whittlemime 413-513 workshop 1 2014

8/18/2019 WhittleMIME 413-513 Workshop 1 2014

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MIME 413 – Strategic Mine Planning with Uncertainty Fall 2014MIME 513 – Mine Planning Optimization under Uncertainty Lecturer: R. Dimitrakopoulos

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Class Project – Part 1

Optimization in Mine Design using Whittle Software

Due date: September 26 th 2014

Earl y bir d submission bonus – by September 23 st 2014: +10%

Late submi ssion penal ty: 10% per day

OUTLINE

1.

Introduction

2. Task

3. Data Files

4.

Instructions


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1. Introduction

Part 1 of the project covers the following topics:

1. Definition of the ultimate pit limit.

2. Determining nested pit shells.

3. Designing pushbacks.

4. Effects of extraction sequence of ore/waste blocks on production scheduling andlong term planning.

Concepts behind Whittle Nested Pits

Whittle uses a Model File containing details of the contents of each block, but, foroptimization purposes, we need a single value for each block. This value is the cash flow(positive or negative) that would result from mining the block. For optimization purposesit is important to assume that the block has been uncovered. It is unnecessary to allow forstripping costs, because the optimizer does this implicitly. If we calculate the blockvalues for a particular model we will get a certain set of block values that, when used in a pit optimization, will lead to a particular pit outline, the optimal outline.

Example 1

For the purpose of this example, assume the pit outline is outline "A" in the followingdiagram.

Figure 1. Pit outline obtained from a single optimization.

Within an optimal outline, every block is "worth mining". Each block consists of zero ormore parcels and, possibly, some undefined rock that can be regarded as another parcel.


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The resultant cash flow from mining a block consists of the sum of the cash flowsgenerated be mining the block’s parcels. A parcel’s cash flow depends on the way wetreat the parcel (i.e. mill, leach, etc.) and the associated prices and costs with the methodof treatment. An increase in all commodity prices while keeping the costs constant may

cause the parcel to be treated differently (e.g. it may now be processed rather than treatedas waste); in this case, the cash flow will always either stay the same or increase.Increasing the prices will not decrease the cash flow obtained from mining a given parcel.Thus, if we increase the prices, the value of every block within outline A will increase orstay the same. No block value will go down. Consequently, every block within outline Ais still worth mining.

Example 2

In addition, if we do another optimization using the new values, the new outline (shownas outline B below) is certain to include the whole of A. It may also include extra blocksthat were not worth mining before, but which are now worth mining.

Figure 2. Pit outlines obtained from two optimizations.

The Whittle Pit Shells node (Optimization program, FXOP)

If we step the prices through a series of values, doing an optimization for each, we obtaina set of nested pit outlines, and this is, in effect, what the Pit Shells node in Whittle does.

It multiplies all of the prices by a series of 50 to 100 "Revenue Factors" ranging,typically, from 0.3 to 2.0, and produces a pit outline for each factor. The reason for producing outlines for the smaller values of Revenue Factor is that we want to produceinner pit shells that highlight the best positions to start mining and to assist with thesequencing. The outlines are often very close together and form an almost continuous"spectrum", where the change in tonnage from one outline to the next is quite small.However, if the grade increases sharply with depth or the ore body is discontinuous, largetonnage differences between adjacent pits can occur. Since all the outlines obey the pit


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slope requirements, it is simple to determine which sequences are feasible when miningout a particular pit.

Example 3

Figure 3. Schematic of nested pits.

In Figure 3, if pit 5 is the ultimate pit, we can clearly mine in the sequence a, b, c, d, e, f,g, h, etc. If the pits are sufficiently far apart to give working space, another possiblesequence is a, f, b, g, k, c, etc. Regardless, given a set of nested pits, these sequences areclearly defined and easy for the computer to trace, and thus can be used to show variousmining schedules in order to obtain projected tonnages, grades and cash flows. Although

each set of outlines is only strictly optimal for a particular set of costs, their usefulnessgoes far beyond this. Provided that the costs used are of the same order, anotheroptimization run with different costs will usually produce a set of pits of similar shape, but are shifted relative to those from the first run. For example, pit number 20 from onerun may be very similar to pit number 25 from the previous run. It is therefore reasonableto simulate mining with wide ranges of prices and costs using the same set of nested pits.Once a set of costs has been settled on, a final optimization using those costs and arepeated simulation can be run as verification.


