Technical Report CVSA AGA

7/25/2019 Technical Report CVSA AGA

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Report Prepared

for

Anglo Gold Cerro Vanguardia SA

Technical Visit ReportCVSA Surface and Underground OperationsReview, Commentary & Recommendations

November 2010

In cooperation with


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November, 2010. Technical Visit Report Surface and Underground Operations p. i

Technical Visit Report - CVSA - November - draft.doc

Technical Visit ReportCVSA Surface and Underground Operations

Review, Commentary & Recommendations

EXECUTIVE SUMMARY

Austin Powder Argentina (APA) offers a supply, load and shoot service for all blastingactivities at the Cerro Vanguardia operations in Santa Cruz, southern Argentina. The provisionof high quality technical service to the mine is an important part of the APA offering to Cerro

Vanguardia S.A. (CVSA). A key part of this technical component is the provision of regularon-site visits y international blasting engineer consultants.

As such, Cameron McKenzie of Blastechnology and Bill Adamson of Austin PowderInternational (API) visited the mine during the 8thto the 10thof November of this year. Thisvisit was supported by the Technical Manager of APA; Emilio Concha Valle.

In accordance with the mixed mining method nature of the CVSA operations, work wasundertaken and visits made to both surface and underground production sites. The needs of

CVSA in both environments were communicated in preliminary presentations delivered byCVSA engineers in a briefing exercise for the visiting consultants.

In response, two general presentations, describing previously discussed and availableAPA/API technology and services (including Blastechnology support) were delivered by APIand Blastechnology.

The three day visit to CVSA on the part of the technical team from Austin Powder Argentina,

Austin Powder International and Blastechnology was an effective and productive exercise.

The visit was spent examining and studying drilling and blasting results (design andimplementation) in both the surface and underground mining environments.

The comments presented in the present section are separated, for clarity, into two groups,

reflecting the two mining environments visited in early November.

Surface Drilling and Blasting

The objectives of the drilling and blasting work in the surface mining context were fivefold:

Review the CVSA performance in terms of pre-split blasting

Review the performance regarding the coordinated implementation of buffer blastdesign and implementation

Comment on practices for the optimised blasting of narrow veined orebodies


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November, 2010. Technical Visit Report Surface and Underground Operations p. ii


Consider the possibility of introducing a modified format of massive blasting in thosepits where the available bench area is present

Comment and participate in the fine tuning of special blast designs for blasting of rockvolumes containing pit dewatering well casings.

Pre-Split

Regarding the pre-split design and implementation, it was confirmed that a number of goodpractices are regularly followed at CVSA; drilling and blasting the pre-split over the full depthof the double bench and designing angled pre-splits are both excellent decisions in terms ofobtaining an optimum result.

The question was asked whether it is better to fire the pre-split blast some time (half a day, a

day, etc.) prior to the main blast, or whether it is more acceptable to fire the pre-split at thesame time as the main blast. Preferences are mixed on this point and there are arguments

supporting both points of view, however at this stage there have been nothing noted in recentexperiments at the mine to indicate a preference for one or the other theory. More workperhaps needs to be done in this regard.

There is scope for further improvement in pre-split effectiveness if a greater effort is made torelate pre-split design to rock mass properties between different pits. CVSA has access to thefull analysis capability of Austin Powder and it is recommended that Austin Powder be invitedto participate more in this optimisation process.

Finally, observations in the field (Pit OD-CB8) demonstrated the dominant influence that in-

situ structure can have over pre-split performance, where in two domains with very similarUCS but significantly different structural characteristics, two very different results were

obtained in terms of pre-split quality. There is a clear difference noted between a result withhigh half-barrel count, and a smooth, even fracture between each, and the case where half-

barrels are separated by uneven, rough rock surfaces that indicate the lack of a completefracture between charged blastholes.

Buffer Blasting

The issue of good buffer blast design remains critical for the success of wall control at Cerro

Vanguardia.

It is clear that the standoff distance for each blast must be matched to the charge characteristicsfor the explosives in use, as well as the angle of drilling. CVSA has altered their standarddesign practice for the better in ceasing to drill angled buffer holes, moving to vertical holesand reducing the crater damage provoked at the crest of the new bench.

Under some conditions, excessive standoff may lead to the result of leaving a crust of cling-onmaterial along some parts of the face of the new bench. Success has been achieved in otheroperations by using a negative angle or drilling back towards the toe of the pre-split for the

buffer row. This allows a suitable standoff distance to protect the crest yet also allows theplacement of explosive energy to remove the crust of unbroken rock.


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November, 2010. Technical Visit Report Surface and Underground Operations p. iii


Narrow Vein Blasting

It is suggested to CVSA that dilution is inevitably, at least partially, related to muckpile

displacement during blasting. The current drilling and blasting designs for narrow veindeposits tend to produce a great deal of displacement this has been confirmed by observationof various video records for a number of ore blasts.

There is potential for use of modified pre-split blast drilling and charging, for reducing theamount of displacement and burden movement velocity. This technique uses the drillingparameters and the explosive charge philosophy but alters the initiation sequence to more

closely resemble a production blast. Previous attempts using this technique have reported quitecoarse fragmentation and lack of movement. It is suggested, in this case, that the number of

pre-split rows be increased gradually in order to reach a balance between displacement andfragmentation. Austin Powder uses at least two modelling approaches to address this challengeand CVSA is encouraged to work with Austin Powder to examine the alternatives in moredetail

Massive Blasting

In 2008 and 2009, Austin Powder International recommended that CVSA consider firinglarger production blasts, re-oriented to fire parallel to the final wall orientation.

Recent events in OD-CB8 suggest that CVSA has found a way to incorporate massive (> 10rows) blast patterns into their production planning process. This will allow CVSA toexperiment with different initiation sequences that have been shown to reduce damage in anumber of mines around the world.

Well Casing Blasting

CVSA has managed to fire a number of controlled blasts in the vicinity of mine de-wateringwell casings in the past. This work has been supported by Austin Powder Argentina withdrilling designs; the current pattern is a derivation of work done several years ago by APA. In

the case of this particular visit, a combination of circular pre-splitting and light fracturingblasts, while encouraging a large amount of displacement for the front face, production rows,

was shown to leave the well casing in good physical condition.

Underground Drilling and Blasting

The development of underground mining operations at CVSA has advanced notably and a visitwas made to the Mangas Centro decline in order to assess the current state of efficiency indrilling and blasting operations.

A number of visual observations were made, as follows;

It is clear that floor control has room for improvement, both in the main decline accessand along level development. There is a tendency for undulation, rising and falling, inthe floor surface and this is likely related to incomplete control of the drilling accuracy

when developing the tunnel access.


