Mine Closure Focus 1 Decommissioning and Closure Plan for Aughinish Alumina Plant SRK Consulting recently submitted a fully-costed decommissioning and closure plan (DCP), for Aughinish alumina refinery on the west coast of Ireland. The DCP included criteria defining the successful, environmentally responsible decommissioning of the refinery, and included a programme to demonstrate the successful implementation of the DCP. SRK’s Glenn Freak notes: “Main focuses of the work were the processing residuals management areas, wharf, mudstack, and peripheral drains and ponds. Minor areas such as a seawall, adjacent bird sanctuary, and non-operational lands were also considered.” The DCP also introduced the possibility of the operations being suspended for a prolonged period. Further proposals included closure of the red mudstack, and implementation of a rehabilitation plan including synthetic liners to restrict rainfall infiltration; revegetation of the mudstack surface, and control of surface runoff water. “Management of contaminated surface runoff water and groundwater will continue for five years,” Glenn concludes. “Thereafter, the water quality is expected to be acceptable.” “Plans included costs for several different closure options” Aughinish posed challenges such as the protection of the adjacent bird sanctuary
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Mine Closure Focus
1
Decommissioning and ClosurePlan for Aughinish Alumina Plant
SRK Consulting recently submitted afully-costed decommissioning and closureplan (DCP), for Aughinish aluminarefinery on the west coast of Ireland.
The DCP included criteria definingthe successful, environmentallyresponsible decommissioning of therefinery, and included a programme todemonstrate the successfulimplementation of the DCP.
SRK’s GlennFreak notes:“Main focuses ofthe work were theprocessingresidualsmanagementareas, wharf,mudstack, and
peripheral drains and ponds. Minor areassuch as a seawall, adjacent birdsanctuary, and non-operational landswere also considered.”
The DCP also introduced the possibility ofthe operations being suspended for aprolonged period.
Further proposals included closure of thered mudstack, and implementation of arehabilitation plan including syntheticliners to restrict rainfall infiltration;revegetation of the mudstack surface,and control of surface runoff water.
“Management of contaminated surface runoffwater and groundwater will continue for fiveyears,” Glenn concludes. “Thereafter, thewater quality is expected to be acceptable.”
“Plansincluded costs
for severaldifferentclosureoptions”
Aughinish posed challenges such as the protection of the adjacent bird sanctuary
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Recovering‘Locked-up’Gold DuringClosure
Natural gravitation of gold to thelowest points in a gold processingplant may result in significantconcentrations over a period of time.This, coupled to the processinventory, yields precious metal (lock-up) value during the closure phase ofa gold processing plant.
“Locked-up” gold typically becomesavailable during initialdecommissioning, covering the finalcleaning operations; and post-demolition, when the foundationmaterial can be reclaimed.
The actual amount recovereddepends on historical criteriaincluding plant design, integrity ofoperations, housekeeping and headgrade. However, the actualprocessing of the gold-bearingmaterials may pose their ownchallenges.
Steve Hordley, Principal ProcessEngineer comments: “The financialbenefits of recovery may beaugmented by the managed disposalof assets. As with many otherprocesses, maximisation of recoveryand disposal requires effectiveplanning and implementation in well-designed, systematic, safe and cost-effective closure.”
“Recovery of gold from final closureis a highly inexact science, and thereare no guarantees about the quantityof material recovered,” concludesSteve. “What is certain is that closuremust be undertaken and thatrecovered gold, together with themanaged disposal of assets, couldgo some distance towards fundingthe final site rehabilitation.”
Wismut GmbH, formerly a joint Russian-East German uranium producer and nowowner of the world’s largest mine closureproject, has been a beneficiary of SRKconsulting expertise since 1992.
With remediation of mining andprocessing facilities a top environmentalpriority of the unified Germangovernment, Wismut estimates the totalcosts of closing and reclaiming itsoperations in the billions of dollars.
SRK’s involvement began with a 1992-93study of the options for controllinggroundwater flow through undergroundworkings in the Ronneburg area. SRKsubsequently was retained to investigateoptions for remediating waste rock. Theassociated environmental concernsinclude acid generation, leaching ofuranium, sulphate and metals, and radonemission. SRK recommended a programof selective relocation of rock to theLichtenberg open pit.
