Parameters influencing full scale sublevel caving material recovery at the Ridgeway gold mine I.D. Brunton a,b, , S.J. Fraser c , J.H. Hodgkinson c , P.C. Stewart b a Newcrest Mining Limited, Cadia Valley Operations, Cadia Road, South Orange, 2800, Australia b The University of Queensland, W.H. Bryan Mining and Geology Research Centre, Brisbane, Australia c CSIRO Exploration and Mining, Queensland Centre for Advanced Technologies, Brisbane, Australia article info Article history: Received 6 August 2009 Received in revised form 21 October 2009 Accepted 19 December 2009 Available online 25 January 2010 Keywords: Sublevel caving Sublevel caving flow Sublevel caving blasting Sublevel caving recovery abstract The literature discusses a number of theoretical, small, and full scale experimental programs, which have aimed at identifying parameters influencing sublevel caving (SLC) material flow behaviour, and therefore ore recovery and dilution. Historically, parameters directly influencing flow behaviour have been found to include the geometry of the extraction layout and drives, sublevel height, blast ring design, material characteristics of the blasted and waste material, and draw control methodology. To date, no detailed analysis of parameters influencing full scale material flow behaviour and recovery in modern SLC mines has been documented in the literature. This paper outlines the analysis undertaken to identify parameters which influence material recovery at the Ridgeway SLC operation. Parameters analysed included those related to drawpoint location, drill and blast design, geology, drawpoint geometry, and draw control. To identify parameters influencing recovery, a Self-Organising Map (SOM) technique was adopted. SOM is considered an ideal tool for analysing complex geological and mining datasets, and for extracting relationships and patterns that typically are not evident by other means. The SOM analysis indicated that a number of drill and blast design parameters were directly or inversely correlated to material recovery at the Ridgeway SLC operation. Blasting parameters dominated correlations with recovery when compared to drawpoint and geological parameters. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Sublevel caving (SLC) is a mass mining method based upon the utilisation of gravity flow of blasted ore and caved waste rock [1]. The method functions on the principle that ore is fragmented by blasting, while the overlying host rock fractures and caves under the action of mine-induced stresses and gravity [2]. The caved waste from the overlying rock mass fills the void created by ore extraction. The original application of the SLC mining method was in soft ground at the Minnesota and Michigan iron ore mines in the early 1900s [3]. The method was later adapted to stronger ore bodies (requiring blasting) enclosed by weaker overlying and wall rock masses. In the past 40 years SLC geometries have increased significantly, resulting in increases of scale and extent of industrial application, and decreases in production costs [4]. Current SLC geometries (Fig. 1) consist of a series of sublevels created at intervals between 20 and 30 m, beginning at the top of the orebody and working downward [3]. A number of parallel drives are excavated on each sublevel, with drives being offset between sublevels. From each sublevel drive, vertical or near vertical blast hole fans are drilled upward to the overlying sublevel. The burden between blast fans are in the order of 2–3 m [3]. Beginning typically at the hanging wall, the burden is blasted against the front-lying material, consisting of a mixture of ore and caved waste. Extraction of the ore from the blasted burden continues until total dilution or some other measure reaches a prescribed level [3]. The next burden is then blasted, and the process repeated. The major disadvantage of the SLC mining method is the relatively high dilution of the ore by caved waste [5,1]. A major factor influencing this dilution is the flow behaviour of the ore and waste material [5–8]. Despite its importance on SLC performance, the mechanics of gravity flow of blasted and caved material is historically not well understood [4]. Material flow behaviour is complex in nature, being controlled by the interaction of a wide range of parameters [1–3,6–14]. Early small and full scale experimental results and theoretical calculations were conducted partly to investigate the influence of these parameters on flow behaviour [6,15–19]. These parameters were related to geometric design considerations (sublevel height, crosscut spacing, drive geometry, ring inclination, and ring burden), draw control ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijrmms International Journal of Rock Mechanics & Mining Sciences 1365-1609/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmms.2009.12.011 Corresponding author at: Newcrest Mining Limited, Cadia Valley Operations, Cadia Road, South Orange, 2800, Australia. E-mail address: [email protected] (I.D. Brunton). International Journal of Rock Mechanics & Mining Sciences 47 (2010) 647–656
Transcript
ARTICLE IN PRESS
International Journal of Rock Mechanics & Mining Sciences 47 (2010) 647–656
Contents lists available at ScienceDirect
International Journal ofRock Mechanics & Mining Sciences
1365-16
doi:10.1
� Corr
Cadia R
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journal homepage: www.elsevier.com/locate/ijrmms
Parameters influencing full scale sublevel caving material recoveryat the Ridgeway gold mine
I.D. Brunton a,b,�, S.J. Fraser c, J.H. Hodgkinson c, P.C. Stewart b
a Newcrest Mining Limited, Cadia Valley Operations, Cadia Road, South Orange, 2800, Australiab The University of Queensland, W.H. Bryan Mining and Geology Research Centre, Brisbane, Australiac CSIRO Exploration and Mining, Queensland Centre for Advanced Technologies, Brisbane, Australia
a r t i c l e i n f o
Article history:
Received 6 August 2009
Received in revised form
21 October 2009
Accepted 19 December 2009Available online 25 January 2010
The literature discusses a number of theoretical, small, and full scale experimental programs, which
have aimed at identifying parameters influencing sublevel caving (SLC) material flow behaviour, and
therefore ore recovery and dilution. Historically, parameters directly influencing flow behaviour have
been found to include the geometry of the extraction layout and drives, sublevel height, blast ring
design, material characteristics of the blasted and waste material, and draw control methodology. To
date, no detailed analysis of parameters influencing full scale material flow behaviour and recovery in
modern SLC mines has been documented in the literature. This paper outlines the analysis undertaken
to identify parameters which influence material recovery at the Ridgeway SLC operation. Parameters
analysed included those related to drawpoint location, drill and blast design, geology, drawpoint
geometry, and draw control. To identify parameters influencing recovery, a Self-Organising Map (SOM)
technique was adopted. SOM is considered an ideal tool for analysing complex geological and mining
datasets, and for extracting relationships and patterns that typically are not evident by other means.
