Dont quote me but I think Cowal is crush, grind, flash float, float, ultra-fine grind, then leach. I'm not a metallurgist but I think that's what it is. I dont think they have a gravity circuit. The float tail is also leached - goes in at 0.2-0.3 g/t and comes out at 0.1-0.15 g/t or something similar - cost about $40-$50m to set that up a couple of years ago and worth it when you're putting 10 million tonnes a year through. From what I remember of the ann the other day DEG are also working on the assumption of a FTL as well as POX.
Agreed on pressure oxidation being tricky and I remember all the instances you mention. Tech has improved in 20 years though and I'm sure lessons have been learned.
An alternative is to go the biox route but that has it's own issues too. It's early days yet. UFG may be a cost effective alternative if it responds to ultra fine grinding. There also may be a refractory and a non-refractory component to the sulphides so the mass pull could be even lower if one can be suppressed in favour of the other. Then there are all the ore sorting and chemistry advances that are currently being made. Tech is constantly changing. Metallurgy can be a black art, chasing a percent here and there.
DEG Price at posting:
76.5¢ Sentiment: Hold Disclosure: Not Held
(20min delay)