Libro_mapping Manual M Einaudi.pdf

MarcoT. Einaudi April 1996 New and ExpandedEdition of DETAILED GEOLOGIC MAPPING OF PROSPECTSAND MINES (EINAUDI.T996)

I. Introduction II. Mappine trenches.ruad cuts.tunnels.benches A. GeneralAspects themapis beingproducedasyou map. Colorcodingis a meansof reducingnote-taking look more criticallyat drerocks Color alsostimulatesthebrain mappingminerals,not alterationtypes. B. Key Featuresof Mapping Scheme The "baseline" Therock side distributionof quarz veins quantifyingthedensity(volVo)of quarz veins Theair side Backgroundalteration Alterationhalos C. Organizationalhints for efficientmapping double-sided aluminumclipboard hard-leadcolorpancils Keepa blotterin your aluminumclipboard Mappingvestswith largepockes , Applyingcolor. maptheyoungestfeaturesfirst partitionyour work Sund up (savestimeandsavesyourpants!) III. Mappine outcrops: usemultipleoverlays A. BaseMap. Iimit of outcrop,culture stnrcure& littrology majorveins

conterts,p. I, mappingmanual,April 19, 1996

B. Alteration Overlay. alterationhalos backgroundalteration

c. Limonite Overlay. color-codedlimoniteassociations secondary copperminerals IV. Color Codes (Fies.3 & 4) A. Lithologiccontactsand structure B. Hypogenemineralization sulfides/oxide silicates,carbonates, sulfates,borates graphicdistinaionbeweendisseminations andveinfillings C. Leached/oxide/supergene sulfides importantminerals graphicrecordingof thedegreeof leaching indigenousversusexoticsecondary minerals D. Alteration of hornblende(and/qr biotite) sites. fresh chloritized epidotized biotized sericitized E. Alteration of feldspar sites. plagioto Kspar Kspar andplagioto albite feldsparsto clays,degreeof clay alth V. Weatherineprcducfs: how to map and reooenize them. A. H ypogenevenrussupetgenealteration. presenceof Kspar indicateslack of sericiticor adv argillic montrnorilloniteindicateslack of sericiticor adv argillic magnetiteindicateslack of inl argill, sericiticor adv argillic of biotitesuggestiveof lack of int argillic, sericiticor adv argillic Presence recognitionof sericiticdt'n in highly weaffreredoutcrops dickite& pyrophyllitediagnosticof hydrothermaladvd argillic hypogeneversussupergeoe alunite

B. Leadredand oxidizedoutcrops. degreeof leachingof primary sulfudesites

oontents,p. 2, mappingmanual,April 19, l99ti

"Glassylimonite" Relictsulfideslockedin unbrokenquru Exoticlimonites VI. Reconnaissance: What to retainfmrT the DetailedMapping Scheme. Rockdescription, especially"productive"porphyries Quartzveinsandveinlets Limoniteassemblages Relativeabundance of indigenousandexoticFe andCu oxides Biotitedistributionpatrerns, especiallyof "shreddybiotite" Magnetiteabundance VII. Fact Maps and Interpretations:The Folio A. Fact maps and follow-up interpretation factmapsshouldbe keptupto-date workinghypotheses interpretation basedon factmapsshouldbe doneat thesamescale smrcturaldetailsneedto be preservedat all scales 3 daysmapping,I dayinterpreting carefullyarchived B. The Folio. basemap vein overlay limoniteoverlay magnetiteoverlay alterationoverlay grade/geochernistry overlays: goologicallyinterpreted e. Compositemaps: explorationmodelsand drill targeting. thecomposite:displayscolorodlineswith limits of key feanrresall on onemap coincidenceof key feaurresto aid in targeting

Fizures Benchmapin sulfide-bearing rocks(unoxidized) Beirchmap in oxidizedrocks "ore" minerals Colorcodesandstylesfor mappinghypogeneandsupergene Colorcodesandstylesfor mappingalterationandveinminerals Examplesof colorcodesandstylesfor mappingunoxidized(hypogene) and leached)exposures. oxidized(supergene, Figure6. Separation of outcropmappinginto layers Figure7. Factorsinvolvedin therelativemobiliryof copperin theaerated andsaturated zones Figure8. Someof BanrHijau'stargeringfeanrres

Figurel. Figure2. Figure3. Figure4. Figure5.

contents,p. 3, mappingmanual,April 19, 1996

MAPPING ALTERED & MINERALIZED ROCKS IN PORPIIYRY Cu-Au ENVIRONMENTS New and Expanded Edition of

DETAILEDGEOLOGICMAPPINGOF PROSPECTS AND MINES(EINAUDI,1996) This reportrepresents andexpansionof previousreports(Einaudi,1995;1996). a refinErnent It waswritrenfollowing themappingcoursesgivenat BanrHijau,lndonesiain March 1996.

I. Introduction Color-codedmappingof key feauresof alteration/mineralization, augmertedby quantitative estimatesof mineraVvein abundance of anitudes(strike& dip, or core-a,risangle)is andmeasurement criticalto successful explorationandminedevelopmeot.This styleof mappingshouldbe usedto complementstandardized numericalmappingdesignedfor computerdatabases.A geologistwho drawswhat s/heseesin therocks hasgreaterflexibility andfreedomof thoughtthanonewho is forced to pigeon-holeeverythinginto a numericalcategory.Further,at thestageof mapcompilationthereis geplogicalandmineralogical no substitutefor ttredetailed,color-coded, notescompiledon factmaps, whosecolor andtexturaldistinctionsallow quickvisualcorrelationof commonfeaturesbetween ourcrops,mine benches, or drill holes. Thedisadvantages of color-codedmappingincludedifFrcultyof makingstandardxeroxcopies thatarelegibleandproblemsassociated with usingcolor pencilsin regionsof heavyrainfall. These disadvantages do not ounveightheadvantages. Color xeroxmachinesandcolor scanners aregening benerandmorewidely available.Hard,water-proofpencilscanbeusedfor mappingin wet conditions:coloralsocanbeaddedlaterwhile transferringthemappeddatato ttrefactmap. Althoughthis ract focuseson mappingin igneousrocksof porphyry-typeenvironments, the approachis easilymodifiedfor applicarionin anydeposittypeor any goologicalenvironment

II. Manping VerticalFaces:trcnches.road crrts.tunnels.benches A. GeneralAspects Themost efficientapproacho mappingverticalwallsis to projectevErythingto a horizonal plane(say,at chestheight).Thehundredsof srike & dip measurements thataretakenduringa day's mappingareall ploneddirectlyon themap;in otherwords,themao is beingoroducedasyou map. Confusionaboutstrikesof faults,contacts,etc,doesD'tariseasofteirasit doeswhendrawingin verticalview or whenrecordingdatain a notebook.You know cxactlywhereto go in thenextcrosscut or trenchto find thatfault, and geologycanbe drawnircTossthe drift from onewall to the other. (NOTE: (l) somefeatureswill not projectto chestheight,e.9.,a flat fault at anklelevel;theserequire notes,a quicksketch,or a projection(seebelow). (2) Whenmappinganunderground declineor a surfacetrenchup a hill, continueto map at chestheight;your map will be an inclinedplane,which later canbe correctedto a differentdahrmplanedependingon theultimategoal). The essentialideais to recordby meansof a p!ryglE tre variousfeanrresof rock type, structure,veins,alterationmineralsandoreminerals(seeFigs. 1-5). Color codingis a meansof reducingnote-takingto somedegree,but, morc importantly,to forcetre geologistto look more criticallyat therocks. Color alsohelpsto visuallystimulatettrebrainduringmappingandaftenpards duringthecompilationprocess. Anotherimporunt aspectof themappingschemeis hat in mappingdteredwall rocks,you are mappingminerals.not alterationq?es. This meansttratyou arcnot classifyingalterationtypesas you