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November, 2010. Technical Visit Report Surface and Underground Operations p. iv


Successful ring blasting within the stopes requires good drilling, which in turn requiresaccurate survey set-up and marking of the ring positions and collaring points. A casewas observed where the ring plane direction was not perpendicular to the axis of the

stope drive this will complicate identification of the correct blastholes to charge andwill probably affect the ease of displacement of the blasted ore.

Survey of the top and bottom of each blast hole will provide important assistance at themoment of deciding on the explosive charging and initiation sequence best suited todeliver a good blast result.

The feedback from surveys of this nature, to drillers, should tend to create a positivefeed-back loop that encourages improved drilling accuracy and precision.

Currently the blasthole rings are fully charged with ANFO and this can lead to powder

factors of around 1.2 kg/t an intensity that is probably excessive and likely topromote damage.

The objectives for optimisation of the underground drill and blasting were stated as;

Reduce damage, particularly to the hangingwall

Reduce dilution strongly related to the previous point.

Optimise drop-raising performance.

A number of suggestions were offered as a means to achieving these objectives, including;

Carry out near field vibration measurement campaigns in the stopes that are beingdeveloped. This technique will permit a diagnostic evaluation of the progress of theblasting and also supply valuable data for the fitting of a predictive vibration model.

Evaluate the geotechnical characteristics/properties of the rock masses in each stope inorder to calculate the critical value of vibration required to initiate fracturing(remembering that in the underground environment, vibration is usually the dominant

mechanism of damage).

Use the fitted model mentioned above, together with the vibration damage criterion to

evaluate and modify blast designs in order to control damage.

The same technique can be adapted to evaluate fragmentation problems and potentialfor improvement, if necessary.

Drop- raising blasting success is strongly affected by at least two factors;

o Drilling accuracy, and

o Percentage void space provide by uncharged drill holes.

Drilling accuracy can be measured and blast designs adjusted to maintain a correct

firing sequence.


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November, 2010. Technical Visit Report Surface and Underground Operations p. v


Electronic initiation systems will also allow firing times to be selected that will permitan optimisation of initiation sequences for each lift of the drop-raise.

Project Team Formation

Both CVSA and Austin Powder possess valuable assets in the form of trained staff,quantitative data, operational resources, specialised software and measurement technology.

These resources will be most efficiently put to use if customer and service provider can agreeto work in a team framework to design and execute specific projects aimed at optimisingtargeted aspects of blast performance.


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November, 2010. Technical Visit Report Surface and Underground Operations p. vi


Report to AngloGold Ashanti, Cerro Vanguardia SA

Technical Visit Report

CVSA Surface and Underground Operations

Review, Commentary & Recommendations

TABLE OF CONTENTS

Page

SURFACE DRILLING AND BLASTING IUNDERGROUND DRILLING AND BLASTING IIIPROJECT TEAM FORMATION V

1. INTRODUCTION .........................................................................................................................1

2. SCOPE OF WORK .......................................................................................................................1

3. SURFACE ISSUES........................................................................................................................3

3.1 WALL CONTROL BLASTING PRE-SPLIT DESIGN AND PRACTICE 33.2 WALL CONTROL BLASTING BUFFER ROW DESIGN 73.3 NARROW VEIN BLASTING CONTROLLING DISPLACEMENT 93.4 MASSIVE BLASTING 123.5 SPECIAL PURPOSE BLASTING WELL CASING PROTECTION 14

4. UNDERGROUND ISSUES........................................................................................................19

4.1 CONTROL OF DAMAGE AND DILUTION 204.2 OPTIMISATION OF DROP-RAISES 26

4.3 OPTIMISATION OF DEVELOPMENT BLASTING 27

5. JOINT PROJECT TEAMS........................................................................................................30

6. CONCLUSIONS AND RECOMMENDATIONS ..................................................................31

6.1 SURFACE DRILLING AND BLASTING 316.2 UNDERGROUND DRILLING AND BLASTING 336.3 PROJECT TEAM FORMATION 35

7. ACKNOWLEDGEMENTS........................................................................................................35


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November, 2010. Technical Visit Report Surface and Underground Operations Page 1 of 42


Technical Visit Report

CVSA Surface and Underground OperationsReview, Commentary & Recommendations

1. INTRODUCTION

Austin Powder Argentina (APA) offers a supply, load and shoot service for all blastingactivities at the Cerro Vanguardia operations in Santa Cruz, southern Argentina. The provisionof high quality technical service to the mine is an important part of the APA offering to CerroVanguardia S.A. (CVSA). A key part of this technical component is the provision of regular

on-site visits y international blasting engineer consultants.

As such, Cameron McKenzie of Blastechnology and Bill Adamson of Austin Powder

International (API) visited the mine during the 8thto the 10

thof November of this year. This

visit was supported by the Technical Manager of APA; Emilio Concha Valle.

In accordance with the mixed mining method nature of the CVSA operations, work wasundertaken and visits made to both surface and underground production sites. The needs ofCVSA in both environments were communicated in preliminary presentations delivered byCVSA engineers in a briefing exercise for the visiting consultants.

In response, two general presentations, describing previously discussed and available

APA/API technology and services (including Blastechnology support) were delivered by APIand Blastechnology.

As a result of this opening exchange of information and needs, it was possible to delineate aScope of Work for the three days of the visit.

2. SCOPE OF WORK

CVSA now extracts mineral from both surface and underground operations, although thissecond source of production is very recent in the historical context of the mine life. The recentvisit, which gives rise to the current report, was therefore considered in two parts; surfaceissues and underground challenges.

Two separate presentations were delivered to the API and APA personnel, both of whichcommunicated the current needs and interests of each production environment.

The material presented in the surface blasting context was interpreted as a request for feedbackon recently completed work in limits blasting and comments on a proposed design for specialpurpose blasting in one of the production pits.

In response to the surface presentation, the following list of bullet points outlines the different

aspects of drilling and blasting that receive attention in the following Sections;


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Contour or final wall blasting

Pre-split design (spacing and charge)

Buffer row or rows (charging and stand-off distance from pre-split)

Blasting in narrow veins

Massive blasting

Special purpose blasting

In a similar manner a presentation was delivered in which the characteristics of the

underground operations were explained and the general CVSA objectives outlined for theunderstanding of the APA/API team (including Blastechnology).

A subsequent visit to one of the newly opened underground operations; Mangas Centro, wasplanned so that direct observation of the mine layout, including Stope drilling and drop

raise/cut-off slot preparation could be carried out.

