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Advanced reverse circulation drilling as a replacement
to blast hole sampling: increasing short term planning
profitability at Cerro Colorado copper mine
Eduardo J. Magri, Julin M. Ortiz (Universidad de Chile)
Rodrigo Moya, Andrs Salazar (Compaa Minera Cerro Colorado)
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Outline
Introduction Cerro Colorado Operation
Cerro Colorado Geology
Methodology
Results Conclusions
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Introduction
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Motivation
Cerro Colorado is a producing open pit mine (~55 ktpd of ore)
This presentation is an attempt to evaluate the economic impact ofreplacing blast hole sampling by advanced RC drilling for shortterm planning, this includes:
Impact of reducing the sampling errors (precision and bias)
Definition of the spacing of the advanced drilling grid
Impact of the grade control methodology and estimation parameters
Impact of the misclassification of geological units (clays)
The approach is based on building conditional simulations ofgrade distributions, simulating the sampling and grade controlprocedures, and evaluating the resulting profit.
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Cerro Colorado Operation
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Cerro Colorado is a porphyry copper deposit located in the Tarapaca Region of Chile
(lat. 2002'S, long. 6915'W), 120 km East of the city of Iquique, at an elevation of2600 m
It belongs to a belt of porphyry copper deposits in the Central Andes
The operation was started by Ro Algom Ltd. in 1994.
Cerro Colorado is an operation of BHP Billiton Pampa Norte, a business unit that alsoincludes Minera Spence located in the Antofagasta Region.
Mining is done by open pit, extracting oxides and sulphides
Background information
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Mining includes oxides and secondary enrichment Ore throughput: 52-55 Ktpd & 19.2 Mtpa
Rock extraction / Stripping ratio: 90 Mtpa / 1: 3.7
Ore Process: Heap leaching and SX-EW Ore type: oxide, secondary sulphide and MSH (mixed of secondary sulphide
& hypogene copper). Ore mineralogy: chrysocolla, brochantite, chalcocite and covellite.
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Metallurgical recovery: 69% Geometallurgical short term planning model considers blending of different clays
Production FY11: 90.5 Kt of Cu Cathodes
Plant capacity (design): 130 Ktpy of Cu Cathodes
Reserves (Probable + Proven): 167.9 Mt @ 0.65% TCu & 0.36% SCu. (c.o.g: 0.3%TCu)
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Background information
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Cerro Colorado Geology
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Cerro Colorado 53 Ma
MetallogenicsBelts
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Regional Geology
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Cerro Colorado Geology
Cerro Colorado is a porphyry copper deposit located in the north-south metallogenic belt, dated from the paleocene-inferior eocene.
The regional geology consists of a andesitic volcanoclasticsequence, from the Cretaceous (Cerro Empexa formation), intrudedby tonalitic and quartz-monzonitic fases from the lower tertiary(porphyries and breccias). These units are covered by volcanic andsedimentary deposits from the Pliocene (ignimbrites and gravel fromthe Altos de Pica formation).
The copper mineralization is related to intrusive events through a
trend NE to EW, in a series of sub horizontal bodies (West sector)and more complex units (East sector) of copper oxides, supergenecopper sulphides and primary copper sulphides in depth. Theextension is approximately 2.3 km in length in the EW direction and1.5 km in the NS direction.
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Cerro Colorado Geology
MineralizationAltos de Pica
60m av-
Lch: 25-75m thick.
CuS/CuT > 0.5 25-125 m thick.
Cu leached >=80 % 10-100 m thick.
Cu leached: 50 79 %
Cu leached< 50 %
(Br-Cr)
(Cs-Cv)
(Cs-Cv-Cpy)
(Cpy>>Cs-Cv)
Gravel - Ignimbrites
Leach cap
Cu Oxides
Supergene sulphides
Mixt sulphides
Primary sulphides
Waste
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Cerro Colorado Geology
Lithological units
Porphyry
Breccia
Andesite
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Cerro Colorado Geology
Lithological units
Porphyry
Breccia
Andesite
Gravel
Ignimbrite
CerroColorado
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Cerro Colorado Geology
Mineralization units
Cerro ColoradoSulphidesOxides
Hypogene MSH
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Cerro Colorado Geology
Alteration units
Cerro Colorado
Potassic Alt.North sector
PhyllicAlt.