Einaudi,p. 2, April 19. 1996

argillicor poussicalterationrypes!) and, map(think of all ttrevariationson thethemeof advanced ideal of recording to the observations you closer coming ratherttraninterpretations. therefore, are Map whatyou see. Notesareusedfor thosefeanrresthatcannotberecordedin ttredrawing,suchasrock relativeagesbetweenfeatures(e.g.,betweenfaults,veins,veinlets,intrusivecontacts), descriptions, sulfideratios.andveinletabundance. Notesarewrinenfor percenttotalsulfides,percentmagnetite. intervalsof thebenchfaceor urnnelwheresuchfeaturesarerelativelyuniformin character. B. Key Featuresof Mapping Scheme here. FigureI represents a map FiguresI and2 illustratethestyleof mappingbeingdescribed a mapof theoxidized(weathaed)equivalenr rocks,whereasFigure2 represents of sulfide-bearing of themappingscherneareillustratedby thesefiguresanddicussedin the Thevariousaspects paragraphs thatfollow. Comparisonof thetwo figures(andFigures3 and5) alsowill allow you to visualizetheresultsof oxidationof hypogene ores(discussed in a separate sectionbelow). ( I ) The "@9" consistsof thetapelaid out at chestheightalonga drift or trench wall. This baselineis surveyedby bruntonandplonedon thefield sheet(takingaccountof irregularitiesin thefacerelativeto thestraightline of thetape). (2) Useeriddedfield sheetsto enablerapidploaingof strikesanddipswith a plastic scale/protractor.The grids representN-S andE-W lines,not linesparallelto therock faceyou are mapping.AssignttreE-W lineto tre long dimensionof your mapsheet(thenortharrowpoins towardthelongdimensionof your shee$for easeof useof your clipboardandfor internal consistency. (3) Locateyour baselinein thecenterof thefield sheetto allow working room (notes anddrawing)on all sides. Starta new field sheetbeforeyou run out of room towardtheedgeof the sheet (4) Beforeyou startmapping,besureto includecoordinates, surveypoints,locality, scale,thedate,andyour name. (5) Note.sandsamplelocationsarewritteir directlyon themappingsheet,ratherthanin thefield notebook.This ensuresthatthis informationis neverseparated from themap. your mapsheetsinto two areas:the"air side"andthe"rock Thebaselineservesto separate side"(seeFigs.l-5). (6) Therock sideis usedto rcord fauls, veinminerals,veinletminerals, featuresareplottedwith disseminations of "ore" mine,rals, andfithologiccontacts.All through-going tnre strikeandthedip is indicated. (7) Because of tre closerelationbetweenthedisuibutionof ouarz veinsandCu-Au gradesat BatuHijau (Fig. 8) andin porphyry-typedeposisin general,a methodof quantifyingthe benveendifferent density(volVo)of theseveinsis highlyuseful. I havefoundthatconsistency geologistscanbeachievedby estimating(for a givensetof veinsanda givenbenchintervd wherethe veinsareof rclativelyconstantspacingandwidth): l) theaveragewidttr of theveitrs,and2) the averagespacingbenveencenterlines. Write thesedown in your notesasa fraction(e.g.,"0.5/6" would indicate0.5 crn average widtr and6 cm averagespacingbeueencenterlines). Dividingout by thisveinset(0.5/6=8 vol 7o). This thefractionyieldspercentof therock thatis constinrted works well for porphyrydeposiswhereveinsoccupydefinitesets;theestimateis madefor approach sucha counthas eachset Theapproach alsois beuertran countingveinwidthsalonga tape,because to becorrectedfor thetnrewidttranddoesn'trecordveinwidthsandspacing.Clearly,theapproachis difticult to apply in rockswheretheveinsaretruelyrandom,but ttris is lesscommonthanis generally filling, you iue raording tte believed.For A-B quartzveins,which most likely representopen-space (pynte witr quare-sericite-pynte veins quara veins volumepercentof ttnt filld openspaces.For D

Einaudi,p. 3, April 19, 1996

(QSP)halos),recordthe "vein width" asthedisuncebetweenouteredgesof theQSP halo:the fractionwill represent thevolVoof therock thatis alteredto QSP. (8) Theair sideis usedto recordalterationmineralsandrock type. Alterationminerals arerecordedby colorcodein two ways. Backgroundalteration.Narrow "imaginarycolumns"alongthebaseline(much asthecolumnsusedfor differentmineralsin loggingcore)areusedto record"background"alteration minerals."Background"alterationis definedhereasanyalterationmineralsthatoccurthroughouta givenvolumeof rock anddo not appqr to be relatedashalosto individualveins. Pervasive biotizationof andesite at BatuHijau is oneexirmpleof backgroundalteration. Alterationhalos. If distinctalterationhalosarepresenton themarginsof fracturesandveinfillings, theseareshownaslinesdrawnalongthestike of thevein andextending out into theair sideof themap sheet For example,at BaruHijau,distinctqz-sericite-(py)haloes,mm to cm wide,occuralongpyrite-qzveins. C. Organizationalhints for efticientmapping (l) Usea double-sided aluminumclipboardthesizeof themappingsheet(8.5X I I inchesin theU.S.) with leatherpencilholdersrivetedto oneor bottrsides. All pencilsandscalesare keptin this clipboardfor easyaccess.Placerubbererasorson theendsof eachpencilfor easyretrieval of pencilsout of theirleattrersleeves ! (2) The imporanceof a hardlead color pencilswhich canbe sharpenedto a fine point cannotbe overemphasized. Pencilsavailablein theU.S.whichmeetthesestandards includeEagle Verithin(or BerolVerithin')andSnedtlerMars-Lumochrom..[Cavearin tropicalclimates.leads tend to becomesoft;in field mapping,rain obviouslyplacesseverelimitationson thequaliryof your drawingevenif water-proofpaperis used. BULtry anyrvay! Keepa blotterin your aluminumclip boardfacingyour map sheet,andkeepttreclipboardclosedandin your mappingvestwhennot in pencilsis anart keepa sharpknife (sameoneyou useto scrarchrocks)to exposea usel. Sharpenine lengthof lead,tapea pieceof sandpaper tothe backinsideof your clipboardfor sharpening ttrepoint, and do final sharpeningby rubbingttrepoint at a shallowangleon a pieceof paperat thebackof your clipboard. (3) Mappingveststhathavepocketslargeenoughfor analuminumclipboardto fit in looselyarecriticalto thesuccessof themappingmettroddescribedabove.loose fit is important because themappingmethodrcquiresa contentback-and-forttr betweenmap sheetandrocks:every time you havefinishedmarkinga feanrreon your map shee!theclipboardis "dumped"backinto its pocket.your handsarefree,andyou cangetbackto breakingrocks. Your vest"organizes"your work environment,muchasthe "desktop"on your computer.Theclipboardis neverdumpedon the ground. (4) Appllringcolor. Feanrres recordedon therock sidecanbecomevery densely spaced(especiallyin highly mineralizedzones)andgreatcareneedsto betakento maintnincolor with very sharppencils.A key techniquein this regardis to mao theyoungestfeaturesfirst separation (e.g.,post-orefaults,youngestveins),thenfollow with mappingtheolderfeaurres.In this way, offseaingof olderfeanrresby youngerfeaturescanbe showneasilyasyou mapandmuchlesserasing is involved! Also, asyou applycolorto represent a vein,applyfirst thecolor of themost abundant mineralas a dashedline; the lessermineralcolorsarethenappliedbaweenthedashesof thefirst and no coloris appliedon top of anofter. (5) Makeseveralmappingpassesfor anygivcnoutcropor lengthof benchface;in otherwords, gligigllJour work. I find thatI necdat leastthreepassesto completeall the observationsandnote-takingttratI need. The first passshouldbe tre onein which you getdown on paperthe major featuresof theoutcrop:descriptionsof lithology, lithologiccontacts(indicatewhether intnrsive,conformable,stratigraphic, or faulted),majorfaults,andmajorttrough-goingveins. [n

