Block Caving - Kuliah Tamu - Herry Purwanto.pdf

Block Caving Mines An Overview and Future Technical Challen

зочин лекц уул уурхайн инженер их сургуулийн Trisakti, Жакарта May 02, 2016 Herry Purwanto - геотехникийн инженер

Private and c

Safety Share

Safety Share

LHD tips Light Vehicle on side Two persons in vehicle NO INJURY

Background

Who are we Rio Tinto is a leading international business involved in each stage of metal and mineral production. The Group combines Rio Tinto plc, which is listed on the London Stock Exchange, and Rio Tinto Limited, which is listed on the Australian Securities Exchange. Rio Tinto comprises five principal product groups – Aluminium, Copper, Diamonds & Minerals, Energy, and Iron Ore – plus central support groups such as Exploration and Technology & Innovation.

Rio Tinto All Operations

Diamonds

Aluminium

Talc

Aluminium Coal Coal

Borates

Aluminium TiO2 / Iron Iron Ore

Nickel

Copper

Talc

Aluminium Talc Alumina

Talc

Copper Aluminium

Aluminium

TiO2

Copper / Gold / Silver / Molybdenum

Aluminium Alumina

Copper / Gold

Iron ore Aluminium

Copper

Bauxite

Diamonds

Iron ore

Alumina

Copper

Uranium Copper Aluminium TiO2

Potash Feasibility & development Existing operation Source: Rio Tinto

Aluminium

Bauxite

Borates

TiO2

Bauxite & alumina Uranium Bauxite Diamonds Coal Salt Coal Alumina Iron ore Aluminium Talc Coal Iron Copper/gold Aluminium

> 90% of assets in North America, Australia and Europe Rio Tinto 2011 gross assets - by region

North America 43%

Europe 18%

1% Indonesia Africa 3% S America 2%

Australia 33%

Data under IFRS Source: Rio Tinto

2011 Gross Assets = $91bn

Underground Block Caving at July 2013

OT RUC

KUC

DOZ Palabora

ADM

NPM

Resolution – Arizona USA.

Argyle Diamond Mine

10

Resolution – Existing Workings

June 2011

Snapshot of future potential

Area on new deep Cu Mineralization (D660)

Deep Copper (SW Alphabet)

Niagara Mine workings (Historic Lead-zinc)

A Bed

Previous 0.7% Cu grade zone •

D556

•

D556

•

501’ @ 0.92% Cu

•

1380’ @ 0.82% Cu

•

Skarn Mineralization

•

Monzonite Mineralization

Oyu Tolgoi - Mongolia

Number 1 Shaft Complex

HUGO DUMMETT DEPOSIT

Indicated Resources – (incl. Entrée JV block; 0.60% Cu equivalent cut-off) - 820 million tonnes @ 1.82% Cu & 0.42 g/t Au - 32.9 billion pounds of copper - 11.1 million ounces of gold

Inferred Resources – (incl. Entrée JV block; 0.60% Cu equivalent cut-off) - 1.31 billion tonnes @ 1.02% Cu & 0.22 g/t Au - 29.4 billion pounds of copper - 9.3 million ounces of gold

Hugo Dummett estimates by Amec Americas and Ivanhoe Mines, March 2007

85k tpd Development Layout

Shaft 4 Maintenance Drift Exhaust Drifts Conveyor Drift Year 8 Drawpoints

Shaft 2 Station

Intake Drifts Shaft 1 Station Shaft 3

Challenges & complexity Extraction Level Infrastructure Hoistroom Batch Plant Crushers (4)

Service Shaft AB Terminal

Conveyors GVDs

Rio Tinto in Diamonds Rio Tinto is a significant diamond producer and the world’s largest producer of natural colored diamonds. Rio Tinto has been in the diamond business since 1979 and today operates three world class diamond mines and an advanced diamond project; namely Argyle in Australia, Diavik in Canada, Murowa in Zimbabwe and Bunder Project in India. Rio Tinto owns and operates the Argyle Diamonds mine in the remote East Kimberley region of Western Australia. Operating since 1983, Argyle has produced more than 800 millions carats of rough diamonds. It is the world largest supplier of natural coloured diamonds, especially in the Argyle Pink.

Diavik Diamond Mine

Winter Minus 40 degrees Celsius

Diavik Diamond Mine

Underground Mine Design June 2011

Location of Argyle Joseph Bonaparte Gulf

Perth Argyle Kununurra

Australia

East Kimberley

Lake Argyle

Argyle Diamond Mine

Perth Canberra

Argyle is located ~ 110 km SW of Kununurra (~3,000 km North-East of Perth)

Discovery of AK1 pipe The geological “pipe” of lamproite rock that is the source of Argyle’s diamonds was discovered in 1979 after a geologist in the exploration team spotted a diamond embedded in an anthill near a creek. After tracing the creek back to its source, a rich diamond deposit was found and the Argyle Diamond Mine had been discovered.