In 1995-96, SRK helped Wismut set up alaboratory testing facility, develop fieldmethods for waste rock ‘grade control’,and recommend methods for blockmodeling and scheduling of the wasterock relocation. SRK also assistedWismut’s decision-making aboutremediation measures for the remainingfourteen waste rock piles in theRonneburg district.
Closing the East GermanUranium Mining Industry
In 1996 and1997, attentionshifted to theNordhalde, thesecond largestremaining wasterock pile at theRonneburg site.SRK assisted inthe design of aborehole gas and temperature monitoringsystem, and carried out detailed analysisof the data to estimate oxidation rates.SRK also provided conceptual designsand cost estimates for remediationmeasures.
SRK’s recent work in the Ronneburg areahas included an audit of the ongoingwaste rock relocation, and assistancewith testing of cover designs for thebackfilled Lichtenberg pit.
SRK’s Daryl Hockley and John Chapmanhave led SRK’s contribution to theWismut project.
Says Daryl: “Our work has been equalparts consulting and technology transfer.Initially the transfer was unidirectional, butthe scale of the project is such that wenow learn as much as we teach. Some ofthe precedents set by Wismut will be thestandard for mine closure activities in the21st century.”
Estimates of closure and reclamation costs are in the billions
Daryl Hockley
Design and Operation for Closureat Kennecott Ridgeway
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SRK, through its long-standing tieswith the Kennecott Ridgeway Mine inSouth Carolina, has helped make thismine a prime example of successfuldesign and operation for closure.
“From the prefeasibilty stage of design,strong emphasis was given to the need tominimise the actual and contingentliability associated with operations andclosure,” explains Rob Dorey, SRKCorporate Consultant. “Closure planninghas been periodically updated throughoutthe mine life, with the detail of the planincreasing as closure approached.”
“The potentially acid generating (PAG)nature of the host rock of this epithermaldeposit required the adoption of pro-active waste rock management. Use ofthe waste rock in construction of thetailings impoundment, with compaction
and encapsulation of PAG waste rock,was incorporated in the design. Thephased development of the two pits alsoallowed the partial backfilling of one pitduring mining of the other.”
As part of the closure planning, SRK hasperformed a number of studies. Theseinclude a surface water mixing and waterquality model, project-wide groundwaterand contaminant transport model andtailings cover model. A detailed evaluationof the methods and viability of achievinglong-term closure was also completed.
The presence of PAG material in the pitwalls required the management of bothbackfill material and water used to floodthe pit. “Lime softening has been used,with a target alkalinity of the pit water tobuffer acid generated by the pit walls andbackfill and contact runoff water from
the site,” Robexpands. “To closethe tailingsimpoundment, amodification of thedeposition systemto regrade theimpoundmentsurface to createpositive drainagewas adopted.”
“With a net positive water balance atclosure, the need to rapidly cover thetailings was accommodated by placingthe cover as a slurry, using the existingtailings deposition system. To date allindications are that performance criteriafor the closure are being met.”
Framework for Coal Mine Closure in Bulgaria
SRK Consulting recently completed itscontribution to new guidelines for closure ofunderground coal mines in Bulgaria, aEuropean Commission-funded PHAREproject covering socio-economic, technical,safety and environmental issues.
Pilot closure programmes were developedfor two mines in contrasting socio-economic and environmental settings:Pernik, in a heavily industrialised city, andPirin in a remote mountain location.
Piers Sadler remarks: “The approach taken toenvironmental aspects was through riskassessment and risk control carried out inparallel with staged site investigation.”
“Complex issues included restitution of state-owned land to its pre-communist owners,and reconciling existing Bulgarian legislationwith EC environmental requirements.” Abandoned surface facilities at the Pirin Mine
Rob Dorey
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In October 1998, eighteen of SRK’ssenior engineers and scientists met inVancouver for a mine closure workshop.
The objectives were to crystallize andsynthesize SRK’s experience in closureprojects, and map out areas of relevantexpertise.
Participants came from SRK offices in SouthAmerica, Africa and the UK, as well asDenver, Reno, Elko, Tucson and Vancouver.
Products of the workshop include severalpapers on various areas of expertise, anda website featuring a ‘knowledge map’that charts the relationships betweentechnical disciplines and project objectives.