Einaudi,p. 4, April 19, 1996

passesyou beginto adddetail. In a secondpass,map veinsandveinlets,diagrammatically subsequent showingtherelativeageof differentveintyp6 (plot theyoungestveinsfirst), andaddalteration alteration.Thethird passcanbedevotedto sulfide(or oxide)minerals,their haloes,andbackground proportions. abundance, andrelative (6) Standup, facingtherocks,while markinga feaureon your mapsheet.This you areorientedwith your rocksandyour map reducestheoddsof plonrnga wrongstrike,bpcause mappingh your Boal;to achievethis goal,thebestmappersdo not efficienqandaccurate sheet.Fa.st" sit downwith theirbacksto theface. (savestime andsavesyour pants!) (7) In reeionalexploration,I recommendtlnt prior to commencinga mapping ourcroosbemappedfirst at a projectat a smallscale(say,l:5,000)thatsomekey representative largescale(say, l:250). Thereasonis thatmappingataluge scalegivesthegeologistthe oppornrnityto spendsometime lookingat therocksin detailandthis enableshim to developan ideaof thekey featuresof a givenprospect Armed with thisinformation,hecanthenmoveout moreconfidentlyat higherspeedat a smallerscale.

III. Mappine outcrops: usemultiple overlavs (i.e.,outcrops),colorcodesfor alteration, In mappingsub-horizontal veins,andore exposures is minerals(limonites)areusedasabovebut afeappliedto successive overlays.Color separation maintained by ploning: . lithologiccontacts, faults,veins,andotherstrucnrreon a basemap(Fig. 6, BaseM.p); . pervasive(or background) alterationandalterationhaloson thefirst overlay(Fig. 6, Overlay#l ); . andoremineralsor theiroxidationproductson a secondoverlay(Fig. 6, Overlay#2). Notesfor thesevariousfeaturesarewrinen on their respectiveoverlays. A. BaseMap. Thelimit of outcropis skerched first on thebasemap(alongwith anyadditional"culhrre"such astrenches,paths,etc)andthe major feanrresof stnrc'urre andlithology aremappedin. Rock-type symbolscanbe assigned to variousunits,andthesesymbolscanbeappliedin blackpencil(ratherthan assigninga color-codeto rock types)alonghe outerperimeterof theoutcropoutline. Veinsare ploneddirectlyon thebasemap,usinf colorcodesfor domine,nt vein-fillingminerals.Notescanbe wri$enoutsidetheoutcropareaB. Alteration Overlay. On Overlay#1, linesareusedo idenffy alterationhaloson veinsshownon thebasemap. Careshouldbe takento ensurethatthe alterationcolor-codeis applieddirectlyover thevein shownon thebase.This poins out theneedto plot theveinsfust on thebasemap,thenquicklyapplythe alteration-halo coloroverthatveinon overlay#1. For example,on Fig. 6, theNE-dippingqu-(Ksparmag) veinsat the north endof the outcrop(basemap) haveKsparalterationhalos(alterationoverlay). Backgroundalterationnotrclatedo individualveinsis shownnextby color-codeddos for the mineralspresenl Becauseonly oneoverlayis usedfor alteration,feldsparsitesandmafic mineral (astheyarein mappingbenchfaces).This turnsout not to bea major sitesarenot distinguished disadvantage, because, for example,a mix of browndotsandolivegreendos impliesclayin the feldsparsitesandsecondarybiotitein the mafic mineralsitcs. The deqlity of dotsshouldreflecthe relativeabundance of alterationmineralsseenin theoutcrop. For example,in Fig. 6, background sericircalterationincreasesin intensitysouthwesterlyandthendeclinesabruptlyinto a zonewith minor asa solid cpidoteandchlorite. As anotherexample,an int€nselysilicificd rock would be represented

Einaudi.p. 5, April 19.1996

orangecoloron overlay#l Out, applythecolorof any minor mineralsfirst asdots,thencolor-inthe orangearoundthedotsin ordernot to getsuperposition of colors). C. Limonite Overlay. This is a key overlay,b@auseultimatclyit will allow you to draw a map ttratdisplaysthe distributionandrelativeabundance of the oxidationproductsof sulfides.Thekey mineralswhose disributionandabundance needto bemappedincludethegreencoppercarbonates andsilicates,black copperpirch(tenorite),glassylimonite(pirchlimonite),goettrite,earthyhematite,andjarosite Togetherwith the alte,ration andvein maps,frredistributionof thesemineralswill allow you to say somethingaboutoriginalsulfidezoningandaboutsecondary dispersionof metals.Wthout such geochemical informationandgeologicalinterpretation, assaysof soil androck chip samplescannotbe properlyinterpreted. Thecolorcodesandsymbolsusedin mappinglimonitemineralsaresummarizedon therighthand-sideof Figure3 andin Figure6 anddetailedin sectiontV.C andVI.B (below). An interpretation of theoriginalsulfidedistributionpatrern,basedon thelimonitesandthestyleof of alterationandveins(shownfor thesameoutcropon Figure4) is illusratedon theleft-hand-side Figure3.

