An Introduction to
Underground Mining
On the Rocks, December 6, 2012
Ron Stewart
Introduction
Challenge
Mine economics - and therefore
investment success - is a derivative
of geology, engineering, metallurgy,
management markets and
management,
jurisdiction.
Our Intent
An introduction to underground
mining - an overview of mining
methods, selection criteria and
what to consider when you are
reading a technical report or
visiting a mine
Source: www.gedc.com
December 6, 2012
2
Underground Vs. Open Pit
Underground
Deposits
Vs.
Open Pit
Relatively small, high grade
Relatively large, low grade
or Deep with sub-vertical ore zone
or Shallow, with sub-horizontal ore
zone
Geology
Resources / Reserves
Structurally controlled veins and
Lithology controlled stockworks,
stockworks
breccias
disseminated zones.
Generally difficult or not cost
Generally cost effective to establish
prove up
p large
g resources /
effective to p
10 to 15 y
year resource / reserve life
reserves
Productivity
500 to 8,000 tonnes per day
5,000 to 100,000 tonnes per day
Environmental
Generally easier to permit, limited
Large footprint from pit, waste
footprint. Relatively cheap to reclaim
dumps and tailings, relatively
expensive to reclaim
Mine Life
To >100 years
10 to 25 years, rarely longer
December 6, 2012
3
Underground Vs. Open Pit Mining
In 2011, only 117 gold mines reported >100,000 oz of gold production
31% or 11.5
11 5 million ounces from 42 underground mines
100,000 to
250,000 oz/a
No.
250,000 to
500,000 oz/a
Ounces
No.
Ounces
500,000 to
1,000,000 oz/a
>1,000,000 oz/a
No.
No.
Ounces
Ounces
Totals
No.
Ounces
Undergound
27
4,105,528
10
2,868,291
4
3,408,803
1
1,100,000
42
11,482,622
Open Pit
42
6,710,672
19
6,349,474
10
6,820,255
4
6,179,000
75
26,059,401
9.2 M oz
10 8 M oz
10.8
62%
38%
69%
10.2 M oz
31%
67%
15%
7.3 M oz
33%
85%
Source: Metals Economics
December 6, 2012
4
Glossary of Underground Terms
Adit
Horizontal mine entrance
Back
The ceiling in an underground tunnel
Brow
Overhead rock at an Adit or Drawpoint
Crosscut
A horizontal drive through an ore body
Drawpoint
Point at which ore is extracted from a stope
Drift
A horizontal drive p
parallel to or along
g an ore
body
Grizzly
A screen or grate above a loading pocket or
ore pass to catch oversized rocks
Jumbo
A mobile drill used in driving tunnels
Loading Pocket
Rock storage compartment
Manway
A dedicated underground opening for
personnel
Ore pass
A vertical or inclined tunnel for ore
transport
Raise bore
A large drill used for vertical or inclined
tunnel drilling
Round
A single blast in a drift or crosscut
Scoop Tram (LHD)
Underground loader (Load - Haul - Dump)
Skip
Shaft bucket for hoisting rock
December 6, 2012
5
Mine Method Selection Criteria
…is
is based on:
Geometry
Depth, shape, thickness, dip, plunge
Rock Quality
Ore zone and host rock competency (structures, stress,
stability)
Ore Variability
Ore uniformity
uniformity, continuity
continuity, grade distribution
Economics
Ore recovery, ore value & mine recovery (losses),
productivity, equipment selection, capital & operating costs,
ore value
value, safety
December 6, 2012
6
Geological & Mechanical Selection Criteria
of Mining Methods
December 6, 2012
7
Underground Stoping Methods
Room and Pillar
Flat to Shallow dip, competent ground conditions
Longwall
Flat to shallow dip, narrow seam ore body
Longhole or
Medium to Steep dip, competent ground conditions and
Sublevel
generally regular ore
ore-waste
waste boundaries
Shrinkage
Medium to steep dip, variable ground conditions and variable
ore-waste boundaries. (Delay in delivering ore)
Cut and Fill
Medium to steep dip, variable ground conditions and variable
ore-waste boundaries provides maximum selectivity.
Block Cave
Steep dip, massive ore body. Limited to no selectivity.
