PCBC Block Cave Scheduling
-
Upload
markusmakualdo -
Category
Documents
-
view
226 -
download
1
Transcript of PCBC Block Cave Scheduling
-
7/24/2019 PCBC Block Cave Scheduling
1/17
1
BLOCK CAVE PRODUCTION SCHEDULING USING PCBC
Tony Diering, Gemcom Software International Inc., Vancouver, Canada
Otto Richter, Gemcom Australia, Perth, Australia
Daniel Villa, Gemcom Software International Inc., Vancouver, Canada
Abstract
Gemcom PCBCTMis a software package which
has been developed over the last 22 years for the
planning and scheduling of block cave mines. This
paper presents an update of the various research and
development activities done to PCBC recently. It
also provides an overview of the current capabilities
of the software including tools for both feasibility
type studies as well as tools for operating mines.
PCBC is used extensively by prospective and
operating block cave mines and some of the recent
applications are described.
Introduction
History
PCBC was first developed in 1988 for the
Premier Diamond Mine in South Africa(Diering,
2000). In 1992, the first production scheduler was
added to the system and in 1994 a significant upgradewas done for Northparkes Mine in preparation for
their Lift 1. PCBC was upgraded to Microsoft
Windows operating system in 1996. In 2002, the
Cave Management System (CMS) was developed for
Freeport DOZ mine and this was upgraded to provide
SQL Server database support in 2003 for Finsch
Diamond mine(Diering, 2004). A new algorithm
called Template Mixing (Diering, 2007) was added to
provide better and alternate flow modeling options to
users.
More recently, various enhancements to the
production scheduler and other areas of the program
have been completed some of which are describedhere.
It is worth noting that the block cave market (in
terms of software) is very limited. As such, it is
difficult to fund high quality research and program
development. We at Gemcom Software International
Inc. have been very fortunate to have companies
sponsor custom development activities within PCBC
over the years. These companies are listed in the
acknowledgements section of this paper.
Typical project workflow
A significant number of block cave projects
have been studied using PCBC over its 20 year
history. During that time, a well used work flow has
evolved which is usually used as a guideline for new
projects.
Conceptually, the steps are as follows:
Figure out what is in the ground (geological
model)
Work out where you want to mine (X,Y,Z limits)
Work out the tons and grade that you will get
from those limits
Work out how long it will take (time)
Optimize and iterate to add further value to the
project.
Repeat the whole process every time a new
geological model is produced as the project
evolves.
The overall steps in the process are described
below:
Footprint Finder. This is an application which
works off the geological block model and whose
primary objective is to help assess the best
elevation (or elevations) for the block caving
footprint (Z extent of the mine)
Generate draw points. Setting up draw points
requires assessment of draw point spacing,
tunnel orientation etc. (X,Y extents)
Construct slice file. This is the process of
conversion of a geological model to be aligned
with the draw points such that each draw pointhas an in-situ (un-mixed) resource above it.
Compute best Height of Draw (HOD). Each
draw column is evaluated to assess the best or
highest dollar value which can be achieved for a
given set of mining costs and product revenue
and recovery factors.
Production scheduling. This is the heart of the
PCBC system. It is important to distinguish
-
7/24/2019 PCBC Block Cave Scheduling
2/17
2
between production (tons and grade produced)
and development scheduling (tunneling and
development). PCBC does production
scheduling. This provides the tons and grade
forecasts for the project which has been
described as the mine planners promise to the
shareholders as to what the mine can produce.
Advanced schedules. No schedule is ever
complete or final. During the project evaluation
stage, new pricing or geometrical options will be
considered and new geological models generated
as the exploration drilling progresses. During
production, new schedules are generated
whenever the actual production varies from the
plan (which is always). So the need for a
scheduler which can run in typically less than 20
to 30 minutes per run is important.
Operating mine set up. Once a mine is going
into production, then it is possible to set up a
database to store production tons and draw point
assay and other observational data. The
importance of accurately recording and
managing the tonnages extracted from each draw
point has long been recognized.
