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Ōńń€€ĢUnderstanding€Our€PlanetĢ€€€€€€€Through€ChemistryĢĢA€U.S.Geological€Survey€HTML€Poster€SessionĢCompiled€by€Joseph€E.€Taggart,€Jr.ĢEdited€by€Carole€A.€Bales€and€Sonja€K.€RunbergĢGraphics€and€photos€by€Richard€P.€Walker,€Shawn€T.€Smith,€and€Steven€M.€SmithĢComposition€by€Margo€L.€JohnsonĢHTML€by€€Joseph€E.€Taggart,€Jr.ĢĢĢĢFigure€captions€in€this€stripped€ascii€version€are€in€.ĢĢINDEXĢForewordĢI.€IntroductionĢII.€Understanding€the€EarthĢĢIIa.€History€recorded€in€chemistry€€€€ĢĢ€€€€€How€old€is€the€Earth?.......Bruce€Doe€(703)€648-6205Ģ€€€€€Elements,€isotopes,€and€radioactivity......Bruce€Doe€(703)€648-6205Ģ€€€€€Digesting€rocks..........Richard€O€Leary€(303)€236-2493Ģ€€€€€.....................................Richard€Sanzolone€(303)€236-1806Ģ€€€€€Disaster€from€space....Glen€Izett€(303)€236-5972Ģ€€€€€......................................Frederick€Lichte€(303)€236-1449ĢĢIIb.€Geologic€processesĢĢ€€€€€Volcanoes......John€Pallister€(303)€236-1023Ģ€€€€€....................Joseph€Taggart,€Jr.€(303)€236-1807Ģ€€€€€Application€of€Neutron€Activation....James€Budahn€(303)€236-4724Ģ€€€€€The€smallest€clues.....Gregory€Meeker€(303)€236-1081Ģ€€€€€...................................Eugene€Foord€(303)€236-4755Ģ€€€€€Analytical€chemistry€in€the€search€for€ore€....Albert€Hofstra€(303)€236-5530Ģ€€€€€Fluids€and€gases€from€tiny€time€capsules...John€Viets€(303)€236-€1906ĢĢIIc.€EnvironmentĢĢ€€€€€Global€change€in€the€geologic€past...Joan€Fitzpatrick€(303)€236-5562Ģ€€€€€............................................................Todd€Hinkley€(303)€236-5850Ģ€€€€€Air€bubbles,€amber,€and€dinosaurs...Gary€Landis€(303)€236-5609Š Ó+#'+ Š€€€€€Recent€methane€from€Gulf€Coast€marshes.....Joel€Leventhal€(303)236-1522ĢĢIId.€PollutionĢĢ€€€€€Acid€rain€steals€our€heritage....Philip€Baedecker€(703)€648-6348Ģ€€€€€...............................................................Victor€Mossotti€(415)€329-5293€Ģ€€€€€The€chemistry€of€mine€drainage.....Walt€Ficklin€(deceased)Ģ€€€€€...........................................................Kathleen€Smith€(303)€236-5788€ĢĢIIe.€Pollution€preventionĢĢ€€€€€Cleaning€up€coal€burning...Curtis€Palmer€(703)€648-6185Ģ€€€€€.............................................Robert€Finkelman€(703)€648-6412Ģ€€€€€.............................................Susan€Tewalt€(703)€648-6437Ģ€€€€€.............................................Allen€Meier€(303)€236-1902ĢĢIII.€Mapping€the€chemistry€of€the€Earth€s€surfaceĢĢIIIa.€Assessment€of€public€landsĢĢ€€€€€Mapping€stream€sediments€for€resource€exploration.....Albert€Hofstra€(303)Ģ236-5530Ģ€€€€€Keeping€track€of€the€resources€of€our€country.....Sherman€Marsh€(303)Ģ236-5521Ģ€€€€€Mobile€laboratories....Betty€Adrian€(303)€236-2483Ģ€€€€€Exploration€for€covered€ore€deposits...David€Grimes€(303)€236-5510Ģ€€€€€Mineral€scavengers€provide€a€clue...Reinhard€Leinz€(303)€236-2449Ģ€€€€€..................................................................J.€Robert€Clark€(formerly€with€USGS)ĢĢIIIb.€Geographic€Chemistry:€€National€Geochemical€Data€BaseĢĢĢ€€€€€Chemistry€of€a€nation€on€file.....Sherman€Marsh€(303)€236-5521Ģ€€€€€...................................................Steven€M.€Smith€(303)€236-1192€Ģ€€€€€10,000€element€determinations€a€day....Paul€Briggs€(303)€236-5553ĢIIIc.€Public€Health€and€Safety:€€Element€maps€of€soilsĢĢ€€€€€Maps€of€natural€contamination.....Ronald€Tidball€(303)€236-5517Ģ€€€€€..............................................................James€Crock€(303)€236-2452€Ģ€€€€€Industrial€sources€of€contamination...Ronald€Tidball€(303)€236-5517Ģ€€€€€Robots€in€the€laboratory.....Richard€O€Leary€(303)€236-2493Ģ€€€€€.............................................Stephen€Wilson€(303)€236-2454ĢĢIV.€Can€we€depend€on€chemical€analyses?ĢĢIVa.€Measuring€qualityĢĢ€€€€€The€importance€of€measurements...Belinda€Arbogast€(303)€236-2495Ģ€€€€€USGS€Reference€Materials€Project...Stephen€Wilson€(303)€236-2454ĢĢĢĢFOREWORDĢĢThis€WWW€document€describes€the€role€of€chemistry€in€issues€vital€to€ourĢeconomy,€health,€and€well-being.ĢĢWhen€we€are€analyzing€a€sample€of€the€Earth,€we€never€ask€if€a€specificĢelement€is€present.€Virtually€every€sample€of€the€Earth€contains€every€naturalĢelement€at€some€amount.€The€more€appropriate€questions€are:€€How€much€of€it€isĢpresent?€€€Is€there€enough€to€be€mined€profitably?€€In€the€environment,€is€itĢdangerous€at€this€level€or€in€this€form?€€And€after€we've€identified€the€issues€thatĢwe€need€to€solve€about€our€planet,€we€then€need€to€ask,€What€clues€can€we€findĢthat€will€give€us€the€answer?€ĢĢWe€will€show€you€how€many€geologic€problems€are€solved€using€routineĢanalyses€of€the€major€components€of€rocks.€We€will€also€show€you€the€complexityĢof€analyzing€trace€amounts€of€common€components€in€extremely€small€samples,Ģsuch€as€rare€samples€of€air€from€more€than€100€million€years€ago,€tiny€samples€ofĢore-forming€fluids€that€were€entombed€in€minerals€300€million€years€ago,€or€smallĢamounts€of€naturally-occurring€radioactive€isotopes€that€are€as€old€as€the€Earth.ĢBecause€some€elements€in€our€environment€are€hazardous€at€trace€levels,€theyĢmust€be€analyzed€down€to€those€low€levels.€The€impact€of€quality€control€onĢanalyses€will€also€be€discussed,€as€well€as€the€production€of€standard€referenceĢmaterials€that€are€distributed€internationally€to€Federal€and€privateĢlaboratories.ĢĢAs€the€primary€Federal€Earth-Science€Agency,€the€USGS€studies€and€providesĢsolutions€to€questions€concerning€our€planet,€assesses€the€mineral€resources€ofĢFederal€lands,€and€serves€as€a€repository€for€geochemical€data€generated€byĢnumerous€Federal€programs.€These€data€are€being€applied€to€new€economic€andĢenvironmental€concerns€and€provide€a€cost€effective€method€to€solve€geochemicalĢproblems,€often€with€no€impact€on€wilderness€or€fragile€refuges.ĢĢĢĢI.€€IntroductionĢQuestions€about€geology€-the€science€of€the€Earth-€can€be€difficult€to€answerĢbecause€many€times€we€can't€safely€get€close€enough€to€the€event.€€Even€if€weĢcan,€our€senses€are€not€sharp€enough€to€detect€everything€that€is€happening.€€TheĢEarth€is€relentless€in€its€course€of€change,€but€the€transformation€occurs€over€aĢvast€amount€of€time.€€Some€geologic€processes€can€take€a€million€years€or€more€toĢcomplete.€€We€know€that€today's€events€have€also€occurred€repeatedly€throughoutĢgeologic€time.€€To€understand€our€planet€Earth,€we€need€to€read€and€interpret€theĢpermanent€records€in€the€Earth's€crust€and€interior.€€These€records€are€the€key€toĢthe€future,€and€many€of€these€clues€are€preserved€in€the€chemistry€of€geologicĢsamples.ĢĢEverything€we€touch€in€our€daily€lives€is€made€up€of€elements.€€There€are€92Ģelements€that€occur€naturally,€and€in€most€cases,€the€human€senses€cannotĢrecognize€these€elements€when€they€are€present€in€a€compound.€€If,€for€example,Ģwe€could€always€recognize€what€something€is€made€of,€there€would€be€no€suchĢthing€as€"fool's€gold"€(a€natural€combination€or€iron€and€sulfur€called€pyrite).€ĢBecause€we€have€difficulty€identifying€these€relatively€pure€compounds,€it's€notĢsurprising€that€when€rock€or€soil€contains€only€a€very€small€amount€of€an€elementĢwe€are€incapable€of€recognizing€the€element's€presence.€ĢĢĢĢUsing€analytical€chemistry,€we€can€even€determine€trace€elements€(elementsĢpresent€at€very€low€levels)€at€the€parts€per€million€(ppm)€or€parts€per€billion€(ppb)Ģlevel.€€It's€difficult€to€comprehend€the€concentration€of€a€substance€at€this€low€aĢlevel.€€To€get€a€mental€picture,€imagine€an€average€3-bedroom€home.€€It€wouldĢtake€about€1€million€marbles€to€cover€the€floors€of€the€home.€€One€part€per€millionĢwould€be€represented€by€just€one€marble€among€all€the€other€marbles.€€For€thatĢsame€marble€to€represent€one€part€per€billion,€however,€it€would€take€20€footballĢfields€covered€with€marbles.ĢĢDifferent€elements€have€different€physical€properties.€These€propertiesĢdetermine€what€methods€can€be€used€to€analyze€each€element€(or€group€ofĢelements).€€The€methods€described€in€the€WWW€document€can€be€applied€toĢmany€different€geological€problems,€but€no€one€method€can€solve€every€problem.€ĢThe€analytical€methods€described€here€are€only€a€few€that€were€selected€to€showĢthe€role€of€chemistry€in€geology.ĢĢĢII.€Understanding€the€EarthĢIIa.€History€recorded€in€chemistryĢHow€old€is€the€Earth?ĢThe€question€of€when€the€Earth€was€formed€and€when€various€events€on€itĢoccurred€has€long€fascinated€humanity.€In€the€past,€various€estimates€of€the€age€ofĢthe€Earth€have€been€made€using€the€available€technology.€All€estimates€of€this€typeĢchanged€drastically€with€the€modern€application€of€radioactivity.ĢĢElements,€isotopes,€and€radioactivityĢĢMatter€is€made€up€of€atoms,€and€atoms€are€made€up€of€a€complex€array€ofĢsubatomic€particles.€Let's€consider€only€three€of€these€particles:€€protonsĢ(positively€charged),€neutrons€(no€charge),€and€electrons€(negatively€charged).