Mine Closure WorkshopAdvances the State of the Art
Workshop organiser Daryl Hockleyelaborates: “Most of our clients do nothave a lot of mine closure experience. Butin SRK we have over 20 people who haveeach worked on at least a dozen closureprojects.”
“We thought that if we could get most ofthose people together, we couldsignificantly advance the state of the art.The challenge is to create a systematicapproach, while at the same timerespecting the variety of project needs.”
SRK ConsultantProfile:Julie Glavin
Julie Glavin joined the SRK Tucsonoffice in early 1999. Julie brings over10 years of mining and civil/construction experience, primarily inenvironmental engineering andcompliance. As a senior engineer inthe Tucson office, she is currentlyengaged in the development of acomprehensive closure program foran existing mining client.
This particular project featurescontributions from SRK technicalspecialists from around the world.Julie also provides specializedconsulting services related to theClean Water Act, NationalEnvironmental Policy Act andwetlands mitigation work.
An extensive SRK project to manageoxidisation-prone residual sulfides in thetailings impoundment at Thompson CreekMine in central Idaho is set to pay futuredividends in the form of significantlyreduced costs and liability.
Situated in the Salmon River drainage,Thompson Creek processes up to 32 000tpd of molybdenum ore. The tailingsimpoundment at the project uses acenterline construction techniqueemploying cycloned sand to constructthe embankment.
The impoundment, designed by SRK inthe early 1980s, is planned to reach anultimate height of 720 ft from toe to crest.
In 1990, residual sulfides in the tailingsproduct were identified as having apotential to oxidize. Of the optionsconsidered to alleviate the impact of this
oxidation, use of a secondary flotationprocess to produce a pyrite concentratewas selected. In this process, the sulfidecontent of the tailings is reduced to alevel at which oxidation is not predictedto significantly impact drainage waterquality.
To dispose of the pyrite concentrate, aseparate delivery system was designed toallow placement of the material within thesaturated slimes zone of theimpoundment. This ‘subaqueous’environment alleviates the potential ofoxidation of the pyrite.
SRK’s Rob Dorey remarks: “Thisproactive step by Thompson Creek hasreduced the contingent liability of closureof the impoundment by the adoption ofoperating procedures to facilitate ultimateclosure.”
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Digital Database Eases Closure Costing &Surface Assets Evaluation at Rossing Mine
Thorough groundwork done by an SRKteam at Rossing mine in Namibia in July1995 has allowed mine personnel to carryout in-house updates of probable closurecosts and, as of 1996, maintain accuraterecords of surface asset replacementcosts for insurance and other purposes.
During the initial visit SRK staff spent timewith all relevant mine personnel to ensurethat a comprehensive database of closurecosts was compiled. Extensive use wasmade of surface layout plans of the mine,and the database was cross-referencedto the plans.
Rossing Mine showing part of the open pit
“A rates build-up was supplied for mostitems,” recalls Peter Labrum, PrincipalEngineer. “This was linked to the maindatabase, enabling the costing to beupdated by simply changing keyparameters in the rates. The finalproduct was supplied to the mine indigital form, enabling them to carry outthe updates in-house.”
In December 1996 SRK completed adetailed schedule of surface assetreplacement costs to enable the mine tocheck its insurance portfolio.
Peter Labrum
“Due to the detailed schedules producedduring the closure costing study, thereplacement cost schedules could bequickly and efficiently produced in a similarupdatable digital format,” says Peter.
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UN Taps SRKfor Omai GoldMine ClosureReview
In the wake of the failure of TailingsDam #1 at Omai Gold Mine, Dr.Geoff Ricks of SRK Consulting wasrecently appointed through theUnited Nations DevelopmentProgramme (UNDP) to independentlyreview the mine closure plans andimplementation.
As the Specialist InternationalConsultant on behalf of theGovernment of GuyanaEnvironmental Protection Agency(EPA), Geoff’s brief was to technicallyreview the plans, and define astructure within which EPA and OmaiGold Mines could implement theclosure plans. In additionrecommendations were to be madeto strengthen the EPA’s effectivenessin regulating the mining operations.
Geoff comments: “The final reportincluded a programme ofenvironmental monitoring, equipmentand training of officers who will beinvolved in monitoring and evaluatingenvironmental impacts.”