CMS can be used to help manage the daily (or
shift based) draw order. This is the daily
tonnage target set for each draw point. This is
essential if a managed block cave is to be
maintained.
Geological/geotechnical monitoring. Tools have
been developed within PCBC to help store,
display and analyze observed data
Least Squares (LSQ) and grade reconciliation
can be used to base schedules on observed assaydata instead of block model data for more
accurate schedules
During the above process, it is essential to have
appropriate tools to interrogate and query the
results generated. Over the years, a substantial
toolbox has evolved based on project and user
requirements.
In this paper
This paper describes the various components in
the PCBC product. It is not intended to provide any
explanation as to how these components work or are
used.
Components of PCBC
The various components of PCBC have evolved
to support the above project workflow. PCBC runs
inside the Gemcom GEMSTMmine planning package
developed by Gemcom Software International Inc.
(Figure 1) The ability of PCBC to work inside of this
framework has proven invaluable over the years and
has allowed our development efforts to focus on the
block cave part of the problem minimizing the need
to develop and maintain the underlying graphical and
database subsystems.
Figure 1 Typical view of PCBC running inside the GEMS
general mine planning package
Components of PCBC are described below
including initial assessment of footprint location,
model set up and mineable reserve assessment, then
scheduling and production management.
Foundation
This is the framework within which PCBC
operates. The various components are summarized
as follows:
Graphical interface
Blocks
Lines
Points
Triangulations
SQL database / workspaces
Profile editors / parameter management
Footprint Finder
Input for Footprint Finder utility comes from a
geological block model together with mining costs,
revenue factors, etc. The program will look at each
level in the block model and then construct vertical
columns accumulating the dollar value. Vertical
mixing is applied to each column using an algorithmbased on Laubschers mixing method (Laubscher,
1994).
This is very useful to obtain an initial idea of
where to locate a footprint and what the initial
footprint shape might be. Figure 2 shows
accumulated columns plotted according to value.
-
7/24/2019 PCBC Block Cave Scheduling
3/17
3
Figure 2 Footprint Finder example on one level
Repetition of this process on each level allows
the tons and value generated to be plotted as showninFigure 3.
-
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
-
100
200
300
400
500
600
700
800
900
1,000
2560
2620
2680
2740
2800
2860
2920
2980
3040
3100
3160
3220
3280
3340
3400
3460
3520
3580
3640
DollarValue(M$)
Tonnage(Mt)
Elevation
Tons Dollar value
Figure 3 Footprint Finder : Tons and dollar value vs
footprint elevation
An example from Freeports DOZ mine is shown in
Figure 4.
Figure 4 Footprint Finder example (DOZ mine)
The higher grade zones are shown in warmer
colors. This type of value plot assists considerably
with the process of defining a reasonable
economically and geotechnically feasible outline.
PCBC
Overall steps of a typical project (from the
program, not project perspective) are as follows:
Set up the initial working environment inside a
GEMS project.
Slice file construction (Figure 5). This is an
integral part of the process. Utilizing user-
defined draw cone shapes, a column of rock
above each draw point is simulated and stored in
what is termed a slice file. The term slice as the
total column is broken into slices which match
the vertical spacing of the geological block
model.
Figure 5 Schematic of block model to slice file conversion
Draw point locations are used to construct a
vertical column which is then intersected with theblock model. The various overlaps of the draw cones
are resolved so as to not double count material and
this is accumulated into the slice file for each draw
point. This is referred to as a NoMix slice file,
since no material mixing has yet been applied.
Figure 6 shows a section of a block model and
the resulting NoMix slice file with one column per
draw point.
-
7/24/2019 PCBC Block Cave Scheduling
4/17
4
Figure 6 Block model to slice file conversion
A variety of material mixing algorithms may
then be applied to the slice file to simulate the
actual material mixing which takes place as
material is extracted from the draw points.
Best HOD. The Best HOD utility will
accumulate tons, grade and dollar value in each
draw column (after application of vertical
mixing) to provide an estimate of mineable
reserves for different footprint shapes. As this
process uses actual draw point locations and
assumed draw column shapes, it is generally
considered more geometrically accurate than theFootprint Finder.