The SOM analysis indicated that a number of drill and blast design parameters were directly or
inversely correlated to material recovery at the Ridgeway SLC operation. Blasting parameters
dominated correlations with recovery when compared to drawpoint and geological parameters.
& 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Sublevel caving (SLC) is a mass mining method based upon theutilisation of gravity flow of blasted ore and caved waste rock [1].The method functions on the principle that ore is fragmented byblasting, while the overlying host rock fractures and caves underthe action of mine-induced stresses and gravity [2]. The cavedwaste from the overlying rock mass fills the void created by oreextraction. The original application of the SLC mining method wasin soft ground at the Minnesota and Michigan iron ore mines inthe early 1900s [3]. The method was later adapted to stronger orebodies (requiring blasting) enclosed by weaker overlying and wallrock masses. In the past 40 years SLC geometries have increasedsignificantly, resulting in increases of scale and extent ofindustrial application, and decreases in production costs [4].
Current SLC geometries (Fig. 1) consist of a series of sublevelscreated at intervals between 20 and 30 m, beginning at the top ofthe orebody and working downward [3]. A number of parallel
ll rights reserved.
ted, Cadia Valley Operations,
).
drives are excavated on each sublevel, with drives being offsetbetween sublevels. From each sublevel drive, vertical or nearvertical blast hole fans are drilled upward to the overlyingsublevel. The burden between blast fans are in the order of 2–3 m[3]. Beginning typically at the hanging wall, the burden is blastedagainst the front-lying material, consisting of a mixture of ore andcaved waste. Extraction of the ore from the blasted burdencontinues until total dilution or some other measure reaches aprescribed level [3]. The next burden is then blasted, and theprocess repeated.
The major disadvantage of the SLC mining method is therelatively high dilution of the ore by caved waste [5,1]. A majorfactor influencing this dilution is the flow behaviour of the ore andwaste material [5–8]. Despite its importance on SLC performance,the mechanics of gravity flow of blasted and caved material ishistorically not well understood [4]. Material flow behaviour iscomplex in nature, being controlled by the interaction of a widerange of parameters [1–3,6–14]. Early small and full scaleexperimental results and theoretical calculations were conductedpartly to investigate the influence of these parameters on flowbehaviour [6,15–19]. These parameters were related to geometricdesign considerations (sublevel height, crosscut spacing, drivegeometry, ring inclination, and ring burden), draw control
Fig. 1. Diagrammatic long section and plan of sublevel caving (after [20]).
(a) Diagrammatic long section of sublevel caving and (b) diagrammatic plan of
sublevel caving.
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practises (excavation strategy and depth of bucket penetrationinto the blasted material), and cave and ore material properties(friction angle, fragment size, and bulk density). It was clearlydemonstrated in the literature that these parameters had asignificant impact on early experimental test results.
Based upon these early results, a number of SLC designguidelines have been presented in the literature to relategeometric, material, and draw control parameters to materialflow behaviour [1]. These guidelines generally consist of a seriesof empirical equations relating mine design and blasted ore andcaved material properties to the width and thickness of anextraction ellipsoid [1,6–12]. Due to the complexity of thematerial gravity flow these guidelines should only provide a firstapproximation to determining flow behaviour parameters [1].
As SLC geometries increased in scale with advances in drilling,blasting, and equipment technologies, it became evident that therelative uniform material flow behaviour described by earlierauthors was not adequate [10,11,14,21–28]. Limited results fromfull scale flow experiments in modern SLC operations [26–29]highlighted a change to an irregular and asymmetrical shapedrecovery zone. This change in material flow behaviour led to a
reassessment of factors which had a direct impact on flowperformance. In addition to the traditional geometric, drawcontrol, and material flow properties, an additional set ofparameters related to drill and blast parameters were recognisedto have a possible impact on observed full scale flow behaviour formodern SLC geometries [26,28,29].