ĢEvery€element€has€a€fixed€number€of€protons€that€cannot€be€changed€withoutĢcreating€a€different€element.€If,€for€example,€we€add€a€proton€to€an€atom€of€sulfur,Ģit€becomes€heavier€and€is€now€an€atom€of€chlorine.€If€we€change€the€number€ofĢneutrons€in€an€atom,€however,€it€has€almost€no€effect€on€the€chemical€propertiesĢand€outward€appearance€but€does€have€an€effect€on€the€atomic€mass.€It€can€alsoĢhave€an€extreme€effect€on€the€atomic€stability€of€the€element.€If€we€take€an€atom€ofĢpotassium€that€has€39€neutrons€in€it€and€add€one€more,€the€atom€now€becomesĢunstable€and€can€radioactively€decay.ĢĢEach€combination€of€an€element€with€a€different€number€of€neutrons€is€calledĢan€isotope.€Isotopes€that€are€radioactive€disintegrate€or€decay€in€a€predictable€wayĢand€at€a€specific€rate€to€make€other€isotopes.€The€radioactive€isotope€is€called€theĢparent,€and€the€isotope€formed€by€the€decay€is€called€the€daughter.€A€radioactiveĢisotope€decays€at€a€constant€rate€proportional€to€the€number€of€radioactive€atomsĢremaining.€A€simple€way€of€describing€the€speed€of€decay€is€to€see€the€time€itĢtakes€for€half€of€the€atoms€of€a€radioactive€parent€to€decay€and€form€the€daughterĢelement(s).€This€is€called€the€half€life.€€Various€events€(especially€melting€of€theĢrock)€will€cause€the€isotopes€in€a€rock€to€redistribute.€When€the€rock€solidifies€itĢcan€be€thought€of€as€starting€a€stopwatch.€By€determining€the€amount€of€theĢparent€and€daughter€isotopes€present€scientists€can€determine€when€the€stopwatchĢstarted.€ĢĢĢĢAs€an€example,€the€parent-daughter€system€used€to€determine€the€age€of€theĢEarth€is€the€uranium-lead€system.€The€decay€of€the€parent€uranium€isotopes€toĢdaughter€lead€isotopes€in€samples€of€the€Earth,€Moon,€and€meteorites€indicatesĢthat€all€the€planets€in€our€solar€system€formed€4.5€billion€years€ago.€ĢĢWhile€determining€the€age€of€the€Earth€is€intriguing,€radiometric€dating€hasĢrecently€been€useful€in€more€practical€issues€like€the€following:€€With€what€age€ofĢgranite€formation€are€ore€deposits€in€a€particular€region€associated?€€How€recentlyĢhas€a€fault€been€active,€and€is€it€likely€to€be€safe€to€build€near€it€now?€€How€oftenĢdoes€a€volcano€erupt€and€how€often€do€landslides€recur?€ĢĢĢ<€On€May€18,€1980€the€Cascade€volcano,€Mt.€St.€Helens,€erupted€exposivelyĢcausing€a€great€deal€of€destruction€and€a€number€of€deaths.€€>ĢĢĢĢĢBecause€different€isotopes€of€an€element€have€different€masses,€they€can€beĢviewed€as€an€arrangement€of€masses€in€a€spectrum.€An€instrument€that€separatesĢand€electronically€measures€a€spectra€of€atomic€masses€is€called€a€massĢspectrometer.€There€are€many€types€of€mass€spectrometers,€but€the€mostĢfrequently€used€in€earth-science€age€determinations€are€magnetic€sector€massĢspectrometers.€These€magnetic€spectrometers€operate€on€the€principle€that€if€youĢput€an€electric€charge€on€an€object€and€throw€it€into€a€magnetic€field,€the€object€sĢpath€will€form€a€circle.€The€radius€of€the€circle€will€depend€on€the€strength€of€theĢmagnetic€field€and€the€mass€of€the€charged€atom€divided€by€its€electric€charge.ĢThus,€if€you€have€a€purified€portion€of€an€element€from€a€sample€with€severalĢisotopes,€each€can€be€made,€in€sequence,€to€travel€the€same€circular€path€to€theĢdetector€by€varying€the€strength€of€the€magnetic€field.€Magnetic€sector€massĢspectrometers€consist€of€at€least€three€components€as€illustrated€at€the€bottom€ofĢpage€4.€€(1)€A€source€of€sample€ions,€(2)€a€magnetic€field,€and€(3)€a€detector.€ĢĢĢĢĢDigesting€rocksĢĢBut€how€do€you€take€a€rock€and€purify€a€portion€of€it€for€mass€spectrometry,Ģand€how€do€you€analyze€a€rock€sample€on€an€instrument€that€only€analyzesĢliquids?€€In€most€cases,€before€a€rock's€chemical€composition€can€be€determined,€itĢmust€pass€through€both€a€physical€and€a€chemical€preparation€to€free€theĢelement(s)€of€interest€from€the€rock€and€present€them€in€a€dissolved€or€liquidĢform.ĢĢInitially,€fist-size€pieces€of€rock€are€broken€down€to€pea-size€fragments€using€aĢcrusher€with€steel€jaws.€A€pulverizer€grinds€this€coarse€material€into€a€powder€asĢfine€as€flour.ĢĢNext,€the€powder€is€further€broken€down,€or€decomposed,€by€using€either€anĢacid€treatment€or€fusion.€During€this€chemical€decomposition,€the€weighed€sampleĢof€powdered€rock€releases€its€elements€into€solution.€ĢĢBecause€most€rocks€are€composed€of€a€combination€of€many€types€ofĢminerals,€each€having€different€chemical€and€physical€properties,€digestion€isĢaccomplished€by€using€a€combination€of€acids.€Most€commonly€used€is€a€mixtureĢof€hydrofluoric,€nitric,€hydrochloric,€and€perchloric€acids,€which€will€decompose€allĢbut€the€most€resistant€minerals.€The€acids€are€heated€with€the€sample€powder€inĢTeflon€containers,€on€a€hot€plate,€or€in€a€specially€designed€microwave€oven.ĢĢIn€the€fusion€technique,€a€powdered€inorganic€reagent€(known€as€a€flux)€isĢmixed€with€the€rock€powder€and€heated€above€the€melting€point€of€the€flux;€theĢmolten€flux€then€attacks€the€sample€and€decomposes€it€into€a€uniform€melt.€TheĢmelt€may€then€be€poured€into€a€mold€and€cooled€for€methods€that€require€aĢuniform€solid€such€as€X-ray€fluorescence€spectrometry€(discussed€in€GeologicĢprocesses€-€Volcanoes€section)€or€dissolved€in€a€diluted€acid€to€create€a€liquidĢsolution.€The€higher€temperatures€(500€to€1,200€C)€and€caustic€nature€of€the€moltenĢchemicals€used€for€fusions€increases€the€efficiency€of€the€decomposition€asĢcompared€to€acid€techniques€and€renders€most€minerals€soluble.€Each€form€ofĢsample€decomposition,€acid€or€flux,€has€its€advantages€and€disadvantages€thatĢmust€be€considered.€In€addition,€the€importance€of€safety€and€simplicity€must€notĢbe€ignored.ĢĢDisaster€from€spaceĢĢOne€of€the€mysteries€of€the€history€of€the€earth€is€the€layer€of€clay€that€wasĢdeposited€around€the€entire€globe€65€million€years€ago.€The€layer€marks€the€K-TĢboundary€the€end€of€the€Cretaceous€and€beginning€of€the€Tertiary€periods.€It€isĢbest€known€as€the€time€when€not€only€the€dinosaurs€but€nearly€half€of€all€life€formsĢbecame€extinct.€ĢĢĢĢAt€the€beginning€of€the€last€decade,€Nobel€Laureate€Luis€Alvarez€and€his€teamĢmembers€discovered€a€9€ppb€abundance€of€the€element€iridium€while€usingĢneutron€activation€analysis€to€study€1-cm-thick€samples€at€the€K-T€boundary€layer.€ĢThe€fact€that€the€high€level€of€iridium€coincided€exactly€with€the€classic€end€of€theĢCretaceous€mass€extinction€event€led€them€to€propose€a€theory€linking€these€twoĢobservations.€They€theorized€that€an€asteroid€between€6€and€14€km€in€diameterĢstruck€the€Earth,€and€the€impact€lofted€enormous€amounts€of€pulverized€targetĢmaterial€high€into€the€Earth€s€atmosphere.€They€speculated€that€this€dust-€size,Ģimpact€ejecta€caused€an€environmental€catastrophe.€€ĢĢĢĢAdditional€research€by€other€scientists€suggests€that€if€the€extraterrestrialĢobject€was€an€asteroid,€it€most€likely€impacted€the€Earth€at€a€velocity€of€50€timesĢthe€speed€of€sound€and€measured€15€km€in€diameter.€Because€asteroids€of€thisĢsize€are€very€few€in€number€in€our€solar€system,€the€object€could€also€have€been€aĢcomet,€most€likely€moving€even€faster,€possibly€170€times€the€speed€of€sound€butĢmeasuring€only€10€km€in€diameter.ĢĢTo€test€the€impact€theories,€we€have€applied€a€new€analytical€technique€calledĢlaser€ablation,€inductively€coupled€plasma,€quadrupole€mass€spectrometryĢ(LA-ICP-QMS).€To€allow€efficient,€rapid,€spatial€sampling,€a€laser€is€used.€TheĢtechnique€is€highly€sensitive€for€almost€all€elements.ĢĢAs€depicted€below,€the€energy€of€the€laser€is€focused€onto€a€spot€about€80Ģmicrometers€in€diameter€(slightly€more€than€the€diameter€of€a€human€hair)€toĢvaporize€and€sputter€material€from€small€zones€of€the€sample.€The€operatingĢcondition€of€the€laser€range€from€1€million€to€1€trillion€watts€per€square€centimeter.ĢThis€incredibly€high€energy€density€is€created€when€the€energy€is€packed€into€smallĢbursts€of€160€microseconds,€which€are€then€focused€with€a€lens€onto€a€very€smallĢspot.ĢĢĢThe€vapor€from€the€sample€is€then€carried€by€a€stream€of€argon€gas€into€aĢ7,000€C€argon€plasma€where€the€vapor€is€ionized.€These€ions€are€then€drawn€into€aĢquadrupole€mass€spectrometer€(QMS).€The€QMS€consists€of€two€sets€of€electricallyĢcharged,€machined€rods.€A€radio-frequency€signal€is€applied€to€both€sets€of€rods.ĢUnder€specific€operating€conditions,€one€unique,€mass-to-charge€ratio€of€ions€willĢbe€directed€down€the€opening€between€the€four€rods€and€exit€to€the€detector.€AllĢother€ions€will€be€lost.ĢĢĢĢThe€LA-ICP-MS€is€sensitive€for€all€the€platinum€group€elements€(PGEs)€thatĢwould€appear€from€an€asteroid€impact.€The€laser,€which€has€fine€samplingĢresolution,€was€used€to€sample€the€1-cm€layer€analyzed€by€Alvarez€and€coworkersĢbut€in€bands€only€0.25-mm€thick.€In€this€way,€we€were€able€to€sample€just€the€layerĢof€PGE-enriched€material€and€found€the€concentration€in€this€zone€to€be€nearly€1Ģppm,€a€factor€of€100€times€higher€than€that€previously€reported.