Reefton 4 and 5 were the most refractory Alexander River samples at 18.5% and 19.8% readily soluble gold. Reefton 6, which was high grade and included visible gold, was the least refractory sample, with 75.7% readily soluble gold. These results confirmed the assumptions made in the Scoping Study that the samples were partially refractory and a flotation stage would need to be a part of the flowsheet.

Each sample was ground to a sizing of 80% passing 75 microns. 50g/t of copper sulphate was used as an activator and 100g/t of potassium amyl xanthate was used as a collector. No attempt was made to optimise these reagent additions.

Four rougher concentrates were collected at intervals of 1 minute, 2 minutes, 5 minutes and a further 5 minutes, giving a total flotation time of 13 minutes. The aim was to understand and provide information on: how well the sulphides and gold floated;whether the flotation tailings would be low enough in gold to be considered as final tailings; and how to expand the flotation testing to produce a concentrate sui for sale or further downstream processing. The rougher flotation results show that the Reefton samples are all amenable to flotation and gold can be recovered into a small concentrate weight at high gold recoveries.

13-minute rougher concentrates averaged 10.9% by weight and recovered, on average, 92.3% of the gold and 95.1% of the sulphides. Flotation tailings are generally low enough to be considered as final tailings. The higher gold grade of Reefton 6 tailings (1.60g/t Au) is probably the result of the high head grade and presence of free gold reported in the geology logs.

Gravity recovery prior to flotation will likely reduce this flotation tailings grade. A composite sample of Reefton 1 to 5 was produced to give sufficient sample for cleaner flotation tests, gravity tests and downstream processing options. In a commercial flotation circuit, where the cleaner tailings are recycled to the rougher circuit, a portion of the gold would report to the cleaner concentrate and an overall flotation recovery of 90% could be anticipated.

A sample of Reefton 7 (not treated by a Falcon concentrator) was treated by flotation to give a rougher concentrate for downstream processing by POX and cyanidation. Results are shown and the gold recovery to flotation concentrate is 95.4% at a grade of 33.8g/t Au. A gravity test was run on each of the Reefton 1-5 composite sample, Reefton 6, and Reefton 7. A 1 kg sample was run through a laboratory Falcon concentrator and produced a high-grade concentrate.

The Falcon concentrate was intensively leached (ICL) to give an indication of the free gold in the Falcon concentrate. The insoluble gold is refractory and joins the gravity tailings for flotation. Reefton 1-5 is estimated to contain 32.2% free gold, Reefton 6, 48.9% and Reefton 7, 24.4%.

These figures demonstrate the requirement for gravity gold recovery in the Reefton flowsheet before flotation. Downstream Processing Whilst the early Study flowsheet envisaged recovering gold by gravity, followed by making a flotation concentrate for sale, the laboratory testing considered the potential recovery of gold from the flotation concentrate. Two options were selected for testing based on literature studies and industry accepted applications, being: · Ultrafine grinding followed by cyanidation · Pressure oxidation followed by cyanidation 12 kg of the Reefton 1-5 sample was floated to produce a rougher concentrate.

Two 400g samples of rougher concentrate were treated for gold recovery. The first sample via ultra-fine grinding (UFG) followed by cyanidation and the second sample by pressure oxidation (POX) followed by cyanidation. A bulk rougher concentrate from Reefton 7 was also prepared for POX testing.

10 shows the comparison of the two downstream processing tests on the Reefton 1-5 flotation concentrate and the POX result for Reefton 7. The ultra-fine grind gave a gold extraction of 22.9%, and the POX test a 98.5% extraction of the gold in the flotation concentrate. For Reefton 7 the cyanide gold extraction after POX was 91.7%. These results demonstrate that the refractory gold is probably in solid solution and needs strong oxidation (or possibly roasting) to liberate the gold for cyanidation.

In conclusion, the Reefton samples tested responded positively to a flowsheet of gravity recovery followed by flotation. Flotation concentrate is high grade and sui for sale or could be treated by pressure oxidation and cyanidation. Based on the testwork results gold recoveries of 90-93% could be achieved.

Historical production from the Reefton goldfield (pre-1950) was based on high grade quartz reef ore using a combination of gravity recovery, followed by roasting on the gravity tailings and cyanidation. More recently Oceana Gold operated the Globe Progress open pit and processed ore with a head grade of approximately 1.4g/t Au using flotation and sending the concentrate to their Macraes operation and processed with pressure oxidation. The recovery to the flotation concentrate was 87.9% and recovery after POX and cyanidation was 94.5%, giving an overall recovery of 82.4%.

Whilst this is lower than Siren's samples it is at a considerably lower mine head grade and had little to no gravity gold. Blackwater ore was successfully processed at two different processing plants between 1908 and 1949. Records indicate that gold recovery was between 85% and 95% using a combination of gravity, flotation and cyanide leach processes.

A Preliminary Economic Assessment considering re-opening of the Blackwater Mine reported ore processing would involve producing a high mass recovery gravity gold concentrate followed by fine gold flotation. This process was predicted to recover in excess of 97% of the gold into a high-grade concentrate. Intensive leaching of the concentrates and electro-winning was estimated to allow production of gold doré bars on site, with anticipated overall recovery in excess of 96%.

The Fosterville mine in Victoria has similar geology to the Reefton goldfield. The processing circuit has gone through a long development phase. The basic flowsheet from 2009 to 2015 involved flotation followed by bacterial oxidation (BIOX) to liberate gold, followed by cyanidation.

From a head grade of 4.62g/t Au the flotation gold recovery was 96.0% and the cyanidation recovery 88.5%, giving an overall recovery of 84.0%. In 2016 the head grade increased to 6.11g/t Au and the flotation recovery improved to 96.6%. Post BIOX cyanidation recovery went to 92.9% and overall recovery was 88.5%.

In 2017 a gravity circuit was added as the ore sources changed. 12.9% gold recovery was seen from the gravity circuit.