Optimising Parameters and Measuring Improved Gold Recovery in a Copper-Zinc Flotation Circuit Myra Falls Operation Trevor Yeomans NVI Mining

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 OF CHANGES
GRAVITY Recovery increase 12
16
MORE OVERALL RECOVERY??
17
MORE OVERALL RECOVERY??
18
MORE OVERALL RECOVERY??
19
Gravity Circuit Audit Model Calibration

• Base Case predicted 14.6 recovery,
• similar to plant actual

20
Modelling - Outcomes

• 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

21
NEW CLEANER CIRCUIT
22
TABLING UPGRADE CIRCUIT

• NEW FLAKE CONC _at_ 65 GOLD TO DORE
• TABLE MIDDLINGS, WITH NO FLAKE
• SOLD AS HISTORIC GRAVITY CONC. _at_ 10000 G/T
• TABLE TAILINGS SENT DIRECTLY TO COPPER
  CONCENTRATE
• NOTE 100 UPGRADING RECOVERY

23
(No Transcript)
24
RESULT OF TABLING
25
Gravity Gold to Copper vs Overall Recovery
26
Overall Gold Recovery vs Tails Loss
27
Overall Outcomes 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.

28
Overall Outcomes 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.