“Other key aspects includedrecommendations on environmentalobligations to be imposed on thecompany, provisions for minimisingenvironmental damage duringclosure implementation and methodsof providing financial sureties”.
The British Coal Authoritycommissioned SRKConsulting to undertakefeasibility studies and detaileddesigns for minewaterremediation at theEdmondsley & Fender formercolliery sites, ranked amongthe most polluting in England.
Piers Sadler, responsible fordischarge characterisationand wetland designs,comments: “The Edmondsley schemeinvolves pumping minewater at 4 l/sec to
a 0.4 ha wetland treatmentarea, within a wildlifeconservation zone providingeducational and recreationalfacilities.”
“The Fender scheme involvesa pipeline river crossing and awetland of about 0.6 ha area.”
SRK was subsequentlyawarded a third feasibilitystudy and detailed design
study for the treatment of minewaterdischarge at Blaenavon in South Wales.
The Edmondsley wetland uses reeds to filter metals which precipitate from the water
“treatmentremediatesone of the
most pollutingsites in
England”
Piers Sadler
Combined Closure Plan and EIA Reportfor Copper Project
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SRK recently completed a fully-costedclosure plan and EIA report for aconfidential client seeking miningapproval for a proposed undergroundcopper mine in Western Europe.
The deposit, consists of 14.3�Mt of high-grade massive sulphide ore located withina sensitive rural environment. Key closureissues included tailings disposal, re-instatement of agricultural land andtreatment of post-mining metal and acid-contaminated mine water.
Glenn Freak, Senior EnvironmentalScientist, comments: “In response to thestrict environmental legislation in Europeand the environmental concerns at theproject site, tailings disposal centred on a
“Mine water investigationsindicated that backfilledworkings should beflooded as quickly aspossible after mining byactive water injection,”Glenn continues. “Thiscreates an inwardhydraulic gradientallowing water quality to
be stabilised by re-circulation andtreatment over two to three years.”
Closure and rehabilitation cost estimatecalculations for decommissioning,demolition, rehabilitation, after-care andmonitoring were made includingprovisions should premature closureoccur.
Clients involved in mergers, acquisitions,share offerings and other transactionsoften underestimate the importance ofclosure costs in the overall valuation ofmining properties.
Examples of closure liabilities recentlyassessed by SRK’s Vancouver officerange from US$750 000 for an advancedexploration site with minimal water qualityimpacts to US$30-million net presentvalue for a mine site with a requirement tocollect and treat acidic water.
“The process of estimatingclosure liabilities starts with aclosure plan,” says KellySexsmith of SRK Consulting’sGeoEnvironmental Engineeringgroup.
“We usually find that people atthe mine site have clear ideasabout closure issues andpossible closure measures. Butthey often haven’t had the time neededto pull those ideas together.”
paste backfill plant to returntailings underground, operating intandem with an engineeredrepository to store dewateredtailings on surface.”
“The design minimises the reducedsurface area required for disposal,restricts pyrite oxidation and allowsprogressive rehabilitation.”
Land use will revert to agriculture once allsite infrastructure is decommissioned,dismantled and removed. Pre-strippedtopsoil, from stockpiles, will be spread onthe re-contoured ground at closure. Toprotect the low permeability membranecover on the repository, low-intensitygrazing is proposed.
Glenn Freak
“Further, the quality ofplans prepared to meetregulatory requirementsis quite variable. Our jobin a liability estimate is toquickly review closureissues and then focus onestimates for the mostcostly items. Given thelimited time available for
these projects, our ability to quicklycompare costs with experience elsewhereis critical.”
Kelly Sexsmith
Steve Hordley
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Steve Hordley of SRK Consultingwas involved in the decommissioningof the President Brand MetallurgicalScheme, part of Freegold, in SouthAfrica’s Free State.
The plant re-treated gold tailingsmaterial, yielding sulphuric acid,uranium and gold. Uraniumproduction ceased in 1990, theflotation, acid and gold operationscontinued until 1995.
Decommissioning activities includedinventory removal and radiologicaldecontamination, asset removal andfinal demolition, including demolitionof the sulphuric acid pyrite roastersand stack, pictured here. The site iscurrently undergoing rehabilitation.
What Goes Up… Must Come Down!
