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Northparkes Mines -Step Change Project
Conference Paper · June 2012
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Northparkes Mines - Step Change Project
Angus R Wyllie, Mine Design Superintendent, Rio Tinto Northparkes Mines
BE (Min) (Hons) UNSW, MAusIMM
Sarah B Webster, Senior Geotechnical Engineer, Rio Tinto Northparkes Mines
BSc (Geology) (Hons) Macq, MEngSci (Geomechanics) WASM, MAusIMM
Abstract
Northparkes Mines (Northparkes) a copper-gold mine in central west New South Wales, Australia has
been operating since 1993. The mine was the first in Australia to utilise block cave mining and is
currently producing at 5.8Mtpa from it third block cave E48 Lift 1.
The Step Change Project, currently in Pre-Feasibility stage, provides an exciting opportunity for
Northparkes to not just expand its’ operations and extend the life of mine but to lead the way in
incorporating new technology and innovation while continuing to contribute to the local communities
in which it operates.
The Pre-Feasibility study will evaluate a series of large tonnage, low-grade areas of mineralisation
within Northparkes’ existing mining leases. The potential exists for a large-scale underground mining
and processing operation (approx 30Mtpa) based on multiple block cave operations using an
expanded version of Northparkes’ highly productive block cave layout. The zones of additional
mineralisation exploited by the Step Change Project represent depth extensions of the E26, E22 and
E48 ore bodies and a new zone of mineralisation GRP314. Significant upside potential exists through
the application of new technologies, upgrade of the existing resources and discovery of additional
resources.
This paper offers an account of the project design and evaluation and the new technologies being
brought in to practise as part of this exciting project.
Introduction
Northparkes Mines (Northparkes) located 27 kilometres north of Parkes in central New South Wales,
Australia operates block cave and open cut mines and an ore processing plant, producing copper-gold
concentrates that are sold to custom smelters in Japan and China. The mine has been operating since
1993 from two open cuts E22 & E27 and three Underground block caves E26 Lift1 & E26 Lift 2 and
E48, which is the current the production source.
North Mining Limited (a wholly owned subsidiary of Rio Tinto) is the manager of the Northparkes
unincorporated Joint Venture, which has the following ownership:
• Rio Tinto (80 %).
• Sumitomo Metal Mining Oceania Pty. Ltd (13.3 %).
• Sumitomo Corporation (6.7 %).
The E26 Lift 1 and Lift 2 block cave’s construction and operation have been covered at previous
Massmin Conferences by Duffield (2000), Silvera (2004) and Ross (2008). The existing operation has
a mine life to 2024 based on current reserves with production from the E48 block cave currently at
5.8Mtpa, ramping up to 6.2Mtpa. Some aspects of the E48 operation are covered within this paper but
the focus is on the Step Change Project.
The Step Change Project
Northparkes completed an Order of Magnitude Study in May 2010 evaluating the potential for a
large-scale underground mining and processing operation based on a series of large-tonnage lowgrade mineralised zones within Northparkes’ existing mine leases. The zones of additional
mineralisation exploited by the Step Change Project represent depth extensions of the E26, E22 and
E48 ore bodies and a new zone of mineralisation GRP314 (Figure 1). In August 2010, the
Northparkes Mines Joint Venture partners approved a Pre-Feasibility Study to further evaluate the
potential for a step change expansion.
Figure 1: Cross-section showing the zones of mineralisation in relation to existing and proposed mine infrastructure.
As part of the Pre-Feasibility Study an extensive drilling program is being undertaken to improve ore
body knowledge, both geological and geotechnical, with 155km of diamond drilling planned from
both surface and underground. The reported inferred resources at the end of the Order of Magnitude
study were 271Mt at 0.55% Cu, 0.26g/t Au. Drilling to date has increased and extended the
mineralised zones and an updated resource statement will be published at the completion of the PreFeasibility study (PFS).
E22 L1
E48 L2
GRP L1
GRP L2
E26 L3
No. Draw
points
257
883
271
615
968
Extraction
level RL
9730
9200
9620
9120
8950
Depth (m)
550
1080
660
1160
1330
Table 1: Step Change Project block cave footprints
Table 1 shows the proposed block caves extraction levels and depth below surface along with the
number of draw points for each footprint which gives an indication of the potential scale of the
project. The PFS drilling program is designed to have the ore body knowledge to a sufficient
confidence level to allow the project to move straight into Feasibility study.
