1. BULK SAMPLING OF MINERAL
PROJECTS
PDAC Convention 2015
Session: The Economic Implications of Grade
Tuesday, March 3, 2015
Henrik Thalenhorst
Strathcona Mineral Services Limited
Meliadine Project 2008
2. PRESENTATION OUTLINE
• Purposes of bulk sampling
• What constitutes a bulk sample?
• Examples & outcomes
• How to treat a bulk sample
• Field sampling and laboratory protocols
• Quality control
• Example – Meliadine Project, Nunavut
• Conclusions
4. PURPOSES OF BULK SAMPLING
1. Verification of resources/reserves. Mineral Projects have failed because of
resource/reserve issues. Actual example from Northern Ontario:
• Determination/confirmation of predicted grade, particularly for nuggety
mineralization (Au, Sn, Rare Earths, Ta and Nb, diamonds)
• First-hand look at the geology and controls on mineralization, grade continuity in
general and distribution of high grades in particular. Confirmation of ore geometry
(tonnage estimate)
• Testing of grade-control sampling procedures
Tonnes Au (g/t) Au (oz)
Year-End 1 Reserves 790 000 6.5 165 000
Production Years 2 to 4 340 000 4.4 47 000
Reserves Mined 43% 28%
5. PURPOSES OF BULK SAMPLING (cont’d)
• Because of the substantial costs, bulk sampling should be undertaken on
projects with a genuine chance of becoming a producing mine, i.e., late in
the evaluation stage. But before feasibility study! Underground openings
need to be laid out so they can be integrated into a future mining
operation.
2. Collection of large samples for pilot testing
3. Sampling of ore sold to, or treated at, a custom facility
7. WHAT CONSTITUTES A BULK SAMPLE?
• Bulk” - Considering the Sample Ratio
Typical drill program:
One in one million
(½ NQ core at 30-metre spacing)
Typical bulk sampling program:
One in fifty
(4 by 5 m drift at 30-metre spacing)
Bulk sample provides much improved
sample ratio and opportunity to observe
geology, alteration and structure
8. WHAT CONSTITUTES A BULK SAMPLE? (cont’d)
• “Bulk” – Considering the Program Size
Bulk sample should comprise from 0.1% to 1% of the resource tonnage
(for underground projects), typically 10 000 to 30 000 tonnes
• “Sample” – Representative
A bulk sample should be representative of the deposit geology and
mineralization and should concentrate on the pay-back tonnage
10. EXAMPLES & OUTCOMES
Project Location Commodity Mining Tonnes Outcome
Brucejack
British
Columbia
Au (Ag) U/G 10 300 Updated Feasibility Study
Cameron Lake Ontario Au U/G 12 000 Project shelved
Farley Lake Manitoba Au O/P 10 000 Mined 1996 to 1999; 1.7 Mt @ 3.9 g/t Au
Meliadine Nunavut Au U/G 33 700 Being developed. Reserves 12 Mt @ 7.4 g/t Au
Nalunaq Greenland Au U/G 23 200 Mined 2004 -2009, 2011/13; 0.7 Mt @ 15 g/t Au
Lockerby
McCreedy West
Minera Dayton Chile Au O/P Determination of heap-leach feed grade
Fort Knox Alaska Au O/P 38 100 Higher RC grades verified; project sold to Amax
Thor Lake NWT Be, RE U/G 750 Flowsheet developed
Verification of Deposit Geology & Grade Estimate
Determination of Mill Head Grades
Resolution of Grade Difference RC/DDH
Mining of Representative Sample for Pilot Testing
Complete
production
tonnage
Results accepted for metal payment
Ni-Cu-PGM-
Au
U/GSudbury
11. PRESENTATION OUTLINE
• Purposes of bulk sampling
• What constitutes a bulk sample?
• Examples & outcomes
• How to treat a bulk sample
12. HOW T0 TREAT A BULK SAMPLE
• USING A SAMPLE TOWER TO PRODUCE SUB-SAMPLES
• Advantages – Usable in remote locations
Allows grade determination for small tonnages
• Disadvantages – Smaller sample ratio and therefore larger sample
error
• TREATMENT IN A RECOVERY PLANT
• Advantages – One-to-one sample ratio, definitive grade
determination
Recovery of (part of) project cost
Establish/verify metallurgical balance
• Disadvantages – Geological detail lost (requires batching of larger
sub-samples to establish mill balance - typically
one week at mill capacity)
• IDEAL – SAMPLE TOWER FOLLOWED BY RECOVERY PLANT
13. PRESENTATION OUTLINE
• Purposes of bulk sampling
• What constitutes a bulk sample?
• Examples & outcomes
• How to treat a bulk sample
• Field sampling and laboratory protocols
14. SUB-SAMPLING WITH A SAMPLE TOWER
Input 100
tonnes
Output 2 x 30 kg Field
Samples
16. SAMPLE PREPARATION AND ASSAYING PROTOCOL
Input Field Sample of 30 kg
Output 2 000-gram Metallics Screen Assay
17. PRESENTATION OUTLINE
• Purposes of bulk sampling
• What constitutes a bulk sample?
