NUMBER 169 DECEMBER 2015-Version 2 Second Version issued December 3, 2015 Newsletter for the Association of Applied Geochemists continued on page 5 EXPLORE NEWSLETTER WISHES TO THANK OUR CORPORATE SPONSORS FOR THEIR SUPPORT Gold Homogeneity in Certified Reference Materials; A Comparison of Five Manufacturers N. W. Brand, Geochemical Services Pty Ltd., Suite 10, 5 Colin Street, West Perth, 6005, Australia, [email protected]INTRODUCTION Certified Reference Materials (CRMs) inserted into analytical batches are a requirement by the international codes governing the mineral industry (JORC 2012; NI43- 101; SAMREC) and reporting to the standards laid out in these codes is a mandatory compliance for publicly listed companies on the Australian, New Zealand and Canadian Stock Exchanges. A CRM is a sample where the concentra- tions of one or more analytes have been quantified by valid methodologies and certified with valid documentation. These certified values are the consensus inter-laboratory mean for an analyte where typically each laboratory analy- ses multiple subsamples of the CRM. For gold (Au) CRMs, one of the key properties is the homogeneity of the CRM sample (i.e. testing for nugget effects). Quantifying this homogeneity by the Relative Standard Deviation (RSD) is critical for assessment of laboratory results and the follow up of quality control (QC) failures. There is vast literature discussing the nugget effect in gold mineralising systems and protocols in reducing the sampling error (e.g., Stanley & Smee 2007), but very little information has been published on the homogeneity of gold CRMs. By their very nature CRMs are assumed to be homogeneous and any variation is attributed to labora- tory error (i.e. the variance attributed to the sampling error is less than the analytical error); so how homogenous are commercial gold CRMs? The homogeneity of a gold CRM sample reflects the capability and competency of a manufacturer to eliminate any nugget effects and provide a homogeneous product that, when analysed, will provide a repeatable result within the statistical limits provided on the CRM certificate. Al- though all manufactures refer to the homogeneity of their CRMs, only one manufacturer (OREAS), measures the homogeneity of the CRMs and provides this information as routine with their gold CRM Certificate of Analysis. Rock- labs undertake a homogeneity and segregation test, but do not provide the actual homogeneity results. This independent study evaluates the homogeneity of gold CRMs from commercial CRM manufacturers at four chosen gold grades (0.5 ppm Au, 1 ppm Au, 3 ppm Au and 9 ppm Au). These grades are typical in mining and explo- ration scenarios and reliable QC data at these grades is critical. This study provides a benchmark for further evalu- ations of potentially “nuggetty” CRM products including, but not restricted to, platinum group elements (PGEs), rare earth elements (REE), and Au. CRM MANUFACTURERS AND THEIR PREPARATION Four auriferous CRMS from each of five manufactur- ers were assessed (i.e. 20 CRMs in total). The CRMs were sourced from five manufacturers, as listed below alphabeti- cally. A summary description of the preparation process is also provided and taken from their CRM certificates: • African Mineral Standards (AMIS): http://www.amis. co.za/. The material was crushed, dry-milled and air- classified to <54 microns. Wet sieve particle size analysis of random samples confirmed the material was 98.5% <54 microns. It was then blended in a bi-conical mixer, systematically divided and then sealed into1 kg Labora- tory Packs. • CDN Resource Laboratories Ltd (CDN): http://www. cdnlabs.com/. Material was dried, crushed, pulverized and then passed through a 270 mesh screen. The +270 mesh material was discarded. The -270 mesh (53 microns) ma- terial was mixed for 5 days in a double-cone blender. • Geostats Pty Ltd (GST): http://www.geostats.com.au/. All CRMs are dried in an oven for a minimum of 12 hours at 110 °C. The dry material is then pulverised to finer than 75 microns (nominal mean of 45 microns) using an air classifier. The material is then homogenised and stored in a sealed, stable container ready for final packaging. • Ore Research and Exploration Pty Ltd (ORE): http:// www.ore.com.au/. Materials are jaw crushed to minus 3 mm, dried to constant mass at 105 °C, barren materials are milled to >98% minus 75 microns and gold bearing material milled to 100% minus 20-30 microns, blending in appropriate proportions to achieve the desired grade, packaging into 60 g and 100 g units in laminated foil pouches and 1 kg units in plastic jars. • Rocklabs (RLB): http://rocklabs.com/. Pulverized feld- spar minerals, basalt rock and barren ironpyrites were blended with finely divided gold containing minerals that have been screened to ensure there is no nuggetty gold. (NOTE no sizing information provided). See also Table 1 for a summary.