Figure 7 Best HOD based footprint (bottom) vs Footprintfinder result (top) (Cadia East)
Figure 7 shows that the results from Footprint
Finder and Best HOD tools are typically quite similar
as one would hope.
Once the basic preparation work has been done,
production schedules can be generated.
A typical schedule requires input of the
following key components (Figure 8):
Sequence to develop the draw points (and
undercut)
Constraints on the maximum draw rate which
can be applied to draw points
Tonnages required in each scheduling period
Information to control the cave shape. It is usual
to look at different strategies and compare
Numerous other inputs, constraints and reporting
control options
Figure 8 Production scheduling components in PCBC
A basic schedule will open draw points
according to the sequence and deplete tons from eachaccording the Production Rate Curve (PRC), apply
material mixing if required and report tons and grade
mined in a variety of formats.
An advanced schedule could look at changing
parameters for individual or groups of draw points,
adjusting the schedule to past tons mined, having the
HOD profile follow a given cave shape and adding
information to report undercut tons separately from
production tons.
Experience has shown that it is very useful to
have a clean and efficient interface between PCBC
and Microsoft Excel. This allows reports to begenerated in a format which can quickly be further
analyzed by engineers.
In addition, when dozens or hundreds of
schedules are being run, it is useful to have what is
called a playback tool. This allows various aspects
of the schedule to be studied visually to look for
trends (or data input errors!)
-
7/24/2019 PCBC Block Cave Scheduling
5/17
5
The production scheduler can just as easily be
used for forward looking schedules or for analysis of
past performance. This is very useful for grade
calibration and reconciliation purposes.
Cave Management System
CMS was originally developed for FreeportDOZ mine and then further refined for use at Finsch
mine. Currently there are seven mines using or
planning to use CMS. CMS aims to generate a draw
order for each draw point every day or shift. It uses
the recent historical (actual) tonnages to adjust and
manage the draw and provides the supporting
database, reporting and user interface to facilitate this
process. At De Beers Finsch mine, CMS has been
closely integrated with the Sandvik Automine
system.
Figure 9 How CMS fits in between historical tons andfuture plans
Figure 9 shows how CMS fits in between thehistorical tons mined and the requirement to adjust
the plan of the next few months (using PCBC
schedules) in a process called Catch-up to fit in
with the long term plan. (Diering, 2004)
Figure 10 Categorization of draw points for priority
assignment
Each draw point can be categorized in a variety
of ways (Figure 10), including over-draw, under-
draw, normal, draw-bell development, wet muck
(which is a safely concern) or as requiring special
treatment. The tonnage for each category is set
accordingly.
Figure 11 Excel map format for draw point result display
Figure 11 shows an example of daily production
data displayed using Excel. It is important to have a
clean interface between the CMS database and Excel
for ease of analysis by the draw control personnel.
LSQ
The LSQ tool is intended for operating mines.
Once a mine has been in operation for a few years, it
will likely have a draw point sampling program. The
draw point assay values can be stored and sorted per
draw point and then composited into 10m or 15m
intervals to provide some averaging of the highly
variable assays.
Subject to a variety of constraints, a least
squares trend line is put through the composites and
then this can be extrapolated for a short distance upthe draw column into what is essentially the un-
mined part of the column (Figure 12).
This becomes particularly useful when the draw
point assays suggest that the draw point should
remain open (usually after 100% draw) when the
slice file values suggest that the draw point should be
closed. For draw points where the sample trend
differs from the slice file, then the slice file values are
replaced with the sampled values for selected draw
points. This is somewhat similar to the open pit
practice of taking blast-hole samples to improve the
local grade of a bench about to be blasted and mined.
Figure 12 shows a single draw column with
sampled values at various heights (HOD) above the
draw point. The graph shows these together with the
trend line and some extrapolated points. Maximum
and minimum grade values are set so that steep up or
downward trends do not generate unrealistic grade
values.
