Chapter 44 AUDITING MINING COMPANIESWord文档格式.docx
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44.1OVERVIEWOFTHEINDUSTRY
44.2ACCOUNTINGPRINCIPLESANDPRACTICES
(a)AcquisitionCosts
(b)ExplorationCosts
(c)DevelopmentCosts
(d)DeterminingtheStartoftheProductionPhase
(e)EnvironmentalRemediationLiabilities
44.3RISKFACTORSANDAUDITREACTION
(a)InherentRisks
(i)AssetRealization
(ii)Contingencies
(iii)Disclosures
(b)AuditStrategy
44.4TYPICALTRANSACTIONS,INTERNALCONTROL,ANDSUBSTANTIVETESTS
(a)Revenue
(i)SalesofMetalsandMinerals
(ii)Tolling
(iii)Royalties
(iv)MineralPropertyConveyances
(v)GainsandLossesfromHedgingTransactions
(b)Expenditures
(i)Acquisition,Exploration,andDevelopmentCosts
(ii)Inventory
(1)MetalsandMinerals
(2)MaterialsandSupplies
(iii)LiabilitiesOtherthanIncomeTaxes
(iv)IncomeTaxLiabilities
(c)DisclosureofRisksandUncertainties
44.1
OVERVIEWOFTHEINDUSTRY
Theprincipaldifferencebetweenminingcompaniesandcompaniesinvolvedinoilandgasproducingactivitiesrelatestothenature,timing,andextentofexpendituresincurredforexploration,development,production,andprocessingofminerals.Generallyintheminingindustry,aperiodofaslongasseveralyearselapsesbetweenthetimeexplorationcostsareincurredtodiscoveracommerciallyviablebodyoforeandtheexpenditureofdevelopmentcosts,whichareusuallysubstantial,tocompletetheproject.Therefore,theeconomicbenefitsderivedfromaprojectarelongtermandsubjecttotheuncertaintiesinherentinthepassageoftime.Incontrast,thecostsrelatedtoexploringfordepositsofoilandgasareexpendedoverarelativelyshorttimeframe.
Theminingindustryiscapitalintensive.Substantialinvestmentsinproperty,plant,andequipmentarerequired;
usuallytheyrepresentmorethan50percentofaminingcompany'
stotalassets.Thesignificantcapitalinvestmentsofminingcompaniesandtherelatedrisksinherentinanylong-termprojectmayaffecttherecoverabilityofcapitalizedcosts.Theauditorshouldbecognizantofthesefactors,amongothers,andshouldassesstheriskthatcostswillnotberecovered.
Thestagesofminingoperationsvarysomewhatdependingonthetypeofmineralandaredeterminedbydifferencesingeological,chemical,andeconomicfactors.Thebasicoperationscommontominingcompaniesareexploration,development,extraction,andmarketing.Somemineralsalsorequiremilling,beneficiationandagglomeration,smelting,solventextraction-electrowinning,orrefining.
Explorationisthesearchfornaturalaccumulationsofmineralswitheconomicvalue.Explorationformineralsisaspecializedactivityinvolvingtheuseofcomplexgeophysicalandgeochemicalequipmentandprocedures.Thereisanelementoffinancialriskineverydecisiontopursueexploration,andexplorersgenerallyseektominimizethecostsandincreasetheprobabilityofsuccess.Asaresult,beforeanyfieldworkbegins,extensivestudiesaremadeconcerningwhichtypesofmineralsaretobesoughtandwheretheyaremostlikelytooccur.Marketstudiesandforecasts,studiesofgeologicalmapsandreports,andlogisticalevaluationsareperformedtoprovideinformationforuseindeterminingtheeconomicfeasibilityofapotentialproject.
Explorationcanbedividedintotwophases,prospectingandexploratorydrilling.Prospectingisthesearchforgeologicalinformationoverabroadarea.Itembracessuchactivitiesasgeologicalmapping,analysisofrocktypesandstructures,searchesfordirectmanifestationsofmineralization,takingsamplesofmineralsfound,andaeromagneticsurveys.Exploratorydrillingisconductedinspecificareasofinterestidentifiedduringtheprospectingphase.Rockandsoilsamplesareexamined,andtheearth'
scrustismonitoreddirectlyformagnetic,gravitational,sonic,andradioactivedata.Basedontheanalysis,targetsfortrenching,testpits,andexploratorydrillingareidentified.Drillingisparticularlyusefulinevaluatingtheshapeandcharacterofadeposit.Analysisofsamplesisnecessarytodeterminethegradeofthedepositandtheextractionmethodtobeused.
Oncethegradeandquantityofthedeposithavebeendetermined,adecisionmustbemaderegardingthetechnicalfeasibilityandcommercialviabilityofdevelopingthedepositforminingactivity.Thevalueofamineraldepositisdeterminedbytheintrinsicvalueofthemineralspresentandbythenatureandlocationoftheiroccurrence.Inadditiontothegradeandquantityoftheore,suchfactorsasthephysicalaccessibilityofthedeposit,theestimatedcostsofproduction,andthevalueofjointproductsandby-productsarekeyelementsinthedecisiontodevelopadepositforcommercialexploitation.
