The next part of this BHP document is mind boggling. How do BHP...

The next part of this BHP document is mind boggling. How do BHP envisage leaching this depth? Leach Pad is 4.9km x 2km wide by 18m high, stacked ore to eventually be 126m depth. We know the sulphides take longer to leach & will continue to leach over a long period of time but what about the percolation of acid down through 126m of pad depth? Must be very good quality agglomeration to go that deep? Or perhaps much larger than CYM's 20mm agglomeration and hence the lower recoveries?
BHP talk about using air injection and higher than 45*C temperatures, same as what CYM have stated. But BHP recovery is way down the percentage scale. At least it's not wasted material.
Escondida metallurgical recoveries for Oxide 62%; Mixed 42%; Sulphide 42% for material processed by leaching or 83% for material processed via the concentrator.