• Examples & outcomes
• How to treat a bulk sample
• Field sampling and laboratory protocols
• Quality control
18. QUALITY CONTROL
• Tracking of individual blasted samples to prevent cross-
contamination
• Determination of all masses sampled and produced to monitor
sample ratio
• Systematic granulometry checks
• Insertion of certified reference materials to monitor assay results
• Systematic duplicate sampling and assaying for all sub-sampling
steps
19. PRESENTATION OUTLINE
• Purposes of bulk sampling
• What constitutes a bulk sample?
• Examples & outcomes
• How to treat a bulk sample
• Typical field sampling and laboratory protocols
• Quality control
• Example – Meliadine Project, Nunavut
24. Geology
• Neo-Archaean rocks (mafic volcanics, turbididic sediments
including iron formation bands, felsic pyroclastics, gabbro
sills) of the Rankin Inlet Greenstone Belt
• Poly-deformed during the late Archaean and the Proterozoic
• At Meliadine, the rocks strike east-west and dip to the north
(overturned at 65°)
25. Gold Mineralization
• Gold mineralization within a stratigraphic package 50 to 100 m
thick structurally above the faulted contact between mafic
volcanics and turbidite sediments with intercalated bands of iron
formation
• Three locations of interest:
• Sulfidized and mineralized iron formation = “1100” Lode;
• Boudinaged quartz vein at the faulted contact between
volcanics and sediments = “1000” Lode; and
• Fifty-metre interval between the two lodes is discontinuously
mineralized and is of interest for possible open-pit mining
33. Grade Continuity
Quartz Vein (1000 Lode)
Grade distribution fairly
erratic requiring tight
drill-hole spacing
Mineralized Iron
Formation (1100 Lode)
Grade distribution more
continuous
High grades at west end
coincident with
secondary quartz-vein
development
34. Reliability of Meliadine Bulk Sample Results
23 Number of Pairs 343
6 Percent of total 81
10.2 Average gold grade original samples 8.0
10.3 Average gold grade repeat samples 8.1
35. Gold-Grade Populations and Capping Levels
Chip-panel and channel samples, 2008 program
Lithology
Number
of
Samples
Original Assays Top Cut (Cap) Capped Assays
Gold
Grade
(g/t)
SD
(g/t)
CV
Gold Grade
(g/t)
Percentile
Gold
Grade
(g/t)
SD
(g/t)
CV
Sediments outside Lode 298 0.9 2.8 3.1 5 96 0.6 1.2 2.0
Sediments within Lode 354 1.9 5.8 3.1 10 95 1.2 2.4 1.9
Iron Formation, “low-grade” 206 4.7 7.0 1.5 20 95 4.3 5.6 1.3
Iron Formation, “high-grade” 482 17.5 16.8 1.0 90 99.8 17.4 16.3 0.9
Quartz Veins 1100 56 31.6 22.7 0.7 90 98 31.1 21.0 0.7
Quartz Vein 1000 336 33.2 46.4 1.4 165 98 31.1 36.9 1.2
Sediments with erratic gold-grade populations (high CV) require significant capping
Mineralized units with “well-behaved” gold-grade populations (low CV) require less
severe capping
Statistical evaluation of all gold-grade populations inside a lode is the wrong
approach
Average gold grades 2008: bulk sample 8.8 g/t; capped channels 9.0 g/t; capped
chip panels: 10.9 g/t
36. Block-Model Predictions and Bulk Sample Results
Resource Model Bulk Sample
DDHs
Spacing
(metres)
Tonnes Au (g/t)
Au
(ounces)
Tonnes Au (g/t)
Au
(ounces)
Mineralized Iron Formation (1100 Lode)
Snowden June
2008
20 15 to 30 6 960 8.6 1 924 6 670 9.1 1 960
AEM 2011 40 15 to 20 9 207 10.9 3 231 8 812 11.6 3 279
Boudinaged Quartz Vein (1000 Lode)
Snowden June
2008
11 10 to 50 4 655 27.3 4 114 4 262 20.9 2 872
AEM 2011 43 10 to 20 8 375 15.1 4 068 7 048 15.9 3 596
1100 Lode – Relatively easy to estimate due to steady width and reasonable grade continuity
1000 Lode – Difficult to estimate due to changing width (boudinaged) and poor grade continuity
37. PRESENTATION OUTLINE
• Purposes of bulk sampling
• What constitutes a bulk sample?
• Examples & outcomes
• How to treat a bulk sample
• Field sampling and laboratory protocols
• Quality control
• Example – Meliadine Project, Nunavut
• Conclusions
38. CONCLUSIONS
• Bulk Sampling provides information crucial for a feasibility
study otherwise not obtainable
(Gold) grade verification, including capping levels
Physical and grade continuity (variogram) verification
Determination of drill-hole spacing required for resource
estimation
Mining conditions (water) and geotechnical information
Large-scale samples for metallurgical testing
• While expensive, bulk sampling is cheaper (and better for
one’s reputation) than a failed mining investment
• Positive side effects include shortening of pre-production
development once a production decision has been made;
availability of initial crushed tonnage for milling