Potassic Alt.Phase 5 low
grade
Topography Phase 7Extreme
north sector
Phyllic chloriticAlt.In deeper levels
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Cerro Colorado Geology
SE view of current pit Blue line A-A: Orientation of sections
A
A
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Cerro Colorado Geology
Ore type units
2000 msnm
2600 msnm
CURRENTPIT
CURRENT
PIT
HYPOGENE
OXIDES
LEACHED
CAP
SECONDARYSULPHIDES
TRANSITIONALSULPHIDES
GRAVEL
A A
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Cerro Colorado Geology
Lithological units
2600 msnm
2000 msnm
CURRENT
PITCURRENTPIT
PORPHYRY
IGNEOUSBRECCIA
IGNEOUS
BRECCIA
PORPHYRYIGNIMBRITE
IGNIMBRIT
EGRAVEL
A A
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Cerro Colorado Geology
Clay units (ARC)
CURRENT PIT
CURRENT PIT
2000 msnm
2600 msnm
ARC9
ARC1
ARC7
ARC7
ARC7
ARC4
ARC
2
ARC1
ARC
6
ARC8
ARC8
ARC
1
ARC7
ARC8
ARC1
ARC Description
1-2-3-9 Detrimental clays
4-5 Clays with moderate effect
6-7-8 Clays that do not affect the process
A A
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Cerro Colorado Geology
Alteration units
CURRENT PIT
CURRENT PIT
2600 msnm
2000 msnm
PHYLLIC
PHYLLIC
PHYLLIC
POTASSIC
POTASSIC
CHLORITIC
ARGILLIC
GRAVELS
CHLORITIC
A A
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Methodology
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Goals
Evaluate the effect of: Information quality:
blast hole sampling error (current) vs advanced RC drilling and sampling(proposed)
Effect of systematic bias
Effect of improving the accuracy of geologcial interpretation
Information quantity:
Blast hole spacing (current) vs different advanced drilling grid spacings(proposed)
Estimation method:
Inverse distance squared weighting (current) vs Ordinary Kriging (proposed)
Estimation parameters
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Methodology
Inputs: Long term planning model UGCUT, Density, ARC (clays)
Drill hole 10.0 m composite database Total copper (CuT), soluble copper (CuS) Solubility ratio (RSol)
Duplicate blast hole data
Total copper (CuT), soluble copper (CuS) Economic and operational parameters (costs, commodity price, W/O ratio,
recovery functions, acid consumption, etc.)
Considerations: Long term geological attributes are fixed (UGCUT, Density, ARC)
Drill hole data are used to infer statistical distribution of the variables and
variograms to be used in simulation Sampling errors for CuT, CuS are inferred from duplicate blast hole data
Output: Simulated realizations at point support of CuT, RSol CuS (dense
spacing)
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Methodology
Definition of the study volume East 71700-73900 2200 m
North 82900-84100 1200 m
Elevation 2270-2530 260 m
Geological units and clay units:
UGCUT Description
2 Oxides
3 Oxides
4 Sulphides
5 Sulphides
ARC Description
1-2-3-9 Detrimental clays
4-5 Clays with moderate effect
6-7-8 Clays that do not affect the process
Long Term
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MethodologyLong Term
Model
Drill holedatabase
Blast holedatabase
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Methodology
Sampling errors: Calculated from duplicated blast hole data
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Duplicate blast hole data - CuS
Error = 24.3%
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Duplicate blast hole data CuS > 0.1%
Error = 15.0%
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Duplicate blast hole data - CuT
Error = 19.9%
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Duplicate blast hole data CuT > 0.1%
Error = 14.0%
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Duplicate data by range
Sampling errors by range of values
Range of grades
Mean Relative Error
(%)
CuS CuT
Average of duplicates > = 0.1% 15.02 13.97Average of duplicates > = 0.0 y < 0.1% 29.04 31.39
Average of duplicates > = 0.1 y < 0.2% 26.71 21.53
Average of duplicates > = 0.2 y < 0.3% 23.74 20.68
Average of duplicates > = 0.3 y < 0.5% 21.53 16.96
Average of duplicates > = 0.5 y < 0.8% 18.23 17.90Average of duplicates > = 0.8 y < 1.2% 22.43 18.54
All 24.34 19.94
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Methodology
1. Ten dense simulation models were builtCoordenate Number
of points
Size (m) Min Coord
(m)
Max Coord
(m)
Extension
(m)
