Company and Mining

23 May 2017


Gold panned from the quartz zone outcrop in 2016


  • Metallurgical test-work reveals excellent gold recoveries at the Aucu Gold Deposit
  • Mining Optimisation Study Update

Summary – Gold Metallurgy

Metallurgical tests were performed on 14 drilling composites representing 96 one metre drill samples. The samples came mainly from the newly discovered Quartz Zone which has an average gold grade of 9.5 g/t gold and an average copper grade of 0.64% copper.

One composite contained over 1% copper but very little gold. The other 13 composites had significant gold and copper values, averaging 10.6 g/t gold and 0.85% copper.  Comparison of fire assay gold analyses with Leachwell bottle roll analyses indicated greater than 96% free milling gold for 10 of the composites. Two composites had about 76% and one composite had 36% free milling gold; these three composites averaged about 2.6% copper which may have affected the Leachwell assays. Screen fire assays showed that on average one third of the gold occurred as relatively large metallic grains.

Summary – Copper Metallurgy

Sequential leach tests quantified the various types of copper mineralisation (oxides, secondary copper sulphides and primary copper sulphides) in each sample. Results showed that:

  • 34% of the copper is present as copper oxide (azurite and malachite);
  • 20% of the copper is present as secondary copper sulphides (chalcocite and neotoesite);
  • 44% of the copper is present as primary copper sulphides (chalcopyrite).

This is consistent with observed geology. The composition of copper types in each hole varies widely and is related to the amount of weathering the ore interval has been exposed too. Samples closer to the surface or a major fault zone tend to be much more oxidised.

Aucu Gold Deposit- Metallurgy Summary

The Company will undertake further metallurgical testing of copper and gold recovery via a combination of gravity concentration and froth floatation.  This would produce saleable high-grade gold/copper concentrates. At this stage of the project, this appears to be the most attractive processing method. It avoids cyanide leaching and associated environmental management problems. Summary metallurgical tables are provided on page three of the release.

Gravity recoverable gold averages 88.6% based on the 69 composites (182 samples) tested in 2016 (see ASX release dated 18 February 2016). Gravity concentration testing has not been conducted for the 2017 composites at this stage.  However, the high levels of free milling gold and coarse particulate gold seen in the current results are positive indicators.

Approximately 64%of the copper occurred as primary and secondary sulphides which are readily recovered to high-grade concentrates by froth floatation.  The remaining 34% of the copper occurs as oxides minerals; these are generally more difficult to recover to concentrates.  Achievable recovery levels and concentrate grades will be investigated in the planned test work.

For further information, please see the link below to today’s ASX announcement.

ASX Announcement