The objective of this part of the visit was to produce a suggestion list for possible jointoptimisation projects to be run by a team combining APA, CVSA and API resources.

The initial list of objectives suggested by CVSA included;

Reduction of dilution as a result of stope blasting

o Control of hangingwall stability

o Optimise pre-split design for the hangingwall

Improve charge design for drop raises and cut-off blasting

Improve generic drill and blast design for production stopes.

In the following section of the report, Surface and Underground objectives will be discussed

under separate headings.


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3. SURFACE ISSUES

The unique characteristics of the surface operations are a consequence of the physical aspectof the orebodies, which lead to the mining of relatively small, yet occasionally quite deep, pitswith a very large (~ 26:1) waste to ore ratio. This physical setting places great emphasis oncontrolling the geotechnical quality of final walls so as to maintain relatively aggressive inter-

ramp and final pit wall angles, thereby maintaining safe working conditions in tight pits.

For this reason, the issues of damage control, controlled blasting and the need for efficienciesin the operational aspects of drilling and blasting are always present in any discussion ofCVSA requirements and objectives, with respect to APA/API technical service.

The technical visit carried out during the 8th to the 10

th of November of this year was no

exception.

As mentioned previously, the primary focus of improving drilling and blasting results atCVSA is usually in the area of wall control and damage reduction. In this direction, twoimportant points raised in the introductory, surface presentation by CVSA relate to thesechallenges. In particular, CVSA requested that APA/API review the physical results of anexperiment intended to examine the potential difference in effectiveness of pre-split blastsfired prior to, or simultaneously with the main production or wall control blasts.

This review was conducted and is described in this report, however the results obtained are notconclusive and it remains apparent that there are benefits to be achieved in re-focussing on

some fundamental aspects of pre-split and buffer row blast design.

Another aspect of CVSA drilling and blasting where, in the opinion of APA/API,improvements are obtainable is that of narrow vein drilling and blasting; specificallyconsidering the need to control the displacement of the blasted ore.

CVSA has carried out experimental field work, looking at the design and implementation ofrelatively massive blasts; two such events were fired in Osvaldo Diez, Cut Back 8 (OD CB8)pit. This new work has encouraged a re-examination of a suggestion offered to CVSA in 2008regarding the re-orientation of large blasts in terms of their initiation sequence and muckpile

displacement vectors. This suggestion is described in more detail further below.

Distinct from all of the foregoing points is the final request tabled by CVSA. As the pits widenwith new cut backs or expansions, the active pit shells begin to encompass elements of mineinfrastructure such as dewatering well casings, that must be kept open as benched are drilledand blasted around them. While not an unknown challenge for CVSA, the local engineeringstaff invited APA/API to participate in refining an existing drilling design and suggestingtiming and explosive charging options.

3.1 Wall Control Blasting Pre-split Design and Practice

The initial question raised by CVSA in connection with the pre-split test blasting in OD-CB8

related to whether a pre-split is best fired prior to the main blast (wether this be a full


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production or perhaps a four-row trim shot) or alternatively, fired simultaneously (butimmediately before) the main blast. The results obtained would appear to be inconclusive as

far as blast scheduling is concerned, however a visual inspection suggests the existence ofother, more important factors that should be taken into account.

In reviewing the CVSA pre-split design protocol there are a number of positive aspects thatshould be highlighted;

Drilling and firing the pre-split over the full extent of a double bench is an excellent practicethat is a major step in optimising final wall results

In a similar manner, industry experience suggests that the use of inclined pre-split drilling(standard practice at CVSA) facilitates the achievement of quality, stable final walls. Care

must always be taken to ensure precision and accuracy in the drilling of each hole so as tomaintain a constant, correct inter-hole spacing.

It is very important to ensure that the spacing and charge profile are adjusted to match thephysical characteristics of the rock mass and the strength of the rock matrix. The optimum

spacing is closely related to the borehole explosion pressure, in turn dominated by explosiveproperties and hole diameter. This calculated spacing, however, may be subject to

modification based on the in-situ fracture conditions for the rock mass in question. Underconditions where sub-vertical structures strike across the intended pre-split plane, spacingshould be reduced and the borehole pressure increased.

When evaluating pre-split quality based on a visual examination of the physical result, it isvery important to focus on the quality of the fracture surface between half holes or halfbarrelsand not simply a count of thenumberof half holes.

The field observation of the results obtained in OD-CB8 highlighted the strong, dominantinfluence of the in-situ structure. The results of pre-split blasting obtained in opposite walls of

the OD-CB8 pit were compared visually and significant differences were apparent. CVSADrilling and Blasting engineers informed APA/API that the intact rock strength values were

similar for both rock masses, on either side of the pit, however the in-situ fracture conditionsare very different.

Figure 1 shows the results obtained on the East side of the pit. An ample presence of half holes

with quite smooth, even fracture plane surfaces between each, suggest that a very good resulthas been obtained in this part of the pit. There is little apparent presence of important in-situstructure with the exception of a continuous, clearly defined fracture plane that daylightsapproximately 3m above the bench floor. This structure dips into the bench face; anotherpositive aspect of the rock mass condition in this wall.


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Figure 1. Pre-split results in the East Wall of OD-CB8 Pit

Figure 2 shows the pre-split result obtained in the West wall of the same pit, where thegeotechnical condition of the rock mass varied notably from that of the East wall. The samenominal pre-split design was applied in both locations and the results obtained were verydifferent. While some presence of half holes is visible in the wall shown in Figure 2, it is clearthat very little evidence of clean fracturing or shearing between half holes is visible. Thisresult highlights the difficulty introduced by the unfavourable presence of structure, and the

need to close up spacing and increase borehole pressure.

Figure 2. Pre-split results in the West Wall of OD-CB8 Pit


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Regarding the enquiry about the most appropriate moment to fire the pre-split, it is difficult tomake a definitive judgement based on the visual evidence available at the time of the visit to

CVSA. A considerable amount of broken rock still remained to be fully excavated andremoved, thereby preventing a safe and clear evaluation. Figure 3 illustrates the situationdescribed. It is recommended that a full set of photographs be compiled for this part of theOD-CB8 West wall, so that a final review may be conducted.

A preliminary examination of the visible wall suggested that local variation in pre-split qualityis more related to local variation in structural characteristics than the difference between prior-

and simultaneous pre-split firing.