Extensive development required
December 6, 2012
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Stope Design Criteria and Grade Control
Dilution and Ore Recovery Factors
Dilution Factor (%)
Recovery Factor (%)
Grade Control
Room and Pillar
5 - 15
90
Face mapping & sampling
L
Longwall
ll
5 - 25
85
F
Face
mapping
i & sampling
li
Longhole or Sublevel
15 - 20
85
Development drift mapping
& sampling with definition
drilling
Shrinkage
10
90
Face mapping & sampling
Cut and Fill
5 - 10
85
Face mapping & sampling
Block Cave
15
95
Drilling Only
December 6, 2012
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Design Vs. Actual Dilution & Ore Loss
Unplanned
p
Dilution
Ore Loss
Planned Dilution
Ore Loss
Designed Stope
Actual Stope
December 6, 2012
10
Development Heading Dilution
Ore in Reserve
Block Model
Planned Dilution
Actual Drift
December 6, 2012
11
Underground Productivity Rates
Tonnes per man-shift
Normal
High
30 - 50
50 - 70
5 - 10
10 - 15
15 - 30
30 - 40
Shrinkage
5 - 10
10 - 15
Cut and Fill
10 - 20
30 - 40
Block Cave
15 - 40
40 - 50
Room and Pillar
Longwall
Longhole or Sublevel
December 6, 2012
12
Mobile Underground Mining Equipment
Scoop Tram
Two-Boom
B
Jumbo
b
Haulage Truck
Raise Bore
December 6, 2012
13
Block Cave Stoping
Sub-Level Caving
Production Rate
>7,500 tpd
Mining Cost Per Tonne
$8.00 to $15.00/tonne
Development Capital
High development capital
Sustaining Capital
$16,000/tonne of throughput
Cut-Off Grade
Low
Oth C
Other
Considerations
id
ti
Hi h upfront
High
f
t capital
it l costt
Massive or disseminated ore body
Rock must break and feed
Surface subsistence must be
allowed
ll
d
Examples
New Afton
Source: Techniques in Underground Mining, SME
December 6, 2012
14
Room and Pillar
Room and Pillar Mining
Production Rate
500 to 35,000 tpd
Mining Cost Per Tonne
$10 - $30/tonne
Development Capital
Low Development Capital
Cut-Off Grade
Low
Other Considerations
Flat or shallow dipping ore body
with limited thickness
Ground conditions - especially the
back must be competent
Examples
No known gold examples, common in
coal and potash mining
Source: Techniques in Underground Mining, SME
December 6, 2012
15
Longwall Stoping
Inclined Longwall stoping
Production Rate
500 to 5
5,000tpd
000tpd
Mining Cost Per Tonne
$150/tonne
Development Capital
High development capital
Cut-Off Grade
High
Other Considerations
Thin ore zones (bedded or tabular)
with regular and parallel ore
contacts
Variable ground conditions
supported by fill
In South Africa ore is mined by
jackleg, small rounds are blasted
and material is scraped down to
draw points
Examples
Witwatersrand reef ore bodies
Source: Techniques in Underground Mining, SME
December 6, 2012
16
Longhole (Sublevel) Stoping
Sublevel Stoping
Production Rate
500 to 5,000 tpd
Mining Cost Per Tonne
$40 to $150/tonne
Development Capital
Modest
Cut Off Grade
Cut-Off
Low
Other Considerations
Most common method for high
productivity, low cost gold mining.
Ore bodies have vertical to steep
dip, can vary in width down to less
than 1.0m, but generally require
regular ore-waste contacts and
competent ground
Examples
Young-Davidson, LaRonde, Kupol,
Jacobina, El Penon, Musselwhite,
p
Chelopech
Source: Techniques in Underground Mining, SME
December 6, 2012
17
Endeavour Silver: Bolañitos –
Longhole Mining Method
Longhole drilling up holes in a
stope. Note remote operation
of the drill improves safety
Mucking a stope remotely with
a scoop (LHD) at a draw-point
Source: Endeavour Silver (EDR-T, BUY Target C$11.00/sh)
December 6, 2012
18
Stoping at Björkdal Mine, Sweden
Note the narrow vein in the
drift back
2.5m wide stope with sill
drift highlighted at the base
Cable bolted back shows
good dilution control
Source: Elgin Mining Inc, (ELG-T, NOT RATED)
December 6, 2012
19
Mining – Narrow Blasthole Stope
December 6, 2012
20
Cut and Fill
Non-captive Cut & Fill Stoping
Production Rate
200 to 2000 tpd
Mining Cost Per Tonne
$100 to $200/tonne
Development Capital
Modest
Cut-Off Grade
High
Other Considerations
Most common selective mining
method for high grade veins and
breccias with variable geometries
Source: Techniques in Underground Mining, SME
and or poor ground.
