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Dilution behaviour at Codelco Panel Cave Mines

A. Susaeta, IAL Ltda, Chile

E. Rubio, Universidad de Chile, Chile

J. Henríquez, Codelco Central, Chile

. País, Universidad de Chile, Chile

Abstract

Conventionally, there are three main parameters that define dilution behaviour in panel cave mining: draw

 point layout geometry (draw point spacing), roc mass fragmentation and draw pattern! "epending on the

ore body, mining geometry, and operational behaviour the underlying gravity flow can be classified as

isolated draw, interactive draw or isolated#interactive draw! "raw point e$traction bac analysis was

 performed at Codelco mines aiming to determine the underlying gravity flow from dilution observations

 performed from % mines of the three mining "ivisions that operate panel caving! &he draw point databaseconsisted of ' draw points and represented *' +illion tons drawn between --* and .'! &he draw

 point database was subdivided by draw point spacing/ fragmentation and drawing behaviour, defining .

representative draw point clusters! &hese clusters were characteri0ed by an empirical dilution curve and an

underlying flow mechanism! 1or every curve, the dilution entry point and the percentage of full interaction

was read! As a result of the study a design and operational guideline is proposed to attain interactive flow of 

 panel caving in different roc masses sub2ect to draw uniformity restrictions!

! "ntroduction

The dilution behaviour in a Panel/Block cave mine is relevant since it defines mining recovery and ultimate

economic return of a given mine design and production plan. Traditionally, the dilution behaviour in a Block 

and Panel cave mine has been computed using template mixings or volumetric algorithms as described byLaubscher (!!"# and computer based algorithms as described by $iering (%&&. The follo'ing chart sho's

a diagrammatic representation of ho' the volumetric algorithm 'ould simulate mixing in a single dra'

column. t is seeing that 'hen extracting slice " of the dra' column dilution starts to enter the dra' point.

This point in the life of a dra' point is called point of dilution entry (P$)# 'hich Laubscher describes as a

function of fragmentation characteristics, dra' point spacing and dra'ing performance. *learly, the

geometry of the dilution curve sho'n belo' 'ould dictate the average grade to be extracted and the ultimate

mining reserves to be mined.

#i$ure ! %olu&etric &i'in$ al$orith&

The method sho'n above consists of the volumetric mixing algorithm introduced first by +eslop andLaubscher (!%#. This method still 'idely used in the mining industry to simulate the process of mixing as

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a result of the underlying gravity flo' process in Block and Panel caving mines. - different algorithm that

includes the differential vertical flo' of fines has been introduced by $iering (%&& that is part of the P*

B* emcom Block *ave suit. -lso, some more sophisticated algorithms that integrate rock mass behaviour 

and the constitutive behaviour of particle interaction have been introduced by Pierce and *astro using

 particle flo' codes and cellular automaton respectively. 0evertheless, it is rear to find calibration of these

sophisticated algorithms and the actual dilution observations performed at the mine sites. Thus, mixing

templates based on simple rules still valid as they can reconcile 'ith the dilution curves presented in this

 paper.

The follo'ing chart sho's a simulation conducted in a single dra' column in 'hich three dilution models

have been simulated in order to state the mining reserves for a given cut off grade. n these models the main

 parameter to define dilution behaviour is the percentage of dilution entry (P$)#. This 'ould characteri1e the

 point at 'hich the first dilution shall be observed at the dra' points.

#i$ure ( Diluted Colu&ns )or PDE*+-, - and /-

Based on a dra' column of &&m of ore of 2 copper and an overlying column of &&m of 'aste of &2

copper the expected mixed grades at the dra' point for the three mixing models presented above are sho'n

 belo'.

#i$ure + rade inside diluted Colu&ns.

-s a result of the above for a cut off grade of &.32 copper the best height of dra' (+recov#, the miningrecovery (2 4ec#, the average grade in the mineable column (Lm# and the copper content (*opper# are

 presented in the follo'ing table. *learly it is sho'n that the impact of the dilution entry point has a

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tremendous implications on defining the mining reserves and the copper content 'hich are the main

 parameters delineating the mining business. +o'ever it should be noted that these results are highly

dependant on the cut off grade and also the ore body under analysis. The results 'ould be 5uite different if 

the ore body had a constant grade 'ithout 'aste on top of the ore body, 'hich is often found in porphyry

copper deposits. Based on these results it is 'orth'hile analyse the dilution behaviour of *odelco mines to

 put all the elements regarding dilution behaviour under perspective, aiming to use these results to further 

calibrate mixing templates or particle flo' codes in the process of stating Panel and Block cave mining

reserves.