-
7/24/2019 PCBC Block Cave Scheduling
6/17
6
Figure 12 Sample compositing and trend line analysis in
LSQ
The LSQ tool can either be run as a stand-alone
tool or right within the PCBC production scheduler.
Operations tools and reconciliation
Once a mine is in operation, there is a variety of
useful ways in which draw point sampling data
(grade, geotechnical and geological) can be displayed
and analyzed. A key reason for doing this type of
work is so that we can better understand if or wherethere is irregular behavior with the cave itself. Some
of the analysis types are listed below:
Use of draw point assays for grade reconciliation
and for calibration of the model
Use of draw point assays for improved short
term forecasting using the LSQ tool already
mentioned.
Use of geological samples to supplement the
reconciliation process or to better understand
horizontal and vertical migration of material
within the cave (Figure 13)
Use of geotechnical (fragmentation) data tobetter understand the relationship between draw
rate at draw points and rock type or mining area.
Use of convergence data in production tunnels to
help prevent excessive closure (or collapse) of
these tunnels. Freeport has shown quite
convincingly at their DOZ mine that a diligent
program of monitoring convergence in these
tunnels is beneficial. In areas where high
convergence rates are observed, adjacent draw
points have an increased tonnage target which
tends to relieve the high stresses.
Seismic data and/or extensometers can be used to
help predict the location of the cave back which
can in turn be used to set up surfaces for
simulation of the rilling process which
migrates material non-vertically.
The residual slice file model can be used to re-
estimate a block model which can be used either
in a multi-lift mining situation or as part of a new
block model for a super-pit which some mines
are considering.
Figure 13 Example of graphical display of geological data
Figure 14 Example of residual slice file to block modelconversion
Figure 14 shows an example in which the
residual slice file (after simulation of mining the full
block cave tons) is used to re-estimate a geological
block model. This block model can then be used for
planning of another future mining block.
Recent Developments
PCBC is over 20 years old and hence should be
considered as a mature product. As such the basicplanning and scheduling work flow is well covered.
On the other hand, being mature and with a good
foundation, PCBC has provided a useful foundation
for a number of recent developments which are
summarized in this section.
Upgrades to material flow tools
Playback utility
Display tools
Each of these is considered in more detail
Material flow upgrades
Material flow is an integral part of the block
cave mining (and material depletion) process. The
entry of dilution is a significant factor in the planning
process and modeling of this has proven to be
difficult. As such, a variety of different mixing tools
have been developed within PCBC and users are then
given the choice as to which approach they would
like to adopt. This is summarized inTable 1.
-
7/24/2019 PCBC Block Cave Scheduling
7/17
7
Method Ease
of use
Linear? Comment
No mixing Easy Yes No mixing base
case (In-situ)
Pre-Vertical
mixing
Easy Yes PCBC Default
(includes pre-
erosion)
Laubscher
mixing
Easy Yes Uses Laubscher
tables
Sequential
mixing
Harder No Older method,
includes
toppling
Template
Mixing
Harder No Most flexible
option available
REBOP
interface
Harder No Not yet
generally
available
Table 1 Material mixing options in PCBC
The linear methods can be applied with the Best
HOD utility to find mineable reserves before the
schedule is run. For the non-linear methods, the
mineable reserve will be a function of the mining
sequence and draw strategy. Therefore, mixing hasto be built right into the production scheduler. This is
one of the key differentiators between PCBC and
other commercial scheduling tools.
The pre-mix option in PCBC was recently
upgraded to allow for the inclusion of a draw cone
erosion mechanism. This is useful as there is
increasing evidence that draw cone radii may not be
as large as is often hoped and also that the draw cone
radius changes with time. A fraction of each slice is
frozen and then an erosion rate is specified which
allows this material to be mixed with material higher
up each draw column.
