Mechanised On Reef Raising At Free Gold`s Bambanani Mine

Mechanised On Reef Raising At Free Gold’s
Bambanani Mine
MR MORTLOCK
Mine Manager, Free Gold - Bambanani Mine
SYNOPSIS
Progress with on reef raise development at Bambanani Mine was being curtailed due to the fact that
inter levels were behind schedule. This meant that to create the necessary ore reserve raises had to
be developed for two levels instead of the conventional one level.
The productivity graph for an inclined excavation flattens out considerably above 60 metres and
these raises were taking many months to hole.
Furthermore the safety and health of persons working in these raises was been endangered because
of the excessive climb to get to the face, the steep dip of the reef as well as the high channel width
of the reef.
Prior to the purchase of Free Gold from Anglogold investigations were done, by the then team, to
utilise an Alimak raise climber to expedite this development. Free Gold continued with the
investigation and this paper describes the project with its successes and failures.
OVERVIEW
Bambanani mine is one of seven Free Gold mines in South Africa’s Free State province.
Bambanani is the deepest mine in the Free State with operations extending beyond the 3 000metre
level, where virgin rock temperatures can reach an exceptionally high 62ºC.
Bambanani has one operating shaft, East Shaft (the former President Steyn No 4 shaft,)
commissioned in the mid-1970's, and a sub-shaft being added in the early 1980’s, which hoists
some 150 000 tpm.
GEOLOGY
The principal reef mined is the Basal Reef, although limited exploitation of the Leader and ‘A’
Reefs has taken place in the past. The Basal Reef strikes north-south and typically dips towards the
east at between 25º and 45º. However in the lower eastern section of the mine the dip steepens to in
excess of 60º. The mine is bounded to the north and south by the mining leases of other mining
companies, and to the west and east by the Stuirmanspan and de Bron faults, both of which have
throws in excess of 1 km.
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Broadly the gold trends align north-east to south-west. The reef horizon is broken by north-south
trending faults with throws of up to 100 m, and by east-west dykes, which have smaller throws.
The Khaki shale overlying the reef to the north can cause local mining dilution problems.
KEY DATA
Name
:
Bambanani (previously President Steyn 4 shaft)
Ownership
:
Free Gold
Mine type
:
Underground, with mining extending to 3 200 m
No of employees
:
4 500 employees
Production/ output
:
2001 - 407,000 oz
Total cash costs in 2001
:
US$230/oz
Reserves
:
13.4 million tonnes @ 7.09 g/t for 3.1 million oz
Resources
:
34.7 million tonnes @ 9.87 g/t for 11.0 million oz
Location
:
Approximately 270 km south-west of Johannesburg, near the town
of Welkom in the Free State Province
R63,153/kg
Mining
Operations are conducted from 1 920 m to more than 3 140 m below surface. The bulk of the
mine’s production is derived from the lower levels of the East sub shaft, with the remainder coming
from remnant pillars on the upper levels of East shaft.
Bambanani’s depth and the nature of its geology, including numerous local aberrations, have meant
that mining sequencing has become essential in the management of seismic risk.
Ore reserve development is conventional hand held drilling on day shift and compressed air loading
for cleaning on night shift. At present some 1 400 metres are developed monthly.
Raises situated 150 metres apart on strike are down dipped ledged, equipped and stoped out on
breast to the limit line. Panels average 25 metres in length, each served by its own gully and ore
pass. Limited centre gully scraping takes place.
Support in stope is by means of 110 x 110 solid timber “Lexus” packs with 110 x 165 packs on the
gullies. RYHP are utilised in seismically active areas as well as in ledging.
Development support is in three phases:
•
•
•
Initial development:
Secondary support:
Tertiary support:
2,3m grouted rods
Wire mesh and lacing
50mm shotcreting and 3,5m grouted tensioned slings
Tramming is done by conventional battery locos and 6t bottom discharge hoppers to the shaft
station.
2
98MW of cooling is utilised on the mine to cool the workings. Cooling is by means of Regional
Bulk Air Coolers, 120 spot coolers and chilled water drilling.
Reef bearing ore is hoisted to surface via the sub and main shafts and transported by rail to the Free
Gold One Plant, adjacent to the old President Brand Mine for treatment.