Geotechnical Considerations
The timely collection of 155km of geotechnical data for use in the determination of geotechnical
parameters and eventual mine design presents a significant challenge. Current data collection is in the
form of traditional diamond core logging, photo logging of old holes and geophysical methods of
Acoustic Televiewer and Full Wave Sonic down hole surveys.
With 6 underground and 2 surface diamond drill rigs operating on a continuous 24/7 roster a high
volume of core is required to be processed. The core shed is staffed by four shifts of geo-technicians
on a rotating day and night shift roster responsible for the traditional Geotechnical core logging which
is split into two areas: RQD log and detail log.
The RQD log is performed for all core on approximate three metre intervals, collecting core recovery,
RQD, microfracture estimate, and counts of open, strong, weak and smooth fractures. The detail log is
performed on 30% of the core and includes structure type, alpha, beta, roughness, planarity and infill
characteristics. A team of experienced geologists is responsible for marking out lithological
boundaries and major structures as well as selecting the geotechnically representative 30% intervals
for detailed logging. Within these representative intervals every discontinuity greater than 1mm is
logged. Although only 30% of core is logged this way, within this percentage, it is possible to
perform statistical analysis of the spacing of discontinuity sets. This detailed spacing data is a
fundamental input to predicting fragmentation of a cave. The number of holes logged hinges on the
geological requirements for resource classification with geotechnical data required on 50m spacings
per rock type for fragmentation and draw zone prediction purposes (Laubscher, 2000). Outside of the
30% detail log, the major structures marked by the geologists are also selected for orientation.
Photo logging of old holes is performed as a QAQC check of core logging and to ground truth
processed data. This is not a regular exercise however has provided a reliable method of comparing
the processed rock mass characteristics within a domain against the actual core photos.
To improve the speed and reliability of data collection within the Step Change Project, Acoustic
Televiewer (ATV) and Full Wave Sonic (FWS) surveys have been performed on 33 holes over the
four mining areas. ATV and FWS surveys are a form of geophysical log where a sonde tool,
connected to a surface logging unit is lowered, via winch, into a bore hole. The ATV tool generates an
image of the borehole by transmitting ultrasound pulses from a rotating sensor and recording the
amplitude and travel time of the signals reflected at the borehole wall. The image of the borehole
reveals discontinuity traces as lower or higher amplitude reflections relative to surrounding rock that
can be traced and resolved to true discontinuity orientations. Benefits of the ATV are:
• a digital record of the hole can be preserved and re-logged irrespective of core cutting
• reduction of time and human error of projecting orientation lines and measuring alpha and
beta angles manually
• structure orientations can be processed within a day of receiving the survey
• orientations can be achieved through broken zones where core orientations are typically lost
• reliable set, orientation and spacing data throughout the length of survey
borehole breakouts can be orientated to determine the principal horizontal stress direction. (
•
Figure 2)
Figure 2 Dark vertical region in ATV survey from break out of hole wall indicating principal horizontal stress
orientation perpendicular to breakout.
FWS surveys measure the waveforms of the tool emitting and receiving sonic impulses. These
waveforms are interpreted using WellCAD to determine P and S wave velocities. The velocities,
along with density measurements, are used to determine the elastic moduli and variations in rock
strength down the hole (Figure 3).
Figure 3 ATV, FWS and logging data for section of hole E48D101.
Three of the planned extraction levels in the Pre-Feasibility study are at depths exceeding 1000m below surface. At
below surface. At this depth, projected, principal stress magnitudes are in the order of 70Mpa and high stress mining
high stress mining conditions are anticipated. Preliminary access development has commenced from the bottom of
the bottom of the E26 Lift 2 decline (9400RL) and is planned to reach 1100m below surface (9200RL) late in 2012
(9200RL) late in 2012 where Hollow Inclusion (HI) Cell stress measurements are planned. As mine design
design commenced in 2011 decisions on stress orientations were necessary early in the Pre-Feasibility stage. The
stage. The combination of historic site HI measurements at around 800m below surface and bore hole breakouts in
breakouts in ATV surveys (
Figure 2) gave confidence to an interpreted East-West principal horizontal stress direction. This
direction was used to orientate extraction drives parallel to the principal stress direction where effects
of stress are minimised during development (Figure 4).
Figure 4 E48 Orientation of stress and major structures used to determine preferred orientation of extraction drives.
