Tonnages are large and will only get much bigger from here -...

Tonnages are large and will only get much bigger from here - however grade is a limiting factor. Lets look at it another way - if all the waste you dig is low grade sub economic - but it has to be moved anyway. You dump it in a big pile apply sprinklers and heap leach the high grade waste (sub economic ore). The waste may well pay for itself to be moved and with an increase in metal prices it becomes low grade ore. Such large deposits are idiot proof for large miners like Rio and BHP who like simple large tonnage deposits (even they cant stuff it up). The problem with these bulk tonnage operations it the upfront capital to get them going (easy for the majors but more difficult for ALK).
Anything less than 10 years to production will be good (hope I haven't burst too many bubbles of those who thought production was just around the corner).
ALK just keeps on quietly delivering - punching well above their weight.

Escondida is a large tonnage low grade operation as comparison (not a direct comparison because we have neither the tonnes nor the grade - but it is what may develop over time) Escondida is 3 porphyry bodies - who knows how many we have ?

https://www.mining-technology.com/projects/escondida/