Graphical Sequencer
The Graphical Sequencer provides an interactive graphical method for scheduling an open pit or underground mine. It provides a method for designing and sequencing mining blocks based on an orebody model and production targets provided by the user. It allows for the scheduling of materials from more than one level of a mine at a time.
| Setup |
| Define Blocks |
| Sequence |
The first option Define Setup is to switch format files at a touch if there are several format files defined. The options Define Format, Define Targets and Create Database are preparatory and you use them infrequently - for example, when setting up the system for a mine, or significant part of the mine; and when altering the basis of the scheduling, such as altering a production target for a period, adding targets for new periods or altering the specification for a material. The last three choices; Define Blocks, Update Database and Sequence Blocks are interactive. Once you have set up the system you use them consistently.
Although in practice you might go to the menu choices in any order, for setting up the scheduling of a new pit it is logical to run them in the order they appear.
What is Scheduling?
There are many considerations that must be made when establishing a mine schedule. A mine schedule should attempt to maximise the profit at the start of the mine and maintain a good cash flow throughout the life of the mine. The advantage of using a computer based scheduling system is that many different mining scenarios can be examined and the one offering the best returns based on the current economic conditions can be used.
A good mine schedule should also maintain a good supply of ore throughout the life of the mine and should take into account the milling characteristics of the different materials in the orebody. The scheduling of different materials in the Graphical Sequencer is achieved by establishing an orebody model that defines each different material with a unique string number.
The amount of waste stripping required needs to be balanced throughout the life of the mine. This will affect the supply of ore, since a poorly scheduled waste stripping program will result in the waste backlogs that need to be shifted before a proper ore supply can be continued.
In summary, the key issues in mine scheduling are:
- achievement of production targets
- interactive design and evaluation of irregular mining blocks
- ability to cope with different ore types
- effective report generation
- preparation of dig plans to maintain a high standard of production control
- capacity of mining equipment such as trucks, shovels and drills
The Graphical Sequencer has features which satisfy all of the above criteria with the exception of equipment scheduling.
Preparing Data for the Graphical Sequencer
Before the Graphical Sequencer can be run there are some things that need to be organised, including the orebody model files, the grade and tonnage requirements for each period to be scheduled and to a lesser extent the mining outlines. The steps described in the following sections must be carried out thoroughly to minimise potential problems when the Graphical Sequencer is run.
Preparing the Orebody Model Files
One of the main inputs to the Graphical Sequencer is a series of orebody model files stored as string files. The orebody model may be represented as string outlines within each file or as block centroids in each file. There must be one orebody model file for each bench to be scheduled.
The orebody model should be organised so that each ore type is given a unique string number to allow for more flexible reporting. The ore type classification may be a function of rock type, grade or both. For example, if the orebody model has two major ore types with different specific gravities, along with three grade classes within each ore type, the string numbers could be:
String 2 - Ore type 1, medium grade
String 3 - Ore type 1, high grade
String 11 - Ore type 2, low grade
String 12 - Ore type 2, medium grade
String 13 - Ore type 2, high grade
An orebody model organised along these lines will allow easy reporting either by ore type or by grade classification. The number of strings used for different grade classes should be sufficient to meet any reporting requirements. It is easier to combine classes than it is to subdivide into grade classes to produce reports. The use of many different string numbers for the orebody model will also allow the engineer to look at the effect of different cut off grades on the scheduling sequence and on the total orebody. The orebody model should represent a reserve model, that is, the orebody inside a pit design. This can be achieved by intersecting the resource orebody model with the pit outlines.
The orebody model should contain a waste boundary in each level. The waste boundary would normally be the outline of the pit design at each level and must be a unique string number. These same outlines would have been used to intersect the resource orebody model as described above.
There is no need to build an ore/waste model that has anti-clockwise segments of waste around the ore strings since the Graphical Sequencer will automatically treat any material outside an ore string or air string but inside a waste string as waste.
If the Scheduling is to be carried out on an operating mine, then those areas that have been mined out need to be excluded from the orebody model.
Establishing the Grade/Tonnage Requirements
Another important input to the Graphical Sequencer is the grade and tonnage requirements for each material type within each mining period. This information is input to the Graphical Sequencer to create a targets file that will be used as a guide when sequencing the mining blocks.
Hint: When you have prepared the orebody model files for each bench, use String File Summary to check integrity and direction of the strings in the model.
Before the grade and tonnage requirements for each period can be determined, a list of the available tonnages for each material type should be generated on a bench by bench basis. As an example the available tonnages for a gold deposit might be:
| Mid Bench | High Grade | Medium Grade | Low Grade | Waste | |||
|---|---|---|---|---|---|---|---|
| Tonnes | Grade | Tonnes | Grade | Tonnes | Grade | Tonnes | |
| 502.5 | 37,000 | 7.31 | 69,000 | 3.78 | 373,000 | 1.76 | 360,000 |
| 499.5 | 55,000 | 7.47 | 65,000 | 3.71 | 399,000 | 1.64 | 295,000 |
| 496.5 | 25,000 | 8.40 | 30,000 | 3.86 | 280,000 | 1.68 | 446,000 |
| 493.5 | 19,000 | 9.86 | 17,000 | 3.74 | 195,000 | 1.70 | 450,000 |
It is also important at this stage to look at the orebody model either on hard copy plans or in the Graphics and to get a feel for where the higher grade areas in the orebody model are.
The proposed mining targets will also be a function of the equipment available for the mining and processing of ore, since these will place final constraints on the amount of material that can be dealt with in any single period. For example, a deposit containing 1.6 million tonnes of ore and 1.6 million tonnes of waste could possibly be mined and processed over a period of four years using a couple of excavators with only a small fleet of trucks. The maximum material that could be mined in any six month period would therefore be 400,000 tonnes.
