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Optimising Parameters and Measuring Improved Gold Recovery in a Copper-Zinc Flotation Circuit Myra Falls Operation Trev

Optimising Parameters and Measuring Improved Gold Recovery in a Copper-Zinc Flotation Circuit Myra Falls Operation Trevor Yeomans NVI Mining. 4000 mtpd copper/zinc flotation mill with gold/silver. Historical Gold Recovery Gravity circuit – 2-5% Copper concentrate – 20-30%

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Optimising Parameters and Measuring Improved Gold Recovery in a Copper-Zinc Flotation Circuit Myra Falls Operation Trev

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  1. Optimising Parameters and Measuring Improved Gold Recovery in a Copper-Zinc Flotation Circuit Myra Falls OperationTrevor YeomansNVI Mining

  2. 4000 mtpd copper/zinc flotation mill with gold/silver • Historical Gold Recovery • Gravity circuit – 2-5% • Copper concentrate – 20-30% • Zinc concentrate – 13-23% • Overall – 35-58%

  3. Gravity Circuit • Installed in 1992, two Knelson CD-30 • CD-30 on “A” Circuit • CD-30 on “B” Circuit • Gravity concentrate shipped offshore • One of the first sites in the world using automated Knelsons • Unusual upgrading step • Cleaning of rougher conc, using CD-30

  4. GOLD RECOVERY STEPS

  5. Myra Falls Upgrading Step-Historical • Primary Knelsons operated on 6 hour concentrating cycles • Concentrate stored in two concentrate hoppers, one for each grinding circuit • Upgrading step: • Once per week, the “A” circuit Knelson was taken off line • The concentrate stored in each concentrate hopper was individually pumped to the A circuit Knelson • This “cleaned” product was decanted, dried, and shipped • The goal was to reduce the mass and increase the grade • No data on efficiency of this process

  6. Typical ‘cleaned’ concentrate, note flakes

  7. Initial Changes • Myra Falls staff thought that shorter cycles and more frequent cleaning would improve results • Change made • Start decreasing primary cycle time from 6 to 1 hour • Start increasing frequency of cleaning step, to once every 12 hours • Result • Significant increase in gravity recovery • Positive influence on overall gold recovery

  8. Question? • Why such an increase? • Was this due to….. • Ore change? • Short cycles? • Frequent cleaning? • How can we measure?

  9. Knelson Gravity Circuit Audit - Goals • What is the effect of Knelson concentrating cycle time on gravity recovery • What are the losses associated with the unusual upgrade step • What alternatives for upgrading are feasible • Tabling • Intensive Leaching • How to maximize primary gravity recovery with the existing Knelson Concentrators • What is the upper limit of gravity recovery, and what additional equipment might be needed Once results of sampling completed, circuit can be modeled

  10. Gravity Circuit Audit - Sampling • Grinding Cyclones • Characterize for GRG recovery to underflow • Characterize GRG in COF before and after upgrading • Primary Knelson recovery – characterize for unit GRG recovery • KC con • KC tails • Upgrade system – recovery characterization • KC feed grade during upgrade • KC tails grade during upgrade

  11. Audit Results – Grinding Cyclones • GRG partition curve typical for finer grind circuits • Some coarser GRG exiting the circuit

  12. Audit Results– Cyclone Overflow • Significant increase in GRG exiting during upgrading

  13. Audit Results- Upgrading • Significant increase in grade of tails in only a few minutes • This was with the already reduced cycle time and more frequent cleaning

  14. Old vs New Upgrade Frequency Previous Current • Primary cycles: 6 hours 1 hour • Cleaning: Weekly 12 hours • Gravity recovery 2-5% 15-20%

  15. RESULT OFCHANGES GRAVITY Recovery increase ~12%

  16. MORE OVERALL RECOVERY??

  17. MORE OVERALL RECOVERY??

  18. MORE OVERALL RECOVERY??

  19. Base Case predicted 14.6% recovery, similar to plant actual Gravity Circuit Audit – Model Calibration

  20. Acacia pilot study carried out Excellent recovery No copper solubility issues Sensitive site for cyanide use (BC Park) Table selected as being a reliable upgrade option Table purchased and installed, Operational April 2006 Modelling - Outcomes

  21. NEW CLEANER CIRCUIT

  22. TABLING UPGRADE CIRCUIT • NEW ‘FLAKE’ CONC @ 65% GOLD TO DORE • TABLE ‘MIDDLINGS’, WITH NO ‘FLAKE’ SOLD AS HISTORIC GRAVITY CONC. @ 10000 G/T • TABLE TAILINGS SENT DIRECTLY TO COPPER CONCENTRATE • NOTE 100% UPGRADING RECOVERY

  23. RESULT OF TABLING

  24. Gravity + Gold to Copper vs Overall Recovery

  25. Overall Gold Recovery vs Tails Loss

  26. OverallOutcomes and Conclusions KNELSON OPERATING CHANGES: • Gravity recovery was increased to 15%, from 2-5%. • Overall Recovery Increase maybe? • Very simple operating changes made to gravity circuit. • Inexpensive test program, confirmed gain, and modelling predicted further possible gains.

  27. OverallOutcomes and Conclusions TABLING UPGRADING CHANGES: 100% stage recovery Gravity recovery decrease ~ -5% Copper conc increase ~ + 12% Overall Recovery Increase YES, ~ + 10% Mill tailings Decrease 0.3 g/t.

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