Template Mixing was introduced in to PCBC in
2006. (Diering, 2007). It allows a variety of mixing
mechanisms to be simulated including vertical
mixing, rilling, toppling and fines migration. (Figure
15)
Figure 15 Movement mechanisms in a block cave
It differs from other material flow algorithms
such as discrete particle and cellular automaton
methods. A major advantage of Template Mixing is
its speed. Figure 16 shows a few steps in a depletion
simulation. Blue represents dilution, yellow is ore
and the intermediate colors represent progressive
mixing as the ore is extracted.
Figure 16 Template Mixing 2D example
Figure 17 shows an example for our sand-box
project using toppling, rilling and normal mixing.
-
7/24/2019 PCBC Block Cave Scheduling
8/17
8
Figure 17 Sandbox example with toppling, rilling andvertical mixing
In 2008, a joint initiative was done with Rio
Tinto, Itasca and Gemcom to provide the potential to
combine the PCBC and REBOP programs. This was
done using a hand-shake mechanism so as to
minimize the changes required to each program and
to keep them as independent as possible to facilitate
future development.
Figure 18 REBOP results displayed in PCBC (Markers leftand cones to right)
Figure 18 shows two examples of REBOP
results plotted within the PCBC program. The results
from REBOP are used directly in the production
scheduler and also for modification of the slice file.
As a separate, but related project, Gemcom
worked with Rio Tinto to calibrate PCBC and
REBOP against one another. Figure 19 shows the
geometry of the calibration problem. 50 fictitious
draw points were located in this block model for
testing purposes.
Figure 19 Block model used for PCBC/REBOP calibration
Results from the calibration exercise were reallyencouraging, suggesting ways to improve both the
PCBC and REBOP modeling processes. A sample
calibration curve of Cu grade is shown inFigure 20.
0.000.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
Jan-08
Jul-08
Jan-09
Jul-09
Jan-10
Jul-10
Jan-11
Jul-11
Jan-12
Jul-12
Jan-13
Jul-13
Jan-14
Jul-14
Cu%
Cu% Rebop vs PCBC (N2E5)
Cu%_M3P3
Cu% Tm4
Figure 20 Example calibration curve for PCBC (orange) vsREBOP (green)
The original version of PCBC used what we
term Laubscher mixing (Laubscher, 1994). This
was replaced by pre-vertical and sequential mixing
options in 1994 in PCBC. However, there are still
projects (or people) who like to be able to compare
back against the Laubscher mixing. So it was re-
introduced into PCBC in 2008. It is also useful forcomparison against Footprint Finder results which
use the same mixing.
-
7/24/2019 PCBC Block Cave Scheduling
9/17
9
Figure 21 Dilution entry. Pre-vertical mixing (top) vsLaubscher mixing (bottom)
Figure 21 shows an example comparing dilution
entry from a single draw column. PCBC pre-vertical
mixing has more of an S-curve dilution entry where
Laubscher mixing has a straight line dilution entry
Playback Utility
This tool is used to playback or study results
from a production schedule. Display options include
Triangular Irregular Networks (TINs), contours, pie
charting, and 3D columns. Playback examples are
shown in the later sections on Freeport DOZ and
Palabora.
Display tools
Over the years, a variety of different graphical
display tools have been developed. The more recent
ones are the Excel interface which allows any draw
point related data to be exported directly into Excel in
the correct cell row and column positions for direct
display in Excel as shown inFigure 22
Figure 22 Excel map transfer utility example
The Excel map format is useful for a single
attribute per draw point such as HOD. However, if
one has multiple attributes (which sum to 100%), a
very useful display option is the pie chart. Theprogram will plot a pie chart at each draw point
location using data directly from the underlying
database from what is called multi-bucket format.
(Figure 23)
Figure 23 Example of Pie chart display
In addition to the static displays available, a
more dynamic display of selected information for
individual draw points by right click or mouse
movement over draw points can be very useful
(Figure 24)
-
7/24/2019 PCBC Block Cave Scheduling
10/17
10
Figure 24 CMS control panel with right click anddisplay information
Other options are size based plots (Figure 13),
3D draw columns (Figure 14) and plotting of draw
points in appropriate shapes.
Project examples
Freeport DOZ
PT Freeport Indonesia has been using PCBC
since around 2000. They are currently mining close
to 80,000 t/d, making it a large block cave mine (T.