IV. Color Codes (Fies.3 & 4) Theseparation of themappingsheetinto air sideandrock side(or ovalays for outcrop mapping)allowsfor efficientuseof colors:in thelist below, 12colorsareusedto recordsome40 differentmineralogical featuresandstructuralfeanrres.Thelist is instructivebecause it indicatesthose feanrresthatcanbe mappedcontinuouslyby hand-lensinspectionof freshly-brokenrock surfacesin igneousrocksrelatedto porphyrysystems.Colorsareidentifiedby "EagleVerithin" (or "Berol Verithin")numbers.Simplificationof thecolorcodingfor regionalmappingis discussed in Section VI below. A. Lithologic contactsand strucfup (recordedon rock side,plot truesrike, dip) black

1. Lithologic ontacts: useyour leadpencil(black).

darkblue

2. Faults (breccias, clays,shears) andfault contacts:useindieo blue 041).

black

3. Foliation,joints, bedding:useyour leadpencilftlack).

(Ploton tggks:i(h). B. Hypogenemineralization(veins/veinlets & disserninations). (Fig. Schernatjc representation of mineraldistributionin appropritecolor 3 & 4). Dots for disseminations, randomshortlinesfor randomveinlets(e.g.,A-vnls) or fracturecoatings,continuous relative linesfor through-goingveins(e.9.,B- andD-veins). Careshouldbe takento approximate vein densitiesand relativeabundance of dissiminaM sulfides/oxidesalongthe faceby thedensityof color addedto map. Plot veinsandveinletswith tnre strikeandindicarcdips. (Fig. 3) sulfides/oxides purple red dark green

l. bornite: puple (752\ 2. drdopyrite: carmincrd (745) 3. molybdenite:green(739)

Einaudi.p. 6. April 19. 1996

med yellow black gray

4. pyrite: cilnaryyellow (735) 5. magnetitghematite:black(mappingpencil) 6. speanlarhematite

orange darkgreen olivegreen yellow-green

Veinlet/veinfillings ottrerthansulfides/oxides (veinshownwith colorof dominantmineral;additionalmineralsindicares by dos alongline) (Fig.a) l. quartz:orange(737) 2. chlorite:green(739) 3. biotite:olivegreen(739 n) 4. epidote:lightgreen(738ln)

C. Leached/oxiddsupergene sulfides(plot on rock side). Schematic drawingsof rexnrres, abundance, mineralogy,anddegreeof leaching.(Fig. 3) Mineralogl. red pastelgreen darkbrown reddishbrown med yellow medblue

l. glassylimonite (conchoidfract,redinternalreflections): carminered (745) (malachite, 2. oxide Cu mine,rals tenorite,etc):truegreen(751) 3. goethite(orangestreak):brown(756) 4. earthy hematite(redsreak);tuscanred ( ) 4. jarosite (yellowto honeyyel'w x'als;paleyel'w streak):canaryyellow (735) 5. supergenechalocite: mediumblue Svmbokfor desreeof leachingin forrrer sulfidesites(mineralsgenerally restrictedto glassylimonite,goettrite, andhematite;i.e.,jarositeandCu oxidegenerallyaretransported/exotic)

I -_

black brown brown red

l. total leadring,emptyleachedcavities(no Fe-oxideleft):blackcircles 2. moderateleadring (limonite-rimmed cavities):browncircles 3. weak teadring(limonitcpsandomorphs and/orboxworks):browndots 4. very weak leadring of chalcopysites(glassylimonite):red dos (exotic)oxideson frac[rresaredenotedby random,sho4 lines Transported (brownfor goethite,Euegreenfor copperoxides).

D. Alteration of hornblende(and/or biotite) sites. (recordedon air sidein innermost column nextto baseline;if alterationoccursasa distincthaloon a fracurreor veinlet,plot tre alteration colorasa lineextendingounvardfrom baseline on air side.) Fig.4. black

l. fresh hornblende(darkblack,glassy,goodcleavage visible):write lower case!!. alongbaseline.

darkgreen

2. drloritizrd hornblende(no shreddytexurrcttut might imply thatthehbl had fint beenbiotitized):er€en039) (pervasivechloriti"ationusesolid greenline; partiallychloritizedusedashedgreen[ine;localchloriteuse dos).

6

Einaudi,p. 7, April 19, 1996

yellow-green

3. epidotizedhornblende:uselight ereen(7381/2).

olive green

4. biotized hornblende (shreddybiotiteoccupyingthehbl site):olive ercen (o39 lnl (solid, dashedanddouedto indicatedegreeof biotization).

darkgreen

on biotitic: 5. drloritized biotized.hornblende(chloriticalt'nsuperimposed (739 green green 12) with dark dots(739) thisis a toughcall!):olive

dark brown

6. sericitizedand/orargillizedmafic minerals(tan-or white-colored pseudomorphsaftermafic mineralsitesincludingmixurresof sericite, brown (756) clays,leucoxene):

black

visible:useleadpencil6lack). 7. mafic sitesabsentor only leucoxene

.-

E. Altenationof feldspar sites. (recordedon air side,outercolum;intensityof color applicationin this columndenotesdegreeof alteration;if alterationoccursasa distincthaloon a fractureor veinlet,plot thealterationcolorasa line extendingounvardfrom baseline on air side.) Fig. 4. magenta

l. of plagioclase to secondaryK-spar (pinkish-lavender huein groundmass plagioclase in magenta and sites): 059)

med yellow

andplagioclase to secondarl Na-spar (hard,whitefeldspars 2. of orttroclase with cleavagepreserved:ygllqq (Z!51 (NOTE: feldsparcoloris not in ev€ry.6ss diegnosticof feldspartype! Usethinsectionsasback-up.Evenif ttratwhitefeldsparurrnsout to be Kspar,you will have rrcordedthedistributionof white Kspar!).

yellow-green

3. of feldsparsto epidote:uselight ereen(73t U2)

darkbrown

4. of feldsparsto serlciteand/or days: usebrcwn (750

none

4a-fresh feldspars:if feldsparis hard,clear,glassy,datk, goodcleavage: leavecolumnblank.

darkbrown

good 4b. incipiently ser'd feldspars:if moderatelyhard,pale-colored, (756) (e.g.,"bleached", dots. buthard):sparsebrown cleavage (NOTE: incipientalt'nof feldsparsto "clays"is difficult to distinguishfrom albitizationandthesetwo alt'nrypescanoccurogether;usethin-sectionback-up)

darkbrown

4c. moderatelyser'd feldspars:if partiallysoft,whiteto palecolors,cleavage presencc{oselysoaccdbrown 056) dots.

darkbrown

but ad. highly ser'd feldspan: if soft whiteto palecolors,no cleavage, outlineof originalfeldsparis preserved(rock-texnrrepreserved): ontinuous brown (756)line applied liehtlv

-.

Einaudi,p. 8, April 19. 1996

darkbrown

4e.penasiye and total hydrolysis:if soft,whiteto palecolors,rock rexture largelyobliterated: continuousbrown (756)lineappliedheavilv. (NOTE: in rockssentainingbo0rplagioclase andor6oclasephanocrysS, because these reactdifferentlyto acidicsolutions,keeptrackof orthoclasesitesseparately(in a third column). This allowsthedistinctionto bemadebeweenintermediate argillicand advanced argillicalteration ).

