the zincs good, page-4

Interesting d,

Just a note - the SRK report suggests AIM consider a regrind circuit to lift recovery, this does not necessarily mean a "finer" product if anyone is curious.

The Perkoa design basis is to produce a "coarse" flotation concentrate (maybe 200-250 micron); any regrinding (if it is to be considered)is purely to lift recovery a few percent and would only apply to a fraction of the concentrate flow.

The "finer" products you refer to (say <150 micron) are likely to come from mines where fine grinding is required to liberate the sphalerite (Zn) particles (e.g. Macarthur River / Ernest Henry in QLD). Fine grinding requires a lot more energy (kWh/t) to get the same recovery - in fact it is an exponential relationship!
"Finer" products will require a slightly different refining technology - I'd imagine companies like Xstrata have patents on them.

IMO Perkoa is probably one of the 'last' traditional (low treatment cost) ZnS operations to be discovered in recent times, hereby allowing the 'traditional' smelters to deal with the 'traditional' concentrate.

That's what attracted me in the first place.

Sack