Casten, 2008). PCBC and CMS are used extensively
for planning and scheduling at the DOZ mine as wellas for daily draw control. Figure 25 shows a plot of
forecast rock types at one step during a production
schedule. Figure 26 shows a plot of HOD for the
same mining step.
Figure 25 Forecast rock types at Freeport DOZ minegenerated in Playback tool
Figure 26 Height of draw profile at Freeport DOZ minefrom Playback tool
Freeport Grasberg
The Grasberg block cave is scheduled to start
production as the Grasberg open pit slows down at
the end of its life. (Figure 27) (Brannon, Casten, &Johnson, 2004) This will be a very large block cave
with production up to 160,000t/d. Numerous
scheduling options have been evaluated using PCBC
and particular emphasis has been placed on effective
modeling of large open pit failures which will
generate additional dilution material.
Figure 27 Grasberg block cave in close proximity to the
large open pit
Figure 27 shows the proximity of the block cave
draw columns to the large open pit.
-
7/24/2019 PCBC Block Cave Scheduling
11/17
11
Figure 28 Column values from Footprint Finder used forfootprint assessment
Figure 28 gives an idea of the variability of the
orebody edges and also alludes to the difficulties in
sequencing and scheduling such a large orebody (grid
size above is 200m!).
Northparkes
PCBC was first used for Northparkes E26 Lift 1
around 1994 and then for Lift 2 planning and
currently for Lift 2 North (Figure 29) (Ross, 2008)
and E 48. Each lift has provided surprises andchallenges from a modeling perspective.
Figure 29Northparkes E26 mining
Salvador
The Salvador mine in Chile has used PCBC
both for the detailed scheduling of individual mining
panels (Figure 30) as well as for combined
scheduling of multiple mining blocks (Figure 31).
Figure 30 Slice file display and layout at Salvador Mine
Figure 31 Scheduling of multiple mining panels at
Salvador Mine
As this is an older mine, current work is looking
to re-estimate the residual grades in older mined out
areas for use with future planning.
-
7/24/2019 PCBC Block Cave Scheduling
12/17
12
Andina
Figure 32 View of three panels (lifts) at Andina mine
Figure 33 Plan of Andina third panel showing grizzly andLHD sectors and existing development
PCBC has been used extensively at Codelcos
Andina mine for a number of years. Challenges in
modeling this deposit include the multi-lift aspect
together with reliable estimation of residual grades of
mined out blocks (Figure 32), the effective
scheduling of grizzly and LHD sectors (Figure 33),
the sheer size of the project and caving issues related
to primary and secondary rock types.
Palabora
The Rio Tinto Palabora mine in South Africa
started block cave production in 2000. (Moss,
Russell, & Jones, 2004)
As the scheduler can work with historical
tonnages as easily as forward looking tonnages, the
playback tool can thus also be used for historical
analysis or reconciliation purposes.
Figure 34 Monthly tonnage display (poor draw control(top) and good draw control (bottom)
Palabora went through a period during which it
was difficult to achieve good draw control.
However, more recently, the draw control has been
much improved. (Pretorius & Ngidi, 2008) This isshown clearly inFigure 34.
Figure 35 Seismic data display example from Palabora
Figure 35, also from Palabora shows a plot of
seismic events for one month together with draw
points and the cave Height of Draw profile (which is
different from cave back profile).
Ridgeway
The Ridgeway Deeps Mine of Newcrest used
PCBC with the Template Mixing option to studyrilling and how this impacted the mineable reserve
and overall production schedule (Burgio & Diering,
2008) (Figure 36)
-
7/24/2019 PCBC Block Cave Scheduling
13/17
13
Figure 36 Section of Ridgeway deeps block cave modelshowing irregular cave propagation on right side
Different scenarios were modeled to see the
effect of limited cave propagation on the East side of
the cave.
Cadia East
The Cadia East project of Newcrest provided
interesting modeling challenges as it is a large multi-
lift project. (Figure 37)Extensive use has been made
of the Footprint Finder tool to assist with
determination of elevations together with more
accurate schedules from PCBC.