V. Weatherineprcducts: how to map and recosrizethem. In mappingalteredrocksin surfaceexposures, mostof thetime we arestruggLing to read throughsurfaceweathering to understand l) ttredegreeto whichmetalshavebeenleached. transported. andredeposited by surfacewatetrs, and2) ttreoriginalhypogene(hydrothermal) disuibutionsof wall-rockalterationandoreminerals.How do we readthroughall ttratpunkyclay? A. Hypogenevetsussupergenealteration. It is especially dfficult to differentiate betweenhypogeneandsupergene alterarion rypesin weathered rocksthatsenrainsd abundantpyrite. This is because thesulfuricacidgenerated-by oxidativeweattrering of pyriteanacksminprals(especially plagioclase) andconvertsthemto various newmineralassernblages thatcanbe similarto forms of hypogeneintermediate argillicalteration(e.g., montrnorillsnite,kaetinite)or evenacid-suHue(advanced (e. g., kaolinite,alunite). argillic)alte,ration Thelaneris especiallytnrein rocksthatoriginallycontained pynteveinswith qe-ser-pyhalos(e.g.. - Dveins),but wherethehalosdid not overlap.On weathering, therock inbenveen thehaloscanbe convertedto a supergeneqE-kaoliniteassemblage andalunitemay precipiatein openfracnrres.The endresult,a rock containingquaru,kaolinite,sericite,andalunite,canbe mistakenfor hydrotrermal advanced argillicalteration.How, then,canonedistinguishbenveenhydrothermalargiliicalteration andargillicweathering?Alttroughnot in everycasedefinitive,thefollowingobservations canhelpin makingthedistinction: (l). in igneousroclcswith originalalkali-feldspar, thepresence of reliccoresof alkali feldsparphenocrysswould suggestthatthergck hadnot undergone pervasiveadvanced argillic(or evenperrrasive sericitic)alteration.Alkali feldspardoesnot surviveeitherpervasivesericiticalteration or advanced argillicalterationat hydrothermaltemperaurres. However,evenin ver]' acidicweathering environments, dkali feldsparcommonlysurvives(in contrastwittr plagioclase, whichgoesreadlyto montmorilloniteor kaolinite).Onealwaysneedsto considerveinshalosandbackground alteration separately in makingthesedistinctions. (2) in igneousrock lackingalkali feldspar,thecall is much more diffrculr In such presence rocks,the of moderateto abundaRt amounsof montmorillonite(rattrerthansericite-kaolinite) would indicatelackof intenseh}'pogenesericiticor advanced argillicalteration.Themontrnorillonite couldbetheresulteitherof hypogeneintermediate argillicalterationor weatrering.Again,make separate observations for halosandbackgroundalteration. (3) The presenceof magnetitein punky clay-richrocks is suggestiveof clay alteration dueto weatheringbecause hypogeneclayalteration(e.g.,intermediate argillic)generallyconverts magnetiteto hematite+rutile and/orpyrite. This underlinestheimportance of mappingmagnetite abundance in all outcrops(alsoseruesasa basisfor interpretationof gmphysicaldata). (4) In rocks thatoriginallycontainedreliativelycoarsegrainedbiotite,thepresenceof fresh-lookingbrownbiotitein otherwieargillizedrock is suggestive of weathering.Like magnetite, biotitecansurviveweatheringrclativelyuqscathed,but is readilyconvertedto chlorite+claysduring intermediateargillic alterationat hydrothermalteinperaurres.

Einaudi,p. 9, April 19, 1996

(5) Intensesericiticalterationoccurringashalosgenerallycanbe recognized evenin themixtureof sericiteandquara in suchhalosis very outcrops.'This is because intenselyweathered (it is stablein acidenvironments) andstandsout asresistenLgrayribs in punky resistentto weattrering rocks. On fust inspection,theseribs may look like grayquaru veins,but recognitionof clay-altered (thoughmuchharderthanpunkyargillizedrockc) relictrock tex$re andthefactthatit canbo scratched givesthemaway. (6) thepresence forms of clayminerals,suchasdickite(wellof high+ernperaure and crystnllizedlcaolinite) aboveabout270"C. This underlinestheimportanceof theyarestableonly at temperatures because by subminingsamplesfor mineralidentification(do your own preliminarymineralseparation pluckingout clay-richportionsof therock or achralfeldsparsites,ratherthansubmininga whole-rock for XRD). (7) h]rpogene versussupergege alunite.Texturesandassociation of alunitecanbe diagnosticof hypogeneversussupegene origin of this mineral.: FEATURE

veins alterationhalos sulfides rcxures color

HYPOGENE

SUPERGENE

3,i?ffi:iir,':fl;ru'ffi::*. *H::Hffi:#Alhqffi:Hi" alunite,possiblywith chalcedonic or pyrophyllite,barite,etc) oPalinssilica& jarosite' lackof haloson aluniteveins

presence of hydrolyticalterationhalos veins on alunite-bearing lackof evidenceof former sulfides evidencethatsulfideswerepresent associated with alunite intergrownwittr alunite massive,porcelanous fine- andcoarse-grained jarosite white,yellow,mixedwith white,yellow,pink

B. Leadred and oxidizedoutcrops. In additionto thefactorssutlinedabove,therearetechniques focusedon the"limonites" thatarevery usefulin broadlyoutlining original,hypogenepatternsof alterationand mineralization.Thesefollow directlyfrom thegeochemistry of leachedandpartlyleached (1995). outcrops,asdiscussed in Einaudi ( 1) Keepingtrackof thedegreeof leachingof primarysulfudesitesis usefulin orderto reconstruct bothhypogenesulfidezoninganddterationzoning. Sericiticzonesleachto a greaterdegreethanpotassiczones.Thedegreeof leachingcanbe recordedduringmapping(see sectionIV.C): increasingdegreesof leachingarerecognized by ttresequence: . .

. .

glassylimonite:lowestdegreeof leaching;copperstill presentin glassy of abundant limoniteandin malachiteand/ortenorite;indicatesabsence pynte andneutralsurfacewaters;poussicor propylitic alterationtypical. low degreeof leachingof Cu andFe in near@: with potassicprotores(or propylitic neutralenvironments associated fringes,but thesewittr lessor no glassylimonite,lackof A,B veins, etc); goethiteboxworks: leachingincreasing oartlvleachedcavities(rimmedwith eoethiteor hematite):indicativeof high pyrite:chalpopyrite ratios,likely thatsericiticalterationis presenq Cu-oxidesandcarbonates unlikely.

