Metallurgy

The following information covers metallurgical testwork conducted on the main Colomac and Goldcrest deposits between 2016 and 2019.  The test program is still at an early stage of evaluation, where it is reasonable to believe that further optimization should improve gold recovery in all process options. At this stage, no further testing is required until a preferred process option has been decided upon. Once the preferred process option is defined, a comprehensive metallurgical study would be necessary to optimize process conditions.

Testwork Highlights To-Date:

  • Studies consistently noted minimal variation in rock hardness for all test samples covering all zones and deposit depths, indicating that both the Colomac Main and Goldcrest sills are relatively homogeneous (Table 2).
  • Based on the collective test results to-date, the Colomac deposit is amenable to all standard gold recovery technologies including, flotation, gravity concentration, cyanidation, and heap leaching (Table 3).
  • A combination of gravity and cyanide leach recovery processes (gravity+cyanidation), as well as whole ore cyanidation methods, have given exceptional results with recoveries ranging in average from 95.1% to 98.0% and 91.3% to 97.2% respectively (Table 3), representing a significant increase in recovery over historical production results of 88.1% (1994 to 1997).
  • Although additional studies are required to fully validate these findings, early indications based on metallurgical results received to-date suggest that a semi-autogenous grinding (“SAG”) ball mill grinding circuit followed by a gravity concentrate leach, and a cyanide leach circuit on the resultant final ground product, represent a promising process route for recovering gold from Colomac rock.
  • Based on the findings of all test work to-date, gold recoveries using heap leaching may be a viable process for low-grade material which would otherwise be discarded as waste.
  • Column leach tests performed to-date resulted in recoveries ranging from 21.3% to 66.0% (107 day run) and up to 69.7% (206 day run) (Table 3).
  • Bottle roll leach tests performed to-date resulted in recoveries ranging from 22.0% to 81.8% (minus half (½) inch crushed material, 10 day run)
  • At this time, no further studies are contemplated until a preferred process option has been decided upon.

 

TABLES

 

Table 1. Head Assays of Colomac Samples (Including Previous Programs)

Sample ID Zone Au Grade (g/mt)
Fire Assay Metallics Screen Analysis Average
2019 MET- 1 2.0 0.39 0.34 0.50 0.41
2019 MET- 2 2.0 0.67 0.84 0.71 0.74
2019 MET- 3 2.0 0.58 0.52 0.40 0.50
2019 MET- 4 3.0 0.47 0.60 0.44 0.50
Average-Colomac 2019 0.53 0.57 0.51 0.54
Colomac 2018 Sample 1 1.0 1.67 2.28 3.77 2.57
Colomac 2018 Sample 2 2.0-2.5 2.15 2.05 2.29 2.16
Colomac 2018 Sample 3 3.0-3.5 2.38 2.41 2.82 2.53
Gold Crest 2018 Sample 4 Goldcrest 1.34 2.30 1.48 1.71
Average-Colomac 2018 1.88 2.26 2.59 2.24
Colomac 2017 High-grade (Zone 1.5) 2.83 7.16 N.A 4.99
Colomac 2016 *South Zone 3.0-3.5 1.16 1.32 N.A 1.24
Colomac 2016 North Zone 1.5-2.0 0.35 0.90 N.A 0.63
Colomac 2016 *Deep 1.5-2.0 0.65 1.69 N.A 1.17
Colomac Master Composite 2016 1.80 2.58 N.A 2.19

* Deep and South Zones Blended into a “Master Composite”. The North Zone was excluded from gold recovery process testing due to unexpectedly low assay grades (see press release dated April 19, 2017).

Table 2. Colomac SAG Design Ore Hardness Test Work Results (Including Previous Programs)

Zone Sample Information SG Solids WSDT (kWh/t) Sd-BWI (kWh/t)
2.0 2019 MET-1 2.69 12.00 14.44
2.0 2019 MET-2 2.74 12.84 14.22
2.0 2019 MET-3 2.67 11.70 14.23
3.0 2019 MET-4 2.75 12.59 14.61
Average Colomac 2019 2.71 12.28 14.37
1.0 Colomac 2018 Sample 1 2.70 13.49 15.43
2.0-2.5 Colomac 2018 Sample 2 2.62 11.74 14.93
3.0-3.5 Colomac 2018 Sample 3 2.71 11.48 13.90
Goldcrest Gold Crest 2018 Sample 4 2.61 16.45 14.88
Average Colomac 2018 2.66 13.29 14.79
3.0-3.5 South Zone 2.76 12.32 14.28
1.5-2.0 North Zone 2.73 13.52 14.38
1.5-2.0 Deep 2.70 14.07 14.10
Average Colomac 2016 2.73 13.30 14.25
1.5 Colomac 2017 High-Grade 2.67 12.69 15.18
Average-Overall 2.69 12.91 14.55