€This€greaterĢconcentration€of€the€PGEs€gives€additional€support€to€the€theory€that€anĢextraterrestrial€body€collided€with€the€Earth€65€million€years€ago.€ĢĢIIb.€Geologic€processesĢĢVolcanoesĢĢVolcanoes€erupt€when€molten€rock€(magma)€deep€in€the€Earth€s€interiorĢmakes€its€way€to€the€surface.€On€average,€for€every€cubic€kilometer€of€magmaĢerupted€from€a€volcano,€3€to€10€cubic€kilometers€are€stored€beneath€the€surface€inĢshallow€reservoirs€called€magma€chambers.€ĢĢWe€can€see€what€these€magma€chambers€look€like€by€studying€ancientĢreservoirs€that€have€solidified€and€been€exposed€by€erosion.€One€of€these€is€HalfĢDome€in€Yosemite€National€Park.ĢĢĢĢĢĢUnder€certain€conditions,€however,€the€magma€and€surrounding€rocks€areĢblown€apart€by€the€release€of€volatiles,€resulting€in€a€dangerous€explosive€eruption,Ģas€happened€on€May€18,€1980€at€Mount€St.€Helens,€near€Portland,€Oregon.€WithĢonly€about€0.5€cubic€km€of€erupted€magma,€however,€this€was€by€no€meansĢconsidered€a€large€volcanic€eruption.€The€1991€eruption€of€the€Pinatubo€Volcano,Ģnear€Manila€in€the€Philippines,€was€approximately€14€times€larger,€involving€aboutĢ7€cubic€km€of€magma.€But€even€the€Pinatubo€eruption€is€relatively€small€comparedĢto€infrequent€giant€eruptions€of€volatile-€and€silica-rich€magma€that€have€occurredĢthroughout€the€history€of€the€Earth.€ĢĢ€ĢĢĢĢMajor-element€chemical€analysis€is€a€front-line€tool€in€the€study€of€volcanoesĢand€volcanic€hazards.€The€analysis€of€a€volcanic€rock€provides€a€fundamental€Ģcommon€ground€for€comparing€the€styles€and€violence€of€previous€eruptions€ofĢsimilar€composition.€During€the€first€half€of€the€20th€century,€these€analyses€wereĢperformed€exclusively€by€classical€wet€chemical€analyses€chemically€separatingĢeach€element€of€interest€from€the€other€elements€in€the€sample.€This€procedureĢwas€extremely€laborious.€A€good€analytical€chemist€could€analyze€only€a€couple€ofĢhundred€rocks€per€year€for€their€complete€major€element€chemistry.€U.S.ĢGeological€Survey€scientists€now€use€technology€called€X-ray€FluorescenceĢSpectrometry€(XRF)€to€perform€the€same€type€of€analyses.€ĢXRF€Spectrometry€starts€at€the€atomic€level.€Atoms€consist€of€protons€andĢneutrons€in€a€central€nucleus€with€electrons€in€different€orbitals€around€thatĢnucleus.€If€an€electron€from€an€inner€orbital€is€knocked€out,€the€vacancy€created€isĢfilled€by€an€electron€previously€residing€in€a€higher€orbit.€The€excess€energyĢresulting€from€this€transition€is€dissipated€as€an€X-ray€photon€with€a€characteristicĢwavelength.€In€X-ray€fluorescence€analyses,€the€electron€vacancies€are€created€byĢbombarding€the€sample€with€a€source€of€X-rays€or€gamma€rays€most€frequentlyĢfrom€an€X-ray€tube€or€a€radioactive€isotope.€By€detecting€the€characteristic€X-raysĢthat€are€fluoresced,€the€element€of€interest€is€shown€to€be€present€in€the€sample.ĢThe€more€abundant€the€X-rays€are,€the€more€of€that€element€is€present€in€theĢsample.€ĢĢBombarding€the€sample€with€X-radiation€does€not€require€a€liquid€sample.€InĢfact,€because€solid€samples€are€more€stable€than€liquids,€virtually€all€samplesĢpresented€to€X-ray€spectrometers€are€solids.€Furthermore,€there€is€almost€noĢpermanent€change€that€takes€place€in€a€solid€sample€analyzed€by€XRF,€allowing€itĢto€be€saved€and€reanalyzed.€This€is€especially€important€for€the€repeated€analysisĢof€the€same€calibration€standards€over€periods€of€years,€permitting€the€use€of€theĢsame€analysis€protocol.€Homogeneity€requirements€are€frequently€solved€byĢdissolving€a€portion€of€the€pulverized€sample€in€molten€flux€that€is€then€poured€intoĢa€mold€and€cooled€to€form€a€solid€glass€disc€with€a€precise,€flat,€analytical€surface.€ĢĢĢĢĢA€team€of€two€analysts,€using€this€method,€can€analyze€over€7,000€samples€aĢyear.€Because€so€many€more€analyses€are€now€available,€geologists€can€answerĢmore€difficult€types€of€questions€such€as€what€changes€are€happening€in€theĢmagma€chamber€during€an€eruptive€cycle.ĢĢAt€a€number€of€frequently€active€volcanoes,€such€as€Mount€St.€Helens€(whichĢhas€erupted€about€every€100€years),€a€thick€and€complex€sequence€of€volcanicĢrocks€has€been€deposited.€Geochemists€and€geologists€can€reconstruct€theĢeruptive€history€of€the€volcano€through€field€studies€and€analyses€of€these€rocks.ĢThey€conclude€that€the€eruptive€activity€at€Mount€St.€Helens€is€separated€by€longerĢperiods€of€repose.€Like€many€other€volcanoes,€there€are€systematic€changes€inĢmajor-€and€trace-element€composition€through€time.€The€1980€eruption€appears€toĢbe€at€the€end€of€a€chemical€cycle€that€began€about€500€years€ago.€ĢWith€this€information€we€can€predict€the€style,€frequency,€and€warning€signsĢof€future€eruptions.€Newly€erupted€lava,€pumice,€or€ash€may€then€be€evaluated€in€aĢhistorical€context.€In€some€instances,€XRF€analyses€can€be€rapidly€completed€inĢless€than€24€hours€by€express€delivery€of€the€samples€to€the€lab€and€electronicĢtransmission€of€data€back€to€the€volcano€being€examined.€This€is€something€thatĢwould€have€been€impossible€for€the€classic€chemist.ĢĢWhile€systematic€changes€in€overall€chemistry€contribute€a€great€deal€ofĢinformation€about€a€volcano,€there€is€still€a€desire€to€understand€more€about€whatĢhappens€deep€within€the€Earth€s€crust€how€the€magma€forms€and€what€triggers€theĢvolcano€into€eruption.€ĢApplication€of€instrumental€neutron€activation€analysisĢĢSome€of€our€understanding€of€the€source€of€molten€magma€has€beenĢobtained€by€analyzing€rocks€for€a€group€of€15€elements€called€the€rare-earthĢelements€(REE).€In€a€type€of€rock€called€basalt,€the€total€amount€of€all€the€REE€s€isĢoften€less€than€100€parts€per€million€(ppm).ĢĢOne€well€proven€analytical€technique€used€to€determine€the€concentrations€ofĢREE€in€rocks€and€minerals€is€instrumental€neutron€activation€analysis€(INAA).€In€thisĢtechnique,€a€rock€or€a€single€mineral€that€the€rock€contains€is€irradiated€using€aĢnuclear€reactor.€This€causes€the€elements€to€become€radioactive€and€to€emitĢgamma€rays€with€distinct€energies.€The€sample€is€then€placed€on€a€detector€thatĢmeasures€how€many€gamma-rays€of€these€energies€are€emitted.€The€number€ofĢdistinct€gamma€rays€emitted€is€proportional€to€the€abundance€of€that€particularĢelement.€ĢĢĢĢTo€understand€what€the€REE€can€tell€us€about€how€magmas€are€formed,Ģscientists€have€devgloped€mathematical€formulas.€These€formulas€suggest€thatĢwhen€certain€minerals€interact€with€molten€rock,€there€can€be€appreciable€effectsĢon€the€rock€s€REE€contents.€In€a€process€called€partial€melting,€for€example,€if€aĢsource€rock€contains€minerals€(such€as€garnet)€that€can€hold€high€concentrations€ofĢcertain€REE,€then€these€elements€tend€to€be€prevented€from€entering€the€moltenĢrock.€Because€Hawaiian€basalts€have€low€concentrations€of€the€heavier€REE,€andĢgarnet€has€high€concentrations€of€heavy€REE,€some€Earth€scientists€conclude€thatĢthe€magmas€have€formed€by€partial€melting€of€a€source€rock€that€contains€garnet,Ģand€the€garnet€held€back€the€heavy€REE.ĢĢThe€smallest€cluesĢĢTo€understand€more€about€the€causes€of€eruptions,€geologists€have€to€lookĢmore€closely€into€the€fine€details€of€the€solidified€magma€samples€to€find€a€recordĢof€the€conditions€before€and€during€eruption.€Mineral€crystals€within€magmas€varyĢin€composition€depending€on€the€surrounding€magma€and€the€temperature€atĢwhich€they€are€formed.ĢĢĢĢMineral€compositions€from€the€1991€eruption€of€Mt.€Pinatubo€indicate€thatĢlow-silica€magma€at€a€temperature€of€about€1,250€C€mixed€with€high-silica€magmaĢ(780€C)€just€before€the€eruption.€Based€on€this€information,€volcanic€rocksĢproduced€in€previous€eruptions€were€analyzed.€The€results€suggest€that€the€1991Ģeruption€is€the€latest€in€a€series€of€eruptions€that€were€triggered€by€the€mixing€ofĢmagmas.€Magma€mixing€has€also€triggered€eruptions€at€a€number€of€otherĢvolcanoes.€ĢĢShortly€after€World€War€II,€physicists€in€the€United€States,€England,€Germany,Ģand€Japan€began€to€perfect€a€new€analytical€instrument€called€the€electronĢmicroscope.€Instead€of€producing€a€visually€magnified€image,€this€new€instrumentĢaccelerated€and€focused€electrons€through€a€column€of€magnetic€lenses€onto€aĢsmall€spot€on€the€sample.€The€ability€to€magnify€objects€is€limited€by€the€energy€orĢwavelength€of€the€radiation€that€is€used€to€observe€the€object.€Because€theĢaccelerated€electrons€from€the€column€have€a€much€shorter€wavelength€than€light,Ģit€is€possible€to€produce€images€at€much€higher€magnifications€than€can€beĢobtained€using€an€optical€microscope.€Today,€the€most€powerful€electronĢmicroscopes€can€produce€images€at€magnifications€as€high€as€1€million€times.ĢWhen€electrons€are€accelerated€into€an€object,€they€interact€with€the€atoms€inĢthat€object€and€produce€three€important€types€of€radiation:€(1)€X-rays€(formed€in€aĢmanner€similar€to€the€way€characteristic€X-rays€are€produced€in€XRF€(see€page€9)),Ģ(2)€the€secondary€electrons€that€are€used€to€see€the€sample,€and€(3)Ģback-scattered€electrons,€which€are€bounced€back€as€a€function€of€the€mass€of€theĢsample.