New closing HIGH, page-114

Dalga currently has a sag mill not a ball mill. The sag mill can run at up to 3.2mtpa when treating oxide ore.
The primary crusher can run up to a 3.5mtpa throughput.

From what I can remember, the plan is to add a ball mill and secondary crusher.
They need to reduce the micron size and perhaps even increase residency time (recoveries could increase from mid to high 80% before shutdown, up to as high as 95% once mill revamp is completed).

Secondary crusher will reduce the ball and sag mill workload as the smaller sized primary ore feed entering the mills from the dual crushing circuit will mean lower power usage and less wear and tear on the ball and sag mills.

I could be wrong on a couple of those details, this is just from memory. There's lots of old info provided by Gascoyne on the mill and crushing circuit from back when Gascoyne was a developer. GR Engineering also had a few details about the Dalgaranga plant on their website.