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NUMBER 169 DECEMBER 2015-Version 2
Second Version issued December 3, 2015Newsletter for the
Association of Applied Geochemists
continued on page 5
EXPLORE NEWSLETTER
WISHES TO THANK OUR CORPORATE SPONSORS FOR
THEIR SUPPORT
Gold Homogeneity in Certified Reference Materials; A Comparison of Five ManufacturersN. W. Brand, Geochemical Services Pty Ltd., Suite 10, 5 Colin Street, West Perth, 6005, Australia, [email protected]
CRM MANUFACTURERS AND THEIR PREPARATION FourauriferousCRMSfromeachoffivemanufactur-erswereassessed(i.e.20CRMsintotal).TheCRMsweresourcedfromfivemanufacturers,aslistedbelowalphabeti-cally.AsummarydescriptionofthepreparationprocessisalsoprovidedandtakenfromtheirCRMcertificates:
EXPLOREispublishedquarterlybytheAssociationofAppliedGeochemists,P.O.Box26099,72RobertsonRoad,Ottawa,ONCanadaK2H9RO.EXPLOREisatrademarkoftheAssociationofAppliedGeochemists.Type and layout of EXPLORE:VivianHeggie,HeggieEnterprises,Thornton,CO(303)288-6540;[email protected]
Information for Contributors Manuscripts should be double-spaced and submitted in digitalformatusingMicrosoft®WORD.DoNOTembedfiguresortablesinthetextdocument.Eachphotoand/orfigure(colourorblackandwhite)shouldbesubmittedasseparatehighresolutiontiff,jpegorPDF(2400resolutionorbetter)file.Eachtableshouldbesubmit-tedasseparatedigitalfileinMicrosoft®EXCELformat.Allsci-entific/technicalarticleswillbereviewed.Allcontributionsmaybeeditedforclarityorbrevity. Formats for headings, abbreviations, scientificnotations, refer-encesandfiguresmustfollowtheGuidetoAuthorsforGeochem-istry:Exploration,Environment,Analysis(GEEA)thatarepostedon the GEEA website at: http://www.geolsoc.org.uk/template.cfm?name=geea_instructions_for_authors Inadditiontothetechnicalarticle,authorsareaskedtosubmitaseparate250wordabstractthatsummarizesthecontentoftheirarticle.ThisabstractwillbepublishedinthejournalELEMENTS onthe‘AAGNews’page.
Feldspar, basalt & iron pyrites with minor fine gold minerals
Geostats50 g Fire
assay
OREAS30-50 g
Fire assay
Rocklabs30 g Fire
assay
Table 2: Summary of CRMs chosen for this study.
MATERIAL RECEIVED Amountscorrespondingtotheminimummanufacturersorderwerepurchased.Tothisend:•Twox100gsachetsofeachofthefourCRMwerepur-chasedfromAMISandreceivedinvacuumsealedfoilpouches;
Photo 1. CRM’s “as received” from the five manufacturers.