ĢĢIn€the€1950€s,€the€French€physicists,€Castaing€and€Guinier,€developed€anĢinstrument€based€on€the€characteristic€X-rays€produced€by€the€electronĢbombardment€of€the€sample.€This€instrument€can€measure€the€number€of€X-raysĢemitted€from€the€small€spot€irradiated€on€the€sample.€By€counting€the€X-raysĢproduced,€Castaing€determined€the€chemical€composition€of€a€portion€of€a€sampleĢno€larger€than€the€size€of€a€human€blood€cell.€This€new€instrument€was€called€theĢelectron€microprobe€(EMP).ĢĢDuring€the€same€period€of€time,€another€instrument€was€brought€intoĢproduction€the€Scanning€Electron€Microscope€(SEM).€Like€the€electron€microscope,Ģit€uses€the€secondary€electrons€created€from€the€sample€s€surface€to€record€anĢenlarged€image€of€the€object.€Its€principal€advantage€is€that€it€deflects€the€electronĢbeam€and€scans€it€back€and€forth€over€the€sample€surface€(called€rastering)€in€aĢpattern€similar€to€that€in€which€wallpaper€covers€a€wall.€ĢĢĢĢThe€secondary€electrons€are€continuously€detected,€and€the€signal€is€directedĢto€a€television€monitor€where€the€image€is€displayed.€Zooming€in€or€backing€out€byĢchanging€the€size€of€the€raster€area€(hence€changing€the€magnification),€theĢscientist€can€use€the€enlarged€image€to€aim€the€scanning€electron€microscope.€AtĢthe€same€time,€X-rays€characteristic€of€the€composition€are€generated.€The€figureĢon€the€bottom€of€page€12€illustrates€the€image€created€by€using€an€X-ray€analyzerĢto€map€the€calcium€content€of€a€0.02-inch€portion€of€a€crystal€of€feldspar€from€theĢ1991€Mt.€Pinatubo€eruption.€ĢĢĢĢAnalyzing€a€single€particle€of€smokeĢĢBecause€of€their€similarities,€EMPs€and€SEMs€overlap€in€their€capabilities.€TheĢmodern€EMP€has€become€a€true€hybrid€that€combines€the€viewing€capability€of€theĢSEM€with€the€analytical€power€of€the€electron€microprobe.€Both€EMPs€and€SEMsĢare€capable€of€obtaining€images€at€magnifications€over€100,000€times.€TheseĢinstruments€can€see€and€then€analyze€something€that€wouldn't€show€up€with€aĢlight€microscope,€such€as€the€following€single€particle€of€volcano€smoke€in€thisĢpicture.€ĢĢĢAnalytical€chemistry€in€the€search€for€ore€depositsĢĢAnalytical€chemistry€plays€a€key€role€in€our€continuing€quest€to€understandĢhow€ore€deposits€form€and€in€the€practical€exploration€for€ore€deposits.€If€you€pickĢup€an€ordinary€rock€that€builds€the€crust€of€the€Earth€and€determine€its€chemicalĢcomposition,€for€every€billion€atoms,€1€to€10,000€atoms€will€be€metallic€elementsĢsuch€as€gold,€silver,€platinum,€mercury,€copper,€cobalt,€nickel,€chromium,€lead,Ģzinc,€molybdenum,€tin,€and€tungsten.€Natural€processes€in€the€Earth€s€crust€haveĢthe€remarkable€ability€to€concentrate€and€purify€certain€rare€metallic€elements€toĢform€unusual€deposits€of€minerals€that€contain€1,000€to€10,000€times€the€amountsĢfound€in€ordinary€rocks.€ĢĢWith€today€s€modern€mining€and€extraction€technology,€it€has€becomeĢpossible€to€mine€very€low-grade€deposits.€For€example,€gold€can€be€economicallyĢrecovered€from€rocks€that€contain€less€than€one€tenth€of€an€ounce€of€gold€per€tonĢof€rock.€But€gold€continues€to€be€expensive€because€of€the€cost€in€locating€theĢdeposit,€mining€the€rock,€and€extracting€the€small€amount€of€gold€in€each€ton€ofĢrock.€All€of€the€inorganic€raw€materials€used€to€manufacture€the€products€of€todayĢs€technological€society€have€to€be€either€mined€or€recycled.€ĢĢAlmost€every€process€that€takes€place€in€the€Earth€s€crust,€whether€from€theĢaction€of€molten€rock,€heat€and€pressure€at€depth,€hot€springs€or€steam,€runningĢwater,€weather,€or€biological€activity€can€contribute€to€the€formation€of€an€oreĢdeposit.€Geologists€use€the€principles€of€chemistry€to€try€to€understand€how€theseĢprocesses€scavenge€elements€from€ordinary€rock,€transport€them,€and€concentrateĢthem€to€form€an€ore€deposit.€Geologists€have€developed€models€that€describe€theĢphysical€characteristics€and€chemical€composition€of€each€ore€deposit€type€andĢhow€they€relate€to€the€geologic€environment€in€which€they€form€similar€to€the€wayĢbiologists€describe€how€an€organism€fits€into€a€particular€environmental€niche.ĢĢĢIn€North€America€and€many€other€parts€of€the€world,€almost€all€of€the€rich€oreĢdeposits€exposed€at€the€surface€have€already€been€discovered.€Most€of€the€ore€yetĢto€be€found€is€not€visible€to€the€human€eye.€Therefore,€geologists€have€had€toĢimprove€their€understanding€and€develop€more€sophisticated€ways€to€detect€whereĢore€deposits€can€occur.€ĢĢTwo€main€approaches€are€used€to€detect€deposits€hidden€below€the€surface.ĢOne€uses€the€ore-deposit€model,€and€the€other€is€based€on€the€detection€of€aĢdispersion€halo€(discussed€on€page€23)€that€extends€for€some€distance€from€theĢdeposit.€ĢĢThe€following€analogy€shows€how€geologists€use€ore-deposit€models.€If€all€butĢthe€tip€of€the€tail€of€an€elephant€was€buried€by€a€landslide,€a€biologist€couldĢrecognize€from€the€skin,€hair,€and€shape€of€the€appendage€that€the€tail€belonged€toĢa€mammal.€With€advanced€testing€of€tissue€samples,€a€biologist€could€prove€thatĢthe€tail€belongs€to€an€elephant€and€could€easily€predict€that€the€body€should€beĢburied€about€1€meter€below€the€tip€of€the€tail.€ĢĢMost€ore-deposit€models€are€not€as€advanced€as€biologists€models€forĢelephants,€but€a€few€are€nearly€so.€Several€copper€and€molybdenum€porphyryĢdeposits,€located€as€deep€as€2,000€to€4,000€feet€below€the€surface,€have€beenĢdiscovered€based€on€small€surface€exposures€measuring€several€feet€across.€TheseĢexposures€were€of€breccia€pipes€(vertical€pipe-shaped€bodies€of€pulverized€rock),Ģwhich€are€known€to€extend€thousands€of€feet€above€the€main€body€of€porphyryĢdeposits.€Because€not€all€porphyries€contain€deposits€of€economic€metals,Ģgeologists€can€collect€and€analyze€field€samples€to€determine€what€metals€theĢporphry€will€contain,€and€if€it€is€worth€drilling.€ĢĢĢĢAnalysis€of€fossil€fluids€and€gases€from€tiny€time€capsulesĢĢA€great€many€ore-deposit€models€are€tied€to€the€cause€of€formation€of€theĢdeposit.€Questions€about€the€environmental€conditions€related€to€formation€of€theĢdeposit€are€temperature,€pressure,€source€of€the€metals,€and€composition€of€anyĢfluids€and€gases€that€transported€and€formed€the€ore€or€associated€minerals.ĢĢMany€crystals€in€the€Earth€s€crust€have€formed€in€some€kind€of€fluid.€SmallĢquantities€of€the€fluid€that€surrounded€the€crystals€during€growth€are€commonlyĢtrapped€as€tiny€fluid€inclusions€within€these€crystals.€In€many€cases,€these€fluidĢinclusions€are€less€than€0.1€mm€but€record€important€information€about€theĢconditions€when€the€ore€was€being€formed.€ĢĢĢĢCurrent€understanding€of€movements€within€continents€reveals€thatĢthroughout€the€Earth€s€history€periods€of€large-scale€fluid€movements€occurred€inĢthe€Earth€s€crust.€Some€of€these€fluid€migrations€resulted€in€the€deposition€ofĢmetallic€ore€deposits€and€accumulations€of€oil€and€gas.€ĢĢCharacteristics€of€fluid€inclusions€are€extremely€variable.€In€the€simplest€case,Ģwhen€fluid€inclusions€cool€from€the€elevated€temperature€at€which€they€formed,€theĢliquid€shrinks€and€separates€into€a€liquid€and€a€vapor€bubble.€DetailedĢmicrothermometric€studies€give€a€reasonable€estimate€of€the€temperature€at€whichĢthe€mineral€was€formed.€Studies€of€this€type€reveal€that€the€inclusions€wereĢtrapped€at€temperatures€from€less€than€50€C€to€over€600€C€and€at€pressuresĢequivalent€to€what€is€experienced€at€the€Earth€s€surface€and€ranging€to€what€wouldĢbe€found€several€kilometers€deep.€ĢĢBecause€of€the€extremely€small€size€of€so€many€fluid€inclusions,€determiningĢthe€composition€of€the€trapped€fluids€is€difficult.€First,€the€total€amount€of€dissolvedĢsolids€is€determined€by€observing€with€a€microscope€the€freezing/melting€points€ofĢthe€inclusions.€The€sample€is€then€crushed€and€rinsed€with€water.€This€water€isĢrecovered€and€analyzed€by€using€a€sensitive€analytical€technique€to€determine€theĢratios€of€the€elements€contributed€by€the€trapped€fluid.€These€ratios€are€used€toĢcalculate€the€composition€of€the€fluid.€The€compositions€range€from€aqueousĢsolutions€with€salt€content€similar€to€rainwater€to€fluids€with€dissolved€solidĢconcentrations€of€over€60€percent€nearly€20€times€the€amount€found€in€seawater.ĢĢĢAnalytical€data€on€fluid€inclusions€are€needed€to€understand€the€chemical€andĢphysical€processes€involved€in€the€formation€of€economic€mineral€deposits.€TheseĢdata€are€also€critical€in€understanding€modern€mineral-deposit€models,€whichĢpromote€cost-effective€mineral€exploration€vital€to€our€healthy€industrialĢeconomy.ĢĢMost€fluid€inclusions€contain€dissolved€gases,€and€in€some€environments€theĢinclusions€consist€entirely€of€gases.€Recently,€the€USGS€has€designed€a€gasĢquadrupole€mass€spectrometer€(QMS)€(see€page€6€for€a€description€of€QMSs)€thatĢwill€analyze€the€amounts€and€chemical€identity€of€gas€ions€in€small€gas€samples.