There are 4 types of gold at Wiluna....1. Oxide gold (none being...

There are 4 types of gold at Wiluna....

1. Oxide gold (none being mined - mainly mined by open pit in the past).
2. Free milling gold in quartz reefs - has been mined at various times, including recently by Apex.
3. Refractory gold in sulfide lodes - the mainstay ore source.
4. Ore types which are a mixture of 2 and 3.

Types 1 and 2 can be treated by conventional cyanidation, with or without a gravity circuit upstream. The advantage of a gravity circuit is that it can increase recovery of coarse free gold and therefore optimise efficiency/residence time/reagent consumption of downstream process = lower costs, higher production.

Type 3 requires pre-cyanidation oxidation - either by roasting, pressure oxidation or bacterial leaching (eg BIOX). Near surface refractory ore is antimony rich but deeper ore is arsenopyrite rich.

These styles require different treatment and therefore separate processing routes. Wiluna has two parallel routes that have at different times been reconfigured to process all refractory ore, 50/50 refractory and free milling and 50/50 refractory and oxide.

Type 4 is difficult because there are refractory and non-refractory components in the same feed and both cannot be recovered, so the choice of treatment route is dependent on cost/benefit of recovering/not recovering each component of feed.

In its long history of feast and famine Wiluna has prospered most at the times when

1. There has been enough free or oxide gold being mined to fill one entire circuit.
2. There has been lots of open pit ore of whatever sort to keep the plant full.
3. The Bulletin orebody was being mined - this was a BIG high grade mother capable of providing all the tonnage the mill could take.