AIG-ADIA Drilling for Geology seminar
1/8/2014
Drilling data inputs to Mineral Resources – The
importance of good systems and procedures
AMC Consultants Pty Ltd
Mark Berry, Principal Geologist
Questions to consider
•
•
Why drill?
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To explore and discover, then if successful:
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To define, quantify, characterise, and classify
What are the goals?
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To generate an estimate of mineral resources
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To convert mineral resources to ore reserves
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To support the decision to build a new mine, or
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To support the continued operation of an existing mine
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AIG-ADIA Drilling for Geology seminar
1/8/2014
JORC Code definition: Mineral Resources
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“A concentration or occurrence of solid material of economic
interest in or on the Earth’s crust in such form, grade (or quality),
and quantity that there are reasonable prospects for eventual
economic extraction”.
•
“The location, quantity, grade (or quality), continuity and other
geological characteristics of a Mineral Resource are known,
estimated, or interpreted from specific geological evidence and
knowledge, including sampling”.
“Mineral Resources are subdivided, in order of increasing
geological confidence, into Inferred, Indicated, and Measured
categories”.
•
Taken from the Australasian Code for reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code, 2012)
JORC Code definition: Ore Reserves
•
•
•
“The economically mineable part of a Measured and/or Indicated
Mineral Resource”.
Includes diluting materials and allowances for losses, which might
occur when the material is mined or extracted, and is defined by
studies at pre-feasibility or feasibility level as appropriate that
include application of Modifying Factors. Such studies demonstrate
that, at the time of reporting, extraction could reasonably be
justified.
Two categories: Probable, Proved.
Taken from the Australasian Code for reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code, 2012)
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AIG-ADIA Drilling for Geology seminar
1/8/2014
2012 JORC Code: Relationship between Exploration
Results, Mineral Resources, and Ore Reserves
Taken from the Australasian Code for reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code, 2012)
For many projects, direct observations based on
drillholes comprise between 0.0001% to 0.001%
of the volume of a mineral deposit
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Drilling data inputs to Mineral Resources:
What information is collected
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•
Location – collar and downhole
Geology
–
–
–
–
–
•
•
•
Lithology
Weathering
Alteration
Structure
Mineralisation
Geochemistry
Geotechnical data
Geophysics
Drilling data inputs to Mineral Resources :
How do we know it is of good quality?
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Systems, standard operating procedures and operating practices
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Observation skills
Data recording methodology
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Data validation processes
Quality assurance and quality control (QA/QC)
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Diamond drilling: Some specific issues
•
Recovery
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Logging and sampling protocol
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While diamond drilling is generally thought of
as producing a better representation of what
is in the ground, obtaining a representative
sample for analysis can be challenging in
some geological environments.
Case
study:
Coal
drilling
Drilling a
highly sheared
coal deposit
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Case
study
Drilling method
(coring)
Case
study
Example of
drill core
recovered
from drilling
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Case study: Minerals drilling
While diamond drilling is generally thought of as producing a better
representation of what is in the ground, obtaining a representative sample
for analysis can be challenging in some geological environments.
Core photograph
of friable vein with
sulphides washed
out and also lost
to tray
Example of core photograph illustrating friable material with sulphides lost
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Case study
Case study:
Recovery
issues
Recovery and core integrity
improve markedly outside
mineralisation, as shown on
the next slide.
Case study
Recorded recovery: waste vs ore
FROM
TO
Drilled length
Measured core length
% Recovery
Recovery
HOLENO
HOLENO
160.9
162.45
1.55
1.55
100
100
Comments
HOLENO
162.45
163.9
1.45
1.45
100
100
HOLENO
163.9
165.4
1.5
1.5
100
100
HOLENO
165.4
166.9
1.5
1.5
100
100
HOLENO
166.9
168.45
1.55
1.55
100
100
HOLENO
168.45
169.9
1.45
1.45
100
100
HOLENO
169.9
171.4
1.5
1.55
103.33
103.33
HOLENO
171.4
172.8
1.4
1.4
100
100
HOLENO
172.8
174.35
1.55
1.55
100
100
HOLENO
174.35
175.8
1.45
1.45
100
100
HOLENO
175.8
177.2
1.4
0.8
57.14
57.14
HOLENO
177.2
177.8
0.6
0.4
66.67
66.67
Ore Zone
HOLENO
177.8
178.6
0.8
0.8
100
100
Ore Zone
Ore Zone
HOLENO
178.6
178.8
0.2
0.2
100
100
Ore Zone
HOLENO
178.8
179.4
0.6
0.55
91.67
91.67
Ore Zone
HOLENO
179.4
180.1
0.7
0.7
100
100
Ore Zone
HOLENO
180.1
180.5
0.4
0.35
87.5
87.5
Ore Zone
HOLENO
180.5
180.9
0.4
0.4
100
100
Ore Zone
HOLENO
180.9
181.3
0.4
0.25
62.5
62.5
Ore Zone
HOLENO
181.3
181.95
0.65
0.65
100
100
Ore Zone
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Case study:
Core sampling
protocols
This is mineralised
This is waste
The geologist must decide
whether to sample using
geological contacts or on
regular intervals that ignore the
geology
Chip drilling: Some specific issues
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Sampling procedures
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Moisture
Recovery
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Drill cuttings are often sub-sampled at site.
This is a key source of potential problems for
mineral resource estimates
Often, the total weight and/or moisture of the
sample interval is not recorded.
•
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Sub-sampling options
Non-biased samples: Riffle splitter design
and usage
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Riffle splitters should follow these rules:
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At least 12 chutes.
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Feed centrally with a well-designed scoop and uniform distribution over
the chutes.
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Feed slowly.
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Even number of chutes.
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No sloping hopper to overfeed the end chutes.
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The size of the chutes should be matched to the size of the particles.
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Non-biased samples: riffle splitter
Potential for biased samples: Poor designs
and/or practices
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Cleaning the sub-sampling system
Sub-sampling: Dealing with wet samples
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Weighing samples at the drill site
Case study: These are all 0.5 m intervals.
Why are they different and consequences?
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Case study: Statistical analysis of recovery
Cu
grade
Relationship between diamond drill core recovery and copper grade. This data set
suggests there is no systematic bias in grade linked to recovery.
Case study: Mineral Resource estimation and
impact of core recovery assumptions
Example showing the effect on mineral resources of different assumptions about
the grade of drill core not recovered.
Resource model re-estimated assuming zero grade for core loss instead of average intercept grade
Assuming average intercept grade
Lode
Tonnes
Au (g/t)
Assuming zero grade
Au oz
Tonnes
Au (g/t)
Au oz
X
165,300
12.1
64,300
165,300
10.6
56,300
Y
52,100
22.3
37,400
52,100
19.0
31,800
Z
27,300
10.7
9,400
27,300
10.3
9,000
Total
244,700
14.4
106,600
244,700
12.6
92,600
Percentage difference in ounces
13.1%
This emphasises why auditors will focus on core and sample recovery, particularly
in certain mineralisation styles.
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AIG-ADIA Drilling for Geology seminar
1/8/2014
Conclusions
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•
For many deposits, drillhole data is the primary data input to the
estimation of mineral resources and ore reserves.
Good systems, procedures and practices are required to ensure
drillhole data is well collected, of high quality, and fit for purpose.
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QA/QC processes must cover all drillhole data inputs to mineral
resources and ore reserves, not just analytical data.
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Good documentation and data management is essential, as there
must be a good audit trail.
These are all prerequisites for a good mineral resource estimate.
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•
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