Bird view of Argyle Diamonds Mine

Lamproite Pipe (AK1)

The Underground Mine

250m beneath the open pit

180m

500m beneath the surface

490m

34km of mine development in addition to the 5km developed as part of the Exploration Decline

Development

34km of mine development in addition to the 5km developed as part of the Exploration Decline

Argyle Underground Mine Overview Block Cave statistics • 250m high • 490m x 180m extraction level

Annual Production • Life of 7 years

• 9.5 million tonnes per year • 20-30 million carats per year

Underground Ore Handling • Twin gyratory crushers • Ore conveyed to surface

Dewatering • Operational Pumping capacity 120 litres per second • Seasonal pumping capacity 1100 litres per second

Add. recoverable resource: 24mt – 70 mcts

Block Caving Why •Worldwide and for many companies, large open pits which have been mined for many years are now reaching their economic limits. •There are few new prospects for large, surface outcropping orebodies to replace the old large pits with new large pits. •Many of the existing pits have extensive reserves below the economic pit limits. It should also be noted however that these are generally low grade deposits. •In order to replace these large open pits, Rio requires a high capacity, low operating cost underground mining method.

How

Issues

•The underground mining method which best suits the needs of replacing open pit mines is block caving.

•As with all things in mining, everything comes at a cost. For block caving this is in the form of:

•Currently operating block cave mines produce up to 120ktpa eg. El Teniente

•Block Cave operating costs are generally around US$3 to US$4.

•But there are issues…..

»

High up-front capital expenditure

»

Longer production ramp-up times

»

Pit to Underground transition

»

“One bite at the cherry”

Where are we going

Undercutting and Extraction

Block Cave Design

Modified from Bartlett and Nesbitt, 2000

Argyle Block Cave Design Section Looking West

Advanced undercut Advanced Block Cave (scheme only) Undercutting

Veranda

Drawing

5

UCL Access

5

2 4

1

3 Developed

1

Zone of construction

Zone of development

Undercut

1.- Drives are developed in the UCL and EL 2.- Undercutting 3.- Draw bell drives are developed below theConstructions, undercut 4.draw bell preparation & blasting 5.- Extraction

Pre-undercut Pre-Undercut Block Cave (scheme only) Undercutting

Veranda UCL Access

Drawing

1

4

3 Developed

2 Zone of construction

Zone of development

Undercut

1.- Undercutting 2.- Developments & constructions in the EL below the undercut 3.Draw bell preparation and blasting 4.- Extraction 33

Lead and Leg

Stress Environment Principal Stress Magnitude vs Depth

1 North

2

Principal Stress

3 2

1

Magnitude (MPa)

σ1

= 2.5 σv

σ2

= 1.5 σv

σ3

= 0.027 MPa/m

= 10%

Convergence at the UCL

= 10%

= 9%

= 8%

Deformed profile

= 8%

= 7%

= 7%

= 6%

= 6%

= 5%

= 5%

= 4%

3.4m

= 3% = 3%

= 2%

= 2%

= 1%

= 1%

= 0.5% = 0.5%

Def (+)

Def (+)

Convergence of UC Drives

Undercut Drive Closure (rates) Convergence Rate (mm/day)

17 16 Extremely High

Undercut area

14 12 10 8 6

Gap Fault System

Very High

5 4 3

High

2 1.5

Fair

1 0.5

Low

0 -0.5

Undercut Drive Closure (cumulative) Cumulative Convergence (mm)

Undercut area

Gap Fault System

Strain (%)

 = 12%  = 11%  = 10%  = 9%  = 8%  = 7%  = 6%  = 5%  = 3%  = 2%  = 1%  = 0.5%

Ground Support Design

Ground support-Why ? The potential for instability in the rock surrounding underground mine openings is an ever-present threat to both the safety of men and equipment in the mine. The simplest form of underground excavation support is that which is installed solely for 'safety' reasons. This support is not called upon to carry very heavy loads due to large wedge failures or to massive stress induced instability, but its function is to provide an acceptable level of safety for personnel and equipment in the mine. The vast majority of underground excavation in mines is supported with one or more support elements, where in general terms a support element is an individual component such as a rockbolt, plate, mesh, cable etc. A support system includes one of more of these elements and the main function of these systems is to keep the excavation open and to prevent fall of ground accidents.

Tunnel in California (Goodman & Shi (1985)).