Mine Design Considerations
The Step Change Project aims to maintain the efficiency integral to Northparkes small footprint caves
and apply that knowledge to larger footprints. Maintaining the high efficiencies achieved at
Northparkes in E26 Lift 2 and E48 Lift 1 is crucial to sustaining the low operating cost/tonne allowing
the exploitation of the low grade deposits. The Northparkes layout shown below (Figure 5) utilises a
single production horizon (no vent or haulage levels) feeding a large capacity jaw gyratory crusher
with electric LHDs.
Figure 5 E48 Lift 1 Extraction Level Layout and Materials Handling System
The efficiency integral to this layout comes from:
• The LHD tramming bucket first to the crusher, no turning on rim drive maximising high
speed tramming.
• The capacity of the crusher and ROM bin able to handle material up to 3m3, reducing need
for secondary break and rehandle of material
• Electric boggers with low operating cost
• Loader Automation with the ability to lockout and separate drives and zones of interaction.
As the time taken to achieve first production is a major driver of block cave NPV the second major
mine design consideration for the Step Change extraction levels is a focus on development efficiency/
constructability. Learning from E48 development, construction efficiency is just as if not more
important than production operability. The Step Change design is focused on; traffic management,
ensuring multiple access point to the extraction level and undercut development; design of truck
loading bays to remove the bogger and truck from the access drive and; improving ventilation flows
during construction when more diesel equipment is employed.
Ore Processing Considerations
The size of the operation is a key value driver, a range of plants between 10-40Mtpa have been
evaluated to determine the optimal production rate for the operation. The throughput rate effects the
capital and operating costs for the project and therefore the economic parameters used in PCBC to
determine the optimal footprint at various cut off values. The ramp up and development sequence of
the different ore bodies has a major effect on project value but the ability to mine from multiple ore
sources during production provides great flexibility for the project. This has required a high number
of iterations to be run to determine the optimal production rate of 30Mtpa.
The proposed new milling/processing circuit is expected to half the current plant operating cost per
tonne through economies of scale and improved technology. The proposed processing plant will
consist of dual train comminution and rougher / scavenger flotation circuits and a single stream
cleaner flotation and concentrate handling system. Two options are being investigated for the
comminution circuit being SAG mill, ball mill and pebble crushing (SABC); and secondary crushing,
tertiary crushing utilising high pressure grinding rolls and ball mills (HPGR). Lab scale testing of E48
Lift 1 ore (current operation) using HPGR has been undertaken in open and closed circuits, with a
pilot scale trial planned on site in May 2012. The use of HPGR could deliver energy savings of
approximately 10-15% depending on ore type providing significant operating cost savings for the
project.
Material Handling System
The current operation utilises a series of inclined conveyors reporting to a 470m deep 6.0m dia shaft
with twin 16t rope guide skips. As part of the Order of Magnitude study the material handling system
options for the project were reviewed considering a number of hoisting shafts versus inclined
conveyor scenarios. The results of the study showed the capital costs, given the level of accuracy of
the cost estimates, was not a clear differentiator between the options. However the option of a full
inclined conveyor system to surface is being taken forward in the Pre-Feasibility study for a number
other reasons:
• Shafts have higher inherent risks - Vertical openings, lower reliability and greater statutory
constraints.
•
•
•
•
Shafts require complex loading stations both design and excavation. As well as additional large
underground excavations for surge bins
The advantage of shafts being faster to depth is offset by Northparkes’ ability to leverage
existing development already 900m below surface.
Conveyors are more reliable having greater visibility/ accessibility for maintenance,
Conveyors offer greater flexibility to the multiple ore bodies, different levels and large
geographical extent of the project.
There have been significant advances with conveyor technology in recent years with stronger belts
allowing the application of larger drive motors and higher operating speeds of the conveyor. The
design of the proposed main inclined conveyors for the Step Change Project intends to take full
advantage of this technology. The 2 legs of the proposed conveyor have evenly matched belts and
drives for commonality of spares and maintence. The conveyors, designed utilising ST10000 steel
corded conveyor belt, are 3.8km long with a 750m vertical lift and design capacity of 4,100tph
connected by single acute angle main transfer station (Figure 6). Each conveyor is to be driven by 2 x
6MW Gearless Motor Drives (GMD) with the first leg’s drive station located on the surface and the
second leg’s located at the transfer station at 9600RL. The number of complex transfer stations
required underground is minimised by achieving the 1500m of vertical lift in two conveyor legs. The
excavation at the 9600RL will be complex due to the size of the drive station; however it is located at
a level where the rock stress is suitable for such a chamber. Access is made easy by its close
proximity to the E22 extraction level allowing excavation early in the project.