Table 3. Metallurgical Test Results (Including Previous Programs)

Process Routes Gold Recovery, %
Heap Bottle Roll Column Column Flotation Whole
Ore Cyanide*
Gravity Gravity + Cyanide*
Cyanide* Cyanide*
~107 days +206days1
Particle Size P80(µm) 12700 12700 12700 75 106 150 150 75 106 150 106
2019 MET-1 42.6 66.0 N.A 90.0 92.8 84.2 93.4 72.5 84.1 91.4 93.8
2019 MET-2 22.0 43.6 88.2 88.8 85.8 95.2 82.2 39.0 52.9 96.0
2019 MET-3 72.4 60.3 95.7 93.4 87.4 94.4 74.9 78.7 74.8 95.9
2019 MET-4 47.7 21.3 86.3 82.6 75.6 91.3 53.6 59.0 50.9 94.6
Average Colomac 2019 46.1 47.8 TBC 90.1 89.4 83.3 93.6 70.8 65.2 67.5 95.1
Colomac 2018 Sample 1 31.5 45.6 57.4 94.9 94.5 92.8 97.1 76.6 75.4 64.0 98.0
Colomac 2018 Sample 2 49.1 46.4 55.5 94.8 94.5 94.2 96.8 75.8 75.0 69.0 97.3
Colomac 2018 Sample 3 47.1 46.1 54.9 92.1 88.6 84.8 96.7 63.3 58.7 53.6 96.3
Goldcrest 2018 Sample 4 49.6 61.1 69.7 98.1 94.9 95.5 97.2 83.0 76.3 74.9 96.8
Average Colomac 2018 44.3 49.8 59.4 95.0 93.1 91.9 97.0 74.7 71.4 65.4 97.1
Colomac 2017 High-Grade 57.5 34.3 N.A 94.6 93.5 90.7 96.4 77.6 74.7 74.9 98.0
Colomac Master Composite 2016 81.8 N.A N.A 94.9 94.1 95.5 96.4 65.4 74.1 76.3 96.5

*Headers identified as “Column Cyanide”, refers to the Column Cyanidation test, “Whole Ore Cyanide”, refers to the Whole Ore Cyanidation test, and “Gravity + Cyanide”, refers to the Gravity + Cyanidation test.

Notes:

1. Samples ran from 206 up to 213 days

 

METALLURGICAL FINDINGS TO-DATE

 

Preliminary metallurgical testing programs were conducted on composite samples collected from annual Colomac site visits since 2016, to confirm the deposit’s amenability to conventional mineral processing flowsheets including gravity concentration, cyanidation and flotation. A comparison of gold recoveries from these different process routes including Bottle Roll and Column Leaching, are summarized in Table 3 above.

Test results are summarized chronologically as tabulated in Table 3.

  1. Gravity Concentration:

All Colomac samples responded well to gravity concentration:

  • Colomac (2019): yielding gravity rougher concentrates containing on average 70.7% of the gold in 3.6% of the feed mass. Upgrading of the rougher gravity concentrates by panning produced cleaner concentrates averaging 36.6% gold recovery in 0.09% of feed mass.
  • Colomac (2018): yielding gravity rougher concentrates containing on average 70.5% of the gold in 3.4% of the feed mass. Upgrading of the rougher gravity concentrates by panning produced cleaner concentrates averaging 40.6% gold recovery in 0.08% of feed mass.
  • High Grade (2017): yielding gravity rougher concentrates containing on average 75.7% of the gold in 3.8% of the feed mass. Upgrading of the rougher gravity concentrates by panning produced cleaner concentrates averaging 45.9% gold recovery in 0.12% of feed mass.
  • Master Composite (2016): yielding gravity rougher concentrates containing on average 71.9% of the gold in 3.4% of the feed mass. Upgrading of the rougher gravity concentrates by panning produced cleaner concentrates averaging 34.7% gold recovery in 0.09% of feed mass.