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2. Project (Part 1) Task & Deliverables

Deliverable for Project Part 1:

A properly documented report that amalgamates the deliverables from each of the three

Steps below , for the mine’s yearly pit design and mine planning study.

Find the optimal ultimate pit limits, design pushbacks and generate a Life-of-Mine(LOM) production schedule for a small gold deposit, so as to maximize its Net PresentValue. Report all findings and justify your choices. For this task, the Whittle softwaremust be used along with the parameters provided in Table 1 and the orebody models inthe files described below. All deliverables for this assignment are discussed in thissection; for information on the related files and steps, refer to the following sections.

Table 1. Parameters for the optimization of the gold deposit.

Slope angle 54 °

Selling price 19.29 $/unit

Selling cost N/A

Mining cost 1.8 $/tonne

Processing cost – Fresh Ore 16.862 $/tonne

Processing cost – Oxide Ore 8.195 $/tonne

Recovery – Fresh Ore 84 %

Recovery – Oxide Ore 90 %

Cut-off 0.3 g/tonne

Model Au unit Grams

Processing capacity 0.2 Mt/y

Extraction capacity 0.5 Mt/y

Discount rate per period 8%


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Step 1: Defi ning the ultimate pit l imit

Define the final pit by choosing amongst the available nested pit shells generated byWhittle.

Deli verables from Step 1:

a) A pit-by-pit graph of undiscounted cash flow per pit shell, where the pit number is plotted on the X axis and the net economic value on the Y axis.

b) A pit-by-pit graph of discounted cash flow per pit, where the pit number is plottedon the X axis and the discounted economic value on the Y axis.

c) Pit-by-pit graph of recovered metal, ore and waste where the pit number is plottedon the X axis and the metal on the Y axis.

d) Plot the required graphs using bar style.

e) All choices made need to be justified and implications briefly explained.

Step 2: Design pushbacks given the ul timate pit l imi t in Step 1

Using the final pit as defined in Step 1, use the automatic pushback selection in Whittleto choose the pushback design. Try at least three different and meaningful numbers of pushbacks and assess the possible implications on the final NPV of the mine; explain thedifferences and related effects.


a) A table that associates a pushback design to its NPV.

b)

Report in pushback-by-pushback graphs ore, waste, metal and cash flows.c) Discuss the implications of the number of pushbacks used and what they

physically represent.

d) All choices must be justified and implications briefly explained.

Step 3: Generate the LOM production schedule of the mine

Using the ultimate pit and pushback design from Steps 1 and 2, generate the LOM production schedule. Use the same processing and extraction capacities as in Table 1.


a) Produce the LOM production schedule and report all related graphs (ore, waste,metal production, and cumulative NPV) for the mine.

b) Describe the differences among the available schedule generating options:Milawa NPV, Milawa Balance and fixed lead.

c) All choices must be justified and implications briefly explained, including the selection of the scheduling option.


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3. Data Files

The folder named “MIME 413 Project Part 1” contains a single estimated (kriged,deterministic) orebody model and a parameter file.

A)

Model File:

Orebody block model files: These types of files are identified by their extension as“mod.” They contain the specification of the block model of the deposit such as block

coordinates, metal grade, ore and waste tonnage etc.

Format : The formats of the parameter and model files are provided in the Whittlesoftware’s manual and the summarised below.

The first line:

X, Y, Z, Number of Parcels, Positional mining CAF, Processing CAF, tonnage

The second line:

X, Y, Z, Rock Type, Tonnage, Metal Content

If the number of the parcel for a block is zero, “the second line” doesn’t exist for that block. If the number of the parcels is 1 or more, “the second line” is written for each of

the parcels for that block.

