The Kalgoorlie ore deposits occur in Pre-Cambrian rocks and essentially consist of calc schist and quartz-dolerite-greenstone. The ores contain free gold and tellurides. Auriferrous pyrite is the most abundant sulphide and is occasionally associated with chalcopyrite, tetrahedrite and arseno-pyrite. The gold associated with the pyrite is in a very fine state and is not liberated even after very fine grinding.
The crushing section reduces run-of-mine ore to minus 1/2 inch which is further reduced by rod mills and ball mills to approximately 75% minus 200 mesh. Rod mill discharge is pumped over strake tables ahead of the ball mills with the concentrate being amalgamated, retorted and finally smelted. Final ground product goes direct to flotation before gold leaching by cyanide.
The pyritic flotation concentrate and tailing are treated in separate thickeners with the overflow from both thickeners going to flotation circuit water storage. Underflows from each thickener are cyanided in separate agitators.
The cyanided concentrate is filtered and the filter cake treated in Edwards roasters with the calcine again being cyanided and filtered. Post-cyanidation is the term used to describe this treatment method. The calcine filter cake is repulped and pumped to the flotation tailings cyanide agitators. Filtrates from both stages of filtering are combined and flow to the high grade precipitation section, clarified, and the gold precipitated with zinc dust. This precipitate is then filtered, roasted, fluxed and smelted.
The tailings cyanide agitators discharge to a washing thickener. The underflow is filtered and the filter cake repulped with barren solution and pumped to the residue dam. Filtrate is circulated back to the washing thickener. Overflow from the washing thickener passes to the low grade precipitation section and is treated similarly to the high grade solution. Barren solution is circulated back to both cyanide sections.
Until 1956, a second 500 ton per day mill operated using a pre-cyanidation flowsheet. In this case, the ground ore was cyanided with the cyanide tailings filter cake) being gassed with sulfur dioxide and then floated for sulfide recovery. Flotation concentrate was then roasted, recyanided, and returned to the grinding circuit. In 1956 this plant was converted to the post cyanide flowsheet.
The Emperor flowsheet is so different that it is presented in detail on two pages. It is unique in that tellurium metal is produced along with gold bullion and copper cement both unusual products from a gold ore. The flowsheet is distinguished in that there are three separate but allied circuits; the main cyanidation circuit supported by roaster calcine cyanidation, a tellurium metal recovery circuit, and a copper cement recovery operation.
The mine ore is washed in a blade type mill after which the minus 4 plus 1/2 inch product is hand picked for removal of waste. The slime portions go to flotation for recovery of sulfides with the slime tailings going to waste.
After grinding, the tellurium and copper minerals are recovered by flotation. The concentrate containing some of the gold goes through an oxidation step with NaOH, Na2C03 and Ca (OCl which renders the gold soluble for cyanidation and the tellurium leachable. The concentrate residue containing copper is roasted and leached for production of cement copper.
The flotation tailings are cyanided for gold extraction following usual practice. The cyanide residue is conditioned with SO£ gas from the copper concentrate Edwards roaster and then floated with copper sulphate and xanthate. After filtration, the concentrate is fed to the roasters along with the above main stream copper concentrate. Flotation tailings are used for mine fill.
Roaster calcines, following leaching for copper, are washed and cyanided separately and then the calcine-residue is fed back through the gassing tower circuit.