how to improve the ramp-up of block caving mines

7/23/2019 How to improve the ramp-up of block caving mines

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“How to improve the ramp-up of

block caving mines” “Cómo mejorar la subida de producción enminas de block caving”

Alfonso Ovalle, Dr. Peter CepuritisAmec Foster Wheeler, Chile



How to improve the ramp-up of block caving mines

MOTIVATION

(Ref. 1)

90

80

70

60

50

40

30

20

10

0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Years

10% 0.91 0.83 0.75 0.68 0.62 0.56 0.51 0.47 0.42 0.39 0.35 0.32 0.29 0.26 0.24 0.22 0.20 0.18 0.16 0.15 0.14 0.12 0.11 0.10 0.09 0.08 0.08 0.07 0.06 0.06 0.05 0.05

8% 0.93 0.86 0.79 0.74 0.68 0.63 0.58 0.54 0.50 0.46 0.43 0.40 0.37 0.34 0.32 0.29 0.27 0.25 0.23 0.21 0.20 0.18 0.17 0.16 0.15 0.14 0.13 0.12 0.11 0.10 0.09 0.09

6% 0.94 0.89 0.84 0.79 0.75 0.70 0.67 0.63 0.59 0.56 0.53 0.50 0.47 0.44 0.42 0.39 0.37 0.35 0.33 0.31 0.29 0.28 0.26 0.25 0.23 0.22 0.21 0.20 0.18 0.17 0.16 0.15

k t / d

D i s c o u

n t

r a t e s

Discount factors

Better production ramp-up will greatly affect NPV of the

project because of higher production in the early years,

usually of the better grades and at higher discount factors

Page 1 of 28




BC RAMP UPS

0

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0 1 2 3 4 5 6 7 8 9 10 11

P r o d u c t i o n , t /

d

Years

Production Ramp-up of BC Mines ____

Teniente 4 S Sector Dec. 1981

Page 2 of 28

(Ref. 2)




BC RAMP UPS

0

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140

0 1 2 3 4 5 6 7 8 9 10 11

P r o d u c t i o n , t

/ d

Years


Teniente 4 S Sector

Esmeralda, El Teniente

Sep. 1997

Page 3 of 28

(Ref. 2)




BC RAMP UPS

0

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0 1 2 3 4 5 6 7 8 9 10 11


d

Years


Palabora Lift 1

Teniente 4 S Sector


Jun. 2001

Page 4 of 28

(Ref. 3)




BC RAMP UPS

0

10

20

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40

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60

70

8090

100

110

120

130

140

0 1 2 3 4 5 6 7 8 9 10 11


d

Years


Cadia East

Palabora Lift 1

Teniente 4 S Sector


Dec. 2012

Page 5 of 28

(Ref. 4)




BC RAMP UPS

0

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0 1 2 3 4 5 6 7 8 9 10 11


/ d

Years

Production Ramp-up of BC Projects ------

NNM, El Teniente 2019

Page 6 of 28

(Ref. 5)




BC RAMP UPS

0

10

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30

40

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80

90

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130

140

0 1 2 3 4 5 6 7 8 9 10 11


/ d

Years


PMCHS,

Chuquicamata

NNM, El Teniente

2018

Page 7 of 28

(Ref. 6)



2018?


BC RAMP UPS

0

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0 1 2 3 4 5 6 7 8 9 10 11


/ d

Years


Palabora Lift 2

PMCHS, Chuquicamata

NNM, El Teniente

Page 8 of 28

(Ref. 3)




BC RAMP UPS

0

10

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80

90

100

110

120

130

140

0 1 2 3 4 5 6 7 8 9 10 11


/ d

Years


Oyu TolgoiPalabora Lift 2

PMCHS, Chuquicamata

NNM, El Teniente

2018?

Page 9 of 28

(Ref. 7)




BC RAMP UPS

0

10

20

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40

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60

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8090

100

110

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130

140

0 1 2 3 4 5 6 7 8 9 10 11


d

Years


and Projects ------

Cadia East

Oyu Tolgoi

Palabora Lift 2

PMCHS, Chuquicamata

Palabora Lift 1

NNM, El Teniente

Teniente 4 S Sector


Page 10 of 28




ATTAINABLE BC RAMP UP

0

10

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30

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60

70

80

90100

110

120

130

140

0 1 2 3 4 5 6 7 8 9 10 11

P r o d u c t i o n , t / d

Years


and Projects ------

PossibleCadia East

Oyu Tolgoi

Palabora Lift 2

PMCHS, Chuquicamata

Palabora Lift 1

NNM, El Teniente

Teniente 4 S Sector


How?