9

Einaudi,p. 10,April 19. 1996

' .

hematite:soethite ratiosindicates @ing increasingly acidconditions;all Cu leached, mostof theFe leached. leached cavities(in somecasesfrlledwith jarositeor alunite)re,present high degreeof lcachingin ver)' acide,nviro[menb:sericiticor advanced argillicalteration, apid-sulfate zones,silica-pyrite-alunite ledges,vuggy sifica:Cu-oxides& carbonates absenl

All of theseforms of limonites(but mainlythegoatrite)aretermed"indigenous", on thebasisof textureasindicatingin-siuroxidationof orginalsulfidesites. (2) "Glass),limonite"is a termappliedto amorphousFe-hydroxide thatcommonly containscopper;this phaseis importantbecause it denotesvery low degreesof leaching(copper still present)andis characteritic (lotsof K-sparandliule or no of weatheringof Dotassie+rotores pyrite,hencelittleacidgeneration).Mappingthedisributionof glassylimonitecanhelpro delineate thechalcopyrite-(bornite) zoneandcommonlythis represents thezoneof highest hypogeneCu-(Au) grade.It is an indigenouslimonite. Glassylimonitehasthefollowing characteristics: . . . . .

glassylooking,like obsidian conchoidalfrachrre darkblackishbrownto black bright ruby-redinternalrdlectionsin sunlight grainsizeandmoryhologyttratmimicschalcopyrite.

(3) Relictsulfideslockedin unbrokenquarz An aid in detineatingoriginal distributionsof sulfideassemblages is to makepolishodsectionsof quartzcollectedthroughoutthe leachedcap. Studyunderthemictoscopein reflectedlight may revealunoxidizedsulfidesthat havesurvivedtheleachingprocess. (4) Exoticlimonitesareall ttrelimonitesthatdo not rcpresent originalsulfidesites. The iron hasbeentransportedin solutionin surfacewatersandprecipitatedalongfracturesin the rock. Exoticlimonitescanbedistinguished from indigeirous limonitesby ttrelackof pseudomorphsor boxworksaftersulfide,by their presenceon randomfracturesthatarepartof the regolithandthatcut all hydrothermalfracores,andby ttreirctraracteristic appeanuceasmassive coatingsand"pains", commonlywith botryoidalandchatoyantsurfaces(if goettrite).Some exoticgoethitetakeson a glassyappearance, but it canbedistinguished from glassylimoniteby thefactthattheglassymateridis only on thesurfaceof thegsnring(you can't"see"into it). An importantpoint is ttratmappingof totalabundance of limonitesdoesnot revealfte originalsulfidecontentof therock (a rock wih l07oexoticlimonitecontained lesssulfidethana rock with with l%aindigeirouslimonite);keeprack of relativeabundance of indigenousandexotic limonitesandtheirmineralogy.

VI. Reconnaissance:What to retain from the DetailedMapping Scheme

Reconnaissance mappingfor porphyry-typedeposisneedsto focuson the standard featuresof lithology andstrucnrreandon someadditionalke],features.Thesearelistedbelowin ordcr of imporance. The list largelyis basedon thosefeanrresttratsurvivetropicalweathering, evenin acidenvironments.Wall-rock alteration,especiallythe "argillic" g4)es,needsto be deemphasized!Reconmappingfocusedon porphyrytargetscanbe doneeffrcientlywittr only five color pencils: bluefor faults,red for porphyries,orangefor quarEveins,groenfor shreddybiotite, andbrownfor limonites.

l0

Einaudi,p. ll, April 19, 1996

A. Rock description,especially"productive"porphyries,includingcolor,textures,and grain size andVoof eachmineralin the rock. of the "productiveporphyry"haveto be In porphyryexploration,thecharacteristics understood andlookedfor: -50Vofine-grained(<0.5mm) aplitic(not aphanitic)groundmass. -50Vaphenocryssrangingfrom 0.1 to 0.3 cm, if quartzphenosarepresenttheyareroundedand embayed(qtzeyes).The significance andimportanceof this rock textureneedsmoreemphasis.It is so important,thatyou couldconsiderassigninga specialcolor (red?)to this rock type! andstnrcturalaniudes. At B" Ouartz veinsand veinlets,includingtheirabundance "map l:5000 scale,oneobviouslycannot all he veinlets",but thekey setshaveto be identifiedand representative strikesanddips plouedon themap. Abundancecanbeestimatedandwriuendown for eachoutcrop.Theimportanceof quarz veinsandveinletsin regionalreconstemsfrom two factors:one,we know theclosecorrelationberweengradeandquarz veinsin porphyry-type deposis,andtwo, quartzveinssurviveweatheringandrernainin outcropasunambiguous evidenceof hydrothermalactivity. Quare veinsareso imporant ttratttreyalsoareworttryof a specialcolor duringmapping(orange?). C. Limonite assemblaees needmoreemphasis.Eachoutcropshouldbeassessed for proportionsof glassylimonite,goethite,earthyhsmatite,jarosite,tenorite,andgreenCu carbonates/silicates. Proportionscanbe visuallyrecordedby a colorcodefor eachof these minerals,or by assigningratiosin pre-assigned order. In r@on,I wouldchoosethelaner approach.In mappinga prospectthatis beingdrilled,I would usecolorcodes.Limonites typicallyarewell-zonedandreprese,nt an excellenttargetingtool. D. Relativeabundanceof indieenousand exoticFe and Cu oxidesalsoneedsto be estimated.Eachourcropueedsto receivea numberthatindicatesthegeologist'sassessment of whethertheCu assaysrepresent transported copperor "in-place"cropper. E. Biotite distribution oatterns. especiallvof "shreddv biotite". areusefulto delineate zonesof potassicalteration,which in BaurHijau-typeporphyriesrepresent theoretargeLBiotitein fine-grainedbiotizedandesitemay not out-liveweattrering, biotitethathas but coarser-grained replacedhornblendein hornble,nde andesitesor in hbl-bearingtonoliteporphyriescommonly survivesweathering.In thecaseof hbl sites,if thebiotitedoesn'tsurvive,is characteristic "shreddy"texilre will survive. F. Maenetiteabundanceneedsto berecordedby visualestimateandmagnetic susceptibilitym€asurern ents.

VII. Fact Maps and Interpretations:The "Folio" Field sheetsaretransferedto threeseparatefact maps. A basefact map servesasthebasisfor drawinganinterpretive geologicalmap with lithologies,struc$re,andveins;analterationfactmaP servesasthebasisfor drawinganalterationmap,anda "limonite"or "ore" factmap servesasthe basisfor drawinga mineralizationmap. The fact mapsandthe interpretivemapsdrawnfrom thefact mapsshouldretainall of the strucoral informationshownon the originalfield shees. Transferof dips of veinsandfauls to the alterationandmineralizationoverlaysis especiallyimporunt, asthis allowsthegeologistto documentthethird dimensionandto explorethestrucnralconrol of ll