ĢThis€instrument€is€extremely€sensitive€(8€parts€per€billion€detection)€and€capable€ofĢmillisecond€speeds€of€analysis€important€for€gas€bubbles€as€small€as€1/100€of€aĢmillimeter€in€diameter.ĢĢThe€QMS€is€used€extensively€to€study€ore-€deposit€models€as€well€asĢenvironmental€and€geologic€hazards.€Examples€include:€€identifying€carbon€dioxideĢas€the€responsible€gas€at€the€Lake€Nyos,€Cameroon€disaster€where€2,000€peopleĢsuffocated€in€1986;€tracking€atmospheric€gases€from€bubbles€in€climate-€study€iceĢcores€of€Greenland€and€Antarctica;€tracing€dispersal€of€smokestack€emissions€andĢgases€of€geothermal€energy€wells€and€springs.€ĢĢĢĢIIc.€EnvironmentĢĢGlobal€change€in€the€geologic€pastĢĢAn€exciting€new€application€of€the€QMS€instrument€uses€a€high-energy€laserĢfired€through€a€modified€microscope€to€open€individual€gas€inclusions€in€ice.€IceĢfrom€Greenland€and€Antarctica€contain€atmospheric€gases€that€were€captured€inĢsnow€as€it€formed.€The€gases€were€retained€as€the€snow€turned€into€ice€andĢformed€bubbles.€Analysis€of€these€bubbles€provides€detailed€information€on€theĢpast€composition€of€the€atmosphere.€ĢĢSea-level€changes,€changes€in€solar€activity,€and,€according€to€someĢastrophysicists,€even€the€signals€from€distant€supernovas,€are€also€recorded€in€theĢice.€Compiling€and€studying€this€record€helps€us€to€evaluate€current€changes€in€theĢatmosphere€and€to€predict€future€trends.€Ice-core€studies€provide€valuableĢinformation€about€the€levels€of€human€pollution,€past€climate€patterns,€sources€ofĢmoisture,€the€altitude€of€the€ice€when€it€formed,€frequency€and€magnitude€ofĢnatural€events,€and€biological€activity€at€the€ocean€surface.€ĢĢAir€bubbles,€amber,€and€dinosaursĢĢAges€of€ice€samples€found€on€the€Earth€cover€a€span€approaching€200,000Ģyears.€But€how€can€we€tell€what€the€Earth€s€atmosphere€was€like€before€that?ĢRecently,€USGS€scientists€have€used€a€gas€QMS€to€determine€the€oxygen€level€ofĢancient€samples€of€Earth€s€atmosphere€from€a€most€unlikely€place€amber.€TheĢfossilized€resin€of€conifer€trees,€amber€is€interesting€to€scientists€as€a€medium€thatĢtraps€insects,€small€animals,€and€plants,€preserving€them€through€geologic€time€forĢfuture€study.€ĢĢ€ĢĢThe€recent€extraction€by€scientists,€of€ancient€DNA€from€organisms€entombedĢin€amber€much€like€in€the€science-fiction€novel€and€movie,€Jurassic€Park€is€anĢexample€of€why€scientists€are€intensely€interested€in€amber.€Minute€bubbles€of€Ģancient€air€trapped€by€successive€flows€of€tree€resin€during€the€life€of€the€tree€areĢpreserved€in€the€amber.€Analyses€of€the€gases€in€these€bubbles€show€that€theĢearth€s€atmosphere,€67€million€years€ago,€contained€nearly€35€percent€oxygenĢcompared€to€present€levels€of€21€percent.€Results€are€based€upon€more€than€300Ģanalyses€by€USGS€scientists€of€Cretaceous,€Tertiary,€and€recent-age€amber€from€16Ģworld€sites.€The€oldest€amber€in€this€study€is€about€130€million€years€old.€ĢĢĢĢThe€consequences€of€an€elevated€oxygen€level€during€Cretaceous€time€areĢspeculative.€Did€the€higher€oxygen€support€the€now€extinct€dinosaurs?€TheirĢdemise€was€gradual€in€the€transition€from€late€Cretaceous€to€early€Tertiary€times,Ģas€was€the€decrease€in€oxygen€content€of€the€atmosphere.€ĢĢĢĢRecent€methane€emissions€from€Gulf€Coast€marshesĢĢThe€Earth€s€atmosphere€is€still€changing.€Natural€environmental€processesĢ(geological,€biological,€and€geochemical)€produce€carbon€dioxide€(CO2)€andĢmethane€(CH4).€These€gases,€along€with€water€vapor,€are€responsible€for€trappingĢheat€at€the€Earth€s€surface.€ĢĢBecause€biological€processes€are€responsible€for€the€production€of€methane€inĢenvironments€where€organic€matter€ferments,€wetlands€(swamps,€bogs,€etc.)€wereĢpreviously€the€principal€source€of€methane.€Now,€however,€the€combination€of€riceĢcultivation€and€cattle€raising€have€taken€over€as€the€principal€contributor.€Studies€ofĢmethane€sources€help€us€to€understand€their€relative€contributions€and€the€factorsĢthat€control€the€methane€production€and€release€to€the€atmosphere.€ĢĢThe€studies€show€that€when€coastal€wetlands€are€flooded€by€sea-level€rise,Ģsalt€marshes€are€inundated,€up-slope€brackish€marshes€become€saltier,€and€someĢfresh€marshes€near€the€coast€become€brackish.€Consequently,€total€methaneĢemissions€decrease€because€salt€marshes€do€not€produce€as€much€methane€asĢfresh€marshes.€ĢĢĢĢUSGS€studies€of€methane€in€Gulf€Coast€Louisiana€indicate€that€brackishĢmarshes€emit€between€one-fourth€and€one-half€the€methane€of€the€fresh€marshesĢthey€replace€during€sea-level€rise.€The€results€of€these€local€measurements€inĢLouisiana€can€be€used€to€project€the€world-wide€effects€of€sea-level€rise€onĢmethane€emissions.€By€the€year€2050,€projected€world-wide,€sea-level€rise€willĢreplace€50€percent€of€coastal€fresh-water€marshes€with€brackish€water€marshes.ĢThis€will€reduce€the€world€s€methane€emissions€by€2€percent.€ĢĢIId.€PollutionĢAcid€rain€steals€our€heritageĢĢIn€addition€to€affecting€people,€plants,€and€wildlife,€air€pollution€also€affectsĢrocks€and€soils.€One€of€the€problems€it€causes€is€the€degradation€of€buildings€andĢmonuments,€especially€those€built€out€of€limestone€or€marble.€These€rock€types,Ģboth€almost€pure€calcite€(calcium€carbonate),€are€commonly€used€throughout€theĢworld€as€a€building€stone.ĢĢĢĢStudies€to€determine€damage€caused€by€air€pollution€have€pointed€to€changesĢin€the€acidity€of€the€air€and€rain.€In€fact,€the€term€acid€rain€is€now€commonly€usedĢin€the€media€as€well€as€scientific€studies.€Acid€rain€affects€carbonate€stoneĢbuildings€and€monuments€in€two€ways.€The€first€is€by€dry€deposition€of€sulfurĢdioxide€gas,€increasingly€contributed€to€the€atmosphere€by€the€combustion€ofĢfossil€fuels.€The€gas€reacts€with€calcium-carbonate€building€stone€to€form€calciumĢsulfate€(gypsum).€As€gypsum€forms€on€the€surfaces€of€the€stone,€it€traps€particulateĢmatter,€forming€a€blackened€crust.€The€effect€of€this€process€is€illustrated€in€theĢfigure€on€this€page.€ĢĢThe€second€effect€of€acid€rain€is€wet€deposition.€Natural€rain€water€is€a€weakĢcarbonic€acid€solution€and€all€carbonate-stone€surfaces€that€are€washed€byĢrainwater€are€subject€to€gradual€erosion.€This€erosion€is€accelerated,€however,€byĢthe€increased€acidity€of€rain€in€the€eastern€United€States,€which€is€often€10€timesĢgreater€than€in€areas€where€acidic€pollutants€are€absent.€ĢĢCurrent€research€on€acid€rain€is€directed€at€defining€the€degree€of€stoneĢdamage€due€to€both€dry€and€wet€deposition.€Scientists€are€measuring€the€effectsĢof€acid€rain€on€historic€stone€buildings€and€monuments€across€the€country.€TheyĢare€exposing€samples€of€marble€and€limestone€to€weathering€at€specific€field€sitesĢand€simulating€depositional€processes€under€highly€controlled€laboratoryĢconditions.€ĢThe€effects€of€both€dry€and€wet€deposition€are€evaluated€by€the€chemicalĢanalyses€of€the€stone€surfaces€before€and€after€exposure€and€of€rain€run-offĢsolutions€collected€from€test€slabs.€ĢĢRecent€research€by€the€USGS€and€other€agencies€conducted€under€theĢNational€Acid€Precipitation€Assessment€Program€has€shown€that€test€samples€ofĢmarble€erode€15€to€30€micrometers€per€year,€while€limestone€(which€isĢless€compact€than€marble)€erodes€from€25€to€45€micrometers€per€year.€(TheseĢmeasurements€are€slightly€less€than€those€of€the€diameter€of€a€human€hair).ĢApproximately€20€percent€of€this€erosion€is€caused€by€acid€rain.€The€remaining€80Ģpercent€is€the€result€of€the€natural€solubility€of€the€stone€in€rain€water.€Because€theĢeffects€of€acid€rain€only€develop€over€an€extended€period€of€time,€high-precisionĢanalytical€chemistry€plays€a€central€role€in€measuring€these€effects.€€ĢĢThe€chemistry€of€mine€drainageĢĢMine€drainage€is€water€that€drains€from€mines.€The€water€can€be€of€the€sameĢquality€as€drinking€water,€or€it€can€be€very€acidic€and€laden€with€highĢconcentrations€of€toxic,€heavy€metals.€In€general,€the€more€acidic€the€water€is,€theĢpoorer€the€water€quality.€ĢĢBecause€the€chemistry€of€water€samples€can€rapidly€change€if€they€areĢremoved€from€the€natural€site,€many€measurements€are€made€in€the€field.€One€ofĢthe€first€of€these€field€measurements€is€for€acidity,€which€is€read€by€a€meter€andĢreported€as€the€pH€of€the€sample.€Water€with€a€pH€of€2€has€a€high€concentration€ofĢhydrogen€ions€and€is€acidic,€whereas€water€with€a€pH€of€7€is€neutral.€A€study€ofĢmine€drainage€in€Colorado,€for€example,€shows€that€the€pH€of€mine€waters€rangesĢfrom€a€low€of€1.8€to€a€high€of€8.€ĢĢA€companion€field€measurement€made€on€mine€water€is€for€specificĢconductance.€This€property€of€water€measures€the€electrical€conductivityĢassociated€with€a€water€sample€and€is€useful€as€a€quick€estimate€of€total€dissolvedĢsolids.€A€low€number€from€10€to€about€200€microsiemens/centimeter€(the€unit€ofĢspecific€conductance€measurements)€could€be€considered€to€be€drinking-waterĢquality.€Specific€conductance€measurement€of€mine€waters€in€the€Colorado€studyĢrange€from€100€to€38,000€microsiemens/centimeter.