0able ! Colu&n re1ort )or di))erent dilution entr2 1oints at 3.4- Cu cut o)) $rade

@0.7COG Hrecov Hnom % Rec Lm Copper  

(m) (m) (%) (%) (t)

PED=35 75 100 75 0.91 !

PED=5 !5 100 !5 0.9 !1

PED=!5 95 100 95 0.9! 93

PED=100 100 100 100 1.00 100

( 5ac6$round and theor2

Traditionally it is understood that dilution behaviour is the result of the underlying gravity flo' process that

takes place in the ore body that has been previously caved. The gravity flo' is induced by the propagation of 

void through the broken ore that lies on the production level cro'n pillar. The fundamentals of gravity flo'

for panel caving currently used began 'ith sand experiments performed by 6arano (!, +eslop and

Laubscher (!# performed at 7habaine mine at the beginning of 3&8s. These experiments 'ere performed

in a threedimensional model of %"&&mm of height and a base of 39&mm x 39&mm. The firs experiment

consists of several dra' points spaced at %&9 mm apart in 'hich dra'ing is performed simultaneously. This

experiment sho' that there are dra'ing 1ones formed of about & mm 'ide in 'hich there is no interaction

 bet'een dra' 1ones. This mode of flo' is often called isolated flo'. The second experiment consists of 

several dra' points spaced at & mm apart in 'hich the dra'ing is performed simultaneously. This

experiment sho's that there is a uniform dra' do'n of the dra' column. This mode of flo' is often calledinteractive flo'. The third experiment consists of setting up the dra' point spaced at :% mm apart in 'hich

the dra'ing is performed simultaneously. This experiment sho's that there is interactive dra' 'ith a large

amount of mixing along the dra' columns, i.e. fines segregation is observed along the dra' column. This

mode of flo' is often called interactive flo'. ;inally the last experiment consists of performing uneven dra'

as dra' points 'ere dra'n se5uentially in a dra' point layout spaced at & mm. The results of this

experiment sho' that there is chimney and there 'as no interaction across the ma

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#i$ure 7 ravit2 )lo8 e'1eri&ents 9Marano, !:/3;

7usaeta (%&&"# reports results from a research pro

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#i$ure Dilution &odels derived )ro& the "solated

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1 &n' &n' em' em' em'

$ &n' em' em' em' on

3 em' em' em' on on

em' em' on on on

5 on on on on on

on on on on on

Then, the life cycle of a dra' point could be characteri1ed as a function of the percentage of the time that a

dra' point has been dra'n non uniform or the amount of tonnage dra' from a dra' point that has been

dra'n uniform. -ll these indicators could assist mining engineers to characteri1e the dra'ing behaviour of a

cluster of dra' points and correlating this behaviour 'ith measured mining recovery and dilution. This

exercise 'as performed at *odelco mines aiming to find at different sites the dilution models presented

 before and perhaps infer on the flo' modes present as a function of different rock masses as means of 

fragmentation, dra' point spacing and dra'ing performance.

( Codelco Mines 5ac6

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the &&2 tonnage extraction. The &&2 tonnage extraction of a dra' point is computed as the tonnage to

reach the interface bet'een insitu economic column and broken rock. ;or example the follo'ing selected

dra' points sho' their uniformity index in a period of time and the evolution of dilution over their life time.

Based on the geometry of the curve P)$- and P)$ are assigned to the cluster and added to the

analysis. .

#i$ure 4 =ni)or&it2 inde' and dilution visualizer.

-ll the analysis 'ere performed for individual dra' points identifying clusters of dra' point sho'ing *E in

a given range. -lso, the clusters of dra' points 'ere selected in such 'ay that rock type and dra' point

spacing 'as the same for all dra' points in the cluster. The follo'ing charts sho' some of the clusters

analysed as part of the study.

(.! E&1irical Dilution Models

- cluster of dra' points from the mine )smeralda of )l Teniente that is located in primary rock and a dra'

 point layout of :x3.% sho's the follo'ing dilution behaviour for different ranges of *E.

#i$ure / Es&eralda 1ri&ar2 roc6 dilution behaviour, !'!4.( la2out.

;igure sho's the observed dilution for dra' points sho'ing a *E in the range of "&&2 and &&&2,

the number of dra' points in the cluster are "F and %& respectively. t must be noted that the behaviour of 

this dra' points are sho'n until :&2 extraction (2)#, nevertheless the dra' points 'here selected by their 

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*E measured upto &&2 of dra'n. t is seeing in the graph that for primary ore there is a interactive dra'

 behaviour for a L+$ : x 3,% m layout, 'here P)$- is highly sensitive to the *E range.

$ra' *olumns of -ndinaL+$ sector are composed only of mixed rock. The diluted material is called

@4hyoliteA 'hich is a geologic marker, included as a fraction of the overburden material. The curve

 behaviour considering dra' points 'ith t'o *E ranges are sho'n belo'.