Experienced mine closure specialistSteve Hordley, joined SRK Consulting’sUK office in 1998 after some 18 years’work in metallurgical operations in SouthAfrica involving production, closureplanning and demolition activities. Stevehas participated in numerous projects,including closure planning andmanagement of operations such asflotation, uranium, gold and sulphuricacid. He also has considerable expertiseencompassing radiologicaldecontamination, decommissioning,precious metal recovery and all aspectsof related health and safety issues.
Steve Hordley
Black Pine Mine Heap Leach Closure
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Black Pine Mining, Inc. (BPMI) contractedin 1995 with WESTEC, Inc. (whose operationswere merged with SRK Consulting in 1998)to prepare a closure plan for their 34-millionton heap leach facility located in the south-eastern corner of Idaho, USA. The heap, avalley fill design, had 50 million gallons ofsolution in process containing cyanide andother constituents in concentrations greaterthan safe drinking water standards.
Background data was collected tocharacterize the physical, geochemical, andother environmental aspects of the heap.Solution treatment methodologies wereresearched and their respective costsevaluated. The results of this work wereused to develop a risk assessment toaddress the potential impacts that thespent ore-solution system could have on
the local environment. Black Pine Mining,Inc., stopped adding cyanide to the heap inJanuary 1998 and began recirculatingsolution. Evaporation proved to be soeffective that land application of spentsolution was not utilized. Further, the weak-acid dissociable (WAD) cyanide level hasbeen consistently declining and was projectedto meet the 0.2 mg/l standard in March 1999.Other constituents previously occurring atconcentrations greater than safe drinkingwater standards have also declined.
“All in all,” said BPMI’s General ManagerCrellin Scott, “closure activities at the mineproceeded at or better than projections.Advanced planning allowed us to proceedwith a minimum of capital and operatingoutlay. This project demonstrates, amongother things, that intensive solution
Val Sawyer
management canshorten the padclosure timerequirements, enhancegold recovery, reducesolution treatmentcosts and control thesolution balance.”
“We interacted closely with BPMI to identifythe most effective means of providing thebest quality service while keeping costsdown”, said Val Sawyer, SRK PrincipalConsultant. “We were able to work directlywith BPMI technical and operating staff tocollect samples, conduct metallurgicaltesting, analyze results, and then form along-term strategy.”
SRK’s ‘ReverseMining’ Experts
SRK’s JohnChapman andDaryl Hockley arebecomingexperts in whatthey smilinglyrefer to as‘reverse mining’.Together, theyhave completedtwo majorprojects involvingthe return ofwaste rock to
mined-out pits. Kennecott’s FlambeauMine in Wisconsin is now backfilledand reclaimed, and backfilling ofWismut’s Lichtenberg pit in Germanyis about half completed.
Pit backfilling raises a number of verypractical questions. In both projects,the objective was to put the most acid-generating material near the bottom ofthe pit, where it would subsequently beinundated with groundwater.
The groundwater will prevent longterm oxidation and acid generation,but will also release any acidity thathas accumulated in the rock during itstime on surface.
SRK, as part of the 120 000-tpdearth-moving operation at Lichtenberg,and 80 000-tpd project at Flambeau,designed programs to sample wasterock during the relocation, measureboth its current acidity and its futureacid generation potential, and addappropriate amounts of alkalinity.
“The resulting system of long-termplanning, sampling, analysis, datareview and short term planning wasvery similar to the procedures used tocontrol open-pit mining,” says John.
“Open pit mining engineers from SRK’sVancouver mining group provided muchof the required mining technology.”
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John Chapman
Closure Sequence
This diagram, which outlines the phasesof the closure sequence, is part of aproactive initiative by SRK Consulting topromote successful and effective mineclosure planning and decision-makingwithin a European context.
Integral to the programme is a report, ATechnical Framework for Mine ClosurePlanning - Technical Review Series No.20, published by the British MineralIndustry Research Organisation (MIRO).Targeted mainly at the mining and mineral
processing industries and regulatorybodies, the framework is designed toassist in the preparation and evaluation ofmine closure plans, providing an overviewof mine closure practices.