Page 11 of 28




ASPECTS THAT GOVERN THE RAMP UP

• Primary issue: the Cave Back Velocity (CBV)must be greater than the extraction velocity

• Undercutting rate Air gaps are to be avoided or minimized

• During cave propagation

Avoid big seismic events

• Extraction rate Fragmentation size at draw point

Design of caving system

Design of materials handling system design

• Risk prevention Operational hazards: rockburst, airblast

Design hazards, due to incorrect assessment of theground conditions

Page 12 of 28




CAVE BACK VELOCITY

• Rock mass properties

– Intact strength & modulus

– Major structures

– Joint network geometry

– Joint strength & stiffness

• Stresses – In situ stress

– Induced stresses• Undercut size, shape and direction

• Draw strategy

• Adjacent mining

• Improving cave propagation

– Breakthrough to lowest elevation

– High undercutting

– Preconditioning the rock mass

Preconditioning

Page 13 of 28




PRECONDITIONING THE ROCK MASS

• Teniente (widespread use of hydrofracturing)

Mitigation of rock bursts

Faster cave back velocity

• Cadia East (intensive pre-conditioning cave back velocity of 1.1 m/d)

Hydrofracturing High undercutting Confined Blasting

150 m

450 m

1,200 m to surfacetook less than 3 years

Page 14 of 28

(Ref. 3)




GREEN LIGHT FOR FASTER RAMP UP

• Cave propagation velocity in hard rock of 1.1 m/d…

NOW A DESIGN PROBLEM

Increase Increase

undercutting rate extraction rate

Page 15 of 28




FASTER RAMP UP

•Increase undercutting rate: – Maximize undercutting velocity

• Post undercutting, if possible

• Establish more than one undercutting front

• Undercutting front in spear shape

•Split levels

– Simple design

– Enhance planning, equipment, services and logistics

• Increase extraction rate:

– Design for more area availability• If LHD, shorter tramming

• RGO option (rock breaker, grizzly, ore pass)

• Continuous mining option

Page 16 of 28




DRAW RATE WITH LHD’s

•

Draw rate with LHD system. Rim crushers arrangement. Long tramming distances

- At 300 m from DP to crusher, a 12 t/bucket LHD produces 3,000 tpd

- If Production Drift is 240 m long and distance between drifts is 30 m, it uses 7,200 m2

- Maximum draw rate possible is 3,000 / 7,200 = 0,42 tpd/m2

- If density is 2.70 t/m3

- Maximum draw down rate is 0.50 / 2.7 = 0.15 m/d- Using 75% utilization factor:

- Maximum Planning draw down rate is 0.12 m/d

240 m

30 mTo rim

crusher

Page 17 of 28




MAKING DRAW RATE FASTER WITH LHD’s

•

Draw rate with LHD system. Ore passes at 120 m & haulage level. Ore pass and rock breaker in Production Drift arrangement

- A 12 t/bucket LHD produces 4,000 t/d (controlled by interference with rock breaker)

- With 120 m between OP and distance between drifts of 30 m, it uses 3,600 m2

- Independent ventilation for each 120 m segment to use an LHD

- Maximum draw rate possible is 4,000 / 3,600 = 1.11 tpd/m2


- Maximum draw down rate is 1.11 / 2.7 = 0.41 m/d

- Using 75% utilization factor


120 m

30 m

120 m

Ore passes to Haulage Level

Page 18 of 28




MAKING DRAW RATE FASTER WITH LHD’s

•

Draw rate with LHD system. Ore passes at 80 m & haulage level. Ore pass and rock breaker in Production Drift arrangement

- A 12 t/bucket LHD produces 4,200 t/d (controlled by interference with rock breaker)