This paper summarises the analysis of data from a full scaleexperimental program conducted over a 3-year period at theRidgeway SLC operation to assess the influence of a wide range ofmeasured parameters on flow behaviour and material recovery.Due to the complex nature of the experimental results, traditionalstatistical methods were considered inadequate for data analysis.To overcome this issue, a Self-Organising Map (SOM) techniquewas utilised. This methodology was considered ideal for attempt-ing to understand the interaction of multiple mining and geologicalparameters on SLC full scale flow behaviour and recovery.
2. Full scale experimental program
The implementation of a full scale experimental program toquantify material recovery has been noted to be crucial for theongoing success of the mining method [28]. Such experimentsprovide detailed information concerning the development andshape of the extraction zone (the shape that defines the originallocation of the excavated material), identify possible sources ofwaste ingress into the ring, and ascertain the degree of flowbehaviour variability. The experimental program undertaken atthe Ridgeway SLC gold mine provided a unique opportunity toassess these factors. These full scale experiments are consideredto be the most comprehensive to date, with 69 individual ringtrials analysed from July 2002 to April 2005.
2.1. Ridgeway SLC operation
The Ridgeway SLC gold operation is located approximately250 km west of Sydney, Australia. The operation is located 3 km tothe north west of the Cadia Hill open cut gold mine, andapproximately 25 km south of Orange, New South Wales. TheRidgeway and Cadia Hill gold mines form Cadia Valley Operations,which is owned and operated by Newcrest Mining Limited. TheRidgeway gold–copper orebody was discovered in November1996, with mine construction and commissioning completed inMarch 2002. The expected mine life of the Ridgeway operation is8 years based on current reserves. Production for 2007–2008 was301,417 ounces of gold and 34,335 tonnes of copper from thetreatment of 5.78 million tonnes of ore.
The Ridgeway deposit is a structurally controlled gold–copperporphyry orebody characterised by stockwork and sheeted quartzveins containing copper sulphides [30]. The deposit is centred ona subvertical monzonite stock of the Late Ordovician to EarlySilurian. The upper portion of the orebody is contained within theForest Reef Volcanics, while the lower portion lies in sediments ofthe Weemalla Formation. The orebody has a maximum dimensionof approximately 400 m east–west, 250 m north–south, and inexcess of 1000 m vertically [30]. Mineralisation extends over1000 m in vertical extent, from 500 m below the surface and isopen at depth.
A transverse SLC mining method was adopted for the deposit,with mining beginning at the 5330 level (approximately 580 mbelow surface; surface 5910 level) and advancing sequentially todepth. Sublevel spacing is 25 m between the 5330 level and 5130level, and 30 m between the 5130 level and 5040 level. Crosscutdrives are 6.0 m wide by 4.7 m high, and spaced to 14 m centres(pillar width 8 m). Blast design consists of a 2.6 m burden, 7–10blast hole pattern, and an emulsion explosive with densities
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ranging from 0.9 to 1.2 g/cm3. Material handling to surface isachieved through a series of orepasses, underground crusher, andconveyor belt to surface.
2.2. Experimental setup
The experimental setup was adapted from previous studiesdescribed by Janelid [18] and Gustafsson [26], which involved theinstallation of markers within the SLC blast burden. However,several key differences existed between these earlier experimen-tal studies and those adopted by the Ridgeway operation. Thesedifferences included the use of a metal marker instead of plastic(Fig. 2a) and the reliance of marker recovery within the materialhandling process by magnetic separation (Fig. 2b). Theexperimental methodology adopted by the Ridgeway operationwas developed over a period of time and is discussed in detail byPower [28]. In summary, the experimental setup involved theinsertion and grouting of markers in purpose drilled 102 mmdiameter holes. Approximately 20,000 markers were installedover a 3-year period, making these trials the most extensiveundertaken by an SLC operation to date.
Fig. 2. Photographs of a metal marker and material handling process (after [28]).
(a) Ridgeway metal marker and (b) marker recovery by magnetic separation in the
material handling system.
Markers were designed to mimic flow behaviour of rock in themine within the limitations of the installation techniquesavailable [28]. They had to be individually identifiable, robustenough to survive the initially blasting process and subsequentcave flow, and be recovered in a relatively easy and reliablefashion to ensure sufficient data for further analysis [28]. Basedupon these requirements, markers were constructed from 42 mmdiameter hollow steel pipe (inside diameter 38 mm) cut to250 mm lengths (Fig. 2a). The pipe was filled with cement in anattempt to match the density of the marker to that of the rockwithin the cave. A four letter code was welded on the pipe touniquely identify each marker [28].
Marker ring location and density of markers placed within thering were important considerations in defining the geometry ofthe extraction zone. The first experimental trial undertaken at theRidgeway operation used 241 markers in one ring planeconsisting of 13 holes (located 1.3 m in front of the blast ringplane) and an in hole marker spacing of 1 m [28]. The results ofthis trial indicated that the experimental procedure was sound. Itdid, however, highlight that the distribution of markers in theburden was not adequate to quantify the extraction zone, inparticular the depth of draw [28]. Based upon this finding, furthertrials were designed with three marker ring planes located at0.65 m (Ring 3), 1.3 m (Ring 2), and 1.95 m (Ring 1) in front of theblast ring plane. A two- and three-dimensional representation ofmarker location for a typical three ring marker trial can bereferred to in Fig. 3a and b, respectively.