This invaluable reference is available forpurchase through MIRO for GBP 200 andcan be ordered by contacting HazelPexton, Secretary, MIRO,telephone: +44 (0) 1543 262957,fax: +44 (0) 1543 262183email: [email protected]
ClosurePlanning
Closure PlanImplementation
MINE FEASIBILITYINITIAL CLOSURE PLAN
INTERIM UPDATES OFCLOSURE PLAN
FINAL CLOSURE PLAN
MINE CLOSURE :DECOMMISSIONING
DEMOLITION
ACTIVE CAREREHABILITATION
PASSIVE CAREREHABILITATION
CLOSE OUTCLOSE-OUT REPORT
AFTER USE RELEASE OF SITE
STRATEGICREVIEW FOR
CLOSURE
PROGRESSIVE REHABILITATIONAND MONITORING
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Escondida Shows It’s Never Too Early to Plan Closure
Though the Escondida deposit hasreserves sufficient for an additional 40 to50 years of mining, Minera EscondidaLimitada (MEL) is making plans now toregularly set aside funds for closing themine and related facilities – an approachexpected to pay significant dividendslater.
The Escondida deposit is 3 100 m abovesea level in the Atacama desert ofnorthern Chile. Mining started in late1990. Recent estimates put reserves atabout 1 800-million tons of ore, with anaverage 1.59% copper. The currentmining rate is about 127 000 tpd.
SRK’s Cam Scott says: “In March 1997,we were contracted to develop a
decommissioning planand cost estimate inassociation with theenvironmentaldepartment of MEL.”
“The objectives were toprovide a comprehensive list of minefacilities to be addressed at closure and,to the extent possible, identify theappropriate closure measure for each ofthese facilities.”
“Where further information or action wasrequired to define the appropriate closuremeasure with a reasonable degree ofconfidence, we were tasked withspecifying action(s) necessary to reducethe uncertainty to an acceptable level.”
The study indicated that thetailings facilities are likely todominate the total closure cost,and that this cost could besignificant.
The closure plan will beperiodically updated to reflect changes inthe mine facilities, technology and thelegal aspects of mine closure.
“However, for now, MEL will use the planas the basis for establishing regularfunding allocations in preparation forclosure,” Cam reveals. “In the long term,this approach is expected to have highlypositive implications for MEL in terms ofclosure quality and minimising eventualclosure expenditures.”
Estimates of closing and reclamation are in the billions
Departure With Dignity – Ten Years Later
SRK recently returned to the scene ofa highly successful mine closure from theprevious decade – the Beaverlodgeuranium mine in Northern Saskatchewan.
Beaverlodge was one of the first operationsof its sort in the very productiveAthabasca Basin. Its closure in 1986 wasthe subject of considerable investigationand careful design, later described in thebook Departure with Dignity.
“Ten years later, SRK returned to the siteto investigate ‘boils’ of radioactive tailingsthrough a cover that had been appliedduring the reclamation” says Cam Scottof SRK Vancouver. “The cause wasfound to be a combination of hydraulicpressures and winter freezing of the coverand upper tailings.”
SRK carried out design calculations andfield investigations to determine the cause
of the problems, and recommended anumber of remediation measures. SRKwas awarded the contract to superviseconstruction of the remediation measuresduring the summer of 1997. Follow upinspections in 1998 demonstrated thesuccess of the work.
A decadeafter closure,reclamation
andremediation
are exemplary
Cam Scott
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SRK’s Vancouver office recentlyassisted Public Works & GovernmentServices Canada (PWGSC) inimplementing closure measures at fourabandoned mines in the Canadian North.
The Rayrock Mine in the NorthwestTerritories was reclaimed by PWGSC in1996. Daryl Hockley and Rod Olausoninspected the site in June 1998 andrecommended minor upgrades andmaintenance.
The same team reviewed plans for PhaseI reclamation at the Discovery Mine, alsoin the Northwest Territories (NWT), in thewinter of 1997-98. After his return fromSantiago, Cam Scott joined the team,and is currently leading SRK’s review ofthe Phase II reclamation plans for Discovery.
Because of their remote location, heavyequipment can only reach Discovery andRayrock by ice roads, a common featurein the NWT. Constructed over frozenlakes and streams, ice roads often areassociated with very high costs owing torequirements for winter mobilization,operation and demobilization before thespring thaw.
The neighboring Yukon Territory is the siteof two other SRK-PWGSC mine closureprojects. The Venus Mine tailings facilitywas reclaimed in 1996, using a ‘WaterlooBarrier’, i.e. a grouted sheet pile wallused to cut off seepage. SRK reviewedthe work in 1998 and recommendedupgrades to ensure dam stability andimprove water cover.