SAMPLE PREPARATION AND ANALYSIS Priortodispatchingthematerialsforanalysis,eachCRMwassubsampledtwentytimesinacleanroom.A10galiquotofeachCRMwasplacedintoaZiploc®plasticbagusingadisposableplasticspatulatoavoidanycrosscon-tamination.ThisprocedurewasrepeatedforeachCRMsothatthesamplesweresequencedinlotsof20,witheachlotcorrespondingtooneCRM. Forthehomogeneitytestwork,InstrumentalNeutronActivationAnalysis(INAA)wasused.INAAisahighlypreciseanduniqueassaymethodthatfocusesontheele-mentsnucleusirrespectiveofthesamplematrixorchemicalformoftheelement.Eachsampleissubjectedtoafluxofneutronstoproduceradioactivenuclides.Thesenuclidesdecayemittinggammaraysthatarecharacteristicforeachnuclide.Whencomparedwithaknownstandard,thein-tensityoftheemittedgammarayscanbequantifiedintoanelementconcentration(Lieser2001). The400x10gsubsamplesweredispatchedtoActiva-tionLaboratoriesLimited(Actlabs)inAncaster,Canada(www.actlabs.com)forINAA;Actlabswereinformedofthepurposeoftheanalysisandrequestedtoweighout1g
continued on page 6
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Gold Homogeneity in Certified Reference Materials… continued from page 5
INTERNAL CRM VARIATION Control charts presented below show the variation inresultsof eachCRMforeachmanufacturer. Figures1 to5(A-Dplots)showgraphicalrepresentationofthe20x1gINAAdatawheretheXaxisrepresentstheorderofanalysis(analyticalsubsamples1to20)fromlefttoright;andtheYaxisshowsthemeasuredINAAconcentrationinAuppb.AsolidredlineshowsthemeanINAAvalue(seeTable4)foreachCRMandforeachgraderange(i.e.0.5ppmAu,1ppmAu,3ppmAuand9ppmAu).ThesameYaxisconcentra-tionrangeandscalehasbeenusedwherepossibletofacili-tate visual comparison between themanufacturers. TheYaxisinFigures1-5(E-Hplots)showsthepercentagediffer-encefromthecalculatedINAAmean.ThesediagramsarenotintendedasverificationchartsforeachCRMbyINAA,butasastandardisedgraphicalcommunicationtool.
EXPLORE NUMBER 169 PAGE 9
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Gold Homogeneity in Certified Reference Materials… continued from page 8
AMIS: Figure 1 graphically depicts results for the AMISCRMs. Individual values for each CRM show a widespreadofalmostrandomdatawithnosystematicvariation.AMIS0267(cert9.05ppm)rangesfrom7.45ppmAuto17.90ppmAu(Fig.1D)whichrepresents-15.8%to+102%dif-ferencefromtheINAAmeanofthisCRM(Fig.1H).Two
43.5% 102%
29.7% 34.2%
Au (p
pb)
Order of analysis
Au (p
pb)
Au (p
pb)
Au (p
pb)
Order of analysis
%ag
e di
ff fr
om M
ean
NAA
val
ue
%ag
e di
ff fr
om M
ean
NAA
val
ue
%ag
e di
ff fr
om M
ean
NAA
val
ue
%ag
e di
ff fr
om M
ean
NAA
val
ue
E
F
G
H
A
B
C
D
Figure 1 samplesshowasignificantdeparturefromtheINAAmean,reporting+43.5%(12.70ppmAu)and+102%(17.90ppmAu)ofthemeanvalue(Fig.1H)andreflects inhomogene-ity (presumably a nugget effect) of theCRM. AMIS0310(cert1.03ppm)alsoshows(Figs.1BandF)significantde-parturefromtheINAAmeanfortwosamples(+29.7%and
Figure 1. Control charts for AMIS CRMs showing INAA concentration (Au ppb) in relation to the certified value [A-D] and the percentage difference from the INAA mean value [E-H].
EXPLORE NUMBER 169 PAGE 11
continued on page 12
Gold Homogeneity in Certified Reference Materials… continued from page 1
+34.2%). This inhomogeneityofAMISCRMshaspoten-tiallysignificantimplicationsforlaboratoryreportingwhere-byauserwouldquestionthelaboratoryresultsbasedontheassumptionthattheCRMishomogeneous.
Figure 2. Control charts for CDN CRMs showing INAA concentration (Au ppb) in relation to the certified value [A-D] and the percentage difference from the INAA mean value [E-H].
