msprograms-pitres dilution in planning reserves-200503

7/27/2019 MSPrograms-PITRES Dilution in Planning Reserves-200503

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In the mining world, handling dilution is one of the main issues with which engineers must deal when plan-ning for reserves. Dilution is the reduction in the grade of Ore material caused by excess mined tonnage dueto more waste being mined. This situation can result from a number of factors; the displacement that occursduring blasting, pre-production mine methods, or weathering can all be causes of dilution.

MineSight Compass includes the well-known PITRES.dat procedure, which enables the calculation ofreserves while accounting for dilution. The procedure can be found in Procedure Groups 3-D Modeling or PitOptimization and Pit Design, Operation: Report.

Starting Up Zone Input File

In order to use the dilution options in PITRES, it is necessary to create a Zone Input le. The Zone Input Filecan be used to set up parameters for individual zones as coded to a ZONE item in the model.

The format for this le is:

Zone Zone # Dens Yield% Recov% Diln% Diln Diln Cutoffs CutName Dens Grades Flags

Although this ASCII le is optional, it must be used for dilution purposes. If the Zone Input File is not used,

all zone codes are assumed to be between 1 and 500, the recovery is set to 100%, and dilution is set to 0 for allzones. Zone parameters can be input to PITRES through the panel/defaults or through the Zone Input File.Although the user can input zone parameters in the Zone Input File, other parameters, such as waste density,could be entered through the procedure panels. Ore density by zone can be read from a model item or fromthe Zone Input File. Note, if the recovery for any zone is set to 0 or if it fails one of the ore/waste grade cutofftests, then it is only reported if the Insitu grade option has been requested (i.e., it will only show up as waste ifthe diluted grade option is requested). Also note that the density model item is an Insitu density. The densityof the dilution comes from the density of the waste within the block, if a waste density item is used, or fromthe waste ore if a 0% recovery is used. Otherwise, it comes from the Zone Input File DilnDens column.

(For more extended information on PITRES and the Zone Input File, please refer to MineSight Help keyword: PITRES)

In PITRES, dilution can be applied to the Insitu orRecovered ore for all blocks, or against the full block

for ore/waste contact blocks. To explain dilution inthis article, a simple PITRES setup will be used with aMineSight 3-D partials le created by a solid as dis-played in the picture to the left.

No Dilution No Recovery (No Losses)

A typical set up for running PITRES without a ZoneInput File is shown in the panels below.

For all the examples, items CUEXP, OTYPE, ORE%,and TOPO were used. The ore/waste cutoff was 0.1.Item DENS was the ore density item.

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Using Dilution for PlanningReserves in PITRES

MineSight Foregroundint

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(Green Solid represents the Zone)


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MineSight Foregroundinthe

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(Using Dilution for Planning Reserves in PITRES continued from page 5)

A portion of the reserves report is shown below:

Reserves are calculated using the following formulas:

Insitu ore (BCM) = TOPO% x ore% x block size = 746,164 BCM

Insitu ore (Tonnes) = S.G. x Insitu ore (BCM) = 2.5 x 746,164 = 1,865, 411 Tonnes

ROM ore (Tonnes) = Insitu ore (Tonnes) = 1,865,411 x 1 =1,865,411 Tonnes

Waste (BCM) = TOPO% x blocks Size Insitu ore (BCM) = 831,995 746,164 = 85,831 BCM(continued on page 7


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Applying Recovery and Insitu Dilution

The application of recovery and dilution in PITRES comes from using a Zone Input ASCII le. Dilution canbe applied to the recovered ore volume (the dilution/waste SG is used to get tonnage); the default calculationis to apply dilution to the Insitu ore tonnage (i.e. before recovery). If in the above example we add a 5% Dilu-tion, that amount will be added to the Run of Mine Ore Tonnes and subtracted from the waste. Also, a 90%recovery will be used on all our zones as specied in the Zone Input File.

To apply 5% dilution and recovery% we must use the PITRES Zone Input le:

ZONE1 2 2.5 100 90 5 2.5

ZONE2 3 2.5 100 90 5 2.5

ZONE3 4 2.5 100 90 5 2.5

Notice that we see yield% at 100. The Yield number is for use in procedure CMPRES.dat and was added tothe PITRES Zone Input File so its a consistent format to use with CMPRES.dat, PITRES.dat, and M650IP.exe.

Panels that need to be modied:

n

A portion of the diluted reserves report is shown here.