Fig. 3. Typical two- and three-dimensional distribution of markers in a three ring
marker trial. (a) 2D distribution of markers (Ring 1, 2, and 3 located 1.95, 1.30, and
0.65 m in front of blast ring plane respectively) and (b) 3D distribution of markers.
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Three ring marker trials usually consisted of 17 marker holes,with approximately 320 markers installed per trial. Furtherrefinements of marker ring locations were made after the eighthtrial, with Ring 3 being removed for selected trials. This resultedin a total of 11 marker holes being drilled, with approximately190 markers installed per two ring trial. A total of 15 and 53individual blast rings were monitored with two and three ringmarker planes, respectively.
2.3. Delineation of extraction zone
Delineation of extraction zones within a trial ring was madewith information obtained from the recovered markers. Thesezones were divided into five levels or categories defining primary(marker excavated from the production level in which it wasinstalled), secondary (marker excavated from the production levelone level below installation), tertiary (marker excavated from theproduction level two levels below installation), quaternary(marker excavated from the production level three levels belowinstallation), and backbreak (marker excavated from previouslyblasted ring due to back break damage) recovery, respectively.Three major assumptions were made for extraction zonedelineation: (1) the extraction zone was delineated as a series of
Fig. 4. Example of delineated extraction
polygons in two dimensions; (2) 100 percent of markers wererecovered by magnetic separation within the material handlingprocess (based upon results of a calibration trial discussed byPower [28]); and (3) installed marker locations represent thelocation of markers after the blasting process (i.e. markers do notmove from their original location during blasting).
Instead of a general ellipsoid shape being fitted to the data, theextraction zone was defined by a number of polygons based uponactual markers recovered. Delineation of these polygons wasbased upon six criteria consisting of: (1) polygon boundarydefined by the half way point between two markers (x and y
directions); (2) polygon boundary bound by the blast ring outline;(3) at least two markers adjacent to one another and having thesame recovery level (primary, secondary, tertiary, quaternary, orbackbreak) were required to define an extraction polygon(i.e. single markers do not define an extraction zone); (4) singlemarkers of a different recovery level to those surrounding it maybe contained in the polygon defining the dominant markerrecovered; (5) markers not recovered in the material handlingprocess are assumed to represent material not extracted from thecave to date; and (6) areas within the blast ring that do notcontain markers are treated as not being monitored, withextraction polygons terminating at these regions (i.e. polygonsdo not extend into areas with no marker coverage). These criteria
zones for two experimental trials.
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were considered important as they provided a systematic andconsistent approach in defining extraction zones. Although thesepolygons do not represent the true shape of the extraction zone,they do provide an insight into the non-uniform nature of fullscale material flow behaviour. An example of delineated extrac-tion zones for two experimental trials can be referred to in Fig. 4.
It is apparent from Fig. 4 that a relatively dense marker patternwith complete ring coverage is required to achieve an acceptablelevel of confidence for the delineation of extraction zones.Without this level of marker coverage the delineation andinterpretation of these zones would be difficult if not impossible.
2.4. Analysis of extraction zone polygons
Traditional methods of extraction zone analysis have beendependent upon quantifying the depth and width of draw, and thepercentage of material recovered [18,26–28]. Early full scalemarker experiments related the depth and width of draw to anassumed ellipsoid shaped extraction zone. Based upon thecomplex nature of the extraction zone polygons delineated forthe Ridgeway marker experiments, the use of the depth and widthof draw was not considered a good descriptor of flow behaviour.
For this paper, the percentage of material recovered from theextraction zone is used to quantify flow behaviour. The percen-tage of material recovered from any given extraction zone can berepresented as both a two- and three-dimensional calculation.Such an analysis provides detailed information concerning thedevelopment of the extraction zone within the blast burden andan appreciation of the overall material recovered within the ring.For the two-dimensional case, the percentage of materialrecovered for any given extraction level is simply the area ofthe extracted polygon divided by the total area of the blast ring.The three-dimensional calculation relied on the assumption thateach marker ring plane represents a volume of material boundedin the third dimension by either the half way point betweenmarker ring planes or the boundary of the blast volume.
For the standard distribution of marker rings within the blastburden (rings located at 0.65 m, 1.3 m, and 1.95 m), the volumetriccalculation for extraction zone recovery highlighted three majorlimitations: (1) for two marker ring planes, the volumetriccalculation for the extraction zone is biased towards marker Ring2; (2) for three marker ring planes, the volumetric calculation forthe extraction zone is biased towards marker Rings 1 and 3; and(3) it is difficult to compare volumetric extraction zone recoveriesbetween two and three ring marker trials. This can be primarilyattributed to marker Ring 3 being absent for the two marker ringtrials, thus biasing volumetric recovery results. Based upon theselimitations, emphasis was placed on the results from two-dimensional extraction zone polygons for recovery analysis.