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Gold Homogeneity in Certified Reference Materials… continued from page 11
Figure 3. Control charts for Geostats CRMs showing INAA concentration (Au ppb) in relation to the certified value [A-D] and the per-centage difference from the INAA mean value [E-H].
Figure 4. Control charts for OREAS CRMs showing INAA concentration (Au ppb) in relation to the certified value [A-D] and the percent-age difference from the INAA mean value [E-H].
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Gold Homogeneity in Certified Reference Materials… continued from page 13
Figure 5 Figure 5. Control charts for Rocklabs CRMs showing INAA concentration (Au ppb) in relation to the certified value [A-D] and the per-centage difference from the INAA mean value [E-H].
ACKNOWLEDGEMENTS AND DISCLOSURE TheauthorwouldliketoacknowledgetworeviewerswhoassistedinframingthisarticleandRobertGarrett,EmeritusScientist,GeologicalSurveyofCanada,forhisconstructivecommentsonthemanuscript.Theauthorhasnofinancialinterests,directorindirect,inanyofthefiveCRMmanufacturers.
continued on page 16
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Gold Homogeneity in Certified Reference Materials… continued from page 15
Wang,Y.&Brindle,I.D.2014,Rapidhigh-performancesampledigestionforICPdeterminationbyColdblockTMdigestion:part2:golddeterminationingeologicalsampleswithmemoryeffectelimination.Journal of Analytical Atomic Spectrometry,29,1904-1911.
Join us for Exploration ‘17October 21-25, 2017, Toronto, Ontario, Canada
Exploration ‘17 is the sixth of the very successful series of Decennial Mineral Exploration Conferences which have been held in the seventh year of every decade starting in 1967. The theme of the Exploration ’17 conference is “Integrating the Geosciences: The Challenge of Discovery”, featuring a multi-national, multi-disciplinary technical programme, exhibition, workshops and field schools.
Decennial Conference Proceedings from the past five conferences (1967, 1977, 1987, 1997, 2007) are available for download on the web site under the ‘Resources’ header.
I. Call to Order – Establishment of Quorum PresidentLeybournecalledtheAnnualGeneralMeet-ing(AGM)toorderat6:00PMlocaltime.Morethan30AAGFellowswerepresent,exceedingthenecessary15requiredforaquorum.
II. President’s report (M. Leybourne) PresidentLeybournethankedtheAAGExecutive,Council,andRegionalCouncilorsfortheircontributionstoAAGduringthetimesincethe2014AGM.HeextendedaspecialthankyoutoGwendyHallforhertremendouscontributiontoAAGasEditorofGEEAsinceitsinception(Volume1,Number1beingpublishedinFebruary2001)to2015.HealsowelcomedKurtKyserasthenewEditorofGEEA.HethankedBethMcClenaghan(Editor)andPimvanGeffen(BusinessManager)fortheircontributionstotheAAGnewsletterEXPLORE.HealsoextendedthankstoPatricedeCaritatforservingasAAG’sliaisonwithEle-mentsmagazineforthepastfewyearsandannouncedthatDennisArnewouldbetakingoverthoseresponsibilities.BrunoLemièreandGemmaBonham-Carterwererecog-nizedfortheiroutstandingcontributionstoAAG’swebsiteandAlArseneaultforhisdedicationtoAAGastheAs-sociation’sBusinessManager.Lastly,PresidentLeybournethankedErickWeiland,RobBowell,SarahLincoln,andRickSchwarzfortheirhardworkastheLocalOrganizingCommitteeforthe27thInternationalAppliedGeochemis-trySymposium. PresidentLeybourneannouncedthatDanielLayton-MatthewsofQueen’sUniversity,Kingston,Ontario,Cana-da,willbeAAG’sDistinguishedLecturerfor2015–2016.
III. Vice President’s report (R. Noble) VicePresidentNoblereportedonprogressinthepubli-cationofBobBoyle’sbookonthehistoryofgeochemistryandcosmochemistry.AneditorialteamisnowinplaceanditishopedthisbookmightbereadyforthenextIAGSin2017. Duringthisyear,AAGhasreceivedthreeupdatesfromRegionalCouncilors.NealBrewardhassteppeddownasRegionalCouncilorfortheUKandRepublicofIreland.VicePresidentNobleextendedhisthankstoNealforhisservicetotheAssociation.