Figure 3. Partially excavated broken rock partially obscuring the view of the final wall, prior to cleanup

As a general guide to pre-split optimisation, the following suggestions are offered;

Review the characteristics of the explosive charge that is employed, including the lengthanddiameterof the cartridges used in CVSA

Whenever and wherever possible, obtain the maximum quantity (and quality) of informationfrom mine geologists or geotechnical engineers, particularly regarding the rock UCS and anindication of the frequency and orientation of fractures with respect to the pre-split lineorientation

Work interactively with API and local APA technical service engineers, who are equippedwith design analysis tools that will assist in evaluating necessary design changes as aconsequence of variation in rock mass quality or availability of explosive and/or drill holediameters.


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An example of the application of one such design tool is given in Figure 4. This software toolallows Austin Powder engineers to evaluate any combination of drill hole diameter, spacing

and explosive characteristics for a given set of rock mass conditions.

Figure 4. Computer aided review of the suitability of a given pre-split design (combination of drill hole diameter,

spacing, explosive and rock mass properties).

Figure 4 examines the case of 25mm pre-split charges of watergel placed in 92mm diameterdrill holes, spaced at 1.2m apart, for a soft to medium (50MPa) rock under dry conditions.

The results indicate that the generated blasthole pressure (55MPa) is sufficient to comply with

the rock requirements, and that the spacing value is within optimum range.

This same tool would be used to adjust explosive and drilling diameters and spacing to adaptto changing rock quality, striving to maintain the dashboard indicators in the green.

It is recommended that a joint initiative between CVSA engineers and geologists, and APATechnical Service engineers will facilitate the ongoing optimisation of pre-split design atCerro Vanguardia.

3.2 Wall Control Blasting Buffer Row Design

The creation of a high quality pre-split is an important step towards controlling damage to thefinal walls in surface mining operations. However this measure alone will not suffice toguarantee reduction in damage intensity. The successful pre-split must be coupled with a welldesigned and executed trim or buffer blast in order to achieve a transition between the fullproduction blast energy condition and the pre-split assisted final wall.

The correct design of the buffer row or rows is critical to the success of limits blasting, as hasbeen discussed in detail in previous reports to CVSA (March, 2008; October 2009). In these

reports the importance of correct positioning of the buffer row (or rows) as well as the issue ofvertical vs. inclined buffer holes has been discussed at length.


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Maintaining an appropriate distance between the buffer row collars and the pre-split (futurecrest of the bench) will assist in controlling the impact of blast vibrations on the wall, whereas

the vertical orientation of the buffer holes will assist in reducing the damage to the crest due tocratering at the collars of the buffer holes.

These design parameters standoff distance and blasthole inclination together with theexplosive charge profile, should be adjusted as a function of ongoing observation of the crestand toe lines that are produced in the field.

It must also be remembered that a variable, and often significant, component of crest damage,as shown in Figure 5, may be the excess concentration of explosive energy resulting from thesub-drill (and explosive contained therein) from the previous bench.

All of the aforementioned aspects must be balanced in order to optimise the final result.

Figure 5. Damage to the crest due to sub-drill from the previous bench and/or the proximity of buffer hole collars

Previous technical reports (March, 2008; October, 2009) have also explained the importance

of maintaining an appropriate standoff distance between the collars of the blastholes in bufferrows and the crest of the pre-split. This distance is adjusted in accordance with the explosiveenergy present in the buffer row; however there may be occasions when the standoff distancemust be increased due to physical limitations of the drilling equipment (dimensions of the drill

rig) or safety standards imposed by the mine management in terms of minimum proximity tothe existing wall.

Under such conditions there is a risk of leaving a crust of cling-on material in front of thepre-split plane, but un-displaced by the trim blast. This remnant material must be removed

mechanically with bulldozer, retro-excavator and/or hydraulic hammers, usually at asignificant cost.


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A design alternative is to drill the final buffer row (if there is more than one) with a negativeinclination, which is to say back towards the toe of the pre-split. This approach is observed in

Figure 6. This technique has been applied successfully at the Sunrise Dam operations ofAngloGold Ashanti in Western Australia and the Anglo American copper operations ofMantoverde, in Chile.

Figure 6. Alternative distribution of buffer row drilling to adjust standoff distance while continuing to avoid

unbroken crust material

Care should be taken to ensure that the accuracy of buffer row drilling is maintained so as notto damage the toe of the pre-split.

Occasionally the increase in distance between buffer row and pre-split has been observed toproduce, to a lesser degree, some incidence of un-fragmented and un-displaced crust in theupper part of the bench face and the solution to this occurrence lies in the careful adjustment ofthe explosive charge in the buffer row, adjacent to the pre-split.

3.3 Narrow Vein Blasting Controlling Displacement

During the technical visit in November of this year the APA/API team had occasion to

examine a number of video recordings of ore blasts. These narrow vein blasts offer significantchallenges to the Drilling and Blasting engineers of CVSA, particularly in the narrow veins

where real thickness might be as little as 0.8 to 1.0m. The challenge is to produce a designsolution of distribution of drilling and charging such that adequate breakage is achieved while

controlling the amount of displacement of the broken ore.


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Figure 8 shows similar trends that occur as charge intensity is decreased, although designparameters vary somewhat from the previously demonstrated case.

The results indicate how modelled projection distances from the front face (constant burden of2.5m) reduce from 70m to 22m as the charge is varied from fully coupled ANFO to the same25mm decoupled charge of Gelamita, as discussed in Figure 7.

Flyrock Projection: Plan View

-60

-40

-20

0

20

40

60

-60 -40 -20 0 20 40 60

Burden Throw Collar Throw

(m)

(m)


-80

-60

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-100 -50 0 50 100

Burden Throw Coll ar Throw

(m)

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-25

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B urden Throw Collar Throw

(m)

(m)

Effect of Explosive Charge

Characteristics on Maximum Burden

Displacement

Standard ANFODiluted ANFO

(reduced energy,

reduced density)

Decoupled cartridged

charge (emulsion or

watergel)

92mm diameter blasthole, standard design (2.5m x 3.0m),10m bench

Figure 8. Estimation of front face displacement distances with varying charge characteristics

CVSA has made some initial investigations in this line of experimentation and whiledisplacement has been controlled, the degree of fragmentation and digability has been found tobe inadequate. APA/API would like to suggest that CVSA continue with experimentation,examining new variations in the drilling and blasting design, such as;

Drilling two staggered rows of blastholes and continuing to load with the same diameterproduct, or

Increase the diameter of the decoupled product used in the narrow vein blasts. APA produces a

range of diameters and the use of 40mm diameter charges should be considered in sectorswhere this technique has given poor fragmentation results.


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3.4 Massive Blasting

In the briefing presentation made by CVSA to the APA/API team, mention was made of a pre-split trial in the OD-CB8 pit. It was also noted that this trial was carried out in association withtwo large production blasts, each comprising in excess of 7 rows. Figure 9 shows the designfor both events.