Figure 6: Inclined Conveyor Layout
The main conveyor design with two long straight legs provides the option for a Tunnel Boring
Machine (TBM) to be used for the development. Discussions are under way with TBM suppliers for
the design of a machine capable of being disassembled, turned and rebuilt UG for the second leg.
The Jaw Gyratory crushers (Krupp BK160-190) used in E26 Lift 2 and E48 Lift 1 are considered the
most appropriate for the Step Change Project for following reasons
• Suitable for direct tipping from multiple drives into a Run of Mine (ROM)ore bin.
• Excellent reduction ratio which maximises mill throughput.
• Product shape is well suited to high speed conveying systems.
The down side of these crushers is the large chamber excavation required. With improved design the
excavation size was reduced by 15% between E26 Lift 2 and E48 Lift 1 chamber (Figure 7). To
further reduce the size of the crushing station excavation work is currently underway with the OEM to
trial an innovative lower profile version of the crusher.
Figure 7 3D Model of the E48 Lift 1 Jaw-Gyratory Crushing Station
Innovation
A tunnel boring system (TBS) developed by Aker Wirth in conjunction with Rio Tinto Technology
and Innovation (T&I) will be trialled at Northparkes. The trial, to commence in July 2012, will
develop the access drive to the E22 ore body 580m below surface, from the E48 Lift 1 operation. The
TBS innovation is focussed on improving single heading development rates to provide rapid access to
the ore body footprint improving the time taken to develop block caves. The TBS is designed to cut
30m radius corners and install two passes of ground support suitable for extraction level
infrastructure. The goal of the TBS project is to achieve double the industry bench mark of 6m/ day
for single heading drill and blast development.
Figure 8 TBS Front End under construction in Germany
Human Resources
As part of the Pre-Feasibility study 3.1km of development was initially approved to provide drilling
platforms for the evaluation program. Northparkes made the decision to purchase development
equipment to undertake this work with the aim of building up an owner operator development team
capable of forming the basis of the Step Change Project. Previous underground development at
Northparkes has been undertaken by contractors.
The Step Change project requires the excavation of over 110km of lateral development providing the
long term scope to justify the capital equipment and training of personnel. Northparkes has been
actively training local personnel since the mine commenced. Most recently 185 people with no
previous exposure to the mining industry were trained during the 2.5 year E22 open cut campaign.
Northparkes is positioned within Rio Tinto as a centre of excellence for underground block caving.
Construction has commenced on a specifically designed training centre at Northparkes to cater for
training of personnel for Rio Tinto’s major development projects across the globe. Northparkes also
currently has a 110% employment policy for professional staff to ensure a strong team with
knowledge of block cave mining is in place to provide momentum to both the Step Change Project
and Rio Tinto’s global block cave projects.
Community and Environment Considerations
Northparkes was awarded Australian Mine of the Year 2010 at the annual Australian Mining Prospect
Awards in recognition for our commitment to best practice environmentally sustainable mining and
our focus on building strong relationships with our local community including our Traditional Owners
and local farmers. Northparkes is a proud sponsor of the GP Cup, helping to recruit doctors to
regional communities and the Parkes Elvis festival, a major local event bring over 15,000 people to
town more than doubling the local population. Our strong level of community engagement has
provided local support for the project and continued community consultation is central to the prefeasibility study. The key driving principle of the project is sustainable development, involving the
assessment of both existing and new technology that will deliver environmental outcomes including
improving water and energy efficiency and biodiversity.
References
Duffield, S. (2000) Design of the second block cave at Northparkes E26 mine Proceedings MassMin
2000, Brisbane, Australia, p335-346
Laubscher, D.H. (2000). Block caving manual. Prepared for International Caving Study. JKMRC and
Itasca Group, Inc: Brisbane.
Ross, I.T. (2008) Northparkes E26 lift 2 block cave – a case study, Proceedings MassMin 2008, Lulea
Sweden, p25-34
Silvera, A. (2004) Undercutting at E26 lift 2 Northparkes, Proceedings MassMin 2004, Sanitago,
Chile, p410-414
Acknowledgements
This paper has been compiled from published and unpublished Northparkes and Rio Tinto reports.
The contribution of all members of the Step Change Project is gratefully acknowledged. Special
thanks are extended to both Northparkes and Rio Tinto Management for their permission to compile
and publish this paper.
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