ĢĢThe€full€characterization€of€mine€water€requires€a€number€of€otherĢinstrumental€and€analytical€measurements€that€are€carried€out€using€both€mobileĢand€laboratory€facilities.€Three€main,€instrumental,€analytical€techniques€are€used€toĢcomplete€the€characterization€of€mine-water€samples.€These€techniques€are:€€ionĢchromatography€(IC),€which€is€used€to€determine€the€concentration€of€fluoride,Ģchloride,€nitrate,€and€sulfate€in€aqueous€samples;€ICP-AES€(discussed€on€page€27),Ģwhich€determines€the€concentration€of€major€and€trace€elements;€and€liquidĢICP-QMS€(related€to€LA-ICP-QMS€discussed€on€pages€5€and€6),€which€is€used€toĢdetermine€elements€below€the€ppm€level.ĢĢWhy€is€it€so€important€to€characterize€mine€drainage?€Because€mine-€drainageĢwater€almost€always€flows€into€a€stream€where€it€can€dramatically€affect€theĢaquatic€organisms€and€the€quality€of€the€water€received€by€downstreamĢcommunities.€To€successfully€reduce€the€effect€of€the€toxic€elements,€theirĢabundances€must€be€known.ĢĢĢĢFrom€the€analytical€chemistry€of€mine€drainage,€scientists€have€concluded€thatĢthe€major€cause€of€high€acidity€of€the€water€is€the€bacterially€catalyzed€oxidation€ofĢthe€mineral€pyrite.€This€acidity€stimulates€the€dissolution€of€many€other€sulfideĢminerals,€resulting€in€the€high€concentration€of€metals€such€as€copper€and€zinc.ĢĢĢWhile€it€is€difficult€or€impossible€to€stop€mine€drainage,€it€might€be€possible€toĢcut€back€the€rate€of€the€introduction€of€toxic€elements€into€the€environment.€ThisĢcan€be€done€by€hindering€the€bacteria€that€speed€up€the€oxidation€of€the€pyrite€orĢby€neutralizing€the€drainage€and€extracting€toxic€elements.€Recent€studies€haveĢshown€that€wetlands€can€concentrate€heavy€metals€from€mine€drainage.ĢConstructed€wetlands€could,€therefore,€be€used€to€accumulate€the€pollution€fromĢmine€drainage.€By€analytical€monitoring€of€the€toxic,€metal€build-up€in€theseĢwetlands€we€can€avoid€any€impact€on€the€wildlife€that€might€try€to€live€there.€ĢĢIIe.€Pollution€PreventionĢĢCleaning€up€coal€burningĢĢWhile€hundreds€of€abandoned€mines€across€the€country€are€releasingĢpollutants,€active€mines€can€also€produce€pollutants.€Among€the€best€examples€ofĢair€and€water€pollution€control€are€advances€in€coal€technology.€For€years€coal€hasĢbeen€a€major€source€of€both€energy€and€pollution€in€the€United€States.€Supplies€ofĢnatural€gas€and€petroleum€are€dwindling.€Alternative€energy€sources€are€notĢexpected€to€contribute€significantly€to€the€energy€needs€of€the€United€States€in€theĢnear€future.€Coal€will€continue€to€play€an€important€role€for€energy€productionĢthrough€the€first€half€of€the€21st€century.ĢĢSignificant€improvements€in€coal€processing€and€burning€in€modern€powerĢplants€have€dramatically€reduced€pollution.€The€process€has€been€improved€inĢthree€ways.€First,€sophisticated€equipment€has€significantly€reduced€fly€ash€andĢsoot€compared€to€the€equipment€used€many€years€ago;€other€specializedĢequipment€greatly€reduces€sulfur-dioxide€emissions.€ĢĢĢĢA€second€way€of€reducing€coal€pollution€is€by€selective€mining€of€low-ash€andĢlow-sulfur€coals€that€pollute€less.€Detailed€chemical€analyses€of€coal€prior€to€miningĢis€required€to€determine€the€concentrations€of€ash,€sulfur,€and€other€toxicĢelements.€A€new€multielement€analytical€technique€that€introduces€the€sample€inĢliquid€form€to€an€inductively€coupled€plasma€quadrupole€mass€spectrometerĢ(ICP-QMS)€is€proving€very€useful€for€this€purpose.€This€technique€can€determineĢover€70€elements€at€the€ppm€to€ppb€levels.€To€analyze€coal€by€this€method,€it€mustĢfirst€be€converted€to€ash,€fused€with€a€flux,€and€dissolved.€The€solution€is€thenĢsprayed€into€the€7,000€C€thermal€environment€of€an€argon€plasma€where€it€isĢionized.€The€resulting€charged€atomic€particles€are€drawn€into€a€high€vacuumĢportion€of€the€instrument€where€a€quadrupole€mass€spectrometer€(shown€inĢDisaster€from€space€section)€separates€and€counts€the€number€of€atoms€for€eachĢdifferent€mass.€ĢĢDetailed€mapping€of€trace€elements€in€a€coal€seam€may€be€required€to€locateĢlow-polluting€coal€resources.€The€major€drawback€to€selective€mining€is€that€onlyĢsmall€quantities€of€clean€coals€exist,€and€those€that€can€be€found€may€be€too€farĢfrom€power€plants€or€too€deep€to€be€economically€recovered.€ĢĢĢĢCoal€cleaning€is€the€third€method€for€reducing€pollution.€Sulfur€minerals€suchĢas€pyrite€can€be€removed€by€using€various€techniques.€Chemical€analysis€of€theĢcoal€and€identification€of€mineral€inclusions€determines€what€cleaning€procedureĢwill€be€most€effective.€This€requires€looking€at€the€coal€under€high-€powerĢmicroscopes€or€performing€tests€that€separate€mineral€and€coal€species€by€usingĢcomplex€physical€and€chemical€techniques.€Understanding€the€chemistry€andĢmineralogy€of€coals€has€contributed€significantly€to€the€progress€that€has€beenĢmade€in€recent€years€toward€the€prevention€of€coal-burning€pollution.ĢĢĢ€For€additional€information€on€environmental€geochemistry€order€a€paper€copyĢof€Understanding€Our€Fragile€Environment€USGS€Circular€1105€a€publication€inĢthe€Public€Issues€in€Earth€Science€Series.€ĢĢĢIII.€Mapping€the€Chemistry€of€the€Earth's€SurfaceĢĢIIa.€Assessment€of€public€lands€ĢĢMapping€stream€sediments€for€resource€explorationĢĢThe€successes€of€the€old-time€and€latter-day€prospectors€have€diminished€theĢlikelihood€for€the€discovery€of€additional€mineral€resources€on€the€surface€of€ourĢplanet.€Yet€our€national€and€global€dependence€on€mineral€resources€continues€toĢgrow€unabatedly,€and€recycling€can€only€provide€a€fraction€of€our€needs.€ByĢnecessity,€today€s€search€for€the€many€minerals€vital€to€society€is€focused€on€oreĢdeposits€that€lie€beneath€the€Earth€s€surface.€ĢĢEarlier€in€this€Circular€(see€page€15),€we€discussed€the€use€of€models€to€locateĢore€deposits.€Another€way€of€locating€mineral€resources€is€by€identifying€element-Ģdispersion€halos.€€Dispersion€halos€are€abnormal€levels€of€the€metals€that€developĢaround€deposits.€This€halo€can€extend€for€long€distances€from€the€deposit€and,Ģonce€recognized,€can€be€used€to€trace€down€the€source.€The€most€familiar€exampleĢof€a€halo€is€the€dispersion€of€gold€nuggets€in€drainages€downstream€from€goldĢmother€lodes.€ĢĢUsing€today€s€technology,€collected€stream-sediment€samples€may€beĢprocessed€and€analyzed€for€as€many€as€40€elements,€giving€an€indication€of€veryĢfaint€halos€at€some€distance€from€a€variety€of€deposit€types.€If€elements€ofĢeconomic€interest,€such€as€gold,€silver,€copper,€lead,€or€zinc,€are€present,€they€willĢbe€revealed€in€these€analyses.€This€process€is€repeated€for€many€samples€until€theĢentire€study€area€is€covered.€ĢĢĢĢĢKeeping€track€of€the€resources€of€our€countryĢĢCongress€has€mandated€the€USGS€to€assess€the€mineral-resource€potential€ofĢpublic€lands,€especially€those€lands€set€aside€as€wilderness€or€proposedĢwilderness.€These€assessments€provide€an€inventory€of€mineral€resources€forĢfuture€generations.€In€1964,€the€Wilderness€Act€was€passed,€and€a€20-year€programĢto€assess€the€mineral€resources€of€U.S.€Forest€Service€wilderness€areas€began.€AĢlarge€amount€of€this€work€involved€the€analysis€of€stream€sediments€to€determineĢthe€presence€or€absence€of€halos.€Subsequent€laws€have€required€mineral-resourceĢassessments€on€additional€public€lands.€The€USGS€also€works€with€the€Bureau€ofĢIndian€Affairs€and€individual€tribes€to€assess€the€mineral€resources€on€Indian€lands.ĢĢĢBy€relating€ore-deposit€models€and€geochemical€data€to€geologic€observationsĢand€plate€tectonic€theory,€geologists€can€predict€what€types€of€ore€deposits€may€beĢfound€in€a€given€geographic€area.€The€USGS€supplies€this€information€to€the€publicĢand€to€other€government€agencies.€Assessments€are€published€by€the€USGS€forĢuse€by€land-use€planners,€Federal,€state,€and€local€government€agencies,Ģenvironmentalists,€and€private€individuals.€Many€maps,€such€as€the€map€of€lead€inĢstream€sediments€of€Colorado€shown€on€page€34,€are€useful€for€both€resourceĢevaluations€and€environmental€assessments.ĢĢĢĢIt€is€important€to€weigh€the€mineral-resource€potential€of€a€tract€of€landĢagainst€other€potential€uses€such€as€water€resources,€grazing,€forestry,€recreation,Ģtourism,€and€scenic€value.€Chemistry€plays€a€vital€role€in€this€assessment€process.ĢĢĢMobile€laboratoriesĢĢĢĢLooking€for€halos€of€mineralized€areas€or€testing€for€pollution€is€like€playingĢthe€game€of€hide-and-seek.€The€target€can€be€found€more€easily€if€you€are€given€Ģhotter€or€colder€clues.€To€provide€these€clues,€analysts€in€mobile€laboratoriesĢperform€chemical€analyses€for€geologists€in€the€field.€As€a€result,€samples€can€beĢevaluated€quickly.€The€use€of€mobile€laboratories€by€the€USGS€dates€back€to€theĢturn€of€the€century.€These€pictures€show€a€mobile€laboratory€used€in€Montana.€ItĢwas€a€horse-drawn€wagon€that€carried€the€necessary€reagents,Ģglassware,€etc.€that€were€set€up€in€a€tent.€ĢĢĢĢĢĢĢOver€the€years,€the€mobile€laboratories€have€become€more€refined.