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Create Block Model Maptek™ Vulcan™ Training

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1 Block Model

Construction

The block model is a geologic model which represents the mineral deposit. It is important to create the most accurate representation possible as block models are the foundation of mining operations. Block models are used to publish resource and reserve estimates, generate mine designs, and develop mine plans.

There are several important block model files in Vulcan:

• Block Model Definition (BDF): A specification that defines how blocks generate.

• Block Model File (BMF): The file which contains generated blocks and any associated values.

• Block Estimation File (BEF): A specification that defines how samples are called to estimate values for blocks in the model.

4 Chapter 1 Block Model Construction

Gather Information Familiarity with the deposit is necessary when modelling. Analyse the deposit and consider appropriate values for the following items.

1. Block model origin defined with X,Y, Z coordinates. The X and Y values of this point represent the lower left corner of the block model viewed in plan view. The Z value of this point is the lowest elevation of the model.

2. Extents are defined as distances in X, Y, and Z directions from the block model origin.

Tip: To determine the block model origin, extents, and rotation:

(1) Load the drillholes.

(2) Draw a rectangle that encompasses all samples. Rotate the rectangle if necessary.

Query corners of the rectangle to determine origin and extents.

3. If there is a noticeable directional trend to the deposit, consider a block model rotated to match.

Note Geologists and mining engineers should communicate during block model creation. Rotated block models may make mine design difficult.

4. Block size define block dimensions in X, Y, and Z directions.

a. Block size is sometimes based on the selective mining unit (SMU). The SMU is the smallest volume of material on which ore waste classification is determined.

b. If uncertain, calculate block sizes which will yield approximately 3 or 4 blocks between samples.

Tip: Load data and measure the distance between drillholes or composites in plan view. Divide by approximately 3 or 4 to obtain a dimension distance.

c. Determine if subblocks are necessary. Subblocks are smaller blocks that are factors of the parent block size. Subblocks are used to better define geologic contacts or to model deposits where a parent block size is appropriate for unmineralised blocks but is too large to adequately model the mineralised material, such as narrow vein deposits.

Note If sub-blocking is deemed necessary, triangulations which represent the sub-blocked areas are necessary.

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5. Determine all required variables, which can store either numeric or alphanumeric values that the block represents. Examples of variable values include grade, geology, and costing.

Add at least one variable to the model for the grade values. A gold deposit estimated with ordinary kriging may have a variable called au_ok.

Construct Block Model 1. Select Block > Construction > New Definition to configure block model

parameters based on deposit knowledge. These parameters are stored in a BDF file.

2. Select Block > Construction > Create Model to use an existing BDF to build an empty block model, which is stored in a BMF file.

6 Chapter 1 Block Model Construction

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2 View Block

Model

Check Extents Check to ensure the block model extents fully encompass the exploration area.

In Vulcan Explorer, block model files display in the Block Model container. Drag the model from Vulcan Explorer into Envisage to view the extents. Compare the model extents with loaded drillholes or samples to ensure the extents capture all required sample values.

Note: Remember to check the Z extents.

If the model is not in the correct location or does not fully encompass the drillhole area, select Block > Construction > Open Definition to open the BDF. Adjust the extents and generate the block model again.

8 Chapter 2 View Block Model

Check Block Sizes Ensure the chosen block sizes are appropriate to the data.

There are several ways to view a block model in Vulcan. However, Block > Viewing > Load Dynamic Model is one of the most popular tools.

1. Select Block > Viewing > Load Dynamic Model to configure display parameters.

Figure 2-1: Load Dynamic Model options

a. Select the block Model name and Variable of interest.

b. Values in the selected variable are used in conjunction with the selected Colour Scheme. If a block model legend exists, choose By Vulcan colour scheme and select an appropriate Colour legend. If no legend is available, Colour by spectrum is a good choice.

c. Accept the remaining panel defaults as shown in Figure 2-1 and click OK.

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2. Select View > Create Section to define a section on which to display blocks. There are many methods available for section definition.

Figure 2-2: Methods for section definition

a. Select Line segment if a design object that defines a proper section is loaded in Envisage. Click OK and click the loaded design object.

b. To pick an arbitrary section, choose to define the plane by 2 points or 3 points. Click OK and digitise points when prompted.

c. Easting, Northing, and Level will create a section on an entered, easting, northing or elevation. Click OK to display the section in Envisage.

3. Block sizes are easy to see in section view. If the model contains subblocks, ensure the subblocked areas respect input triangulation limits.

Figure 2-3: Example block model loaded with triangulations

10 Chapter 2 View Block Model

4. If subblock adjustments are required, select Block > Construction > Open Definition to open the BDF. Adjust the subblock values and generate the block model again.

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3 Grade

Estimation

Estimation Overview Choose an estimation method for grade estimation. Some of the estimation methods offered in Vulcan are:

• Nearest neighbour

• Inverse distance

• Kriging o Simple o Ordinary o Indicator

• CoKriging o Simple o Standardized o Ordinary

Inverse distance estimation is a simple estimation and requires little setup. Some universities require the use of kriging in final projects, but inverse distance is a good method to compare and validate the results of kriging.

A nearest neighbour estimation is achieved by an inverse distance estimation where the number of samples to estimate a block is restricted to 1. Nearest neighbour is a basic estimation technique often used to validate the results of other estimation methods.

12 Chapter 3 Grade Estimation

Kriging requires more setup but is widely used in industry. Knowledge of variography is essential to good kriging estimation.

Select Block > Grade Estimation > Estimation Editor to configure estimation parameters and estimate blocks.

Estimation Resources The Vulcan help file contains information on geostatistical modelling and explains various variography parameters. Information on how to use Vulcan variography and kriging tools is also located in the help file. See Envisage > Block > Appendices > D Geostatistical Modelling > Contents.

The following website contains valuable geostatistics information. The website is in-progress, so check back frequently.

http://geostatisticslessons.com/

Some colleges and universities have access to Mineral Resource Estimation through a SpringerLink academic license. The campus library or professors may have a paper copy.