Estimacion puntual, propiedades de las estimaciones; estimacion por intervalos de confianza
3 estimacion de recursos jm rendu
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Transcript of 3 estimacion de recursos jm rendu
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21 Junio 2010
Estimación de Recursos y Reservas:Problemas Frecuentes
Jean-Michel Rendu
Executive Consultant
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General Outline
Estimation Process
Drilling, Sampling, and Sample Preparation
Mining, Metallurgical and Economic
Factors
The Human Factor and Quality Control
More Challenges for Competent Person
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Relationship between Exploration Results, Mineral Resources and Mineral Reserves
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EXPLORATION
RESULTS
MINERAL RESOURCES
MINERAL RESERVES
INFERRED
INDICATED PROBABLE
Increasing level of
geoscientific knowledge
and confidence
MEASURED PROVEN
Consideration of mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors
(the "Modifying Factors")
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Estimation Process: Resources
Sampling and
Deposit
Characterization
Deposit
Modeling
Need for More
Geologic
Information
Preliminary
Technical and
Economic
Parameters
Resource Estimation
Reasonable Prospects for
Eventual Economic
Extraction?
Resource
Reporting
Abandon or
Sell Project
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Estimation Process: Reserves
Resource
Model
Need for more geologic,
metallurgical, geotechnical,
environmental information
Modifying Factors: Mining,
metallurgical, economic, marketing,
legal, environmental, social and
governmental factors
Mine Design
and
Production
Scheduling
Reserve
ReportingCashflow
and Risk
Analysis
Need for more economic,
marketing, legal, social,
governmental information
Abandon or
Sell Project
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SAMPLING METHODS
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Exploration and Data CollectionDrill Hole Sampling
•Core Holes
•Normal (Direct) Circulation
•Reverse Circulation
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CORE HOLES
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High Core Recovery = No Grade Bias?
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Problems with Core Sampling
•Poor Recovery
•Selective Recovery
•Loss of Fines during: Core Washing Core Cutting Core Splitting Crushing and Pulverizing
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Is a core sample representative of what is in the ground?
•What percentage recovery is acceptable?
•Is 98% acceptable?• Recovered: 98% at 0.30% Cu• Lost: 2% at 3% CuShould be: 100% at 0.35% Cu (+18%)
• Recovered: 98% at 0.30% Cu• Lost: 2% at 0% CuShould be: 100% at 0.29% Cu (-2%)
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Loss of Fines During Core SplittingWhere does it Happen? (Guillotine; Saw)
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Size Distribution in Porphyry Copper Deposit
Rock Type 1
0
10
20
30
40
3/4" 1/2" 1/4" 10# 32# 65# - 65#
Weig
ht
%
%C
u
Size fraction
%Cu Weight %
Rock Type 2
0
10
20
30
40
3/4" 1/2" 1/4" 10# 32# 65# - 65#
Weig
ht
%
%C
u
Size fraction
%Cu Weight %
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Core Splitting Problem
•Broken core in box
•Splitting method 1
•Splitting method 2
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Comparison of Blast Hole and Drill Hole Grades•Old Method:
Take broken material from top of core box
Fines are left inside box
Blast holes are much higher grade than core samples
•New Method: Split core evenly Blast holes are
slightly higher grade than core samples
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Old Method
New Method
0,00
0,10
0,20
0,30
0,0 0,5 1,0 1,5 2,0
Bla
st
Ho
le
-D
rill
Ho
le G
rad
e
Drill Hole Grade
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Normal and Reverse
Circulation
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Problems with Normal Circulation Rotary Drilling
•Is Normal (Direct) Circulatrion Rotary Drilling as “Bad” as Claimed? YES!
•Water is the Enemy, whether Injected or from Underground
•Can it Ever be Used? Yes, to Determine Whether there is
Mineralization But Not to Characterize Mineralization
(Depth, Thickness, Grade)
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Problems with
Reverse Circulation Drilling
•Is Reverse Circulation Really Much Better than Normal Circulation?
Usually Yes Bypass Contamination Face Sampling Bits Water is the Enemy, whether Injected
or from the Ground
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Problems with Reverse Circulation Drilling
Face Sampling Bits
Water is the Enemy
Water inflow can
result in sample
contamination
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Problems with Reverse Circulation Drilling
•Sample Splitting
Too Much Water Bag Overflowing Loss of Fines Use of Micropores Speed or Quality?