2.5. General observations of extraction zone
Visual assessment of extraction zone delineations indicatedthat polygons do not correspond to the classical ellipsoid flowtheory first proposed by [6]. This confirms findings from previoushistoric small and full scale SLC flow experiments[1,5,11,14,21,24–29,31–33] that noted the extraction and move-ment zones were not a true ellipsoid for these particularexperiments. Based upon the Ridgeway results, some generalobservations were made concerning the shape and extent of theextraction zone: (a) The primary extraction zone recovery ishighest in Ring 3 (0.65 m from the blast ring) and diminishes inRings 1 and 2; (b) the primary extraction zone recovery isgenerally made up of one discrete flow zone (or continuous flowzone) in Ring 3 and ‘fingers’ of ore recovery in Rings 1 and 2; (c) the
primary extraction zone recovery did not generally reach thewidth of the blasted ring; (d) the number of markers recovered inthe previous ring (backbreak) varied significantly and weregenerally confined to Rings 1 and 2; (e) the extraction zonerecovery for secondary, tertiary, and quaternary generally di-minishes with level of recovery (i.e. secondary is higher thantertiary which in turn is higher than quaternary); (f) secondary,tertiary, and quaternary recovery generally occurs as relativelysmall discrete zones within the blasted ring; and (g) portions of theblasted ring still remain un-recovered after quaternary extraction.
It can generally be concluded that the shapes of the extractionzones were irregular in nature (not described by an ellipsoidshape), with primary recovery consisting of an area of ‘continuousflow’ near the blast ring plane (marker Ring 3) and ‘fingers’ ofrecovery further from the blast ring plane (marker Rings 1 and 2).The backbreak extraction zone is relatively common, with highestrecoveries occurring in marker Ring 1 (ring plane closet topreviously fired blast burden). Secondary, tertiary, and quaternaryrecoveries occur as relatively small discrete zones within theblasted material.
3. Self-Organising Map (SOM) analysis
The SOM technique is a data analysis tool that allowsvisualisation of relationships within and between various fieldsof complex datasets [34]. It was first proposed by [35], and hassince become one of the most popular neural network methods[36]. The SOM approach has been used in a wide variety of fieldsincluding finance, industrial control, speech analysis, astronomy,petroleum, and earth sciences [37]. The algorithm provides a non-parametric mapping (regression) that transforms an n-dimen-sional representation of high dimensional, nonlinearly relateddata items to a typically two-dimensional representation, in afashion that provides both an unsupervised clustering and ahighly visual representation of the data’s relationships [38].
The main task of SOM is to act as an exploration tool foracquiring an understanding, and for generating hypotheses about,the properties of the dataset [36]. Compared to the manyalternative algorithms, the strength of the SOM is its versatility.The SOM technique has a number of capabilities and advantagesthat make it ideal for analysing geological and mining-relateddatasets, including [34,36,38]: (a) robust handling of missing andnoisy data; (b) determining dependencies and relationshipsbetween variables and statistical properties of individual vari-ables; (c) identifying clusters or natural groups in the data, andthe properties of those clusters; (d) an ability to identify anddefine subtle relationships within and between diverse data suchas continuous and categorical variables; (e) no required priorknowledge about the nature or number of clusters within the data(unsupervised); and (f) no assumptions about statistical distribu-tions of variables or linear correlations between variables.
Due to the advantages of the SOM technique, the Common-wealth Scientific and Industrial Research Organisation (CSIRO)-Exploration and Mining have developed a software package calledSiroSOM. SiroSOM has been specifically developed to utilise SOMfor the analysis of spatially located geoscience data. This softwarehas been used across a range of datasets including soil, rockchipand downhole geochemistry, airborne and downhole geophysics,and rock mechanics and geotechnical issues. SiroSOM is used forthe analysis of the Ridgeway full scale experimental results.
3.1. SOM dataset
The SOM dataset was constructed to explore the impact ofvarious parameters on extraction zone and total extraction zone
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Table 1Summary of SOM dataset parameters investigated for extraction zone recovery.
GL Drawpoint width (m) 60 5.93 0.47 4.90 6.80 Actual drawpoint width at gradeline (1.5 m above floor of production drive)
Brow drawpoint width (m) 28 4.69 0.61 3.00 5.60 Actual drawpoint width at brow (roof) of drawpoint
Hang-ups 60 – – – – Any hang-ups reported at drawpoint (Y/N)
Fragmentation 60 2.02 0.37 1.44 3.17 Fragmentation uniformity index obtained from photographic analysis method (Split)
Oversize count 60 6.10 6.30 0 36 Number of oversize particles counted (fragment length41 m)
Actual percent draw (%) 60 133.19 19.25 98.84 186.05 Actual tonnage of material excavated from ring relative to design blast tonnage
Geology
No. of thrust faults 62 0.10 0.35 0 2 Number of thrust faults mapped in blast burden (fault dipo451)
No. of vertical faults 62 0.31 0.67 0 3 Number of sub-vertical faults mapped in blast burden (fault dip4451)
Total no. of faults 62 0.40 0.71 0 3 Total number of faults mapped in blast burden
Degree of veining 27 10.63 8.96 1 40 Amount of quartz veining per metre (visually estimated)
Fig. 5. Cross-section (looking north) of blast ring designs for 10, 8, and 7 hole
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recovery. Total extraction zone recovery is defined as theaccumulated extraction zone recovery for any given recoverylevel. It therefore provides details concerning total recoveredmaterial from the extraction zone for primary up to quaternaryexcavation. For this analysis total recovery included backbreak.