These two blasts are of interest because they combine production blasting with buffer rows ina manner that is very similar to the technique recommended in the March, 2008 report,submitted by Austin Powder and Blastechnology.

Incidence of Massive Blasting

CASO N2CASO N 1

Figure 9. Massive blast events designed for CD-CB8

Figure 10 revisits the change in design that was suggested previously in order to reduce theimpact of blasting on the final wall of the pit. The conventional trim blast practice appliedcommonly in many parts of the international mining industry has been shown to inducereaction forces, under certain circumstances, that impose a compressive/tensileloading/unloading cycle on the final wall that has a propensity to cause rock mass damage.

The change to a design such as that shown on the left of Figure 10 will produce benefits indamage control due to a redirection of the reaction forces away from the final wall, as well as

the partial screening of the wall from blast induced vibration. The large volume of rock blastedin one event also implies further benefits in terms of operational efficiency. The single large

blast involves less frequent interruptions to production during blasting for evacuation ofpersonnel and equipment and allows excavation and haulage equipment to spend moreuninterrupted time in production.


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Voladuras MasivasVoladuras Masivas

Prctica convencional,

CVSA

Voladura masiva

Figure 10. Massive blast event design suggested in March, 2008

The successful implementation of the massive blasting approach will involve certain changesin the drilling and blast design and the following factors are suggested for consideration by

CVSA engineering staff;

An additional row of buffer holes with reduced charge should be added to the design

The initiation point for the blast should be close to the final wall, at the beginning of thesecond buffer row

The initiation sequence should be such that the blast is oriented towards the excavator, alongstrike, and not towards the pit

An increase in powder factor of between 10 15% should be considered so as to avoid a tightmuckpile

Massive, deep blasts will tend to produce higher muckpiles and this can produce certaindifficulties for front end loaders. Timing should be modified to facilitate forward displacementof the muckpile as much as possible.

With the previous point in mind, CVSA should consider the application of electronicdetonators as a means of achieving more control over displacement as well as enhancing

fragmentation. An accurate evaluation of the relative costs of this technology will indicate thatthe increase in cost per tonne of blasted rock is marginal


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3.5 Special Purpose Blasting Well Casing Protection

The mining sequence at CVSA occasionally leads to the need for drilling and blastingactivities in close proximity to casing pipes for dewatering wells, previously installed aroundand outside the initial pit shells. CVSA described the importance of avoiding damage to thesesites and estimated the cost of losing such a well casing in as much as US$ 150.000.

Figure 11 illustrates the desired result; a successful blast that left the well casing intact (thisexample comes from a previously fired blast).

The Objective

Avoid damaging and losing the

well (and many USD $$)

Figure 11. Desired state for results of Well Casing protection blast

Figure 12 shows a theoretical design that has its origins in a suggested course of actiondeveloped by APA previously. The fundamental protective measure is found in the circular

array of holes distributed around the well casing. Choices available include firing these as acircular pre-split or perhaps as a type of post-split to clean off the rock around the well casing.

It may be observed that a linear pre-split is incorporated into the blast, tangential to the circulararray of holes. The purpose of this line is to cut the observed volume in two, allowing a more

cautious approach to be taken to this second section at a later date.

The principal features in the design include an outer ring of holes that are available for lightcharging, and an array of standard production holes.

Figure 13 shows the actual as-drilled distribution of blastholes and this information was usedto select the sequence of blast events in the order intended to protect the well casing.


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WELL CASING TO BE BLASTED

IN pit OD-CB7

Figure 12. Theoretical Design for Well Casing Protection Blast

Well Casing BlastWell Casing Blast

Circular Pre-split

Well

Light Charges

Figure 13. As drilled result for the Well Casing Protection Blast

The intention of the blast sequence was to pre-fracture the zone immediately around the wellcasing, prior to the detonation of the production holes, understanding that the broken yetrelatively undisturbed rock should provide a filter for the vibrations produced in the rest of the


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blast. The firing of light charges around the circular pre-split would achieve this fragmentationwithout inducing any relative displacement around the well casing. The distribution of

explosive charges, air and stemming is shown to the right of Figure 13.

Well Casing BlastWell Casing Blast

Minimal Powder Factor

(~ 80 - 100 g/t, ignoring

the pre-split charges)

Normal Powder Factor

Pre-fracture the zone

around the well casingbefore detonating the

main explosive charges

Figure 14. Description of powder factor, sector by sector

Figure 14 indicates the zone of rock around the well casing, which would be pre-fracturedwithout damaging the casing, thereby protecting it from the physical effects of the remainderof the blast.

The order of firing or sequence of initiation for the blast is highlighted in Figure 15, below.


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Figure 15 shows the sequence of initiation of the different sections of the blast:

1. The main pre-split was fired instantaneously

2. The circular pre-split was fired 17ms later so as to reduce the instantaneouslydetonating charge weight

3. The second ring of lightly charged holes was fired to complete the process of pre-fracturing of the rock around the well casing

4. Finally the main production holes were fired in such a sequence as to direct the rockmovement away from the well casing in all directions.

Initiation SequenceInitiation Sequence

4. Production charges

3. Light charges

1. Main Pre-split

2. Circular Pre-split

Figure 15. Initiation sequence for well casing blast

Finally, Figure 16 shows a view of the resulting muckpile immediately following the blast andprior to the commencement of excavation.

Observation of the visible section of the pipe suggested that the well casing remained

undamaged.

The most complicated aspect of the process was the sequencing of the blast using pyrotechnicdelay systems and detonation cord. The use of electronic delays would greatly facilitate theprocess of tying in these complicated blasts.


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Voladura de 09 NoviembreVoladura de 09 Noviembre

Figure 16. Blast result prior to the commencement of excavation


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4. UNDERGROUND ISSUES

As a means of reducing the overall waste to ore ratio, as well as reducing per ounce productioncosts, CVSA has begun to develop some of the existing veined deposits in the mine usingunderground mining methods. Three underground mines are in varying stages of developmentat this time;

Mangas Norte

Mangas Centro

Osvaldo Siete

Of these three, Mangas Centro is actually in production and has completed some early stopingwhile continuing to develop the decline and lower levels.

Mining is conducted using long hole open stoping methods with a mixture of up-hole drillingand down-hole charging or loading. The orebodies are identical, geologically and physically,to those veins previously mined using surface techniques and similar challenges exist in theunderground environment; particularly wall damage and dilution (although the specificdamage mechanisms may vary to some extent). At the depth at which underground mining istaking place, the veins have similar dimensions to those exploited on the surface.