Closing Abandoned Mines in the Canadian North
SRK inspected the Arctic Gold & Silver(AGS) tailings facility site in June 1998,and has since carried out a completeinvestigation and submittedrecommendations for the closure work.
Construction specifications are now beingdrawn up by PWGSC.
“AGS is a good example of thechallenges posed by abandoned mineclosures in the Yukon,” Daryl points out.“Issues that needed to be assessedincluded re-processing of the tailings,which might provide employment for thelocal First Nation and, on a completelydifferent tack, the long term stability of awater retaining structure constructed by abeaver (Cam calculated the factor ofsafety to be just a little over one!)”
Abandoned tailings facility near Carcross, Yukon Territory
Ian Brackley
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Mine ClosureServices‘Down Under’
In 1998, SRK transferred some of itsNorth American mine closureexpertise to Australia.
Prior to moving to Australia, JohnChapman, a chemical engineer, spent10 years working on mine closures inCanada, the U. S. and Europe.“Although mine closure regulations inmany states of Australia are not asstringent as those of North America,many clients appreciate theperspective that comes from workingwith stricter environmentalregulations,” says John. Mostrecently, Normandy Mining Companyhas been taking advantage of John’sexperience by having him review finalclosure plans for their Mt. LeyshonMine in Queensland and theWoodcutters Mine in the NorthernTerritory.
John Chapman
Closure Study for Cerro Do LoboTailings Impoundment
Neves Corvo Copper Minein Portugal is owned bySomincor, the state miningcompany, with Rio Tinto aminority shareholder. Thepyritic tailings are depositedunder water, to prevent acidgeneration.
SRK was appointed torevise the tailingsimpoundment closure plan.Five different methods ofoperation and closure were considered,including combinations of disposal as aslurry or paste, deposition by sub-aqueous or sub-aerial methods, andclosure under a water cover or beneath alow-permeability cover.
The tailings is placed sub-aqueously behind a rockfill embankment
The assessment of thepreferred option wasinfluenced by the desire toapply tried and trustedtechnology, by the need toprevent oxidation of thetailings, and by the need foran environmentally-acceptablesolution which minimised thelong-term maintenance afterclosure.
The closure study wasfollowed by a risk analysis to determinethe probability and consequences oftailings dam failure followed by acatastrophic flow slide, and to identifychanges required to reduce the risk to anacceptable level.
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Palabora’s Closure Database Saves Cost and Manpower
Early development of a database ofprobable closure costs for South Africa’sPalabora open pit mine provided apayback in subsequent years in the formof reduced cost and manpower neededto update this key information.
The initial cost-estimate was completed in1993 by a multi-disciplinary SRK team led
by Peter Labrum and Ritchie Stuart.
They spent a week at the minesite in thenorth-eastern part of the country,assessing and quantifying all closureaspects with the help of surface layoutplans. These were cross-referenced todetailed schedules of cost items preparedby the team.
In 1998 Peter Labrum, accompanied bySRK colleague Brian Read, returned toupdate the costing.
“Due to the experience of the team andthe nature of the 1993 database it waspossible to complete the review fairlyquickly using a very small team,” Labrumreports.
SRK Consulting has considerableexperience in assessment of backgroundor historic environmental qualitystandards, and using this information toprovide practical guidelines for theassessment of potential degradation.
“Many mining operations, on closure, arefaced with meeting stringent guidelinesfor soil, sediment and water quality,”explains Rob Bowell, PrincipalGeochemist. “In many cases theseguidelines are based on drinking waterguidelines which may not only beunsuitable for a mining district, butunobtainable due to geology and naturalbackground.”
A survey by SRK prior to sitedevelopment of the Ashanti GoldfieldsGeita project in Tanzania, demonstratedthat historic mining has had less impact,than current artisan mining.
In some cases, little data and severalepisodes of mining overprint each other,complicating environmental assessmentsuch as at the Getchell Mine Nevada,where gold is associated with high levelsof arsenic sulfides, and environmentalrelease of arsenic is a major concern.
As part of the closure plan for the openpits and assessment of pit lakes, the SRKdetailed hydrogeochemical studyrevealed, groundwater is strongly
compartmentalisedat Getchell.