Once the average mining rate has been determined, a table of proposed mining targets for each period can be drawn up. The tonnages should be estimated first for each material on each level within each period by using a table like the one shown below.
Preliminary scheduling targets:
| Period | Bench 502.5 | Bench 499.5 | ||||||
|---|---|---|---|---|---|---|---|---|
| HI | MED | LOW | WASTE | HI | MED | LOW | WASTE | |
| 1 | 34,000 | 60,000 | 18,000 | 126,000 | - | - | - | - |
| 2 | 3,000 | 9,000 | 73,000 | 100,000 | 32,000 | 31,000 | 120,000 | 32,000 |
| 3 | - | - | 80,000 | 70,000 | 15,000 | 20,000 | 150,000 | 85,000 |
| 4 | - | - | 40,000 | 64,000 | 8,000 | 14,000 | 70,000 | 120,000 |
| 5 | - | - | - | - | - | - | 59,000 | 58,000 |
| 6 | - | - | - | - | - | - | - | - |
| 7 | - | - | - | - | - | - | - | - |
| 8 | - | - | - | - | - | - | - | - |
| tot | 37,000 | 69,000 | 373,000 | 360,000 | 55,000 | 65,000 | 399,000 | 295,000 |
| Period | Bench 496.5 | Bench 493.5 | ||||||
|---|---|---|---|---|---|---|---|---|
| HI | MED | LOW | WASTE | HI | MED | LOW | WASTE | |
| 1 | - | - | - | - | - | - | - | - |
| 2 | - | - | - | - | - | - | - | - |
| 3 | - | - | - | - | - | - | - | - |
| 4 | 7,000 | 8,000 | 50,000 | 25,000 | - | - | - | - |
| 5 | 12,000 | 20,000 | 120,000 | 95,000 | - | - | - | - |
| 6 | 6,000 | 2,000 | 60,000 | 220,000 | 4,000 | 8,000 | 50,000 | 40,000 |
| 7 | - | - | 50,000 | 106,000 | 15,000 | 9,000 | 40,000 | 180,000 |
| 8 | - | - | - | - | - | - | 100,000 | ? |
| tot | 25,000 | 30,000 | 280,000 | 446,000 | 19,000 | 17,000 | 190,000 | 220,000 |
The average grade for each material type on each bench can then be used to provide the average grade of each material within each period. These are estimates only and will be used as a guide when sequencing the pit.
An example of the type of final grade/tonnage table that should be drawn up is given below.
Proposed targets for an example gold deposit:
| Period | High Grade | Medium Grade | Low Grade | Waste | |||
|---|---|---|---|---|---|---|---|
| Tonnes | Grade | Tonnes | Grade | Tonnes | Grade | Tonnes | |
| 1 | 34,000 | 7.31 | 60,000 | 3.78 | 180,000 | 1.76 | 126,000 |
| 2 | 35,000 | 7.46 | 40,000 | 3.73 | 193,000 | 1.69 | 132,000 |
| 3 | 15,000 | 7.47 | 20,000 | 3.71 | 230,000 | 1.68 | 155,000 |
| 4 | 15,000 | 7.90 | 22,000 | 3.76 | 160,000 | 1.68 | 209,000 |
| 5 | 12,000 | 8.40 | 20,000 | 3.86 | 179,000 | 1.67 | 153,000 |
| 6 | 10,000 | 8.98 | 10,000 | 3.76 | 110,000 | 1.69 | 260,000 |
Preparing the Mining Block Files
The proposed mining blocks files can be prepared by:
- drawing some rough outlines on a series of plans and digitising them in using the Digitiser functions,
- generating a regular grid of blocks using the Grid Tools functions, or
- preparing the blocks interactively in the Graphical Sequencer itself.
The latter is generally the best method since a report on each block can be calculated as you design it. The mining blocks can be generated elsewhere if you desire but a full description of the Define Blocks option is given elsewhere.
The mining blocks should roughly cover a predetermined area and should have a shape that best represents the proposed way in which the orebody will be mined. This could be a series of long narrow strips or it could be a series of (roughly) square shaped blocks. In an underground mine, each mining block may represent the area that will be mined for each ring that is drilled. The mining blocks that are near the edges of the orebody or the mine design should extent slightly beyond those limits to ensure that all material is covered by a block.
You are now ready to use the Graphical Sequencer to design your mine schedule.
Data Files Used by the Graphical Sequencer
The Graphical Sequencer uses these types of mining data files:
| Orebody Model | String files containing the ore outlines, waste outlines and voids on each bench to be scheduled. |
| Mining Blocks | String files which simulate mining blocks, sometimes called schedule blocks. The mining blocks may represent slots forming a regular grid and act as an overlay on the orebody model. The mining blocks could also be irregular polygons. |
| Format file | A text file with the extension '.fmt' created by the Define Format menu choice. It defines the format of a database which stores your data. It is an important file, and advisable to keep a backup copy for safety. Being a fixed format text file it can be corrupted by editing with a text editor. |
| Target file | An indexed file with the extension '.trg' created by the Define Targets menu choice to contain the production targets for each defined material and grade ratio. |
| Schedule file | An indexed file with the extension '.sch' created and modified by the Sequence Blocks option to keep track of the mining blocks already sequenced. |
| Database files | Files created by the Create Database menu choice and the types of files are dependant on the particular Database Management System you choose. When you use the Update Database menu choice after defining or sequencing blocks, the Graphical Sequencer adds new information to these files. |
| Initialisation file | A file used by the Graphical Sequencer to retain the names of the Format, Target and Schedule files used in the last session to quickly load data from these files to use as defaults for subsequent sessions. The file is called 'sched.ini' and is created in the directory you are working in. |