A visit was made to the operations of Mangas Centro in order to observe first hand the qualityof the rock mass, the dimensions and quality of the development blasting, the commencement

of the down-hole drop raising and the condition of the stopes; walls, drilling, etc.

CVSA presented APA/API with a short list of desired outcomes in the drilling and blastingprocess in the underground operations and the original list of five points can be simplified tothe following three;

Reduction of dilution as a consequence of reducing wall damage from stope blasting

Improve drilling and blasting design for the drop raises used for creating initial cut-offslots in stope preparation

Improve generic drill and blast design options and practices for production stopes

Additionally, this report will offer commentary on the importance of good design andimplementation practices for development blasting, particularly as it effects stopedevelopment.

More importantly, APA/API offers definitive and specific suggestions regarding a joint

initiative between CVSA and Austin Powder to investigate the damage mechanisms operatingin the underground mining environment and develop a series of preventative measures thatwill make possible a reduction in dilution and damage.


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4.1 Control of Damage and Dilution

The incidence of dilution in long hole stoping extraction of gold, silver, etc. is very closelylinked to the incidence of blast induced damage. In the underground environment the principlemechanism of damage is stress induced fracturing as a result of excessive vibration levels inturn resulting from the detonating explosive charges.

API has developed software tools that allow the prediction of vibration levels for any givencombination of explosive, drilling and rock mass. Examples of the application of thismodelling process capability will be given subsequently in this report.

In order to be applied confidently as a predictive tool, the modelling technique requires thatcertain site specific parameters be adjusted based on the analysis of field measurements carriedout within the mine, in the production area.

This measurement and modelling is ideally suited as a candidate for a joint team projectinvolving APA/API and CVSA. A simple description of the steps required for this project

follows.

The data needed in order to adjust the parameters of the predictive model can be collectedduring a vibration monitoring campaign focussed on a single stope, ideally measuring allavailable blasting events from the commencement of the development of the stope.

Point of Focus

Drilling Level Stope; Installation of Triaxial Geophone

Figure 17. Vibration monitoring scenario for stope characteristation

Figure 17 is a plan view of a hypothetical stope, showing the upper level from which the ringsof blastholes will be charged. The red symbol at the intersection of the crosscut and ore drive

represents the position of a triaxial geophone array installed in the vein along the stope axis.


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Fitting of Near Field VibrationModel

Near field vibration predicion

models (Holmberg y Persson)

Vibration intensity depends onthe characteristics and

geometry of the charge

Figure 19. Vibration model format and fitted data

With this fitting complete the adjusted model is used within the framework of Austin Powders

blast design and analysis software; QEDPlus, to predict likely vibration levels at specific

distances from specific charges, emplaced within the fitted rock mass.

In order to equate the estimated vibration levels with a known physical effect, a mathematicalrelationship between rock mass property response and vibration level is required.

An approximate guide is derived from Hookes Law whereby a critical value of particlevelocity, PPVcrit is defined as that vibration intensity at which new fracturing commences in agiven rock mass. The critical value of peak particle velocity is calculated as;

E

VPPV PTcrit

.

Where: Tis the tensile strength of the intact rock

E is the elastic modulus, and

Vpis the P wave velocity in the same material

Based on this key value, it is possible to calculate other threshold estimates such as theintensity required to extend existing fractures (0.25 PPVcrit)

With a suitably fitted vibration model and a quantitative criterion for estimating damage itbecomes feasible to analyse a range of design options in terms of the probability of producingdamage in a given rock mass. As a concrete and relevant example, Figure 20 illustrates two


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cases for a stope ring blast in a hypothetical case where the critical vibration limit for damagehas been established. It is considered that the dark grey contour level (see Figure 20) indicates

presence of damage.

The charge design on the left suggests that there will be blast damage to the hangingwall witha high probability of dilution.

The right hand side image represents a modified design where the charge in the blastholeclosest to the hangingwall has been changed, substituting a laterally decoupled charge for theoriginal fully coupled charge. The grey shaded contour has changed, as may be observed, andnow coincides with the hangingwall plane. This situation, while hypothetical, should representa decrease in damage and a reduction in dilution.

Waste Dilution to the

Hangingwall

Figure 20. Reduction in damage and dilution contours

This vibration contour / damage criterion analysis can be applied to the case of stoping inMangas Centro once the vibration model has been fitted and geotechnical properties obtainedand analysed to calculate the critical vibration intensity.

During the introductory underground presentation delivered by CVSA it was revealed that thepowder factor calculated for the current blast design is approximately 1.2 kg/t. This valueseems quite high and suggests that there may be over-break of hangingwall and footwall.Certainly it is suggested that the possibility of reducing this powder factor merits analysis.

Although at this time, APA/API has neither a fitted vibration model nor a valid vibrationdamage criterion; Figure 21 illustrates the analysis of a design, similar to that currently used in

the Mangas Centro mine. The image to the left indicates a ring that has been fully chargedwith ANFO, whereas in the image to the right the footwall charge has been replaced with a


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Drilling Deviation

The energy goes where the explosive goes, which in

turn goes where the blasthole goes

Figure 22. Reduction in damage and dilution contours

Using the same example as that shown in Figure 21 the effect of only one deviated hole isanalysed. In the case of a production blast, the deviation of one hole into the hangingwall

would produce significant damage, inducing a high percentage of dilution located locallyaround this particular ring. This scenario is illustrated in Figura 23.

Cerro Vanguardia Mangas Centro

With Hole Deviation

Figure 23. Damage impact of a single hole deviation into hangingwall


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4.2 Optimisation of Drop-Raises

One of the key areas of concern for CVSA as regards the underground operations is thedevelopment of expertise in the drilling and blasting down-hole drop raises. These openingsare required for ventilation and access ways as well as the first steps in the creation of a freeface slot at the commencement of a new stope.

Once again drilling accuracy is a critical success factor for successful development of dropraises, particularly because of the high density of drilling (and powder factor) in a smallvolume. Figure 24 applies the vibration damage analysis to demonstrate the effect of deviationin only one of the blastholes. Given that any or all of the holes may demonstrate some degreeof deviation, the original designed spatial relationship between charges will changesignificantly with depth. Successful blasting of this type of situation might well require a

variation in the initiation sequence applied at different depths. This type of analysis and designimplementation is within the capabilities of the APA/API technical team.

Cerro Vanguardia Mangas Centro

Deviation in Drop Raises

Figure 24. Effect of drilling deviation in terms of vibration contour distribution for down-hole drop-raise

Another important factor in achieving success in drop raise blasting is to ensure an adequatepresence of empty, uncharged easer holes within the volume to be blasted (typically theseholes should be reamed out to a larger diameter perhaps 102mm). There is a directproportionality between the effective relief volume of empty holes and the probability ofsuccess in firing drop raises.