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VIII. Symposia (D. Cohen) Thebidtoholdthe2017IAGSinFlorence,ItalywasrejectedbyCouncilbecauseofconcernsaboutsomeofthecostestimates.TheAssociationiscurrentlyinvestigatingholdingthe2017IAGSinCanada.Moreinformationwillbeavailableinthenextfewmonths.
IX. Other business PresidentLeybourneopenedthemeetingtoquestionsfromtheattendingAAGFellows.Avarietyoftopicswerediscussedthatwererelatedtoothersectionsoftheminutesandconcluded.
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EXPLORE NUMBER 169 PAGE 19
Recently Published in ElementsVolume 11, no. 4 Social and Economic Impact of Geochemistry TheAugusteditionofElementsfocusedonthemanywaysthatappliedgeochemistryimpactssociety.Itstartswithanoverviewoftheimpactofgeochemistry(Ludden,Albarède&Coleman),looksathowgeochemistryisusedinmineralexploration(Kyser,Barr&Ihlenfeld)andthenatnewchallengesandmaterialsinthefieldofenvironmentalmineralogy(Calas,McMillan&Bernier-Latmani).AnarticlebasedonacasestudyfromtheCityofLondonexamineshowgeochemistrycanbeappliedtourbanplanning(Ludden,Peach&Flight),whilstanotherexplorestheuseofstableisotopesinforensicgeochemistry(Ehleringer,Chesson,Valenzuela,Tipple&Martinella).Thefinalcontributionexplorestheusesofmetalstableisotopesinmedicine(Rakovan&Pasteris).TheAAGSocietyNewsincludedasummaryofthesuccessful27thIAGSbyErickWeilandandanabstractofBobGarrett’sthought-provokingarticleonQA/QCplotsthatappearedinExplore167.Therecertainlyshouldbesomethingfornearlyeverygeochemistinthisvol-ume!
Volume 11, no. 5, Supergene Metal Deposits TheOctobereditionofElementsfocusesonsupergenemetaldeposits.Itbeginswithanoverviewofthegeologicalandeconomicsig-nificanceofsupergenemetaldeposits(Reich&Vasconcelos),exploressupergenealterationoforedeposits(Dill),paleoclimaticsignaturesofthisdeposittype(Vasconcelos,Reich&Shuster),theuseofCuisotopesinunderstandingsupergeneprocesses(Mathur&Fantle),predictinggeologicalcorrosionwithelectrodes(Renock&Shuller-Nickles),andfinisheswithanexaminationofthegeomicrobiologyofsupergenemetaldeposits(Zammit,Shuster,Gagen&Southam).TheAAGSocietyNewsincludedashortobituaryforEricHoffman,aswellascitationsforthewinnersofthe2014and2015goldandsilvermedals.Thisiscertainlyanissueforthoseinvolvedinregolithgeochemistryandwithaninterestinsupergenemineraldeposits.
Regular Members StephenDeWitConsultingGeologist3020MeadowDriveNanaimo,B.C.CANADAV9R7C6Membership#4307 SusanDriebergPrincipalGeochemist,RioTinto224N2200WestSaltLakeCity,UTUSA84116Membership#4308 EvgeniaLebedevaGeochemist,Intertek156CanningHighwaySouthPerth,WAAUSTRALIA6151Membership#4310 DouglasC.MenziesConsultingGeologist,Geoinsite16CullenDriveKiama,NSWAUSTRALIA2533Membership#4311 Student Members JasmineA.MoertleCaliforniaStateUniversity,LongBeach6750E.RosebaySt.LongBeach,CAUSA90808Membership#4309
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CALENDAR OF EVENTSInternational,national,andregionalmeetingsofinteresttocolleaguesworkinginexploration,environmentalandotherareasofappliedgeochemistry.TheseeventsalsoappearontheAAGwebpageat:www.appliedgeochemists.org.
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