Parameters investigated for possible correlation to extractionzone and total extraction zone recoveries were broadly dividedinto four categories–trial location, blasting, drawpoint, andgeological parameters (total of 29 parameters). Particularparameters were chosen based upon those identified in theliterature to influence recovery, and the extent and reliability oftheir associated dataset. The marker trial locations weredescribed by the northing, easting, and reduced level (R.L.) ofthe centroid of the blast ring located at the roof of the productiondrive. A summary of the blasting, drawpoint, and geologicalparameters investigated are contained in Table 1 and in thefollowing sections ([29] provides a detailed discussion of theseparameters).
patterns.
3.1.1. Blasting parameters
Blasting parameters relate to the actual implemented drill andblast design recorded by mine personnel. They were subdividedinto blast hole geometry (number of blast holes, toe spacing,spacing/burden ratio), explosive distribution (total charge length,powder factor, model peak particle velocity (PPV) rock breakagecriteria), explosive properties and initiation (explosive sleep time,nominal delay time, and primary detonator location), and blastperformance (detonation issues related to vibration monitoringrecords). For the dataset analysed, explosive type (emulsion),blast ring dump angle (101 towards the cave), and blast holediameter (102 mm) were the same for all trials.
Historically, the drill and blast design at Ridgeway has beenbased upon ten, eight, and seven hole blast patterns (Fig. 5). Thedesign change from a ten to eight hole blast pattern was achievedby removing the shoulder holes (holes 1 and 10) in the ten holepattern. This resulted in a steeper shoulder hole angle in the eighthole pattern, and an increase in subsequent blast ring apex height(in lower sublevels). A further design modification from a eight toseven hole blast pattern resulted in the removal of one apex hole(hole 5) in the eight hole pattern.
The resulting changes in drill and blast design have resulted ina wide range of design powder factors (0.94 kg/m3 to 1.46 kg/m3)being implemented for the full scale marker trial period. This
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provided a unique opportunity to investigate the direct impact ofvarious drill and blast design parameters on SLC material flowrecovery.
3.1.2. Drawpoint parameters
Drawpoint parameters relate to the observed conditions at thedrawpoint during excavation of the blasted marker trial ring.Parameters can be subdivided into actual drawpoint geometry(drawpoint height, width at gradeline (1.5 m above floor level),width at brow (estimated by site personnel)), material hang-upand fragmentation (hang-up present (yes or no), fragmentationuniformity index calculated from photographic analysis, numberof oversize particles greater than one metre in length), and actualpercentage of material drawn (relative to design tonnage of blastring). Material hang-up and fragmentation assessments weremade by site personnel every 200 to 300 tonnes excavated(during ore sampling for grade control purposes).
3.1.3. Geological parameters
Geological parameters relate to the number of fault structuresand degree of quartz veining (veins per metre) observed in theroof of the production drive (in the blast burden of the markerring trial). These parameters are routinely recorded by sitegeologists for every development advance taken. Fault parametersare subdivided into the number of thrust (dipo451), vertical(dip4451), and total number of fault structures. It should benoted that these parameters only represent faulting and veiningin the vicinity of the production drive and not over the entireheight of the blast ring. It however provides an indicative guide to
Table 2SOM correlation coefficient between various parameters and extraction zone recovery
Parameters Recovery
Primary (% area) Secondary (% area)
Ring 1 Ring 2 Ring 3 Ring 1 Ring 2 Ring 3
Blasting
No. of blast holes 0.27 0.35 0.38 0.25 0.31 0.36
Toe spacing (m) �0.19 �0.23 �0.27 �0.26 �0.29 �0.40
Spacing/burden ratio �0.22 �0.24 �0.20 �0.32 �0.32 �0.44
Actual charge length (m) 0.21 0.37 0.43 0.34 0.35 0.41
Actual powder factor (kg/m3) 0.15 0.41 0.61 0.25 0.29 0.25
Actual percent draw (%) �0.30 �0.23 0.03 �0.51 �0.21 �0.52
Geology
No. of thrust faults �0.18 �0.38 �0.53 �0.16 �0.30 �0.29
No. of vertical faults 0.28 0.04 0.04 �0.12 0.22 �0.03
Total no. of faults 0.21 �0.08 �0.14 �0.18 0.12 �0.13
Degree of veining �0.37 �0.32 �0.37 0.52 0.55 0.51
the degree of geological structure influencing the marker trialblast.
4. SOM correlation analysis and results
The SOM approach provides a rigorous methodology toidentify possible correlations for further data exploration andanalysis. Any estimate of the relationships between particularinput parameters can be ascertained by computing the correlationcoefficient between a particular parameter and the rest of thevariables ([29] discusses the SOM parameters and processimplemented for this analysis). Tables 2 and 3 summarises thecorrelation coefficients between various parameters andextraction zone and total extraction zone recovery parameters,respectively. The correlation coefficient value ranges from a valueof �1 to 1. A correlation coefficient greater than or equal to 0.50indicates a significant relationship between two parameters[37,39]. A correlation coefficient less than or equal to �0.50indicates a significant inverse relationship between twoparameters [39]. Cells in Tables 2 and 3 with correlationcoefficients greater that 0.50 and less than �0.50, werehighlighted in bold and italics, respectively.