Sub Shaft History
During the sinking stage of the sub shaft a decision was made to not develop 98 and 93 levels. The
stations were cut to just off the shaft barrel.
The idea was to reduce the number of operating levels off the sub shaft and to speed up
development on the other levels. At some stage incline shafts would be raised from 100 and 95
Levels creating the inter levels of 98 and 93.
Inter Level Inclines
As is well known, the raising of an incline shaft the establishment of an inter-level and the
equipping thereof is no easy task. The 100 – 98 incline system was started in 1996 and will be
completed by September 2003. A period of some 8 years.
The result of this is that 98 level lags some 800m from 95 level and 450 metres from 100 level.
Raise Development
To generate ore reserve it is necessary to raise from 100 level to 95 level, by passing 98 level an
incline distance of in excess of 200 metres at a dip of 40º.
Attempts were made to do this conventionally in the past but as the raise approached the inter-level
elevation efficiencies became too poor and conditions deteriorated making the raise hazardous to
develop. A decision was taken to not develop above one level.
In the late 1990’s Anglogold set up New Technology Forums and this problem was one tasked to
them. The idea of a Raise Climber was looked at but the decision was made by Free Gold in
February 2002 to go ahead with the project.
THE ALIMAK RAISE CLIMBER
The Alimak is by no means new technology; they have been around since 1948. Alimak AB was
founded in 1948 and is headquartered in Skellefteå, Sweden. Apart from mining/underground
construction equipment, Alimak manufactures passenger/materials hoists and work platforms for
the construction industry as well as permanently installed rack & pinion lifts for various industrial
applications.
Alimak has subsidiaries in France, Germany, U.K., Italy, Canada, USA, Brazil, Singapore, South
Korea and Australia and furthermore distributors in some 40 additional countries Alimak AB is the
manufacturer of the Alimak Raise Climber for applications in mining and underground civil
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engineering. The company's range of underground equipment also covers shaft enlarging
platforms, winches and service/inspection lifts.
The introduction in 1957 of the Alimak Raise Climber and the Alimak Method of Raising signified
an enormous improvement of working conditions, safety, speed and accuracy in raise driving.
Alimak, until then known as a supplier to the construction industry only, entered the mining world
with a product and principle, which was - and still is - unique in this field of activity.
Originally developed for mining applications, the Raise Climber has gradually been improved to
suit all kinds of raising in mines and underground civil engineering projects like shafts and
penstocks for hydro-electric power plants, ventilation shafts for road tunnels etc...
The over 2 300 Raise Climbers delivered so far have been used to drive more shafts and raises than
any other system; in all kinds of rock, pilot and full-face, vertical and inclined, and even for raise
and vein mining.
The Alimak Method consists of five steps, which make up a cycle: Drilling, Loading, Blasting,
Ventilation and Scaling. The Raise Climber serves both as a work platform and as a means of
transport to the work site.
It runs on a guide rail anchored to the hanging wall. Using curved guide rail sections, the direction
of travel can be changed at any time; forward, backward or sideways.
Alimak Raise Climbers are available with air, electric or diesel/hydraulic drive units. The longest
shaft driven in one step so far is 1 050 m (Norway). The platform can be any shape and size. The
largest work platform supplied so far measured more than 30 sq.m.
THE ALIMAK RAISE CLIMBER AT BAMBANANI
The decision was made to not purchase the equipment but to utilise a contractor on a blasted unit
rate to develop the raise. The contractor chosen was Welprop Mining Services who were tasked at
preparing the cross cut and to develop a standard raise from 100 level to 95 level.
The raise was developed conventionally for 18 metres prior to the installation of the equipment. A
further 15 metres was developed when deterioration of the sidewalls started. It was decided to ledge
this out and install cementitious packs and then to continue advancing by means of a T raise and a
stoping width of 1.2 meters.
This also proved to be unsuccessful as the sidewalls of the raise below the packs also deteriorated
causing the support to fall out.
The final decision was to take a full reef cut of 2.2 metres and 6.6 metres wide. This method was
used until the stopping distance just below 95 level. A travelling way was then blasted from the
wide raise to the cross cut on 95 level.
