What is Digger

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  • Isaaks & Co Specialists in Spatial Statistics

    1042 Wilmington Way Emerald Hills CA 94062 Phone 650-369-7069

    ed@isaaks.com

  • Isaaks & Co Specialists in Spatial Statistics

    1042 Wilmington Way Emerald Hills CA 94062 Phone 650-369-7069

    ed@isaaks.com

    September 7, 2015

    What is Digger?

    Digger is a C++ computer program for the design of constrained optimum

    dig line design for open pit grade control. This document provides an

    example using Digger. The example is based on a single blast of gold ore

    containing approximately 135,000 tonnes of material. The blast contains

    3,913 ore control model (OCM) blocks each measuring 2m x 2m x bench

    flitch. Table 1 provides a sample of the input block model with a BlastID, block

    coordinates, density, and gold grades. The BlastID variable is generally coded as

    BlastID=1 if the block belongs to the current blast and BlastID=0 if the block is outside

    of the current blast. The statistics of the ore control block model grades are given in

    Figure 1.

    A map showing 5 different ore types defined by au g/t cutoff grades is shown in Figure 2.

    Note that waste is defined as containing less than 0.4 g/t au. However, the map in Figure

    2 identifies high and low grade waste blocks by their light and darker grey colors. The

    purpose of this distinction is to illustrate that where waste blocks are included in non-

    waste dig lines, they are usually high grade waste blocks with grades just under the waste

    cutoff grade (see Figure 4) thus minimizing dilution.

    Table 1: An Example of the Input Ore Control Block Model

    BlastID x y z Density Au

    1 720051 7788935 1473.3325 2.59 0.4423137

    1 720051 7788937 1473.3325 2.59 0.57111032

    1 720051 7788939 1473.3325 2.59 0.71380657

    1 720051 7788941 1473.3325 2.59 0.5656906

    1 720051 7788943 1473.3325 2.59 0.53483204

    1 720051 7788945 1473.3325 2.59 0.43616024

    1 720051 7788947 1473.3325 2.59 0.30077431

    Figure 1: Histogram and statistics of the ore control block model au grades in g/t for blast 456A. Note

    there are 3,913 blocks in the blast which contains approximately 135,017 tonnes.

  • Isaaks & Co Specialists in Spatial Statistics

    1042 Wilmington Way Emerald Hills CA 94062 Phone 650-369-7069

    ed@isaaks.com

    Figure 2: A map showing the spatial patterns of ore types for blast 465A. The ore control model blocks

    measure 2m x 2m x bench flitch.

    Figure 3: This figure shows a set of dig lines designed at a minimum mining width of 6m in the mining

    direction and 6 m perpendicular to the mining direction. The mining direction was set to an azimuth of 62

    degrees which coincides with the directional trend seen in the pattern of mineralization.

    As you can see, Digger enables the user to rotate the dig lines so that their design

    coincides with either a digging direction or mineral trend or both. However, if you have

    worked with rotated models, you know they can be confusing. Digger gets around this

    by creating a new model rather than rotating the current ore control block model. Also

    Digger generally re-sizes the blocks to 1/5 of the minimum mining width. For example,

    for a 6 m minimum mining width, the original OCM blocks would be resized to 1.2 m.

    Digger then proceeds to design dig lines on the new resized model. The new re-sized

    OCM for blast 456A with dig lines is shown Figure 4.

  • Isaaks & Co Specialists in Spatial Statistics

    1042 Wilmington Way Emerald Hills CA 94062 Phone 650-369-7069

    ed@isaaks.com

    Figure 4: This figure shows the re-sized model built by Digger for dig line design. Note the blocks have

    been reduced in size to 1/5 of the minimum width and rotated to the digging direction. Note that where the

    dig line polygons include waste blocks, the waste blocks are generally high grade waste as indicated by

    the dark grey color. For blast 465A, the dilution resulting from the inclusion of waste in non-waste

    polygons is generally less than 2%.

    Digger output is captured in 3 files;

    A .csv txt file containing the dig line polygons. An example is shown in Table 2. Note that this file is generally up loaded into the client grade control software

    with a simple mouse click through a Python script.