Conceptual Stability assessment

42

Quartzite

Quartzite: falling or sliding of blocks and wedges are expected Lamproite & Dolerite

Mudstone

Lamproite & Dolerite: localized brittle failure of intact rock and movement of blocks Mudstone (average): localized brittle failure of intact rock and unravelling along discontinuities Poor Mudstone & Gap Fault Areas

Poor mudstone and Gap Fault areas: sliding, crushing, squeezing and major convergence would be expected.

Damage mechanism: Squeezing and major convergence is expected in Gap Fault and Mudstone areas

After Martin, Kaiser & McCreath (1999)

43

Rock Properties Intact Rock Properties (average) Parameter

Rock Units Lamproite

Dolerite

Quartzite

Mudstone

UCS (MPa)

85

66

104

35

E (GPa)

55

65

52

38

0.26

0.36

0.22

0.24

58

55

59

40

u RMR1976

Source: BFP, Block cave study – geotechnical model, August 2002

LEGEND ORE (LAMPROITE) DOLERITE QUARTZITE MUDSTONE FAULT TRACE GAP FAULT SOUTH 17

Geotechnical Domains & EL

DOMAIN 1: NE MUDSTONE DOMAIN 2: NE QUARTZITE

DOMAIN 3: DOLERITE DOMAIN 4: MAJOR FAULTS & CONTACTS DOMAIN 5: NW & SE MUDSTONE

DOMAIN 6: LAMPROITE (OREBODY)

Rock Mass Classification (Q)

45

An overview of rock support design

Note that there are hundreds of kilometres of mining and civil engineering tunnels around the world which have been successfully mined and operated without support. These tunnels are either in very good quality rock or they are used infrequently enough that safety is not a major issue. The decision on when support is required in such tunnels is a very subjective one, since there are very few guidelines and those which do exist vary widely from country to country.

Why do we support? Excavation Failures Draw Point X/cut

Excavation Failures Bullnose and Camel Back

Excavation Failures Draw Point

Excavation Failure Extraction Drive

Major Excavation Failure Guillotining of friction bolts

Excavation Failure Shearing and bulking of the walls

Major Excavation Failures Face Failure in Poor Ground

Major Excavation Failures Steel sets in Extraction Drive

Major Excavation Failures Extraction Drive Strain Burst

Sidewall-rib failure

Best support system –Rock itself

Geotechnical vulnerabilities: remnant pillars & UC detention

The Importance of quality in undercutting Undercut & Extraction Level Schematic North-South Section Stresses Remnant Pillar (“Bridge”)

Stress Transfer

9715 UC Level

Major Apex

EL Drive

Draw Bell

Damage

EL Drive

9700 Extraction Level

59

The Importance of quality in undercutting Stress concentration due to remnant pillar Strength Factor

North

Unstable

Stable

60

Remnant Pillars & Closure (El Teniente Mine)

Esmeralda Collapse report, Fernandez & Constanzo, 2008

El Teniente Ground Closure – over 4 Mths

Esmeralda Collapse report, Fernandez & Constanzo, 2008

Remnant Pillars – El Teniente

Esmeralda Collapse report, Fernandez & Constanzo, 2008

Kimberley

Cullinan Diamond Mine

Cullinan Diamond Mine

Freeport Indonesia

Probe Holes – Remnant Pillars Displacement

North

(+)

(-)

Remnant Pillar Identified

Good!!

Convergence in the Extraction Level Advance direction Stress

Undercut

40m 1

Extraction level drive Convergence

Advance direction

Undercut

Stress 20m 2 Extraction level drive Convergence Stress Undercut

Advance direction

0m 3 Extraction level drive Convergence

Undercut Stress

Extraction level drive Convergence

-20m 4

Rock mass stress conditions UCL Abutment

Undercut

5

4

Pre-mining

3

1

2

Distance to UC Front and Maximum Principal Stress S1 (MPa)

65 60

5

Abutment

Pre-mining

55 50 45

4

40

3

35

2 30

1

25 20 0

20

40

60

80

100

120

Distance to UC Front (m)

140

Uncontrolled Flow of Material (UFM)

71

Flooding

Flume & real time sensor in Citect To monitor inflow to Flood dam

CCTV camera To monitor the condition

Safety gate to be closed when flow >250 L/s

Back 73

Design Challenges 100% 80% 60% 40% 20% 0%

% Domain 4 100% 80% 60% 40% 20% 0%

% high risk 100% 80% 60% 40% 20% 0%

DISTRIBUTION OF DOMAIN 4

% medium risk

DISTRIBUTION OF HIGH RISK (RED) AND MEDIUM RISK (YELLOW) DRAWPOINTS

Cave Monitoring State of Art

Thank you