4.1. Extraction zone recovery
Of the parameters analysed, blasting-related factors werefound to dominate correlations with extraction zone recoveries.In particular, blasting was found to be strongly related to primaryrecovery in marker Ring 3, and to a lesser extent tertiary
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recoveries in marker Rings 1 and 3. For primary recovery inmarker Ring 3, blasting parameters correlating with recoverywere powder factor, PPV breakage criteria, explosive sleep time(inverse), blast detonation issues (inverse), and nominal delaytime. Similar parameters were noted to impact tertiary recoveryin marker Ring 3 (additional parameter of charge length alsoimpacted this recovery). Tertiary recovery in marker Ring 1 wasinfluenced by the number of blast holes, toe spacing (inverse),spacing to burden ratio (inverse), charge length, PPV breakagecriteria, and detonation issues (inverse). It should also be notedthat backbreak recovery in marker Rings 1 and 2 was inverselyrelated to nominal delay time.
From the observations discussed above, blasting parametershad the largest influence on marker Ring 3. This is not surprisingconsidering that this marker ring is closest to the blast ring planeand therefore the most likely to be impacted by blasting.
It is also interesting to note that secondary recovery was notinfluenced by blasting parameters (except for primary detonatorlocation marker Ring 3), but in turn tertiary recovery is (markerRings 1 and 3). No reason for this observation is apparent, exceptpossibly for the offset of production drives from one SLC level tothe next (primary production drives are located directly abovetertiary production drives). An inverse relationship related todetonation issues indicate that no detonation problems correlatedto increased recovery.
Drawpoint and geological parameters found to correlate withextraction zone recovery included drawpoint width at gradelineand brow (inverse), the number of drawpoint hang-ups, oversizecount, percent draw, number of thrust faults (inverse), and degreeof veining. Of these parameters, only drawpoint width at grade-line, percent draw, and degree of veining had correlations on a
significant number of recovery parameters. Drawpoint width atgradeline was inversely related to primary recovery in markerRings 2 and 3, and tertiary recovery in marker Ring 3. Actualpercent draw was inversely related to secondary recovery inmarker Rings 1 and 3, and directly related to quaternary recoveryin marker Ring 1. The degree of veining was found to correlate tosecondary recovery for all three marker ring planes.
4.2. Total extraction zone recovery
As for extraction zone recovery, blasting parameters domi-nated correlations with total recovery including backbreak.Charge length, powder factor, PPV breakage criteria, explosivesleep time (inverse), and blast detonation issues (inverse) relatedto recovery parameters for all levels of recovery (primary toquaternary). Additionally, the number of blast holes, toe spacing(inverse), spacing to burden ratio (inverse), and primary deto-nator location related to total secondary to quaternary recoveryparameters. For total primary recovery, all identified correlationswere associated with marker Ring 3. For total secondary andtertiary recovery, correlations were associated with marker Rings2 and 3, while for total quaternary recovery they werepredominantly associated with marker Rings 1 and 3.
As with extraction zone recovery, blasting parameters are onlyrelated to marker Ring 3 for total primary recovery (this would beexpected as primary extraction zone and total primary extractionzone recoveries are similar). Differing to extraction zone recovery,these correlations were generally extended to total secondaryrecovery for marker Rings 2 and 3. A possible explanation of thedisparity is that the primary recovery component dominates the
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total secondary recovery value (i.e. primary recovery is muchhigher than secondary recovery). With primary recovery formarker Ring 3 being highly correlated to blasting parameters, thiscould lead to correlations being extended to total secondaryrecovery. This argument could also be extended to total tertiaryand quaternary recovery relationships.
Drawpoint and geological parameters found to correlate withtotal extraction zone recovery included drawpoint height(inverse), drawpoint width at gradeline (inverse), number ofthrust faults (inverse), and number of vertical faults. Of theseparameters, only drawpoint width at gradeline and number ofthrust faults had correlations with a significant number of totalrecovery parameters. Drawpoint width at gradeline is inverselyrelated to total primary, secondary, and tertiary recovery inmarker Ring 3. The number of thrust faults was inversely relatedto total primary to quaternary recovery in marker Ring 3, andtotal secondary and tertiary recovery in marker Ring 2.
5. Blast-related recovery theories
Based upon the analysis results, a number of possible theoriescan be proposed with regard to the impact of blast parameters onextraction zone recovery. Although the correlations analysed donot necessarily prove causality, the correlations can be ‘inter-preted’ in casual terms to propose a number of blast-relatedtheories with respect to recovery. To develop these theories, bothcorrelations between blasting parameters and extraction zonerecovery as well as blast-related inter-parameter correlationsneed to be considered [29].