Close control over measurement of depths and lengths of explosive charges is also an essential

part of successful raise blasting. Over the course of the full depth of the raise, blasthole


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deviation may produce changes in the spatial relationship between different holes, therebychanging the effective pattern of the holes at different depths. Two blastholes that were placed

adjacent to one another when collared at the top of the raise may be notably distant at themidpoint of the raise, while other holes may have become much closer. This variation in holeposition should be investigated and quantified by surveying top and bottom coordinates ofeach hole and plotting the position of each hole at successive depths. This may allow initiationsequences to be changed as needed to provide an ordered initiation of the blast.

Austin Powder (APA/API) can offer CVSA support in this task using the QED Plus software.

4.3 Optimisation of Development Blasting

During the visit to the operations of Mangas Centro, it was observed that the regularity of thefloors of both the main decline and the level development drives could be improved. As withall aspects of drilling and blasting, the accuracy and precision of the drilling is extremelyimportant. Figure 25 shows the effect on vibration contour distribution for a standarddevelopment blast when only one contour blasthole has an excess of lookout angle applied. Inreality it can be common for a number of separate blastholes to suffer from drilling errors,both in terms of collar position and angular deviation.

Horizontal Development

Drilling Accuracy ControlEffect of lack of care with drilling

Figure 25. Effect of blasthole drilling inaccuracy (for one hole) on vibration contour distribution

This phenomenon will tend to produce irregularity in the dimensions of the developmentheadings, affecting rock mass stability, but also affecting the quality of any subsequentproduction blasting drilling that is undertaken from this particular horizon. Excess back-break

to the roof of the drive will affect the likelihood of collaring errors for up-holes, uneven floor


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levels will add difficulty when attempting to drill accurate down-holes. Uneven perimeters fordrill drives will make it very difficult to emplace a production drill rig correctly.

Figure 26 represents the result of a development blast (together with a view of the intendeddesign outcome) measured in a Chilean underground mine, using survey techniques. Over-break is plainly visible, particularly in the roof of the drive. However it may also be noted thatthere is some irregularity in the floor and RL.

Possible Errors

Horizontal development profile - overbreak

The production blastholes are drilled from the same development drive that weexcavate

Figure 26. Example of irregular drive outline as a result of over-break

The drive shown in the image was intended for use as a drilling horizon for producing adrawpoint bell excavation, using up-holes inclined at a number of different angles. Theaccuracy of the subsequently drilled holes was poor, as a result of not being drilled from aregular, even floor, nor being collared at an even, well blasted roof surface.

Figure 27 indicates a range of drilling difficulties that may arise as consequences of irregularroof and floor surfaces.


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Extreme Consequences

Effects of errors in excavation of development gallery drillinghorizon

The production blastholes are drilled from the same development drive that we

excavate

Figure 27. Drilling errors induced by irregular drill and blast results in horizontal development headings


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5.

JOINT PROJECT TEAMS

The technical visit of November 8 10 of this year, and the analyses that form the bases ofthis report have confirmed that there are yet several challenges and opportunities forimprovements in the efficiency and effectiveness of a number of processes associated withdrilling and blasting at Cerro Vanguardia. This is equally the case for surface and undergroundmining operations.

In recent years Austin Powder has demonstrated the capacity to conduct field investigationprograms capable of demonstrating that improvements in process efficiency are quite feasible;in the areas of both fragmentation (2007) and final wall damage control (2008 and 2009).

Austin Powder is convinced that the way towards achieving additional advances andconsolidating these successes into the normal design and implementation practices at CVSA isto establish joint investigation teams whereby both CVSA and APA/API, supported byBlastechnology, work together execute specific process improvement projects (initiatives),pooling resources and responsibilities to achieve greater and more lasting advances in a rangeof areas of optimisation.

The tripartite project teams would comprise members from CVSA, APA andAPI/Blastechnology, each contributing with experience, knowledge and resources. These

resources could be broadly grouped as follows;

CVSA

Human and information resources from management and functional teams such as;

Geology; lithological and structural data, mapping and interpretation

Geomechanics; rock mass data, slope designs, fracture mapping

Engineering; planning and survey resources, field measurements, design input

Cost analysis where appropriate for benefit evaluation

Austin Powder

On-site Technical Service engineers

Instrumentation for measurement of blast and explosive performance

Detailed modelling capability including vibration, damage, flyrock and fragmentationsimulation and prediction

Analysis and recommendations with the support and periodic presence of CameronMcKenzie and Blastechnology


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Using these joint resources, teams can be defined for specifically identified projects. Theteams can then follow a clear process of planning, execution, documentation and reporting of

the results to CVSA and Austin Powder management.

The same project based philosophy will be relevant and applicable for both surface andunderground blasting environments.

The objectives of the teams should include;

Control of damage; final pit walls, hangingwall and footwall contacts in undergroundstopes, roof and floor.

Control of dilution; surface and underground

Efficiencies in mine development; uncovering veins for blasting, accessing mineralresources underground, bringing stopes on line in optimum time, etc.

Downstream benefits associated with fragmentation and materials handling.

The team concept will benefit from a clear specification of leadership and responsibility rolesin both CVSA and Austin Powder. The success of these initiatives will be favoured by thenomination of on-site responsible parties who can call on other required resources as becomesnecessary for each project.

6. CONCLUSIONS AND RECOMMENDATIONS

The three day visit to CVSA on the part of the technical team from Austin Powder Argentina,Austin Powder International and Blastechnology was an effective and productive exercise.

The visit was spent examining and studying drilling and blasting results (design andimplementation) in both the surface and underground mining environments.

The comments presented in the present section are separated, for clarity, into two groups,reflecting the two mining environments visited in early November.

6.1 Surface Drilling and Blasting

The objectives of the drilling and blasting work in the surface mining context were fivefold:

Review the CVSA performance in terms of pre-split blasting

Review the performance regarding the coordinated implementation of buffer blastdesign and implementation

Comment on practices for the optimised blasting of narrow veined orebodies


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Consider the possibility of introducing a modified format of massive blasting in thosepits where the available bench area is present

Comment and participate in the fine tuning of special blast designs for blasting of rockvolumes containing pit dewatering well casings.

Pre-Split

Regarding the pre-split design and implementation, it was confirmed that a number of goodpractices are regularly followed at CVSA; drilling and blasting the pre-split over the full depthof the double bench and designing angled pre-splits are both excellent decisions in terms ofobtaining an optimum result.