#i$ure : Mi'ed roc6 colu&n dilution behaviour, !+'!+ >HD >a2out.

t is seeing again that a better uniformity of dra' performance leads to a lo'er dilution entry, both in

 percentage of extraction and total dilution up to &&2). The Ped1a G Ped1i sho' interactiveisolated flo'

 behaviour.

$ra' columns of -ndinaParrillas (gri11ly# dra' points are composed only of secondary rock according

'ith the rock definition mentioned above. The diluted material is @4hyoliteA and the sector is characteri1ed

 by four gri11ly layoutsC !x!, !."x!, !x and !x.F. -nalysis 'as performed grouping data as it is sho'n in

the follo'ing graphs considering uniformity analysis until the &&2).

#i$ure !3 Secondar2 roc6 dilution, :': ? :.7': rizzl2 >a2out

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#i$ure !! Secondar2 roc6 dilution, :'!! ? :'!!.+ rizzl2 >a2out

(.+ Dilution Results Su&&ar2

The summary of all the analy1ed data is presented in Table F, 'here the three dra' function variablesC

geometry is defined by the Layout/6ethod, the fragmentation by the 4ock column description (secondary,

mixed and primary#, and the dra' uniformity by the Eniformity index (2 uniform H semi uniform tonnage

dra'n of the column up to &&2 extraction#. The flo' behaviour of each of the different cases is defined as

solated ;lo' (s#, nteractive ? solated ;lo' (# and nteractive ;lo' (n#, considering the shape of the

dilution curve. The flo' mode is also characteri1ed by its dilution entry point for the isolated and interactive

flo' (Ped1i G Ped1a#. The number of dra' points that belong to each of the different data clusters is also

 presented in the table.

0able 7 Su&&ar2 o) PED@A and PED@" )or Selected Clusters

*'ne ector L,;oo/  Dr,2Po'nt-

Roc?co6

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Po'nt- co6

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distribution across the ore body. There are some other considerations to include in the analysis as layout

 productivity, fragmentation, development cost, ore body characteristics. The optimal dra' point layout

should obey to a comprehensive analysis that includes all these aspects of the mine design. t is aimed that

the table presented above could support the dilution analysis related to the decision of dra' point spacing.

7 Conclusions

The dilution curves constructed for *odelco mines presented in this paper follo' the dilution models

 proposed by the solated nteractive flo' theory. t is inferred that all the three modes of flo' are present at

*odelco mines the different modes unfold for different dra' point layout and fragmentation.

t 'as sho'n that the dra' performance has a tremendous effect on the dilution behaviour of a dra' point. n

 particular 'hen dra' point spacing has been designed in such a 'ay that interaction is minimal the relevance

of even dra' is crucial to achieve solated nteractive flo'.

;or a mixed rock mass the recommended dra' point spacing is Fm to achieve solated nteractive dra'

'ith performing even dra'. ;or primary rock the dra' point spacing should be at the most :m to achieve

solated nteractive flo'. . 7everal operations around the 'orld 'ill be looking at Block or Panel cavedesigns for their ore bodies that are in the range of mixed and primary rock. The tendency to use 'ider dra'

 point spacing could eventually affect the dilution behaviour and the overall mining reserves.

t is interesting to note based on the results sho'n above that the overall trend for a dilution perspective is to

reinforce the use of close spaced layout dra' points. This result goes against the industry trend of using

'idely spaced layout in order to achieve higher productivity and more reliable rock mechanic design.

 0evertheless, it is highly important to revie' the basics of mine design that must be founded in the ore body

characteristics and geological setting rather than 5uick and incomplete economic return. The sustainability of 

 block and panel cave operations 'ould force the industry to look at methods that could enhance the 'ay ho'

dilution behaves 'ithin the mining and metallurgical processes in order to optimi1e energy consumption.

Iet, it is believe that in years to come must attention shall be addressed over dilution behaviour disregarding

too much attention over economic return could not only

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Laubscher, $.+., %&&&. NBlock cave manual, design topicC dra'point spacing and dra' controlN. ;or the

nternational *aving 7tudy !!3%&&&, The Eniversity of ueensland, Brisbane, -ustralia.

Laubscher, $.+., !!". N*ave mining the state of the artN, The Oournal of the 7outh -frican nstitute of 

6ining and 6etallurgy, vol !" no &, pp %3!%!F.

+eslop, T.., and Laubscher, $.+., !. N$ra' control in caving operations on 7outhern -frican *hrysotile

-sbestos minesN, in $esign and Jperation of *aving and 7ublevel 7toping 6ines, pp 33:33". )d. $.4.

7te'art. 76)-6), 0e' Iork.