€Since€theĢ1960€s,€these€laboratories€have€provided€USGS€geologists€and€geochemists€withĢover€1€million€analyses,€providing€timely€information€for€evaluating€theĢmineral-resource€potential€of€public€lands.€€ĢĢĢĢĢĢĢThis€research€is€based€on€the€idea€that€buried€ore€deposits€may€release€traceĢamounts€of€ore-related€elements€that€are€transported€through€the€overburden.ĢThese€trace€elements€that€are€found€at€the€surface,€however,€may€have€beenĢoriginally€introduced€with€the€transportation€of€the€overburden€and€don€tĢnecessarily€indicate€the€presence€of€a€covered€ore€deposit.€The€ability€toĢdistinguish€between€the€trace€elements€already€in€the€overburden€and€thoseĢmigrating€from€an€ore€deposit€would€provide€a€powerful€tool€for€subsurfaceĢexploration.€Two€of€the€methods€that€are€currently€being€researched€by€the€USGSĢare€ground-water€analysis€and€selective€chemical€extractions€of€overburdenĢsamples€for€the€loosely€bonded€migrating€elements€on€the€surface€of€the€gravelĢfragments.ĢĢGround€water€collected€from€wells,€springs,€and€drill€holes€may€provide€cluesĢto€the€presence€of€covered€deposits.€This€water€moves€very€slowly€through€theĢoverburden€until€it€discharges€at€the€surface€as€a€spring€or€seeps€into€a€body€ofĢwater.€Subsurface€flow€rates€vary€from€almost€zero€to€over€100€feet€per€year.€TheĢslower€rates€cause€water€to€have€a€longer€contact€time€with€the€subsurfaceĢgravels,€rocks,€and,€if€present,€ore€deposits,€permitting€minute€amounts€of€metalsĢto€be€leached€from€the€rocks.€ĢĢĢDetecting€gold€in€a€ground-water€dispersion€pattern€requires€an€extremelyĢsensitive€analytical€technique.€The€USGS€has€developed€a€method€for€detectingĢgold€in€water€at€the€one-part-per-trillion€(ppt)€determination€level.€One€ppt€could€beĢrepresented€by€one€marble€on€20,000€football€fields€(almost€39€square€miles)Ģcovered€with€marbles.€ĢĢIn€this€technique,€gold€ions€are€removed€from€relatively€large-volume€waterĢsamples€by€the€use€of€anion-exchange€resin,€in€a€manner€similar€to€the€exchangeĢof€ions€that€takes€place€inside€a€commercial€water€softener.€Later,€the€gold€ions€areĢstripped€from€the€resin€and€analyzed€using€graphite-furnace,€atomic-€absorptionĢspectroscopy.€(AAS€is€discussed€in€the€Maps€of€natural€contamination€section)€ĢĢĢĢĢĢĢĢMineral€scavengers€provide€a€clueĢĢThere€is€another€way€of€detecting€the€trace€elements€carried€from€a€depositĢby€ground€water.€Ground€water€is€drawn€upward€by€evaporation€at€the€surface.ĢDuring€this€upward€migration,€trace€elements€in€the€water€are€affixed€to€minerals€inĢthe€overburden.€The€affixation,€or€bonding,€may€range€from€weak€to€very€strong.ĢThe€strength€of€this€bonding€depends€on€the€chemical€nature€of€both€the€traceĢelement€and€the€host€mineral.€The€differences€in€bond€strength€is€comparable€toĢthe€difference€between€the€weak€electrostatic€attraction€that€holds€an€inflatedĢballoon€to€a€wall€and€a€nail€driven€into€a€stud.ĢĢMinerals€that€are€capable€of€scavenging€trace€elements€from€ground€waterĢwith€increasing€bond€strength€include€hydrated€aluminum€silicates€(clays),Ģsecondary€carbonates,€amorphous€(noncrystalline)€oxides€of€manganese,€and€theĢamorphous€and€crystalline€oxides€of€iron.€Trace€elements€scavenged€by€theseĢminerals€are€removed€by€treating€samples€of€overburden€with€chemicals€that€reactĢselectively€with€each€mineral€phase.€Sequential€selective€extractions€are€used€toĢrelease€trace€elements€from€the€host€minerals€in€the€order€of€increasing€bondĢstrength€such€as€clays€first€and€crystalline€iron€oxides€last.ĢĢThe€principal€advantage€of€selective€extractions€is€that€they€facilitate€theĢdistinction€of€elements€that€have€migrated€from€other€sources€from€those€normallyĢpresent€in€the€overburden.€Thus€the€presence€of€a€gold€deposit€in€Nevada€mayĢwell€be€indicated€by€the€occurrence€of€gold,€or€its€associated€elements,€arsenic€andĢantimony,€in€a€specific€mineral€phase€in€the€overburden.€ĢĢIIIb.€Geographic€chemistry:€€National€Geochemical€Data€BaseĢChemistry€of€a€nation€on€fileĢĢFor€many€decades,€samples€of€geologic€materials€(rocks,€soils,€sediments,Ģwaters,€and€others)€have€been€chemically€analyzed.€The€geochemical€dataĢcollected€from€these€and€other€scientific€programs€and€projects€provide€the€basisĢof€a€growing€national€geochemical€data€base.€A€part€of€the€data€base€containsĢchemical€analyses€of€stream€sediments€from€hundreds€of€thousands€of€drainageĢbasins€throughout€the€United€States.€These€analyses€represent€the€chemistry€ofĢsurface€materials€in€these€basins€and€may€be€used€in€many€applicationsĢconcerning€health,€the€environment,€and€natural€resources.€(See€the€map€on€pageĢ34€for€an€example€of€lead€in€stream€sediments€of€Colorado.)€ĢĢĢĢ10,000€element€determinations€a€dayĢĢOne€of€the€principal€methods€of€analyzing€samples€that€shows€up€frequentlyĢin€the€National€Geochemistry€Data€Base€is€inductively€coupled€plasma-atomicĢemission€spectrometry€(ICP-AES).€This€method€provides€a€rapid€and€precise€meansĢof€monitoring€up€to€50€elements€simultaneously€for€minor-€and€trace-€levels.€TheĢICP-AES€technique€is€widely€regarded€as€the€most€versatile€analytical€technique€inĢthe€chemistry€laboratory.€ĢĢWhen€the€sample€solution€is€introduced€into€the€spectrometer,€it€becomesĢatomized€into€a€mist-like€cloud.€This€mist€is€carried€into€the€argon€plasma€with€aĢstream€of€argon€gas.€The€plasma€(ionized€argon)€produces€temperatures€close€toĢ7,000€C,€which€thermally€excites€the€outer-shell€electrons€of€the€elements€in€theĢsample.ĢĢĢĢThe€relaxation€of€the€excited€electrons€as€they€return€to€the€ground€state€isĢaccompanied€by€the€emission€of€photons€of€light€with€an€energy€characteristic€ofĢthe€element.€Because€the€sample€contains€a€mixture€of€elements,€a€spectrum€ofĢlight€wavelengths€are€emitted€simultaneously.€Just€as€rain€breaks€sunlight€into€aĢrainbow,€the€spectrometer€uses€a€grating€to€disperse€the€light,€separating€theĢparticular€element€emissions€and€directing€each€to€a€dedicated€photomultiplier€tubeĢdetector.€The€more€intense€this€light€is,€the€more€concentrated€the€element.€AĢcomputer€converts€the€electronic€signal€from€the€photomultiplier€tubes€intoĢconcentrations.€The€determination€portion€of€the€process€takes€approximately€2Ģminutes€to€complete.€In€1€day€a€chemist€using€the€ICP-AES€can€analyze€200Ģsamples€for€a€total€of€10,000€elemental€determinations.€ĢĢIIIc.€Public€health€and€safety:€€Element€maps€of€soilsĢĢMaps€of€natural€contaminationĢRecently,€an€environmental€problem€was€solved€by€mapping€the€soilĢchemistry€in€the€San€Joaquin€Valley€of€California.€In€the€1980€s,€wildlife€managersĢnoticed€increasing€reproductive€failure€among€nesting€water€birds€at€the€KestersonĢWildlife€Refuge€in€the€northern€end€of€the€San€Joaquin€Valley.€Chemical€analysesĢof€tissues€from€both€birds€and€fish€indicated€toxic€levels€of€selenium.€The€questionĢwas€not€only€why,€but€why€at€that€particular€time?€What€had€suddenly€changed?€ĢĢĢĢĢĢĢĢĢĢIrrigation€of€arid€soils€in€the€San€Joaquin€Valley€began€in€the€1870€s,Ģaccumulating€salts€in€shallow€ground€water€perched€on€impermeable€clay€layers.ĢWithin€a€decade,€farmers€recognized€the€need€for€drainage€facilities€to€lower€theĢlevel€of€salts€in€the€ground€water€or€risk€permanent€loss€of€agricultural€capacity,Ģbut€the€problem€persisted.€Finally€in€1960,€California€voters€approved€financing€forĢthe€State€Water€Project€that€included€an€extensive€drainage€system.€Between€1968Ģand€1975,€85miles€(of€the€projected€290€miles)€of€the€San€Luis€drain€facility€hadĢbeen€completed€with€a€temporary€termination€at€Kesterson€Wildlife€Refuge,€stillĢmany€miles€short€of€the€Sacramento-San€Joaquin€Delta,€its€projected€destination.ĢĢĢĢBy€1978,€drainage€into€Kesterson€had€increased€significantly.€Unseen,€theĢselenium€levels€were€also€increasing€and€by€1982€had€built€to€toxic€levels€in€theĢfood€chain€of€the€wildlife€refuge.€Fish€were€affected€first€followed€by€waterfowl.ĢUltimately,€the€ponds€were€closed€and€filled€in€as€the€quickest€solution€to€anĢenvironmental€disaster.€One€question€remained€where€did€the€selenium€comeĢfrom?€The€eastern€side€of€the€San€Joaquin€Valley€has€a€deficiency€in€selenium,Ģand,€in€fact,€livestock€grazing€in€the€area€needed€to€have€selenium€added€to€theirĢfood€as€a€supplement.€So€why€did€Kesterson€have€too€much€selenium?€ĢĢFurther€chemical€studies€focused€on€the€Panoche€Fan,€the€source€of€most€ofĢthe€drain€water.€Through€chemical€analyses€using€hydride€generation€atomicĢabsorption€spectrometry€(AAS),€high-selenium€soils€were€found€and€mapped€nearĢthe€mountain€front€on€mud-flow€debris€derived€from€selenium-enriched€marineĢshales€in€the€Coast€Ranges.ĢĢAAS€uses€a€bright€source€of€the€element€s€characteristic€light,€usually€from€aĢlamp€whose€cathode€contains€a€large€amount€of€the€element.€This€light€is€thenĢpassed€through€a€cloud€of€non-excited,€ground-state€atoms€from€the€sample€whereĢit€is€absorbed€proportional€to€the€amount€of€the€element€present€in€the€cloud.