“For many of thesecompartments,bedrock groundwaterquality is poor whencompared to waterquality guidelines,” Bowell continues.“However, SRK’s study indicated that littleconnection occurred between the deepbedrock aquifers and the shallow alluviumaquifers that are the main source of waterin the area. This information is being usedto propose modifications to the waterquality guidelines for the site to accountfor natural variations in background waterquality.”
Rob Bowell
WISMUT Nordhalde - Pyrite Fraction Remaining and Oxidation Rate
WISMUT Nordhalde - Water Saturation and Liquid Velocity
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Modeling O2 and Thermal TransportProcesses for Waste Rock Closure
Over the past few years SRK has beendeveloping computer models to simulateacid generation and leaching processesin waste rock piles as a means to betterassess rehabilitation options.
Acidity generation is the result of aseries of heat-producing chemicalreactions between sulfide minerals,oxygen and water. Because oxygensupply is often the limiting control onoxidation rate within a pile, accountingfor the processes of oxygen transporthas been a fundamental component ofthese models.
One important aspect of this modellinghas been calibration to field data. Forexample, SRK laid out an installationand monitoring program for Wismut’sNordhalde. Eight boreholes wereinstalled with instrumentation equippedto monitor oxygen concentration andtemperature at intervals throughout thethickness of the waste pile.
Under SRK’s recommendations, Wismutcollected a year’s worth of data, resultingin one of the most comprehensivedatabases of its kind.
SRK undertook subsequent calibration andmodelling using the code TOUGH-AMD.Results of the modelling showed the futureacidity-generating potential of the dump.
Other clients of SRK that have benefitedfrom this type of modelling include NicoletMinerals (formerly the Crandon MiningCorporation), Kennecott’s Flambeau Mineand Cominco’s Red Dog Mine in Alaska.
SRK’s Jason Smolensky says: “Thistechnology gives us a unique insight intothe significant processes that lead toacidity generation within a waste pile andallows prediction of future rates andduration of oxidation.”
“Modelling also allows us to assessvarious rehabilitation measures at arelatively low cost.”
Modelling Results – Convective Case – Conditions at year 30
Jason Smolensky
New SRK Officein Yellowknife
SRK now has a full-time presence,and a major closure project, inYellowknife NWT.
As well as being the capital ofCanada’s Northwest Territories,Yellowknife is the main staging pointfor mining operations throughout thearea, including the new Ekati andDiavik diamond mines. SRKwelcomes Stephen Schultz to theteam as our man in Yellowknife.Stephen and several of our Vancouverstaff are busy assessing alternativesfor managing 280,000 tonnes ofarsenic-rich dust that was leftunderground when the nearby GiantMine declared bankruptcy. SRK wasawarded this high profile, multi-disciplinary project after a Canada-wide competitive bid.
SRK is cooperating with theDepartment of Indian Affairs andNorthern Development and the newsite owners, Miramar Giant Mines Ltd,to assess alternatives for in situstabilization, extraction and/or re-processing of the dust.
Discourse on mine closure is becomingincreasingly topical, asexisting mines move towardsthe end of their operationsand greenfields projects aresubject to the ‘do not open ifyou cannot close’ philosophy.
Simultaneously, discussion isbroadening from biophysical,engineering and rehabilitationaspects to the more nebuloussocio-economic impacts ofclosure.
It is not difficult to conjure up a comp-rehensive list of socio-economic impactsrelated to mine closure, the challenge israther in untangling the web of socio-economic impacts so as to devise and
• Parties responsible formitigation of impactsparticipate from the verybeginning of the process.This can be difficult whenimpacts and responsibilitycannot be clearly definedand responsible parties areunaware of, or unable/
unwilling to assume responsibility.
• Sufficient financial resources are setaside, in advance, for the managementof closure planning and closure relatedimpacts. Generally socio-economic
impacts requiremanagementyears in advanceof closure.
• Tensionsbetween what is
acceptable closure for biophysical andengineering impacts, and that of socio-economic impacts, be defined andresolved.
SRK recognises that mining is not asimple case of ‘open and close’. Wecontinue to partner clients to resolve themyriad of challenges, associated withmine closure, as part of the planning ofgreenfields projects and for existingoperations pending closure.