Figure 37 Multi-lift example from Cadia East, Newcrest
Finsch
The Finsch Block 4 block cave is an example of
mining beneath an old open pit (Richter & Diering,
2004) (Figure 38). As mining progresses, additional
pit wall material is failing into the developing cave.
The remaining ore and ore/waste combination has to
be continually updated as additional material fails
into the cave.
Figure 38 Schematic of open pit, cave zone and Block 4draw points at De Beers Finsch mine
Figure 39 shows a section with some of the
residual draw columns. These are trimmed against
the known topography and the new failure material
(red) then starts to mix with the existing material
(blue). The mixing zone is shown by theintermediate colors.
Figure 39 Addition of new failure material and mixing of
this material with existing cave rock mass
Figure 40 is similar toFigure 39 except that the
sequential mixing in PCBC is turned off. This
example shows the importance of being able to
model this process in a non-linear manner. The final
mineable reserve is required to be adjusted monthly
or every time the failure surface is modified.
Additional tools in PCBC allow for the addition of
anticipated material for the remainder of the life of
the Block 4 block cave as well.
-
7/24/2019 PCBC Block Cave Scheduling
14/17
14
Figure 40 Addition of new failure material withoutadditional mixing
Calibration examples
Freeport DOZ
A detailed description of the calibration curves
in figures Figure 41 and Figure 42 is beyond the
scope of this paper. (Villa, Prasetyo, & Diering,
2008) Figure 41 is for grade and it shows the extent
to which the PCBC model can be changed to improve
the fit actual against actual observations.
Figure 41 Freeport DOZ. Calibration of grade
Figure 42 is for the Marble rock type. It shows
how the original PCBC marble curve (bottom) can be
changed to more closely approximate the geological
draw point observations (higher curves).
Figure 42 Freeport DOZ. Calibration of Marble rock type
Geological observations are made routinely at
draw points of up to 8 different rock types. These
were also fed into the geological block model so that
comparisons could be made of the observed vs model
rock types. Figure 43 shows the modeled rock types
vs time and Figure 44 the observed rock types vs
time. A detailed study of the differences between the
two can be very informative and lead to ways to
improve the model which may not be apparent from
the grade model / assays. The geological modeling
thus provides another dimension into the
calibration process.
Figure 43 Geological composition from block model andPCBC production schedule
Figure 44 Geological composition based on draw point
observations
Palabora
Work has been done at Palabora to improve the
short term grade estimates using the LSQ tool
described above. Figure 45 shows the improvement
in the short term comparing the PCBC LSQ forecast
vs Samples.
-
7/24/2019 PCBC Block Cave Scheduling
15/17
15
Figure 45 Measured vs PCBC standard and LSQ adjusted
grades
Figure 46 shows a similar set of graphs, but
comparing hang up frequency. In this case, there was
no initial model forecast for hang-ups, but based on
the LSQ approach, a reasonable forecast for short
term hang up frequency was achieved.
Figure 46 Measured vs LSQ modeled Hang-ups
Salvador
Various calibration runs were done at Salvador
mine. Two examples are shown in Figure 47 and
Figure 48. A detailed explanation of the curves is
beyond the scope of this paper, but the graphs show
how mixing parameters were adjusted to improve
both the model results and the confidence in other
forecast results.
Figure 47 Various PCBC runs vs assayed results for IWsector, Salvador mine for 8 years
Figure 48 Various PCBC runs vs assayed results for ICE
sector, Salvador mine for 17 months
Example of block model adjustment
In this example (Figure 49Figure 35), variousattempts were made to calibrate the PCBC results
with the observed mill feed grades. However, the
PCBC grades were too high irrespective of the
mixing parameters used. This is an example in which
the underlying block model is at fault. Re-
estimation of the block model with different
interpolation parameters has largely resolved this
discrepancy.