ĢNext,€the€light€goes€to€a€monochrometer,€that€separates€the€energy€wavelength€ofĢinterest.€The€light€is€then€converted€into€an€electrical€current,€amplified,€andĢrectified.€A€computer€calculates€the€quantity€of€the€element€in€the€samples.€ĢĢWith€the€selenium€data€generated€by€AAS,€the€source€of€the€selenium€in€theĢwildlife€refuge€was€studied.€Is€the€source€of€the€selenium€natural€or€caused€byĢhumans?€The€answer€is€both.€The€occurrence€of€selenium€in€the€soils€and€groundĢwater€of€the€Panoche€Fan€is€perfectly€natural.€Humans,€however,€are€interactingĢwith€one€part€of€the€natural€hydrologic€cycle€in€which€elements€are€transportedĢfrom€minerals€to€the€ultimate€sink€the€ocean.€Here€the€elements€would€have€beenĢnaturally€recycled€by€reprecipitation€as€minerals€in€marine€shales.€By€increasing€theĢamount€of€rainfall€(via€irrigation),€human€activity€has€sped€up€the€leaching€ofĢselenium€out€of€the€Panoche€fan€sediments.€ĢĢThe€temporary€halt€of€the€San€Luis€drain€had€left€the€project€205€miles€shortĢof€the€sea,€and€the€drain€water€was€instead€contained€in€holding€ponds.€The€extraĢwater€turned€the€holding€ponds€into€wetlands€where€birds€that€used€the€flywayĢmade€nesting€sites.€The€ultimate€solution€to€the€San€Joaquin€drainage€may€lie€inĢfinishing€the€drain€and€discharging€the€water€directly€to€the€ocean€so€that€natureĢcan€recycle€it€into€marine€sediments€again.€ĢĢTo€some€people,€the€Kesterson€Wildlife€Refuge€has€been€considered€anĢenvironmental€disaster.€Nevertheless,€it€has€served€as€an€environmental€lesson.ĢThe€holding€ponds€demonstrate€the€feasibility€of€creating€wetlands€to€clean€upĢsome€forms€of€metal€pollution.€They€also€prove,€however,€that€if€we€createĢwetlands€for€bioremediation,€they€cannot€be€built€and€left€untended€without€risk€toĢwildlife.€The€levels€of€toxic€elements€being€concentrated€in€the€wetland€will€have€toĢbe€monitored€so€that€they€do€not€build€up€to€levels€that€are€toxic€to€wildlife.€€ĢĢIndustrial€sources€of€contaminationĢĢA€similar€cause€for€environmental€concern€is€the€presence€of€mercury€in€theĢagricultural€soils€of€the€Panoche€Fan.€To€the€west€of€the€San€Joaquin€Valley,€aĢmajor,€mercury€mineralization€district€is€located€near€the€town€of€Idria.€The€NewĢIdria€Mine,€operated€between€1858€and€1972,€was€the€second€largest€mercuryĢproducer€in€North€America.ĢĢStreams€that€drain€the€north,€east,€and€south€sides€of€the€mining€district€allĢcontribute€sediment€to€the€Panoche€Fan.€Chemical€analyses€of€soil€samples€fromĢthe€Fan€clearly€show€that€the€soil€contains€elevated€mercury€levels.€These€highĢlevels€of€mercury€could€be€caused€by€a€combination€of€natural€geochemicalĢdispersion€(as€discussed€on€page€23)€and€mining€activity,€considering€the€timeĢperiod€of€major€mercury€production€at€the€New€Idria€Mine.€ĢĢLike€the€selenium,€the€mercury€data€were€generated€using€AAS.€The€rocksĢwere€digested€and€the€solution€was€then€reduced€to€form€elemental€mercury,Ģwhich€was€separated€as€mercury€vapor€and€measured€with€AAS.€This€method€isĢcalled€the€cold€vapor-AAS€method.€ĢĢRobots€in€the€laboratoryĢĢGeochemical€studies€generate€large€quantities€of€samples€to€be€analyzed€inĢthe€laboratory.€Although€technological€advances€have€produced€vastĢimprovements€in€analytical€measurements€and€data€reduction,€the€manualĢpreparation€of€samples€has€remained€a€time-consuming€problem.€As€a€result,€oneĢof€the€most€rapidly€growing€areas€in€laboratory€automation€is€the€use€of€roboticsĢfor€sample€preparation.€ĢĢĢĢĢA€laboratory€robot€generally€consists€of€an€arm,€a€hand,€and€a€pair€of€fingers.ĢThese€components€are€programmed€to€duplicate€the€sample€preparation€usuallyĢperformed€by€a€laboratory€technician.€The€centrally€positioned€robot€movesĢsamples€in€and€out€of€laboratory€work€stations.€Each€work€station€performs€aĢspecific€function€such€as€dispensing€acids,€mixing,€heating,€centrifuging,€filtering,Ģand€weighing.€ĢĢThere€are€several€advantages€to€the€use€of€robotics.€Robots€have€improvedĢproductivity€by€a€factor€of€2€or€3.€Because€sample€preparation€requires€the€use€ofĢhazardous€chemicals,€the€robot€minimizes€human€exposure€to€these€chemicals.€ByĢdelegating€the€repetitive€applications€to€the€robot,€the€technician€is€available€toĢassume€greater€responsibilities.€Finally,€robots€provide€consistency€in€sampleĢpreparation€and€improve€the€precision€of€the€data.€ĢĢIn€USGS€laboratories,€robotics€have€been€applied€to€a€range€of€techniquesĢincluding€sample€disaggregation,€the€decomposition€of€tens€of€thousands€ofĢsamples€per€year€for€the€ICP-AES€methods,€the€weighing€of€7,000€charges€of€fluxĢper€year€for€the€XRF€major€element€analyses€method,€and€other€similar€sampleĢpreparation€methods.€The€use€of€laboratory€robotics€continues€to€increase€as€theĢbenefits€from€each€application€are€realized.€€ĢĢĢIV.€Can€we€depend€on€chemical€analyses?ĢĢIVa.€Measuring€qualityĢĢThe€importance€of€measurementsĢĢOne€of€the€tasks€facing€scientists€is€to€measure€and€define€unknownĢquantities.€These€measurements€are€important€because€they€can€warn€us€ofĢpotential€hazards€from€volcanoes€and€environmental€contamination€or€help€usĢdevelop€our€mineral€resources€to€stay€competitive€in€the€worldwide€economy.€InĢEarth€sciences,€the€measurements€of€geological€samples€are€used€in€making€policyĢdecisions.€These€decisions€can€affect€all€Americans€in€topics€ranging€from€pollutionĢprevention€and€control€to€evaluation€of€mineral€resources€and€wilderness€areas.ĢĢĢDecisions€are€made€every€day€based€upon€measurements€of€variousĢsubstances€(or€areas€containing€them).€Without€quality€measurements,€misleadingĢor€dangerous€conclusions€could€be€drawn.€ĢĢThe€uncertainty€of€measurementsĢThere€are€many€difficulties€associated€with€making€measurements.€QualityĢassurance€involves€minimizing€mistakes€and€correcting€problems€before€theĢinformation€is€used.€ĢĢWhen€an€archer€releases€an€arrow€at€a€target,€both€the€distance€from€whichĢthe€archer€shoots€and€the€size€of€the€target€define€what€is€considered€acceptableĢaccuracy€and€precision.€Shots€from€5€yards€would€be€expected€to€hit€closer€to€theĢbull€s-eye€than€shots€from€50€yards.€If€the€arrows€miss€the€target€completely,€theĢarcher€is€considered€inaccurate.€The€closer€together€repeat€shots€hit€the€target€toĢeach€other,€the€more€precise€the€archer.€The€strength€and€dexterity€of€the€archer,Ģthe€acuity€of€the€archer€s€eye,€the€adjustment€of€bow€sights,€wind€conditions,€andĢthe€number€of€shots€taken€also€contribute€to€the€accuracy€and€precision€of€theĢarcher.€A€laboratory€procedure€is€similar€in€the€need€to€understand€the€variablesĢinvolved€and€the€possibilities€for€error.€ĢĢSearching€for€the€bestĢĢA€mistake€in€measurements€can€impact€decisions€made€on€endangered€animalĢhabitat,€mineral€exploration,€or€remediation€of€an€environmental€problem.€When€aĢquality€assurance€program€claims€99.9€percent€accuracy,€consider€what€that€couldĢmean€in€terms€of€error:€€1€hour€of€unsafe€drinking€water€per€month,€16,000€lostĢpieces€of€mail€per€hour,€or€176,000€checks€deducted€from€the€wrong€bankĢaccounts€every€day.€The€quest€is€for€100€percent€accuracy€and€precision,€even€if€itĢis€not€attainable.€€ĢĢThe€USGS€Reference€Materials€ProjectĢĢIn€the€field€of€analytical€chemistry,€reference€materials€serve€an€important€roleĢin€the€development€of€new€techniques€and€the€periodic€testing€of€establishedĢmethods.€Used€correctly,€reference€materials€provide€investigators€with€aĢmechanism€to€objectively€compare€their€results€with€established€values€andĢdetermine€if€any€bias€exists.€ĢĢIt€was€this€drive€to€produce€quality€data€that€led€the€USGS€and€theĢMassachusetts€Institute€of€Technology€in€the€early€1950€s€to€jointly€develop€theĢfirst€geochemical€reference€materials.€This€early€work€started€a€USGS€tradition€ofĢpreparing€high-quality€reference€materials€that€are€used€for€both€domestic€andĢinternational€geochemical€programs.€To€date,€29€different€geochemical€standardsĢhave€been€produced€with€an€estimated€worldwide€distribution€of€over€20,000€units.ĢĢĢĢĢInitially,€the€need€for€quality€control€led€to€the€development€of€several€silicateĢrock€standards€that€were€important€in€such€diverse€activities€as€the€lunar€program,Ģore-genesis€studies,€and€volcano€monitoring.€When€the€mining€and€explorationĢindustries€clamored€for€reference€materials,€the€USGS€responded€by€generating€six€Ģexploration€standards€designed€to€contain€elevated€concentrations€of€keyĢelements.€The€USGS€involvement€with€the€mining€industry€continues€today€withĢthe€recent€development€of€coal€and€gold-ore€standards,€which€will€be€useful€inĢresource€appraisals.ĢĢEnvironmental€concerns€are€becoming€a€major€part€of€the€national€agenda,Ģand€the€USGS€Reference€Material€Project€provides€quality€reference€material€to€aidĢin€this€field€of€study.€A€major€emphasis€of€this€effort€will€be€to€conduct€cooperativeĢstudies€with€other€Federal€agencies,€thus€helping€them€respond€to€national€needs.ĢĢńń