ground
Classic cut-and fill used jack-leg
mining in captive stopes
Now far more common for
mechanized cut and fill with small
jumbos and scoops
Examples
Buckhorn, Rice Lake, Macassa, El
Cubo
Source: Endeavour Silver (EDR-T, BUY Target C$11.00/sh)
December 6, 2012
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Cut-and-Fill Advance at Endeavour’s El Cubo Mine
And-Bx
VEIN
And-Bx
Jumbo advance on wider veins
and access drifts. Increased
productivity and reduced costs
ORE
Jackleg drilling on narrow and
irregular veins increases
selectivity reduces dilution –
selectivity,
but is slower and more labour
intensive
Source: Endeavour Silver (EDR-T, BUY Target C$11.00/sh)
December 6, 2012
22
Jackleg Miner In a Cut & Fill Stope
Source: San Gold Corporation (SGR-T, BUY Target C$1.80/sh)
December 6, 2012
23
Scaling a Heading In a Cut & Fill Stope
Source: San Gold Corporation (SGR-T, BUY Target C$1.80/sh)
December 6, 2012
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Mining – Narrow Cut & Fill Stope
December 6, 2012
25
Shrinkage
Non-captive Cut & Fill Stoping
Production Rate
100 to 2,000 tpd
Mining Cost Per Tonne
$125 to $200/tonne
Development Capital
Relatively High Capital
Cut-Off Grade
High
Other Considerations
Steep dip and relatively competent
rock with regular ore - waste
b
boundaries
d
Source: Techniques in Underground Mining, SME
Delayed ore mining as ore is used as
a platform for drilling
p
Examples
Rarely
y used - Guanajuato
j
,
Francouer
Source: Endeavour Silver (EDR-T, BUY Target C$11.00/sh)
December 6, 2012
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Mucking & Haulage
Scoop (LHD) Mucking a Stope
Ore transfer to a Haul Truck
(in cases
where an ore pass system is used, scoops haul
ore to dump points underground)
Haul Truck to Surface (as a general rule
ore can be trucked as much as 300 to 400m
vertically)
Source: Endeavour Silver (EDR-T, BUY Target C$11.00/sh)
December 6, 2012
27
Ore Handling and Ancillary Services
Main Ingress / Egress
•
Shaft, cage & skip
•
R
Ramp
Air Cooling System at LaRonde
Ore Handling Systems
•
Ore passes, shoots
•
C
Conveyance
Ground Control
•
Bolting
•
S
Screening
i
•
Shotcrete
Ventilation
•
Fans
•
Heating / Cooling
Water
•
Collection
•
Pumping
Screening and Bolting at Lapa
Source: Agnico-Eagle (AEM-T, BUY Target C$70.00/sh)
December 6, 2012
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What We Look For When We Go Underground
1.
Focus on employee safety, hazards or safety risks
2.
Housekeeping specifically at shaft stations and work faces
3.
General structural geology (faults, joints, slips, orientation and
frequency of structures)
4.
Ground conditions (Areas screened, bolted and reinforced as
well as quantity of loose rock behind mesh)
5.
State of ramp, haulage drifts – (how well maintained they are)
6.
Water ingress (amount, collection, ponding)
7.
Air quality (dust level, smoke, air temperature)
8
8.
General state of the equipment and age
age, tire wear and cuts
9.
Rock fragmentation – oversize in scoops, trucks or on grizzly
10. Mood and engagement of the workforce
December 6, 2012
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An Introduction to Underground Mining
Remember tag-in before you go underground
T k your time
Take
ti
Always make sure equipment operators can
see you.
Don’t shine your
D
y
light
g directly
y at others
Stay safe, sure footed and alert
Source: Colossus Minerals (CSI-T, BUY Target C$8.00/sh)
December 6, 2012
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