- With 80 m between OP and distance between drifts of 30 m, it uses 2,400 m2

- Independent ventilation for each 80 m segment to use an LHD






80 m 80 m 80 m

30 m

Ore passes to Haulage Level

Page 19 of 28




MAKING DRAW RATE FASTER WITH RGO

• RGO System (rock breaker, grizzly, ore pass)

Rock breaker directly on draw point to a grizzly

Grizzly connected to short ore pass

Lower collection level (with panzer feeder going to sizer or central OP)

• Concepts of RGO System

Rock breakers are teleoperatedo Less ventilation required

o More operating hours possible

Production drifts belong to secondary blasting and hang up crews! High area utilization possible

No diesel drives

Page 20 of 28

(Ref. 8)





2.000

2.500

3.000

3.500

4.000

4.500

5.000

0 30 60 90 120

P r o d u c t i v i t y ,

t / d

% Extraction

t/d, 20" x 36" grizzly

t/d, 20" x 20" grizzly

• Rock Breaker Productivity (Ten 4 Fw test, primary ore)

Page21 of 28

(Ref. 8)





• RGO System (rock breaker, grizzly, ore pass)

Draw rate calculation of RGO System

- One rock breaker produces 2,300 t/d (lowest rate at 30% extraction)

- One rock breaker for every 4 DP, or 40 m. Distance between drifts of 30 m, it uses 1,200 m 2

- Independent ventilation for every three rock breakers






|

40 m

30 m

40 m 40 m 40 m 40 m 40 m

Page 22 of 28




MAKING DRAW RATE FASTER

LHD,

240m

LHD,

120m

LHD,

80mRGO,

15%E

RGO,

45%E

RGO,

75%E

RGO,

105%E

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,700,80

0,90

1,00

1,10

1,20

D r a w

R a t e , m / d

Block Caving Systems

Draw Rates,LHD and RGO Systems

Page 23 of 28




EVALUATION OF RAMP-UP INCREASE

The following block cave project was evaluated with normal and steeper

ramp-up production periods, caused by the following:

UNDERCUTTING RATE:

Increased from

34,000 m2/yr to

48,000 m2/yr for 2 years

DRAW RATE:

Increased from

0.20 m/d to 0.40 m/d

RESULT:

Ramp up was shortened

from 9 to 4 years

Page 24 of 28




EVALUATION OF RAMP-UP INCREASE

MUS$ %

NPV (8%) SLOW RAMP UP: 455 100

NPV (8%) FAST RAMP UP: 1,009 222

Total increase: 554 122

Due to Draw Rate increase: 400 88

Due to Undercutting Rate increase: 154 34

Page 25 of 28




CONCLUSIONS

• Intensive preconditioning of the rock mass green light for higherextraction rates

– High Undercut: helps early draw rates and prevents collapses

– HF preconditioning: proven technology to improve the caving velocity

– Forced Fragmentation Blasting: drill and blast to break base of columns

– Vertical Shaft: to connect UCL to surface that serving as path/guide

• BC designs need to increase extraction rates

– LHD systems: can go up to around 0.50 m/d, with difficulty

– RGO system: can go beyond 0.50 m/d, with ease

• Ramp up of BC projects can be shortened, with very important increase of

the NPV.

Page 26 of 28




REFERENCES

1. Mass caving maximum production capacity, Alfonso W. Ovalle, Amec International; University of Chile,

MASSMIN 2012, June 11-14, 2012, Sudbury, Ontario, CANADA2. Lecciones Aprendidas Explotación El Teniente, A. Ovalle, Set. 2006

3. Block caving with Rio and NCM, Credit Suisse, 27 Set 2012, Visit Report

4. Newcrest Mining Company Quarterly Reports

5. Presentación NNM, J. Revuelta, Nov. 2013

6. Presentación PMCHS, S. Fuentes, Abr. 2013

7. Turquoise Hill Resources Ltd. Oyu Tolgoi 2014 Technical Report, October 2014, Job N° 14003, OreWin,

Independent Mining Consultants, Figure 1.7, 2014 Reserve Case processing, pg. 28

8. Martillos picadors semi-móviles en Teniente 4 Norte Fw, 1990. Comunicaciones con A. Moyano.

Page 27 of 28




END

Thank you for your attention

Page 28 of 28

how to improve the ramp-up of block caving mines

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