X (East) 1100 2.0 71700.0 73900.0 2200.0
Y (North) 600 2.0 82900.0 84100.0 1200.0
Z (Elevation) 26 10.0 2270.0 2530.0 260.0
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Methodology
2. Block average represent the truthCoordenate Number
of points
Size (m) Min Coord
(m)
Max Coord
(m)
Extension
(m)
X (East) 1100 2.0 71700.0 73900.0 2200.0
Y (North) 600 2.0 82900.0 84100.0 1200.0
Z (Elevation) 26 10.0 2270.0 2530.0 260.0
Coordenate Number of
blocks
Size (m) Min Coord
(m)
Max Coord
(m)
Extension
(m)
X (East) 220 10.0 71700.0 73900.0 2200.0Y (North) 120 10.0 82900.0 84100.0 1200.0
Z (Elevation) 26 10.0 2270.0 2530.0 260.0
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Methodology
Correlations for pairs of variables
CuT vs CuS
= 0.4 0.9
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Methodology
Correlations for pairs of variables
CuT vs RSol
= -0.3 0.3
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Methodology
Correlations for pairs of variables
CuS vs RSol
= 0.4 0.5
The variableswith lowercorrelation are
CuT / RSol
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Methodology
Implementation details: Point simulation of CuT and RSol for each unit (UGCUT) with
hard boundaries. Models are combined by geological unit.
CuS can be deduced at point support from the simulated valuesof CuT and Rsol:
CuS = RSol x CuT
Block average over grades to block support simulations of
grades at block support No ratio is ever block averaged
Reblocked models represent the truth (10 cases), which areused for comparison purposes
M h d l
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Methodology
Point simulation is done by geological unit: Declustering / Transformation
Variogram modeling
Point conditional simulation
Validation: histogram / variogram reproduction
Declustereddistributions
Gaussiandistributions
M th d l
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Methodology
Variable Unit ModelSill
contributionRange 1 Range 2 Range 3
NS_CuT 2 +3
Rotation N45E/0 N45W/0 N0/-90
Nugget 0.15
Shperical 0.55 25.0 30.0 25.0
Shperical 0.30 350.0 230.0 115.0
NS_CuT 4
Rotation N45E/0 N45W/0 N0/-90
Nugget 0.15
Shperical 0.38 90.0 85.0 65.0
Shperical 0.47 680.0 530.0 95.0
NS_CuT 5
Rotation N0/0 N90E/0 N0/-90
Nugget 0.10
Shperical 0.40 95.0 90.0 100.0
Shperical 0.50 450.0 330.0 185.0
NS_RSol 2 +3
Rotation N0/0 N90E/0 N0/-90
Nugget 0.20
Shperical 0.35 40.0 40.0 35.0
Shperical 0.45 450.0 450.0 140.0
NS_RSol 4
Rotation N0/0 N90E/0 N0/-90
Nugget 0.20
Shperical 0.20 85.0 85.0 70.0
Shperical 0.60 630.0 630.0 95.0
NS_RSol 5
Rotation N0/0 N90E/0 N0/-90
Nugget 0.15
Shperical 0.35 90.0 90.0 130.0
Shperical 0.50 450.0 450.0 190.0
Variogrammodels
M th d l
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Methodology
Dense simulation CuT grades
M th d l
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Methodology
Block support simulation CuT grades
M th d l
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Methodology
3. Dense point simulations are sampled at different grids: 6 x 6, 8 x 8 (current blash hole grid), 10 x 10, 12 x 12, 14 x 14, 16 x 16,
18 x 18, and 20 x 20m
The exact simulated value represents a sample without error (or withnegligible RC error)
M th d l
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Methodology
Dense simulation CuT grades
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Methodology
Samples over a 20 x 20m grid, without error added CuT grades
M th d l
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Methodology
4. A Gaussian random error is simulated and added (or subtracted) tothe actual value:
14% error for CuT
15% error for CuS
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Methodology
Dense simulation CuT grades
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Methodology
Samples over a 20 x 20m grid, without error added CuT grades
Methodolog
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Methodology
Samples over a 20 x 20m grid, with error added CuT grades
Methodology
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Methodology
5. Grades are estimated over 10 x 10 x 10 m blocks: Input:
CuT and CuS samples without error for a given grid spacing
CuT and CuS samples with error added for a given grid
Estimation method:
Current short term estimation plan ID2 with search radii 12.5m horizontaland 5.0m vertical, 1/6 samples
