Portia Gold Processing Circuit

In the past, lower than expected throughput i.e. approximately 50 tph (versus design of 100 tph) for the Portia Gold Processing Plant was mainly due to the nature of the Portia gold ore material and this contributed to lower than expected tailings densities being achieved.

The Light Grey Clay is disaggregated relatively easily in the trommel.

For the Kaolinite Clays and the Saprolite materials, a log washer and attrition cells are used in the processing circuit.

The slurry from the disaggregation circuit is passed across some coarse gold traps or riffle boxes before final screening. The underflow containing the finer gold passes through a pair of parallel Knelson concentrators to further concentrate the gold.

The combined gold concentrates from the riffles and the Knelson concentrators are batch processed over large Wilfley (shaking) tables followed by a final cleaner Gemeni table to produce a gold concentrate for smelting into a gold dore bar.

Recent changes (Figure 3.25, September 2016) in the riffles to tailings circuit are defined below:

1. adding in a vibrating screen and additional riffle boxes. This screen will be much more efficient than the current DSM screen;
2. adding in a primary, secondary and tertiary jig circuit to treat the screen oversize. The tailings from the secondary and tertiary tails are directed to the Knelson concentrators;
3. adding a ball mill to grind the primary jig tails and return it and the entrained gold to the circuit;
4. running the logwasher in parallel to the trommel. This action will increase the throughput and help 
bring up the density to the riffles;
5. cycloning the Knelson feed to thicken feed to the Knelson concentrators to improve fine gold 
recovery with the additional benefit of densifying the final tailings that are deposited in the tailings 
cells;
6. the overflow from the cyclones will potentially be directed to a slimes settling dam ('SSD') to settle 
out entrained very fine gold and clay sized fraction. Initially, the overflow will be directed back to the 
tails bin until the SSD is constructed; and
7. associated pumps and instruments to facilitate the modifications.

No cyanide or chemicals are used in the process other than small volumes of nitric acid used occasionally required for gold ‘clean-up’ to remove minor impurities from gold concentrate prior to smelting.

When smelted into gold dore bars, the presence of certain impurities above threshold concentrations set by the Gold Refinery can result in the dore bars either being rejected by the refinery or financial penalties being applied. Hence, removal of the impurities prior to shipping is highly desirable. Nitric acid oxidation provides fast removal of impurities.




http://minerals.statedevelopment.sa.gov.au/mining/approved_peprs

The proof for these design changes to the gold processing circuit should be evident in the next Portia gold production numbers, so we should all look forward to the next ASX Quarterly Report due at end of February 2017.


Cheers

These are only my random thoughts and it does not constitute investment advice. Before acting on any information you read and before making any financial or investment decisions, you should always consult your advisor(s) or other relevant professional expert