Figure 4. Example of a mod file when opened in a text editor.


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B) Parameter File

In this workshop, all the necessary parameters for the design and planning of the pit are

provided. For more information, see the “Whittle Parameters” document included or theWhittle help manual.

The parameter file: parfile.par

Format : The format of the parameter file is summarised as below.

1 dx dy dz x0 y0 z0

(block dimensions along x, y and z directions and the origin of model)

2 nx ny nz

(number of blocks along x, y and z directions)

3 ABI MCAF PCAF PRNT RSTINT RSTME

[active block indicator, positional mining CAF(1=use CAF, 0=do not use), processingCAF(1=use CAF, 0=do not use), printing index (1:quantity of unprocessed material printed, 0:quantity of unprocessed material not printed), restart interval and restart time]

4 1 nx 1 ny 1 nz

(sub-region block limits)

5 1 30 0.0

(number of slope regions, number of benches to generate structure arcs, default blocktonnage)

6 0.0 54.0

(slope bearing angle, pit slope)

12 4 0 4 4 0 $

(decimal places to write: block ton, total ton, revenue factor, currency total, currency-character)

13 1.000 1.000 1 2 1.800 1

(general block tonnage, dilution factor, [recovery, the selling cost ratio; not used,] air flagA=consider air blocks in optimization(1) or do not (2), air flag B=air blocks not included

in the result file (1) or air blocks within the ultimate pit are included (2)-Air flag A must be 1, or all air blocks in the model file are included (3), reference mining cost, oreselection by cutoff (1) or by cash flow (2))

14 0.1657506

(revenue factor as single number or range start-step size-end)


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18 GOLD 1 4 4 4

(element type, position in the file, decimal places for gold in the block: total unit of

element, grades and cut-offs for this element.

20 GOLD 0 19.2900

(element, selling cost/unit, price/unit)

21 OXOR 1.000 0 1.000

(rock type, mining CAF, rehabilitation cost/ton, processing throughput factor — speed of processor for a particular rock type)

25 MILL OXOR 8.195

(processing method, rock type, processing cost/ton)

26 GOLD C 0 0.900 0 0.300 0

(element type, cutoff controlled (C) or not controlled (N), processing cost/unit, processrecovery fraction, recovery threshold, minimum and maximum grade).

4. Task Instructions

The computer session of this first part focuses on the basics of using the Whittle software.This is only useful to those who have not used Whittle previously. This section coversimporting data into Whittle, generating pit shells and ultimate pit limits, designing

pushbacks from pit shells and optimization with the Milawa-NPV option. Some of thetraditional sensitivity analysis, such as varying commodity price and processing capacityare also included in the notes, but is not necessary for this assignment. You are, however,encouraged to explore these features if desired.

The data set used in this assignment is generated from an estimation method (ordinarykriging). The estimated orebody model will be used as input and the resulting schedulesand pushbacks obtained in the first part are referred to as the “base case” during analysis

performed in subsequent assignments.


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1 Import Deposit Data in to Whittle

a. Make a new directory in your personal network drive (P:\ drive) called “ProjectPart 1”.

b.

Copy the files: ‘parfile.par’ and ‘kriging.mod’ from the folder provided into the“Project Part 1” directory you just created.

c. Open Whittle and import parfile.par and kriging.mod files as follows:

d. Click on create a new project and press OK.

e. Type project name: Project1, select the project directory by clicking on thedirectory icon on the right side - P:\Project1\. Whittle should automaticallycreate a “working” directory - P:\Project1\working_Project1. Click on “next”,for import type, choose “Whittle block model”. Browse the folder you createdto find “kriging.mod” as the model file to import, and “parfile.par” as the parameter file to import. Then, click on finish and “yes” to confirm. If there areany additional windows that appear asking for parameters, simply keepselecting “Next” or “Finish” until they go away.


