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Installation and Optimization of a Gravity Circuit at Northgate Minerals Kemess Mine Eliab Roman – Kemess Mines Michael

Installation and Optimization of a Gravity Circuit at Northgate Minerals Kemess Mine Eliab Roman – Kemess Mines Michael Fullam – Knelson Gravity Solutions. Northgate Minerals Kemess Mine. 52,000 tpd copper gold mine located north in Northern British Columbia Copper – 75 million lbs/year

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Installation and Optimization of a Gravity Circuit at Northgate Minerals Kemess Mine Eliab Roman – Kemess Mines Michael

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  1. Installation and Optimization of a Gravity Circuit at Northgate Minerals Kemess Mine Eliab Roman – Kemess Mines Michael Fullam – Knelson Gravity Solutions

  2. Northgate Minerals Kemess Mine • 52,000 tpd copper gold mine located north in Northern British Columbia • Copper – 75 million lbs/year • Gold – 300,000 ounces/yr

  3. Northgate Minerals Kemess Mine • Two main ore types • Supergene, high copper/native copper ore • Hypogene, copper sulphide ore

  4. Hypogene ore • “High pyrite” hypogene ore starting to be processed • Low is 3-5 pyrite ratio, typical 4 • high is 5-15, typical 7 • This will also be similar to Kemess North ore, which is an identified new resource • This ore is fine grained, and requires fine regrind size to liberate chalcopyrite from pyrite. • This causes losses of free gold in cleaner circuit

  5. 2005 AMTEL Mineralogy Study • Change in ore caused high losses of fine free gold in cleaner scavenger tails • Free gold mostly <10 microns • Could these losses be reduced with the addition of a gravity circuit?

  6. Data required for determination of gravity recovery • Target stream was the regrind cyclone underflow • Model gravity recovery in regrind • Common to model gravity recovery in primary circuits • Never been done in regrind • Modelling gravity recovery • Ore • Classification • GRG unit recovery • Samples sent to Knelson • Rougher concentrate • Cyclone feed, underflow, and overflow

  7. GRG of the Rougher Concentrate • “GRG Test of the rougher concentrate • Two stage test • Process “as is” • Grind to p80 of 38 microns, same as regrind circuit

  8. Classification • Samples of cyclone streams for GRG determination • GRG partition curve calculated • Curve showed unusual shape at fine sizes • Likely sample processing issues

  9. GRG Unit Recovery – Problem 1 • No hard data on Knelsons operating in regrind • Different from primary applications • Fine GRG • Fine gangue • High sg gangue • Large amounts of pyrite (concentrate bed erosion) • Need data • Pilot or full scale?

  10. Gravity Recovery • Initial modelling using “assumed” Knelson unit reocvery showed good potential for meaningful gravity recovery, but…. • The goal was not simply to recover gold by gravity, it was to reduce losses in cleaner scavenger tails by using gravity • To quantify benefit, need full scale installation • Decision made to install single Knelson XD-30 VG on trial • Very modest installation costs • No pumping • Add gravity con to final con • Structure required to support concentrator (~$250,000)

  11. Optimization Program • Large Optimization program carried out jointly by Kemess and Knelson • Cone style (six cones styles tested) • Fluidisation water flow (low to high) • Cycle time (5-15 minutes) • G force (60-150) • Feed density (undiluted/diluted) • Feed rate (38-134 mtph)

  12. Results - Optimization Program • Best parameters • Short cycle times • “Low” range of fluidisation water flow • High g force (~150g) • Of the operating parameters, cycle time most dominant

  13. Results – Cone Styles • Generation 7 Cone • Fully fluidised, high mass yield • Low water flow

  14. Gravity Recovery Gravity Circuit Operating Conditions • One XD-30 operating with G7 cone, and fully optimized • Treating 40-50 mpth (~25% of CUF) • Gravity recovery of ~10% of total gold (to regrind)

  15. Gravity Recovery Why regrind, and not the primary circuit? Kemess primary circuit, modeled recovery in 2003: • Four XD-48’s at 300-400 mtph each • Four 6’ x 16’ screens • Pumping • Capital investment of several $M • 5-9% recovery by gravity • The advantage of being able to model recovery

  16. Gravity Recovery Benefit Knelson on/Knelson Off trials • Two sets of on/off trials • Each set consisted of multiple days of Knelson on/Knelson off, with samples of rougher con and cleaner-scavenger tails collected

  17. Preliminary Results • 1.0-1.8% overall gold recovery benefit at 10% gravity recovery (by assay) • Ore dependent (higher pyrite, higher benefit) • 2,700-5,000 ounces/yr • $1.7-3.0 M/year, but shipping penalty of ~$300k/year for additional concentrate produced, which is added to final copper concentrate • Rapid payback

  18. Quantify Recovery Benefit • Characterize gold in cleaner-scav tails, with and without gravity • Knelson lab unit • AMTEL, mineralogy • Results pending

  19. Cycle Time – the down side • Shorter is better, but… • Produces more con • “Pollutes” the copper con • Costs money to ship

  20. Cycle Time – Remedies • Grade biased to fines • Gangue biased to coarse • Top 50% mass accounts for 5% gold distribution • SCREENING

  21. THANK YOU

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