Reserves are now calculated as in the following:

Insitu Ore (BCM) = TOPO% x ore% x block size = 746,164 BCM

Insitu Ore (Tonnes) = S.G. x Insitu Ore (BCM) = 2.5 x 746,164 = 1,865,411 Tonnes

Recovered Tonnage = Insitu ore (Tonnes) * Recovery

Dilution Tonnage = Insitu ore (BCM) x Dilution % x DilDensROM Tonnage = Recovered Tonnage + Dilution Tonnage

= 1,865,411 x 0.9 + 1,865,411 x 0.05 = 1,772,140 Tonnes

Waste (BCM) = TOPO% x blocks size Insitu Ore (BCM) x Recovery%

= 831,995 - 746,164 x 0.9 - 746,164 x 0.05 = 123,140 BCM

Grade Diluted = (Grade * Recovered Tonnage + DilGrade * Dilution Tonnage)/ROM Tonnage = 0.490

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Dilution applied after Recovery

No changes in our PITRES Zone Input le:

ZONE1 2 2.5 100 90 5 2.5

ZONE2 3 2.5 100 90 5 2.5ZONE3 4 2.5 100 90 5 2.5

To apply dilution after recovery use the appropriate PITRES option:

By using the option to apply dilution after the recovery reserves change to:

The formulas used are the same as in the previous example, except for:

Dilution Tonnage = Insitu ore (BCM) x Recovery% x Dilution % x DilDens

Dilution on Contact Blocks

A contact block is dened as a block that contains both ore and waste. In model items, this generallytranslates to a Topo%>total Ore% and Ore%>0. Also, a block can be dened as a contact block if a 0% recov-ery is applied to a zone in a block from the Zone Input File, or if the grades of a block fail to pass the ore/waste cutoff test in PITRES. An example of such a case would be a leach cap; it may be modeled but nevermined as ore.

Using contact block dilution, the non-missing grades from the wasted zones override the dilution gradesfrom the Zone Input File and are weighted by the density of the material being wasted.

For contact block dilution also note, the dilution % is based upon a full block volume rather than beingapplied against only the ore%. This allows consistent dilution quantity regardless of the amount of ore in theblock. For example, if you want ve feet of dilution on a 50-foot bench, enter 10%. This means each block thathas an ore/waste contact with a total mineable ore more than a user specied minimum ore%, will get thesame amount of dilution. The dilution for this option is only applied against the rst recoverable zone.

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(Example of Contact Blocks Based on Topo% > Ore%)

(Example of Contact Blocks based on Recovery and Fail waste/cutoff)

To apply dilution to contact blocks only, use the PITRES option below:

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For this case, if we run reserves on the same blocks as in previous examples, applying dilution before recov-ery on contact blocks only and applying different recoveries (as in Zone Input le below)

WASTE 1 2.5 100 0 0 2.5

ORELG 2 2.5 100 65 5 2.5

OREMG 3 2.5 100 80 5 2.5

OREHG 4 2.5 100 95 5 2.5

The reserves will be:

Using Minimum Ore%

Since Contact Dilution is applied against a full block volume, you may not want to dilute blocks that have asmall ore%. PITRES allows you to specify a Minimum Ore% value for this:

y using t is prompt, any oc s wit t e tota ore% ess than the specified Minimum Ore% value arenot diluted.

NOTES: Dilution considerations when usingTopo Clipping and Take Ore First Options

Using either of these two options affects the way PITRES calculates Insitu ore, i.e., it also affects dilution. Ifthe ore has been interpreted so that it is clipped at the Topo, the user must make sure that all the ore is minedfrom the surface blocks. The normal calculation is to take the block partial x Topo and apply it to all material

types. For example, if ore had been clipped at Topo such that ore%=60 and Topo%=80 and 100% of the blockwas being mined, the normal method would be to mine 1.0 * 0.8 * 0.6 = 0.48 for ore and 1.0 * 0.8 * 0.4 = 0.32 forthe waste. This means that 12% of the ore is accounted as waste. If the ore rst option is used, it takes all theore (60%) rst, and the rest (20%) is considered to be waste. The take ore rst for all blocks should be usedwhen the pit bottom follows the footwall of the ore. The same example as above could be used reversing thepartial and the Topo to 80% and 100% respectively.

As you can see, PITRES provides a set of options for reserve planning when dilution is present. If youhavent already, give these options a try. Contact MINTEC, inc. Technical Support with any comments orquestions you may have.

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Remember to take advantage of the MINTEC discount!

msprograms-pitres dilution in planning reserves-200503

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