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f. Check the parameters loaded and run the program by clicking on the third man

icon . A green check mark should appear beside “New Block Model”.

g. Under “New Block Model”, select the “Description” tab and change the blockmodel’s description from “New Block Model” to “Kriged Model”.

h. Under the “Formats” tab, set the “Units” for Element GOLD to “gram”. Notsetting the correct units in Whittle can lead to misleading results.

i.

Press the “Accept” button to accept the changes.

j. Now, click on each of the tabs and check what information is provided.

k. When finished, select the “Check Data” button to ensure that all data has beencorrectly entered.


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2 Generate Ultimate Pit Limits

a. Click on “New Slope Set ” on the left and description tab on the right. Type“Kriging Slope Set” for the description and click on “Accept” keeping all the

values as default. Click on “Profile” tab and check the parameters to ensure thatthe slope angles are correct, as per the assignment requirements (Section 2).

b. Click on “New Pit Shell s ” on the left and description tab on the right. Type“Kriging Pit Shells” for the description. All of the parameters for this nodeshould have been read from the parameter file but you should verify them all.Once again, it is important to be mindful of your units (% recovery, gradesexpressed as decimals, units for selling on market, etc.) When finished, press“Accept”.


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c. Right-click on “New Schedule Graph” on the left side and choose “Cut Branch”from the menu. Repeat for the “Pit by Pit Graph” node.

d. Click on description tab of the “New Operational Scenario” node and type“Operational Scenar io-1 .” Click on “time cost” tab and change the discountrate. Then, Click on the “limits” tab on the right side and change the value ofthe extraction and processing limits. Additionally, ensure that the units for“Element limits” is set to grams. Then, click on “accept”.

e. Add Pit by Pit Graph: Right click on “Operational Scenario-1” and add “Pit byPit Graph”. Click on “description” tab and type “Pit by Pit Graph-1”. Onschedule tab, ensure that “fixed lead” is selected with “0” value. In the“Definition” tab, delete all the lines below “tonnage of waste rock”. Then add anew value to be displayed by clicking in ‘add’ select “Output” on the left andselect “Undiscounted revenue and cash flow” on the right, and choose “Open Pit


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Value”. In order to generate various graphs (as outlined in the assignmentdeliverables), you will need to repeat this step and select the correct propertiesto save. You will likely need to explore the various options to be able to get thecorrect graphs. Do not hesitate to include a new graph not outlined in the

assignment deliverables if you believe it helps you justify your points in yourreport’s discussion. Click on add to selection list and best case, click on OK.Then, click on OK and accept it by clicking “accept” in the gener al window.Then, run the program by clicking the running man icon.


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f. Generating the pit li st : Right click on the Kriging Pit Shells and select “Other”-“Export Pit List”. Select the directory you created and change the name to


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h. Click on the “Graph” tab and press zoom button. Click on the preferences. Type

DCF on the Title of Y-Axis. Select only “Open Pit Value” and unselect the

other options. Click on the 2nd

Y-Axis preference tab and unselect “Use multipleY-Axis” because you have chosen only one display (there is no need to displaythe 2nd axis). Click on “Style preferences” and select “Open pit value for the best case.” Change the Style to Bar, and Colour to red. Click on Graph tab to

see the modified plot. Repeat these steps to generate your graphs required forthe assignment deliverables. Be sure to comment on your results.


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3 Generating Pushbacks from Pit Shells

a. We will first create pushbacks using the automatic pushback selection tool.Right-click on “Pit by Pit Graph-1”, and select “Copy Node”. Right-click on“Operational Scenario-1” and select “Paste”. Change the name of the node

(“Description”) and re-name it to “Pit by Pit Graph- # PB” where # is thenumber of pushbacks you wish to test. Under the “Schedule” tab, and under“Specified case pushback definitions”, select “Auto” and enter the number of pushbacks you would like in your design. Select the “Definition” tab, and press

“Edit”. You can now enter the final ultimate pit shell to be considered (the limitof mining); enter the ultimate pit shell number defined in Step 2 (g,h) in the“End” textbox. You will not need to worry about the graphs in this step, as theywill be generated in more detail in the following step. Press the running manicon to run the pushback designs. After the algorithm has finished running,under the “Schedule” tab, you will see numbers listed in order beside“Pushbacks used for last run”. These tell you the optimal pit shell combinations

that Whittle has chosen, given the number of pushbacks you have selected. Youwill need to write down these numbers, as they will be required in thefollowing step (Step 3 b). Repeat this step for various numbers of pushbacks bycopying the node and pasting under “Operational Scenario-1”, and changing thenumber of pushbacks.