Improved estimation plan ordinary kriging with search radii 30.0mhorizontal and 5.0m vertical, 4/16 samples
Requires variograms of blast hole grades for kriging
Methodology
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Methodology
Estimated block grades by ID2, samples withouterror added CuT grades
Methodology
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Methodology
Estimated block grades by kriging, sampleswithout error added CuT grades
Methodology
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Methodology
Estimated block grades by ID2, samples with erroradded CuT grades
Methodology
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Methodology
Estimated block grades by kriging, samples witherror added CuT grades
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Methodology
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Methodology
Methodology
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Methodology
Parameters required:
Recovery function
Acid consumption: function of CuS and recovery
Drilling, sample preparation and analysis costs Sample preparation and analysis = 10.0 (US$/sample)
RC drilling cost = 20.0 (US$/m)
Blast hole drilling cost = 14 (US$/m) incluides 1 m subdrill
UG CuT UG = Ox / Sulf ARC Recov (%)
2 o 3 Ox 1, 2, 3, 9 69
2 o 3 Ox 4, 5 72
2 o 3 Ox 6, 7, 8 80
4 o 5 Sulf 1, 2, 3, 9 64
4 o 5 Sulf 4, 5 67
4 o 5 Sulf 6, 7, 8 72
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Results
Results
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Results
Results
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Results
Main result
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Current situation:BH with error + ID2 1/6
Proposed situation:RC with low error + KR 4/16
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Blast hole gridNo extra drilling cost
Any other grid spacingrequires additional drilling cost
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Reducing the error requiresRC drilling cost
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Difference due to reduction ofgeological misclassification
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Sampling error reduction andreduction in geological
misclassification pays foradditional drilling cost
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Current situation:BH with error + ID2 1/6
Proposed situation:RC with low error + KR 4/16
Results
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Results
Sensitivities showed that: 5% systematic bias results in: 8-12 million dollars when inverse distance is used
0-1 million dollars when ordinary kriging is used
Copper price does not change the recommendation and improving thegeological knowledge (from 2 to 5% misclassification) is more relevant
RC drilling cost is an important parameter, as the additional drillingrequired when an advanced grid is used, may become very costly andovercome the profit made by better knowledge (either due to bettersamples or to better interpretation)
Fluctuations due to spatial variability (between realizations) are small
compared to those due to geological interpretation: Up to 4 million dollars when inverse distance is used
Up to 1 million dollars when kriging is used
Results
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Results
Losses are more significant when using inverse distance
Implementing ordinary kriging is simple for short term plan andreduces the conditional bias
Using more samples in the estimation improves the results
RC cost is significant and should be lowered as much as possible toincrease the profit
The use of an advanced drilling grid benefits the final result in twoaspects: A more careful sampling and sample preparation procedures may be
implemented
A more detailed and accurate interpretation of the geological attributes
of the blocks may result and input in advance in the short term plan The study showed that implementing an advanced drilling grid with a
spacing of 18x18m may impact improve the profit in 130 milliondollars over the five years period evaluated.
Acknowledgements
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Acknowledgements
ALGES Lab Advanced Mining Technology Center
Universidad de Chile
Department of Mining Engineering
Universidad de Chile
Compaa Minera Cerro Colorado