    A .csv txt file containing the resized OCM block model. The file contains the OCM and dig line ore type for each block as well as the gold grade etc. Each

    OCM block is also identified by a polygon number. Thus, one can quickly

    identify all blocks for any particular polygon for checking purposes. An example

    of the output is given in Table 3.

    A third .csv text file output by Digger is shown in Table 4. This file contains key statistics for evaluating a set of dig lines. For example, contents include;

    o Date and time of run o Input file names, and key control parameters. o In situ tonnes and grade by ore type (before dig line design) o Misclassification summary. This summary tells you the tonnes and grade

    of each misclassified ore type within each of the dig line ore types.

    o Dig line tonnes and grade by ore type (after dig line design) o And finally we have ore loss, dilution and grade statistics. There are many

    ways to quantify ore loss and dilution. Digger summaries are kept simple

    so they are easier to understand. For example ore loss and dilution are

    calculated as follows;

    / = total dig line tonnes / total in situ tonnes for each ore type.

    If the calculated ratio above is greater than 1.0, it indicates dilution. If it is less than 1.0,

    then we have ore loss. The logic is simple. There are X number of in situ tonnes of each

    ore type available for mining before dig line design. However, the actual number of

  • Isaaks & Co Specialists in Spatial Statistics

    1042 Wilmington Way Emerald Hills CA 94062 Phone 650-369-7069

    ed@isaaks.com

    tonnes that can be mined given the minimum mining width constraint may be more

    (dilution) or less (ore loss) following dig line design.

    Grade statistics follow the same logic. Before dig line design, Digger calculates the

    average grade of each in situ ore type. Then following dig line design, Digger calculates

    the average grade of each dig line ore type. The dig line average ore type grades will be

    delivered to the mill, stockpile, leach pad etc. given an efficient mining method and

    minimum unplanned dilution. Thus, ideally, we would like to see the ratio of the in situ

    and dig line grades as close to 1.0 as possible.

    Table 2: An example of the Digger output

    dig line polygon file in .csv format.

    x y z N Oretype

    720049.7 7788937.4 1473.3 1 W

    720049.2 7788937.2 1473.3 2 W

    720049.5 7788936.6 1473.3 3 W

    720050.0 7788935.6 1473.3 4 W

    720050.6 7788934.5 1473.3 5 W

    720051.1 7788933.5 1473.3 6 W

    720051.4 7788932.9 1473.3 7 W

    720052.0 7788933.2 1473.3 8 W

    720053.0 7788933.8 1473.3 9 W

    720053.5 7788934.1 1473.3 10 W

    Table 3: An example of the resized and rotated block model output by Digger

    BLPLY x y z au ocm-ot dig-ot sg PolyNo

    1 720049.98 7788936.91 1473.33 0.571 LG W 2.558 2

    1 720050.55 7788935.85 1473.33 0.442 LG W 2.558 2

    1 720051.11 7788934.79 1473.33 0.442 LG W 2.558 2

    1 720051.67 7788933.73 1473.33 0.442 LG W 2.558 2

    1 720049.92 7788939.6 1473.33 0.714 MG LG 2.558 10

    1 720050.48 7788938.54 1473.33 0.714 MG LG 2.558 10

    1 720051.04 7788937.48 1473.33 0.571 LG LG 2.558 10

    1 720051.61 7788936.42 1473.33 0.571 LG LG 2.558 10

    1 720052.17 7788935.36 1473.33 0.389 W W 2.558 2

    1 720052.73 7788934.3 1473.33 0.389 W W 2.558 2

  • Isaaks & Co Specialists in Spatial Statistics

    1042 Wilmington Way Emerald Hills CA 94062 Phone 650-369-7069

    ed@isaaks.com

    Table 4: DIGGER SUMMARY INFORMATION FOR DIG-LINES 465A

    DIGGER Version August 20 2015 11:00AM

    Date and time ==> Mon Sep 07 13:32:10 2015

    Working with OCM file C:\Users\ed\Google Drive\AhafoDigger2015\Digger\Digger\465A.csv

    Working with Digger Control File AhafoControls.txt

    Azimuth of Digging Direction ==> 62.0 or 152.0

    The effective selective mining unit is 6.0 by 6.0 by 3.3 m or 120 cubic m

    Read 11004 1.2 by 1.2 OCM Blocks,

    ---In situ OCM ore type tonnages---

    Tonnes W ==> 63196

    Tonnes LG =