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Production details:
Crew Day Shift:
- Drillers
- Team
- Loco
- Winch
- Team Leader
3
6
2
1
1
TOTAL 13
Night Shift:
- Winch
- Team
- Team Leader
2
1
1
TOTAL 4
Travelling Time:
- Midway: 5 minutes up 5 minutes down
- Top:
13 minutes up 13 minutes down
Support Pattern:
See Rock Mechanics Recommendation Appendix
Drilling Pattern:
Full Cut:
2.2m stoping width
4 rows
61 holes
Breaking Point – 5 hole burn cut
Explosives:
Anfex
Fuses and Igniter Cord
Time Blasting
Reef Metres Raised per Month
25
20
15
10
5
0
Jan Feb M ar Apr M ay Jun July A ug Sept O ct Nov Dec
5
Prog Reef Metres Raised per Month
250
200
150
100
50
0
Jan Feb M ar Apr M ay Jun July Aug Sept O ct Nov Dec
Square Metres Achieved per Month
140
120
100
80
60
40
20
0
Jan Feb M ar Apr M ay Jun July Aug Sept O ct Nov Dec
Prog Square Metres Achieved per
Month
900
800
700
600
500
400
300
200
100
0
Jan F eb M ar Apr M ay Jun July Aug Sept O ct Nov Dec
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CONCLUSION
The project has been a success in the following areas:
Safety
Only one dressing case was recorded for the 12 month period
Production
Average advance below 98 level was 20 meters for the wide raise per month.
Average advance above 98 level was 17 meters per month.
Sampling
Full width stoping allowed the total channel to be sampled
Bambanani has a history of raising on bottom cut and waste thus only allowing bottom cut
sampling. This method has improved the sampling statistics.
Costs
Although not part of this presentation due to contractor confidentiality the unit costs compared well
with conventional raising and ledging.
Overall Summary
The project achieved its objective in that the raise was successfully developed from 100 to 95 level.
Furthermore by changing to a wide raise we now have a ledged raise ready for equipping and then
full stoping.
The full width stoping has given us confidence in the values of the area.
The final conclusion is that a second unit will be installed in the very near future and that by the end
of 2004, we envisage 5 of these units doing the steep raises expected from 103 to 100 level where
dips of in excess of 60º are envisaged.
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ACKNOWLEDGEMENTS
My thanks to the following:
Peter Steenkamp, Operations Manager Free Gold for allowing me to present this paper.
Welprop Mining Services for their dedication to the Project and for research material for the paper.
Free Gold – Bambanani Mine Ore Reserve Department for their assistance in obtaining plans,
pictures etc for the paper and the presentation.
Lastly to Dave Bowden, Shift Boss of Welprop, for his outstanding commitment to safety,
production and conditions in the actual mining of the raise.
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View of the Cross Cut
Stoping of the ledge
9
The ventilation pipe in the ledge
The man cage on the way up
10
At the top of the raise looking down
Drilling the face
11
The rails attached to the hanging wall
Getting out of the man cage
12
Rails on the hanging wall
13
14
15
About to ascend
16
Ascending
At the reeling unit
17
Mark Glasspool – Mine Manager Free Gold Joel
18
Mine Standard of a Wide Raise
BURN CUT
PLAN VIEW
70º
70º
FAN CUT
FAN CUT
HOLES ANGLED AT
70º TO THE FACE
TOWARD BURN CUT
(BREAKING POINT)
DIP
GULLY
FOOTWALL
LIFT ONLY
FRONT VIEW
19
General Locality Map
20
Structural Plan
Isometric View
21
Section Through the Shafts
75 Level
89 Level
91 Level
95 Level
103 Level
Free State Goldfields
22
Standards
3.3m
3.2m
2.5 m
Alimak Raise
Gully Center line
1m
6.6m
2.4m
2.3m
2m
2.3m
Not to scale
Section view
Mining &
support
sequence
0.2m
1.0m
1.0m
2.0m
1.5m
Plan view
Not to scale
23
Mining &
support
sequence
0.2m
1.0m
1.0m
2.0m
1.5m
Plan view
Not to scale
24