Augur: Excellent gravity gold recovery from Wonogiri
Wednesday, October 22 2014 - 04:29 AM WIB
ASX-listed Augur Resources Ltd reported Wednesday the results of further metallurgical testing of the sulphide mineralization from the Randu Kuning deposit at the Wonogiri project in Central Java.
The company said that metallurgical test work investigated gold only recovery process options including gravity separation and cyanide leaching along with other diagnostic leaches. For this test program, two sulphide ore composites were prepared.
One was a ?low-grade? composite containing 0.55 g/t gold, 1.1 g/t silver and 0.23% copper which is typical of the disseminated and stockwork, vein hosted, porphyry-type mineralization.
The other was a ?high-grade? composite containing 1.26 g/t gold, 1.4 g/t silver and 0.27% copper deemed representative of the higher grade, structurally controlled, breccia/fault hosted (feeder) zones.
Both composites were of a primary, sulphide ore type compiled from core drilled within the conceptual starter pit. Sulphide ore represents over 90 percent of the resource.
The testwork was completed in Jakarta at PT Geoservices under the direction of Peter Wallwin of PWA Limited, based in Malaysia.
The following results were obtained:
Four size fractions were evaluated for gravity recoverable gold using a Falcon centrifugal concentrator.
? Low grade composite shows average gravity recovery of 5 1.0%. This includes ≤36% in coarse fractions (>75 micron) and very high recovery of 71% in the fine grained fraction (≤75 micron).
? High grade composite shows average gravity recovery of 34.8%. This includes poor recovery (≤11%) in the >150 micron fraction but significantly better recovery of ≤60% in the ≤75 micron fraction.
? grains of ?free? gold were seen in the ≤75 micron fractions of both composites.
Diagnostic leaching was performed on the gravity residue (tails) of both composites to determine the recovery by carbon in leach (?CIL?) as well as the association of residual gold contained/retained in other mineral species such as carbonate, silicates, pyrite and arsenopyrite.
? CIL recoverable gold results were good for both composites. Recoveries averaged 83.2% in the low grade composite and 83.9% in the high grade composite.
? The high grade composite showed a range in CIL recoverable gold from 71.3% in the fine fraction (≤75 micron) to 93.2% for the coarse (>300 micron) size fraction.
? The low grade composite showed a range in CIL recoverable gold from 74.1% in the fine fraction (≤75 micron) to 89.8% for the coarse (>300 micron) size fraction.
? Only a very minor amount of gold is determined to be associated with pyrite or arsenopyrite, with 0.6% in the low grade composite and 2.5% in the high grade composite. This is significant as the results indicate that the ore is not of a refractory nature.
Four size fractions were evaluated for gold recovery using direct cyanide leaching.
? Overall gold recovery was 62.5% for the low grade composite and 50.6% for the high grade composite.
? 72% to 82% of the gold in the low grade composite was recovered in the >75 micron fractions and only 48% of gold was recoverable in the fine (≤75 micron) fraction.
? 75% of the gold in the high grade composite was recovered in the >300 micron size fraction and only 47% in the ≤75 micron fraction.
The lower gold recoveries in the fine fractions [≤75 micron) of both composites is anomalous given that the opposite is true for the GRG. This relationship will be investigated in future testwork.
Although the results reported here are preliminary they are sufficiently encouraging to warrant further detailed testing. Future testwork will investigate optimization of these tests and also of previous metallurgical testwork which investigated recovery of both gold and copper via flotation processing to produce a copper-gold concentrate.
The flotation results indicated 89.0% recovery of gold and 93.4% recovery of copper to produce a high quality marketable concentrate with grades of up to 21.2% copper and 90.6 g/t gold. The objective of future work is to determine what combination of metallurgical parameters would be most efficient for processing the Randu Kuning gold and copper mineralization.
Editing by Reiner Simanjuntak