It is difficult to determine which blasting parameters arepotentially influencing recovery results due to the experimentaldesign of the marker trial. However, based on the analysis thefollowing four theories were considered: (1) a fundamentalchange in drill and blast design with the removal of blast holes,leading to a reduction in explosive weight and poorer explosiveenergy distribution, results in lower extraction zone recoveries (inparticular primary recovery for marker Ring 3). The reduction inthe number of blast holes in turn impacts on total secondary toquaternary extraction zone recovery either directly (due to factorssuch as poor fragmentation and limited swell) or indirectlythrough reduced primary recovery (leading to subsequent lowertotal secondary to quaternary recoveries). Recovery in the markerring planes is directly related to proximity of the blast ring plane.A reduction in the number of blast holes results in a significantreduction in recovery for marker Ring 3, with this impactdiminishing for marker Ring 2, and not being evident for markerRing 1; (2) an increase in explosive sleep time (generallycorresponding with a decrease in actual power factor) leads topoorer explosive performance (in particular VOD), resulting inlower extraction zone recoveries (due to factors such as poorfragmentation and limited swell). The increase in explosive sleeptime in turn impacts on total secondary to quaternary extractionzone recovery either directly (due to factors such as poorfragmentation and limited swell) or indirectly through reducedprimary recovery (leading to subsequent lower total secondary toquaternary recoveries). An increase in explosive sleep time resultsin a significant reduction in recovery for marker Ring 3, with thisimpact not being evident for marker Rings 1 and 2.; (3) the changeof the primary detonator location from the midpoint to toe(generally corresponding with a decrease in actual powder factor)leading to poorer detonation of the explosive column (partialdetonation or lower VOD of explosive column), resulting in lowerextraction zone recoveries (due to factors such as poor fragmen-tation and limited swell). The change in detonator location in turnimpacts on total secondary to quaternary extraction zone
recovery either directly (due to factors such as poor fragmenta-tion and limited swell) or indirectly through reduced primaryrecovery (leading to subsequent lower total secondary toquaternary recoveries); and (4) a combination of blast parametersdiscussed in the first three points impact, to some extent,extraction zone recovery and total secondary to quaternaryextraction zone recovery either directly (due to factors such aspoor fragmentation and limited swell) or indirectly throughreduced primary recovery (leading to subsequent lower totalsecondary to quaternary recoveries). Recovery in the marker ringplanes is directly related to proximity of the blast ring. Combinedchanges in these blast parameters result in a significant reductionin recovery for marker Ring 3, with this impact diminishing formarker Ring 2, and not being evident for marker Ring 1.
Of the theories proposed, it is considered that the most likelybased on the analysis is the theory outlined in point one. Theremoval of a blast apex hole (eight to seven hole blast designs)had a significant impact on both blast geometry and explosivedistribution parameters. It is considered that such a significantchange in these parameters would lead to changes in blastedmaterial properties (fragmentation and bulk density) and result inlower recoveries.
6. Conclusions
The Ridgeway full scale marker trials provided a uniqueopportunity to assess measured factors influencing extractionzone recovery. However, such complex datasets are normallydifficult to analyse using traditional statistical multivariatemethods. To overcome this issue, a neural network Self-Organis-ing Map (SOM) technique was adopted to analyse the dataset.This methodology is ideal for attempting to understand theinteraction of multiple mining and geological parameters on SLCextraction zone recovery for the full scale recovery experimentalprogram.
SOM correlation coefficient values indicated that blastingfactors are the most dominant parameters correlating to extrac-tion zone recovery. Blasting parameters (charge length, powderfactor, PPV breakage criteria, explosive sleep time, detonationissues, and nominal delay time) were found to be strongly relatedto primary recovery in marker Ring 3, and to a lesser extenttertiary recoveries in marker Rings 1 and 3. Non-blastingparameters found to have a significant number of correlationsto extraction zone recovery parameters included drawpoint widthat gradeline, number of thrust faults, and degree of veining.
As for extraction zone recovery, blasting factors were found tobe the most dominant parameters correlating to total extractionzone recovery (including backbreak). Charge length, powderfactor, PPV breakage criteria, explosive sleep time, and blastdetonation issues related to recovery parameters for all levels ofrecovery. Additionally, the number of blast holes, toe spacing,spacing to burden ratio, and primary detonator location related tototal secondary to quaternary recoveries. Non-blasting para-meters found to have a significant number of correlations to totalextraction zone recovery (including backbreak) parametersinclude drawpoint width at gradeline and number of thrust faults.
The most likely theory based upon this analysis is that afundamental change in drill and blast design with the removal ofblast holes resulted in lower extraction zone recoveries (in particularprimary recovery for marker Ring 3). The reduction in the number ofblast holes in turn impacted on total secondary to quaternaryextraction zone recovery either directly (due to factors such as poorfragmentation and limited swell) or indirectly through reducedprimary recovery (leading to subsequent lower total secondary toquaternary recoveries). Recovery in the marker ring planes is directly
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related to proximity of the blast ring plane. A reduction in the numberof blast holes results in a significant reduction in recovery for markerRing 3, with this impact diminishing for marker Ring 2, and not beingevident for marker Ring 1.
Acknowledgement
The authors wish to thank Newcrest Mining Limited whoprovided the data used in the development of this paper.
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