2. Whole Ore Cyanidation:

Seventy-two hours baseline cyanidation test results conducted on P80 150 µm ground whole-ore samples at 40% solids in 1.0 g/L NaCN. All Colomac samples responded well as follows:

Colomac (2019): yielding an average gold recovery of 93.6% at an average cyanide and lime consumption of 1.7 kg/t and 0.33 kg/t respectively;

  • Colomac (2018): yielding an average gold recovery of 96.9% at an average cyanide consumption of 1.62 kg/t and 0.13 kg/t lime respectively;
  • High Grade (2017): yielding a gold recovery of 96.4% at an average cyanide consumption of 1.86 kg/t and 0.26 kg/t lime respectively;
  • Master Composite (2016): yielding a gold recovery of 96.9% (also in 72 hours) at an average cyanide consumption of 1.73 kg/t and 0.24 kg/t lime respectively.

3. Bottle roll leach of half inch (½"): 

Colomac bottle roll leach test results are summarized as follows:

  • Colomac (2019): Bottle roll leaching of half inch (½") crushed materials for 10 days resulted in 46.1% gold extraction averagely;
  • Colomac (2018): Bottle roll leaching of ½" crushed materials for 10 days resulted in 44.3% gold extraction averagely;
  • High Grade (2017): Bottle roll leaching of ½" crushed materials for 10 days resulted in 57.5 % gold extraction averagely;
  • Master Composite (2016): Bottle roll leaching of ½" crushed materials for 10 days resulted in 81.8% gold extraction averagely.

4. Column Cyanide Leach of half inch (½"):

Colomac column leach test results are summarized as follows:

  • Colomac (2019): Gold extractions from 107-day column leaching of ½" crushed samples varied from 21.30% (2019 MET-4) to 66.10% (2019 MET-1), averaging 47.80%;
  • Colomac (2018): The test results showed gold extractions varying from 46.10% (Colomac 2018 Sample 3) to 61.10% (Gold Crest 2018 Sample 4) in 107 days. Further cyanidation resulted in final gold extractions varying from 54.90% (Colomac 2018 Sample 3) to 69.70% (Gold Crest 2018 Sample 4) in 200-plus days;
  • High Grade (2017): The test results showed gold recovery of 34.3% in 107 days with a residue grade of 3.15 gpt Au.

5. Sulphide Flotation:

Flotation was proven effective for all Colomac samples at grind sizes ranging from 75 µm to 150 µm as summarized below:

  • Colomac (2019): 87.6% of gold was recovered on average into around 4.8% of feed mass;
  • Colomac (2018): 93.3% of gold was recovered into around 9.0% of feed mass;
  • High Grade (2017): 92.9% of gold was recovered into around 6.8% of feed mass;
  • Master Composite (2016): 94.8% of gold was recovered into around 7.4% of feed mass.

6. Gravity + Cyanidation:

A combination of gravity pre-concentration followed by cyanidation of gravity tailings at P80 105 µm grind was proven effective for all Colomac samples:

  • Colomac (2019): achieved gold recovery of 95.1%;
  • Colomac (2018): achieved gold recovery of 97.2%;
  • High Grade (2017): achieved gold recovery of 98.0%;
  • Master Composite (2016): achieved gold recovery of 96.4%.

 

FUTURE TESTING

 

Preliminary testwork indicates that the Colomac deposit is amenable to all standard recovery technologies, with no adverse materials detected. These preliminary metallurgical results indicate that a standard SAG ball mill grinding circuit with or without gravity concentrators on cyclone underflows, and followed by a gravity concentrate leach (if applicable), and a cyanide leach circuit on the resultant final ground product, would be the best process options to consider for recovering gold from Colomac.

At this time, no further testing is contemplated. Going forward, a preliminary economic analysis of the flowsheet alternatives would be required to conclusively determine the CAPEX/OPEX for each flowsheet considered. Such a study would allow for a more focused metallurgical test program to be developed for testing samples from future sampling campaigns. Such studies may contemplate broadening future sampling to include other satellite gold zones and other zones to depth within the mineralized sills, with the main objective to confirm that the metallurgical responses observed so far will apply over a broader range of head grades, zone locations, and depths within the deposit.

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