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SAMPLING IN
UNDERGROUND
MINES
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Some Underground Sampling Methods
•Core Samples: Location, Orientation, Deflection
•Blast Hole Samples: Water, Sample Collection
•Chip Samples
•Channel Samples
•Muck Samples
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Channel Sampling
How do I Sample This?
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Chip Sampling
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Channel SamplingChannel Sampling
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Chip SamplingSampling of
Broken Muck
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Stockpile Sampling:
Is this a Good Sample?
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Compare Size of Scoop with Size of Material
Sampled
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Sampling of Individual Loads
Sample (10 kg) Loader (1 tonne)
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Comparison of Bucket and Drum Samples
30
0%
5%
10%
15%
20%
25%
30%
4 2 1 1/2 1/4 6 12 20 45 100
Weig
ht
%
Size Fraction (inch/mesh)
Size Distributions
DRUM SCOOP
4 2 1 1/2 1/4 6 12 20 45 100
Gold
Gra
de
Size Fraction (inch/mesh)
Grade Distributions
DRUM SCOOP
Material > 4
inches very
high grade
In Drum,
20% > 4 inches
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ESTIMATION OF MINERAL RESOURCES
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Deposit Modeling and Estimation of Mineral Resources
A Deposit Model is not a Resource
• A Resource must show Reasonable Prospects for Eventual Economic Extraction
• Technical, Economic and Other Assumptions must be Made, Albeit at a Preliminary Level.
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DEPOSIT MODEL AND MINING METHOD
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- Deposit Model and Mining Method -
•Different Models for Different Mining Methods
Open Pit or Underground
Bulk Mining or Selective Mining
High or Low Cutoff Grades
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DEPOSIT MODEL AND METALLURGICAL PROCESS
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- Deposit Model and Processing Method -
•Different Models for Different Processing Methods
Copper Oxide, Sulfide, Transition
Gold Cyanide Amenability
Mill Throughput, Power Consumption, Acid Consumption
Recovery
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What is a Representative
Geometallurgical Sample
•From Laboratory Test to Semi-Industrial Test to Full Scale Operation
Many Small Samples Few Large Samples According to Geology High Grade, Low Grade, Near Surface, At Depth
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Resource and Reserve Estimation
Economic Considerations
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Estimation of Mineral ReservesEconomic Analysis
•Which Commodity Price Should be Used?
Who Decides and Who Signs the Competent Person’s Report?
Beware of External Pressures• Use a High Price to Report Higher Reserves• Use a Low Price for Tax or Other Reasons
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THE HUMAN FACTOR
ESTIMATION IS BY PEOPLE FOR PEOPLE
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Resource Estimation Quality Control
•Maintain Effective Communications with:
Those Generating the Data (Geologist, Driller, Laboratory, Surveyor, etc.)
Those who will Use the Model (Mining Engineer, Metallurgist, Project Engineer, Environmentalist, Management)
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Resource Estimation Quality Control
•Have Regular Meetings throughout the Entire Modeling Process with Detailed Review at Beginning and End
•Ask for and Compare Geologic Interpretations from Different Geologists
•Use More than One Modeling Method. Compare Results. Explain Differences
•Consider Outside Reviews.
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Crocodiles Lurking in the Murky Waters
- Warnings to Competent Person -
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Challenges for the Competent Person
•Corporate Objectives:
Raise Funds for Continuous Project Development
Grow the Company by Bringing a New Mine to Production
Sell the Deposit
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Challenges for the Competent Person
•Competent Person Objectives: To Do the Best Technical and Ethical Job he/she
Knows How to Do To Answer Management’s Questions The Answer May Differ from Management’s
Expectations
•Maximizing Personal Bonus (or the Boss’s Bonus) must NOT be a Competent Person’s Objective.
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Blast Hole Sampling Methods
1 - Rocket Sampler
•Where to take the sample? Too close: underestimation Too far: Overestimation
•How deep should the sampler go?
•What should be the diameter of the sampler? Too large: hard to push through Too small: not representative
•Now many samples per blast hole?
Rocket Sampler
FINAL OBJECTIVE:
A TECHNICALLY AND
ECONOMICALLY SUCCESSFUL
MINING OPERATION
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THE
END