Thedevelopmentstageofproductioninvolvesplanningandpreparingforcommercialoperation.Developmentofsurfaceminesisrelativelystraightforward.Foropen-pitmines,whicharesurfacemines,theprincipalprocedureistoremovesufficientoverburdentoexposetheoreormineral.Forthesemines,aninitialcutismadetoexposethematerialtobemined.Forundergroundmines,dataresultingfromexploratorydrillingisevaluatedasabasisforplanningtheshaftsandtunnelsthatwillprovideaccesstothedeposit.Substantialcapitalinvestmentinminedevelopment,machineryandequipment,andrelatedfacilitiesgenerallyisrequiredinthedevelopmentstage.
Thegoalattheminingstageofproductionistobreakuptherockandoretotheextentnecessaryforloadingandremovaltotheprocessinglocation.Avarietyofminingtechniquesexiststoaccomplishthis.Thedrillingandblastingtechniqueisutilizedfrequently;
analternativeisthecontinuousminingmethod,inwhichaboringortearingmachineismountedonaforwardcrawlertobreakthematerialawayfromtherockface.
Afterremovalfromtheminesite,thematerialmayrequirefurtherprocessingsuchasmilling.Thefirstphasetypicallyinvolvescrushingandgrindingtheoretoasizethatwillfacilitatetheliberationofmetalfromthewastematerial.Thisisperformedinseveralsteps;
watergenerallyisusedinthegrindingprocess,andtheendproductofthisphaseisusuallyacombinationoffinelygroundoreandwatercalledslurry.
Formostmetalores,thesecondmillingprocedureisconcentration,whichinvolvestheseparationofthemineralconstituentsfromthewasterock.Thisusuallyisdoneusingseparationtechniquessuchasflotation,leaching,andprecipitation.Flotationisaprocessinwhichheavymetallicsubstancesaremadetoclingtothebubblesofanoilyfrothandrisetothesurface,fromwhichtheycaneasilybeskimmedoff.Thisprocessisusedprimarilyforconcentrationsoforesthatcontaincompoundsofsulfur.SincemostofthemetalproductionintheUnitedStatescomesfromsulfideores,flotationisthemostcommonlyusedconcentrationprocessinthiscountry.Flotationisusednotonlytoseparatethemineralfromthewasterock,butalsotoseparatedifferentmineralsfromeachother.Leachingandprecipitationareparticularlyimportantforrecoveringmetalsfromoxideores.Leachingisaprocessofextractingmetalsfromtheorebyselectivelydissolvingtheminasuitablesolvent,suchaswater,sulfuricacid,hydrochloricacid,oraweaksolutionofsodiumorpotassiumcyanide.Themetalisthenremovedfromthesolutionusingchemicalorelectrochemicalprecipitationtechniques.Heapleaching,anothermethodforrecoveryofvariousmineralsfromlow-gradeoredeposits,isasignificantfactoringoldproduction.Eventhoughtherecoveryofthemetalsinheapleachoperationsisoftenmuchlowerthaninotherprocesses,heapleachingisneverthelessacost-effectiveprocessduetothelowunitcostsassociatedwithit.
Beneficiationandagglomerationrelatetoferrous(iron)mining.Beneficiationisthedressingorprocessingoforeforthepurposeofregulatingthesizeofthedesiredproduct,removingunwantedconstituents,andimprovingthequality,purity,orassaygradeoftheore.Beneficiationtechniquesincludecrushing,screening,andwashing,andalsoinvolvetheuseofgravity,magnetic,andflotationmethods.Smallparticlesofironoregenerallyaresubjectedtoanadditionalprocesscalledagglomeration.Thisisaprocessinwhichthebeneficiatedparticlesarefusedtogetherintolargerbitsorpelletsthatareeasiertohandle.
Smeltingistheprocessofseparatingthemetalfromimpuritieswithwhichitmaybechemicallyboundorphysicallymixedtoocloselytoberemovedbyconcentration.Mostsmeltingisaccomplishedthroughfusion,whichistheliquefactionofametalunderheat.Insomecases,chemicalprocessesareusedinsteadof,orincombinationwith,heatingtechniques.Sincemetalsoccurinavarietyofcombinationswithotherelements,thesmeltingtechniqueutilizeddependsonthecharacteristicsoftheconcentrate.Theprincipalsmeltingprocessesincluderoasting,"
true"
smelting,andconverting.Roastingisaheatingprocessusedprimarilyforsulfideoresasameansofdrivingoutthesulfur."
True"
smeltingistheprocessofseparatingthemetalfromitschemicalbondswithwastematerialbymelting.Theprocessofconvertingentailsblowingoxygen-enrichedairthroughmoltenmetal,causingoxidationandremovalofsulfurandotherimpuritiesfromthemetal.
Refiningisthelaststepinisolatingthemetal.Theprimarymethodusediselectrolyticrefining,inwhichanelectricalcurrentseparatesmetalsfromasolutioninsuchawaythatby-productscanberecovered.Forexample,inelectrolyticrefiningofcopper,platesofimpurecopper(anodes)aresuspendedbetweenthinplatesofpurecopper(cathodes),andbothareth