distribution system losses in a large industrial site?

I'm doing a rough estimate of end-use power consumption at a large mine and mineral processing facility.  The main supply is 138 kV and there are a lot of motors at 600V and 4160V levels.  Anyone have a rough estimate of total distribution losses?  I.e. the difference between real power measured at the 138kV utility connection and the sum of real power consumed in all the end-loads?  Power factor is typically about 85-90%.  I'm just looking for a very rough estimate.  E.g. 1%, 2% or 4%. Thanks!