Einaudi,p. 12.April 19. 1996

patternsandthepossibilityof post-oreoffses on fauls. A mapwithoutan]' alteratioD/mineralization strikeanddip sl'mbolsis not a geological map. A. Fact maps and follow-up interpretation aretwo stepsthatgo hand-in-hand wi0r field mapping,obviously. Bottt of thesestepsneedto betakenroirtinelyandin a timelyfashion. The mappingprojectshouldnot beconsidered comoleteuntil suchtimeasthefactmap hasbeen usedto constructinterpretivegeologicbasemapsandrelevantoverlays.Supervisorsshould ensurethateachgeologistis give,nthetime to work with, andthink about,his mapping.A rough estimateis that 3 daysof field mappingrequiresI day of ransferringtre mappingto a fact map anddoingtheinterpretive work. (1) factmapsshouldbe keptup-to-dateby ttreindividualgeologiston a daily(or at Ieastweekly)basis (2) oncea significantareahasbeenmapped,but well beforemappingof the chosenareahasbeencompleted,thegeologistshouldbeginto makeinterpretive overlays.These will beworkinehypotheses thatwill aidhim ashecontinuesto map. (3) interpretation basedon factmapsshouldbe doneat thesamescaleasttrefact mapsandshouldretainall the strucnrraldetailrecordedin thefield. Uldmately,theseworking sheeswill bereducedin orderto generate a smaller-scale map,but theimportantstnrcturaldetails needto bepreserved at all scales(I haveseentoo manygeologicalmapsthathaveno dip symbols, andthatdisplayphotolinearsinsteadof faulfsacanlly mappedin thefield). (4) eachgeologistshouldbegiventhetime necessar.v to completethe interpretation.A reasonable schedule for planningpurposesis 3 daysmapping,I dayinterpreting. TheInterprctivephaseshouldbedoneby handin fuUcolor. Oncethemapsarecompleted,but not before,thefactmapandinterpretations canbehandedoverto thecomputer(assumingthereis a justifiableneedto do so). (5) thehand-drawnfactmap,fully color-coded, represents a majorinvesunentof time andmoney. It shouldbe carefull!,archived,andthenam{s) of thegeologist(s)anddatesof work shouldbewriuenon eachfaa map. B. The Folio. The following typesof informationshouldbe displayedin a folio setderivedfrom thefield mappingphase: (l) basemap: lithologies,strikeanddipsof bedding,faults,contacts, majorveins. (2) eachoverlayis drawn on a gray-scaleversionof thebasemap,so thatthey "standalone"(e.g.,lithologiccontacts, theoverlay faults,etc,arcvisiblewithouthavingto ove,rlay on thebasemap). (3) vein overlalr: all largeveinsandrepresentative veinletsets(color-codedto dominantmineral)plonedto truestrike,illusrativedipsindicated;veinabundance contoured. (4) limoniteoverla],:disributionof glassylimonite,goethite,earthyhematite, (absent, jarosite,tenorite,andgreencopp€roxides. Color applid to indicaterclativeabundance and low, moderate, high). Areasof dominantlyexoticversusdominantlyindigenouslimonite.s versus Cu-oxidesshouldbeidentified.Basedon mappingof limonites,areasof py-dominance cp-dominance shouldbeoutlined. (5) magn*iteoverlay:Illustratethedisributionof magnetite, disseminated, vein/veinleEor replacement, andcontourfor abundance. (6) alterationoverlalr: emphasison mine,ralsrattrerftan alterationtypes;try simply clays,sericite,silicaledges, showinglimits of mineralssuchasseondarybiotite,chlorite,e,pidote, jasperoids,erc.

T2

Einaudi,p. 13,April 19, 1996

i-

Finally,with regardto folios,a completefolio alsoincludestopography,geochemical and geophysical In theirrelationto thegeologicalmaps,thefollowing dataanddau interpretations. poins areimportant: (7) themagnetiteoverlayproducedduringthefield mappingphase(andwhich couldincludemagneticsusceptibility measurements on theoutcrop)canbeusedto interpret groundandairbornemagnetics. (8) theraw geochemical dataon soil, strezrm sediment,or rock-chipsamples, geologist geologically who generated shouldbe interpreted andhand-drawnby the thegeological mapsandoverlaysdiscussed above.The patternsof gradedistributionshouldreflocthis conceps of gradecontrol. Computergenerated contourmapsof assayresuls shouldbeusedonly if there is no geologicalmappingavailable. C. Comoositemaos: exolorationmodelsand drill tarpetine. HereI brieflv discuss thefinal andvery importantproduct or raisond'Atre,of thefolio: thecompositeof key features. A trivial exampleof thisapproachis givenby Figure8. Figure8 is re drawnfrom portionsof a folio ttratwasoneof ttreprojectscompletedduring ttremappingcourseheldat Bau Hijau in lvlarch1996. Thefolio displaysthefollowing feaores: lithologies,faults,threeclassesof quartzvein abundance, andhand-contoured soil geochemisry for copperandfor gold. Additionally,we hadavailablea l:10,000scalealterationmap. We anemptedto pull out of this daa setthekey feanrresthatwould helparget a drill holeinto the centerof theorezone. It is clearfrom Figure8 ttrattheouterlimit of abundantquarz veins(-+5 volVo)egrlinssthe+0.5 VoCumneat depth. Additionally,thefollowing is evident: . . . . .

outermostedgeof secondary biotite outetrlimit of rarequara veins outerlimit of moderatequare vens (l-Z%o) outerlimit of abundantqz veins(+SVo) presence ofporphyries

distancefrom +0.57cCu 300- 400 m 200 m 150m 0m 0m

In theabsence of a drilled-outreserve,thecompositemapcouldshow thelimit of glassy limonite. Additionalfeaturesthatshouldbe displayedon a compositewould be stnrcnrral directionsof quartzveins,limis of sericiticalterationandotherhydrothermalalterationtypes,and limits of indigenouslimonites. A final exercisettratcanbe doneto aid in targeaingis to generate map. By a "coincidence" this I meanthattherearecertainfeatureswhosecoincidence in spaceyieldsstrongerevidencefor a targetthananyindividualfeanrreby itself. As an example,thefollowing coincidences wereused duringtheMarch 1996mappingcourseasindicatorsof themost favorabledrill targetsat Baur Hijau (listedin orderof increasingfavorability): . . .

A: coincidenceof abundantquartzvens and highestcopperin soil B: coincidenceof abundantquare veinsand,highestgold in soil C: coincidence of A andB

Therationalefor coincidence A is ttrata copperanomalyassociated with abundantquartrveinsis (raher more likely to representindigenous ftan ransported,)copper. Had we hadthedata,we would haveusedcoincidence of quaraveinswith glassylimoniteandwittr highestrock chip copper. CoincidenceC reinforcesA andB. All tre argets basedon coincidenceC overliethe +0.5 VoCuzoneat deph.

l3

-

Illapping

technique

for

vertlcal

rock

faces

tDaliA 6nloqist date seale

air side l n clu d € w tlttGn notes t o r ob se r va tl ons on r o ck te xtur e s, su!f lde t a t lo s an d r bund!nce, a n d q lz vn abundance

m afic m a n e r a l a lte r a tlo n co lu m n

45% apliti( O.O5 mm 9.m..lO % hbl tonolite.45% phenos, 3-5% qtz eqes, eqe 4O% 2-3 mm plaq phenos: no qtz vnlts: v n lts: tr cp, local fresh hbl; tr epid in f alds sites

a so l i n o

rock side

tonolite. as a bv; A-$ vnlts O.l l6 wl cp: overall l-2 % cp; sec Ksp & maq absent to n o lite. as a bv; A vnlts O.O5ll: A-8 vnlts lllO; overall lO% cplbnl:ksp halos on all qtz vnlts; tr mag tn A: 4-5 7o maq overall. tonolite, as abv; A-B vnlts ov era ll 3-4 % cp: | % maq.

t22

O 214 wlcp:

tonolite.5O% aplitic g.m ,l5% hbl phenos, no qtz eAes: 35 % 3-5 mm plaq phenos; 3% pq in D-vns lllO: tot pg 5-8%; no mag.

tonolite.45% aplitic g.m.,l O% hbl phenos, 5-6% qtz eqes, 4O% 3-4 mm plag phenos. A-B vnlts wl cp O.l l2 O, D-vns olfset g-vns; overall 5% cpl pg 2; no m ag.