The question was asked whether it is better to fire the pre-split blast some time (half a day, aday, etc.) prior to the main blast, or whether it is more acceptable to fire the pre-split at thesame time as the main blast. Preferences are mixed on this point and there are argumentssupporting both points of view, however at this stage there have been nothing noted in recentexperiments at the mine to indicate a preference for one or the other theory. More workperhaps needs to be done in this regard.

There is scope for further improvement in pre-split effectiveness if a greater effort is made torelate pre-split design to rock mass properties between different pits. CVSA has access to thefull analysis capability of Austin Powder and it is recommended that Austin Powder be invitedto participate more in this optimisation process.

Finally, observations in the field (Pit OD-CB8) demonstrated the dominant influence that in-situ structure can have over pre-split performance, where in two domains with very similarUCS but significantly different structural characteristics, two very different results wereobtained in terms of pre-split quality. There is a clear difference noted between a result withhigh half-barrel count, and a smooth, even fracture between each, and the case where half-barrels are separated by uneven, rough rock surfaces that indicate the lack of a completefracture between charged blastholes.

Buffer Blasting

The issue of good buffer blast design remains critical for the success of wall control at Cerro

Vanguardia.

It is clear that the standoff distance for each blast must be matched to the charge characteristicsfor the explosives in use, as well as the angle of drilling. CVSA has altered their standarddesign practice for the better in ceasing to drill angled buffer holes, moving to vertical holesand reducing the crater damage provoked at the crest of the new bench.

Under some conditions, excessive standoff may lead to the result of leaving a crust of cling-onmaterial along some parts of the face of the new bench. Success has been achieved in otheroperations by using a negative angle or drilling back towards the toe of the pre-split for the

buffer row. This allows a suitable standoff distance to protect the crest yet also allows the

placement of explosive energy to remove the crust of unbroken rock.


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Narrow Vein Blasting

It is suggested to CVSA that dilution is inevitably, at least partially, related to muckpiledisplacement during blasting. The current drilling and blasting designs for narrow veindeposits tend to produce a great deal of displacement this has been confirmed by observationof various video records for a number of ore blasts.

There is potential for use of modified pre-split blast drilling and charging, for reducing theamount of displacement and burden movement velocity. This technique uses the drillingparameters and the explosive charge philosophy but alters the initiation sequence to moreclosely resemble a production blast. Previous attempts using this technique have reported quitecoarse fragmentation and lack of movement. It is suggested, in this case, that the number ofpre-split rows be increased gradually in order to reach a balance between displacement and

fragmentation. Austin Powder uses at least two modelling approaches to address this challengeand CVSA is encouraged to work with Austin Powder to examine the alternatives in moredetail

Massive Blasting

In 2008 and 2009, Austin Powder International recommended that CVSA consider firing

larger production blasts, re-oriented to fire parallel to the final wall orientation.

Recent events in OD-CB8 suggest that CVSA has found a way to incorporate massive (> 10rows) blast patterns into their production planning process. This will allow CVSA toexperiment with different initiation sequences that have been shown to reduce damage in anumber of mines around the world.

Well Casing Blasting

CVSA has managed to fire a number of controlled blasts in the vicinity of mine de-wateringwell casings in the past. This work has been supported by Austin Powder Argentina withdrilling designs; the current pattern is a derivation of work done several years ago by APA. Inthe case of this particular visit, a combination of circular pre-splitting and light fracturingblasts, while encouraging a large amount of displacement for the front face, production rows,was shown to leave the well casing in good physical condition.

6.2 Underground Drilling and Blasting

The development of underground mining operations at CVSA has advanced notably and a visitwas made to the Mangas Centro decline in order to assess the current state of efficiency in

drilling and blasting operations.

A number of visual observations were made, as follows;

It is clear that floor control has room for improvement, both in the main decline accessand along level development. There is a tendency for undulation, rising and falling, in


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the floor surface and this is likely related to incomplete control of the drilling accuracywhen developing the tunnel access.

Successful ring blasting within the stopes requires good drilling, which in turn requiresaccurate survey set-up and marking of the ring positions and collaring points. A casewas observed where the ring plane direction was not perpendicular to the axis of thestope drive this will complicate identification of the correct blastholes to charge andwill probably affect the ease of displacement of the blasted ore.

Survey of the top and bottom of each blast hole will provide important assistance at themoment of deciding on the explosive charging and initiation sequence best suited todeliver a good blast result.

The feedback from surveys of this nature, to drillers, should tend to create a positivefeed-back loop that encourages improved drilling accuracy and precision.

Currently the blasthole rings are fully charged with ANFO and this can lead to powderfactors of around 1.2 kg/t an intensity that is probably excessive and likely topromote damage.

The objectives for optimisation of the underground drill and blasting were stated as;

Reduce damage, particularly to the hangingwall

Reduce dilution strongly related to the previous point.

Optimise drop-raising performance.

A number of suggestions were offered as a means to achieving these objectives, including;

Carry out near field vibration measurement campaigns in the stopes that are beingdeveloped. This technique will permit a diagnostic evaluation of the progress of the

blasting and also supply valuable data for the fitting of a predictive vibration model.

Evaluate the geotechnical characteristics/properties of the rock masses in each stope inorder to calculate the critical value of vibration required to initiate fracturing(remembering that in the underground environment, vibration is usually the dominantmechanism of damage).

Use the fitted model mentioned above, together with the vibration damage criterion toevaluate and modify blast designs in order to control damage.

The same technique can be adapted to evaluate fragmentation problems and potentialfor improvement, if necessary.

Drop- raising blasting success is strongly affected by at least two factors;


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o Drilling accuracy, and

o Percentage void space provide by uncharged drill holes.

Drilling accuracy can be measured and blast designs adjusted to maintain a correctfiring sequence.

Electronic initiation systems will also allow firing times to be selected that will permitan optimisation of initiation sequences for each lift of the drop-raise.

6.3 Project Team Formation

Both CVSA and Austin Powder possess valuable assets in the form of trained staff,quantitative data, operational resources, specialised software and measurement technology.

These resources will be most efficiently put to use if customer and service provider can agreeto work in a team framework to design and execute specific projects aimed at optimisingtargeted aspects of blast performance.

7. ACKNOWLEDGEMENTS

Austin International and Blastechnology wish to acknowledge the support and assistance

provided by CVSA geomechanics, geology, mining and production personnel, and inparticular the cooperation and involvement of Sergio Sancho, Gustavo Sarapura and all thestaff at CVSA.

Documents

Technical Report CVSA AGA