Figure 49 Calibration example in which the block modelrequired re-estimation
Example involving old mining areas
This example considered two separate runs. In
the first (Figure 50), the block model was notadjusted correctly for historic mining. Once this had
been recognized and appropriate changes made to the
area in which mining had taken place, a much better
fit between PCBC model grades and observed mill
grades was obtained. (Figure 51)
-
7/24/2019 PCBC Block Cave Scheduling
16/17
16
Figure 50 Grade curves measured vs PCBC beforeadjustment for mined out area
Figure 51 Grade curves measured vs PCBC after
adjustment for mined out area
Concluding remarks
PCBC has been applied to a variety of different
block cave projects and mines over the last 20 years.
Every project has its own unique challenges some of
which have been described in this paper. As the
program has evolved to meet these new problems, its
capability has been enhanced.A key component of the modeling and program
development process has been the ongoing
calibration of PCBC against observations / sampling.
This process has clearly indicated that it is not always
the material mixing which required the most
adjustment. Careful attention is also required in areas
of past mining, or for open pit failure material or
even to the geological block model itself.
The calibration examples also clearly show the
benefits to be gained from doing a calibration
exercise using both grades and rock types. In each
case, a clearer understanding caving mechanisms is
gained from the work. This type of calibration also
strongly justifies the effort of taking draw point
samples for grade and rock types.
The development process for PCBC has been
significantly enhanced by collaborative projects with
key clients and this assistance is gratefully
acknowledged.
Acknowledgements
The authors would like to thank the following
mining companies for permissions to publish
information and figures pertaining to their projects in
this paper: Freeport-McMoRan Copper & Gold Inc.,
Rio Tinto, Newcrest Mining Limited, De Beers
Consolidated Mines Finsch mine, Codelco DivisinSalvador, Codelco Divisin Andina and Palabora
Mining Company.
The authors also gratefully acknowledge
assistance with the development of the software from
Freeport-McMoRan Copper & Gold Inc., PT
Freeport Indonesia, Rio Tinto, De Beers
Consolidated Mines Finsch mine, Codelco Divisin
Andina and Palabora Mining Company.
References
1. Brannon, C., Casten, T., & Johnson, M. (2004).
Design of the Grasberg block cave mine.
MassMin, (pp. 623 - 628). Santiago.
2. Burgio, N., & Diering, T. (2008). Simulating
irregular cave propagation using PCBC.
MassMin, (pp. 1033 - 1042). Lulea.
3. Diering, T. (2004). Combining long term
scheduling and daily draw control for block cave
mines.MassMin, (pp. 486 - 490). Santiago.
4. Diering, T. (2000). PC-BC: A block cave design
and draw control system. MassMin, (pp. 469-
484). Brisbane.
5.
Diering, T. (2007). Template Mixing: A
Depletion Engine for Block Cave Scheduling.
APCOM, (pp. 313 - 320). Santiago.
6. Laubscher, D. (1994). Cave Mining: State of the
Art. SAIMM, October, 279 - 293.
7.
Moss, A., Russell, F., & Jones, C. (2004).
Caving and Fragmentation at Palabora:
-
7/24/2019 PCBC Block Cave Scheduling
17/17
17
Prediction to Production. MassMin, (pp. 585 -
590). Santiago.
8. Pretorius, D., & Ngidi, S. (2008). Cave
management ensuring optimal life of mine at
Palabora.MassMin, (pp. 63 - 72). Lulea.
9. Richter, O., & Diering, T. (2004). Production
Scheduling at Finsch Diamond Mine. MassMin,
(pp. 453 - 458). Santiago.
10. Ross, I. (2008). Northparkes E26 Lift 2 block
cave A case study. MassMin, (pp. 25 - 34).
Lulea.
11. T. Casten, L. R. (2008). P.T. Freeport Indonesia's
Deep Ore Zone mine - expanding to 80,000
tonnes per day.MassMin.Lulea.
12. Villa, D., Prasetyo, R., & Diering, T. (2008).
Calibration of mixing model to predict grade at
Freeports DOZ Mine. Massmin, (pp. 1053 -
1062). Lulea.