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b. Adding Mining Width (combine pit shells to pushbacks): Right-click on“Kriging Pit Shells” select “Add” and “Mining Width”, then, click on the“Description” tab and type “Kriging Mining Width - # Pushbacks” (where # isthe number of pushbacks you want to consider). Click on the “Definition” tab

and type in the desired mining width (justify your parameters in your report). Ifyou are unsure of any of the parameters in this menu, please refer to the help filein Whittle. Then, in “Pushback definition”, click on edit pushbacks and type inthe desired pit shells numbers to be considered as pushbacks. These were madeavailable to you in Step 3 (a) under “Pushbacks used for last run”. Run the program to combine pit shells to pushbacks. You will need to repeat this step foreach pushback configuration you wish to test (# of pushbacks in design). It isrecommended that you save these as new scenarios


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c. Right click on your pushback scenario created in the previous step (KrigingMining Width - # Pushbacks), and select “Add” then “New OperationalScenario”. Whittle should add the correct parameters, however if they areincorrect, be sure to put in the correct parameters (Discount rate and Processing

limit), as per Step 2 (d) . Right click on your new operational select and select“Add” then “Pit by Pit Graph”. Under the “Schedule” tab, ensure that“Specified Case Pushback Definitions” is set to “Manual”, and you will need to

add your pushbacks. Press the “Add” button, and then enter your pushbacks inincreasing order (e.g. if you have 4 pushbacks, you would enter “1 2 3 4”). Press

“OK”. Under the “Definition” tab, ensure that Whittle will generate the correctgraphs that you require. When ready, press the running man button. Under the“Graphs” tab, you should now be able to see your graphs for the pushbacks (i.e.

not pit shells, as shown in the previous step). You will need to re-do thisanalysis according to the various # of pushback scenarios you have chosen.Compare what happens in pushback tonnages, ore tonnages, etc. to justify your

decision on number of pushbacks in your design before going on to the nextstep.

d. Generating Pit li st Kr igb.pil : Right click on “Kriging Mining Width”, tools-exporting pit-list- select the working directory and change the name to krigb.pil,export it. Here, this pit list contains block coordinates and the numberrepresenting the pushbacks. You will need to do this for which ever design (# of pushbacks) you deem best. The output file is required for the next part of theproject.

4 Optimization with Milawa Algorithm

a. New Schedule Graph: Create a production schedule by right clicking on the newoperational scenario (whichever was deemed optimal from the previous step),selecting “Add” then “Schedule Graph”. In the “Description” tab, type “K rigingSchedule – Milawa NPV”. In the “Specified Case Scheduling Algorithm”section of the “Schedule” tab, select “Milawa NPV”. Add “Manual” pushbacks by clicking “add” on the right side (Add as many pits as needed e.g. if you have4 pushbacks, you would enter “1 2 3 4”). In the “Definition” tab, delete all thelines below “Discounted open pit value” and click on add. Then, click on“output” on the left, and on the right choose “element and grade” . Choose “Qtyof output from ( /UO*) to have

quantity of gold in the output file. Click on “add to selection”, choose “GOLD”,from “MILL” for “specified case”, and OK. Click “accept”. Feel free to addwhatever graphs necessary to justify your decisions in your report’s discussion.Then, run the program by clicking on 2nd running man. Repeat this step for“Milawa Balanced”. Discuss the differences between the output schedules,

which one you think is more effective, etc.


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whittlemime 413-513 workshop 1 2014

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