Includewdttennotc8 for key obsarvstlonsrelatlng to dructurus, contrct3, and velns

2 m fault zone:]W claA. '- HW bx, normal offset of intrusNe (ontact iffeg intusive contact

tocalitA qeologist date scale

lVlapplng

air side

technlque

for

vertlcal

rock

faces

m atlc m in e r a l a lte r a tlo n co lu m n

I n clu d € wr llten notos t o r ob a e r va tlona on r o ck t€ xlu r o s, llmonlt€ c h ar a ct€llstl c s, a nd qtz vn abundance bnolite,45% apliticO.O5mm g.m ,lU" hbl phenos, 75% qD eA6,40%2-3 mm plag phenos:no qz

basel i ne

rock side

Includewrflt€nnol€s for koyobsorvatlono relatlng to alructurca,contacts,andvelns

bnolite, as abv; A-8vn9 O.l16wl ql lim: secKspar and mt absent. brplite, as aW: A vnlE O.O5ll,A-$ vnlts Illo; vnlB gl lim + Cu-ox;Kspar halm on all qD vnlE:tr mt in A-vnlE; 4-5%maq o,terall. tonolite:A-8 vnlE O214wl gl lim;tr Cu -ox;felds frah;mfrs biod & chlotld tonolite:no qDvnlE: D-vns lllO:local fr6h hbl, but mosdg *r'd; abund leachd cavs wl ear hm + aoeth: lo(al jarosite: no

2 m fault zone;V^lclau, t- HW bx: normal olfset of inttusNe conftct

o88

bnolite: A-8 vnlE O.l2O:D

vnsoffsetA-8 vntE,goetlite onlA; no mt

1

85

72

irrea intuslve contact

D-vn swarm; Illo. D-vtE cut infrusive @ntact, A-B qu vnlE cut bA late Wrph.

= = ' .n J oP [l X.p

Flg. 3 Colo. co(br and .tyl.. tor r gPlr|g hypogpm and .up.?grn. rdt. 'o?!'nl

UORE"MINERALS

M,T,E i n.udlA. or96

P LO TTED O N RO CKSI DE H Y P OGE N E VEIN/ VNLT D}98'D SULFIDE

S UP E RG E I { E oxoE til8s'D VEIN/ VNLT

pyrllo

,arosllo

NONE

earlhyhemallle '. :.

NONE

ooothlt€

NONE

coppSr oxEos

chalcopyrlte

glasryllmonite ..'.'

/

l.'.'^99o

rl.

/y'

f

".'".rro"i.n,ilo-S t j ,,] '" ". .

/

l/:=.

..'.'.

f . '":'

bornlle

t{ONE

magn0lil0

magnetO {rrlkn)

hm EPeCUlsr

lpecularhematlte'. (r!lhl)

HYPOGENESULFIDES

.

... /:> '

:' '1;;

OXIDtrEDEOUIVALETT gla!! llmonlle,Cu-ox,

bornlte

CnaE O P y r[ t

s<-'+\-

. t.\

-o\,1i: S.' ..o\$)*"

pv,y -.

1.> ."o' _ o d\(i..inr6-rnrd cavados -i

o)€ o crvatos, :- teached ^\ o ---..,-d-crc ),":"oo hsmatlte, hsm aerthy .errhy :' ->. 61 -.-\o

and JrtoEll€

Flg. a Color co(b. frd dyL. for nr.pplng diarttlon rnd v.in mlncrlla.

NON.OREMINERALS

ll T Ehrudl.ADr96

AIR SIDE WALL.ROCK ALTERATION XINERALS

ROCK SIDE VEII|FFILLING IIINERALg

VEINHALOS PEBVAS IVE //

' \

*'

, _-

//

,i

"""

'."'S lllca

quartz

"."'

' .',' btotlt o

s6c0nda ry biotlte

:

..'.'

tt

//

K-tetdspar

secondaryK-f6ldspar

Na-loldspar

seconderyNa-16ldspar

€pldols

epidols

' ,',' chlorlle s.rlclt6,cley

PERVASIVEALT'N, HALOS

ft

chlorll€

t,

-" t ,

lIt-

rerlcllo,clays

/tz

VEINS,VEII{-FILUNGIIINERALS F(EK EDE

-'a.a-; bio.n{ Ynllt '\

rl---"' -

Ii l EF C OL U T I{ : rlt'n in mh siles

-\

-'\..

-(K!p)

\

\S-: \\

qtsvns

Fig.5 Examplesof color codesand styleslor mapplngunox'd(hypogene) and ox'd (supergene)exposures. M.T.Einaudl, Apr96 AIR SIDE

R(rcK$DE

HYPOGENE

AIRSIDE

OXIDIZED-WEATHERED

ROCKSIDE 89

1-..--t. a-' It 6d

o

l \'.

e'

Flg.6 Separatlon of outcrog mapplnginto laysrs. M,T Einaudi. Aor'96

MAPPING USINGOVERLAYS OUTCROP VEINS BASE MAP: LITHOLOGY,STRUCTURE, aTz D90'<9t€ qd-kspar4glass x limonite)vns r

x x

lntrusve @nrtct

I

x

x

+

toNorg.rE PORPH

'\

+

I m wide fault bx '- -

-tt a

\,

t

t+

"

{- t - r rf

+- t '+O +e

9 a

rro'

-t

/1

a

+- a r*

A,

X asp halos

qE-ser
| r

k l. "

+o

I

t,I'Ftii;;i

Kpar hatos

glass limonite

ftXr*t i''it{i, t.li';:.i;j"riitt

OVERLAY #1: ALTERATION

1 leachedpA sites. earthA hem & Frosite

c1

Cu-ox

indigenous goel:hite

Fig.7 FactorsInvolvedIn relatlvecoppermobllltyin the aeratedandcaluratedzones. M. T .Eine u di. A o r9 6

pervesiveserlcilic alterallon Inhibits lormalionof supergene clays

abundant sup6rgene clays WE A K L Y LE A CH ED glassylimonite, indiganeous goelhllo (Cu-ox) ,/

abundantsupergene clays,decr€ asing

I , MO DE RA T E L Y L E A CHE Di

0utwald

I sr n o n cL ,' v

L E A CHE D // ' (hematite) .,' hemalite,/ ./ Ja.osite, /

goelhile,

i

exolic Cu-ox

SATURA TEZONE D

S UHF A C E

TABLE **",""-"ff WATER superg6n€ chalcoclle P OTA SIC S

POIASSIC wrlh

cppy ,i , , , ' cp-py,; . ,, ,,,

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