SA Garwin Epithermal Vein Presentation April2011

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Transcript of SA Garwin Epithermal Vein Presentation April2011

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    Characteristics, Processes, Products,Characteristics, Processes, Products,and Interpretationand Interpretation

    Noel C. WhiteNoel C. White

    Modified by Steveodified by Steve Garwinarwin for Southern Arc Mineralsor Southern Arc Mineralsodified by Steveodified by Steve Garwinarwin for Southern Arc Mineralsor Southern Arc Minerals

    Selodongelodong Camp SW Lombok Indonesiaamp SW Lombok Indonesia

    155 thh April 2011pril 2011

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    A ver im ortant st le of old de osit

    Can be very big: Lihir PNG 170 Mt 3.5 /t Au

    Porgera, PNG 85 Mt @ 5.8 g/t Au, 33 g/t Ag

    Can be ver rich: Cripple Creek, USA 630 t Au in veins grading 15 - 30 g/t

    Hishikari, Japan 220 t Au, Honko veins 70 g/t Au, 49 g/t Ag

    p erma go epos s arevery important economically

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    Epithermal Gold Deposits: Production + Reserves (~2000)

    .

    Alkalic LS subt e

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    Total Au and Agin Low and IntermediateSulfidation Epithermal

    Deposits

    (n=58)

    LS

    LS (alkalic)

    IS

    Au AgGemmell, 2004

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    Value of Epithermal Deposits (Au and Ag)

    16Ag $ LS (alkalic)Au $390 US/oz

    Low and Intermediate SulfidationEpithermal Deposits on ly

    14

    u N=4

    10 Low sulfidationIntermediate

    sulfidationn$(US)

    6

    8

    Billio

    N=12

    4

    ~5 Moz Au eq.

    0

    2

    sslias

    kari

    areede

    uro

    roraataimb

    oriakorah

    nillolianbaldecasnaovotitauio

    atoe

    al

    ideilos

    lloncow

    nceacikkemaareng

    aimaesdieinoanelsrogper

    mai

    onab

    lic

    ngoidashlinu

    el

    onrdia

    ihi

    Mtnleyeroreraeeklam

    GoldenCr

    ProfitisIl

    Hishi

    BaiaCre

    MtA

    uAra

    SacaVict

    GunungPong

    TonaFresK

    SanCrist

    Coms

    tockL

    Zacate

    RosiaMont

    Bereg

    TayBa

    G

    uanaj

    Pac

    ucha-

    SunnyM

    MogoCra

    ElBroOv

    Kar

    angah

    Takata

    BaiaM

    Gosow

    LebongTanPer

    ThaB

    Kushi

    Oat

    Montan

    aTunBull

    Sle

    Kono

    ElLi

    Misi

    RepPajiM

    M

    cLaugEs

    ElPe

    CerroV

    anguaW

    RoundB

    Emp

    Por

    CrippleCr

    Lado

    Gemmell, 2004

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    Location of Principal Epithermal Gold Deposits

    of epithermal deposits

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    Refers to deposits formed at low temperature.

    The term Epithermal was coined by

    .

    Lindgren in 1933 based on

    observations ofmineralogy of ores and alteration

    textures of ores and alteration

    an n erences a outtemperature of deposition

    depth of formation

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    Their characteristic minerals and textures

    mineralogy and zoning

    Formed at low temperatureso o o o- , -

    Developed at shallow crustal levelst icall

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    p erma epos s s ow a var e y odeposit styles they are not all the same!

    characterized nor fully understood weare stil l learnin !

    Not all epithermal deposits contain gold

    some are dominated by other metals,notably Ag, Zn, Pb, Cu, Sn

    Some are closely related to intrusions,

    some are not. The related intrusions neednot be porphyry copper-related intrusions

    erm no ogy s very con use

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    Origins of Deposits

    If we consider the origins of epithermaldeposits we can distinguish three classes

    deposits: two formed dominantly from

    end-member fluids, and one from acombination:

    Magmatic

    Magmatic-meteoricMeteoric

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    MAGMATIC-METEORICMAGMATIC METEORIC

    111 1

    2

    3

    2

    3

    2

    3

    2

    3

    4

    km

    4

    km4

    km

    4

    km ?

    Textures: restricted Textures: diverse, modest Textures: diverse,

    spec acu ar

    LOW SULFIDATIONHIGH SULFIDATIONINTERMEDIATE

    SULFIDATION

    Au-Ag-Cu Au-AgWhat I will describe

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    Fluids: magmatic dominant in coremixed with meteoric on marginsMetal Associations:1 I-type: a) Cu-Au-Ag

    - -2 S-type: Sn-Ag-(Zn-Pb)3 A-type: Au-Ag

    Alteration:

    1

    a, an : prox ma very ac3 proximal not seen; distal neutralExamples:1a Le anto, Phili ines

    2

    Summitville, USAChelopech, SlovakiaEl Indio, Chile4 ,San Gregorio, Peru

    2 Cerro Rico de Potosi, Bolivia3 Emperor, Fiji

    m

    Porgera, PNG

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    Fluids: dominantl meteoric, withhigh salinity magmatic fluids at depthMetal Associations:

    Ag-Zn-Pb-(Au)- - - -

    Alteration:mostly neutral pHExamples:

    1

    Fresnillo, MexicoComstock, USA

    Thames, New Zealand

    2

    ,

    4

    m

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    u s: me eor c magma cMetal Associations:

    Au-Ag (very minor Zn, Pb)Alteration: hypogene neutral pH;

    gas condensates acid

    Examples:McLaughlin, USA

    1

    ,Waihi, New ZealandGunung Pongkor, Indonesia

    2

    4

    m

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    Where do they occur?

    - ,

    Low- Sulfidation

    - ,

    High-Sulfidation

    Calc-alkaline to alkalinevolcanic arcs (tholeiitic rare)

    Subaerial environments

    Calc-alkaline volcanic arcs

    Mostl subaerial environments,

    Mostly intermediate to distalvolcanic settings

    rarely submarine

    Proximal volcanic settings

    In volcanic rocks or basement In volcanic rocks, rarely inbasement

    White and Hedenquist, 1995

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    Form of Deposits

    Low-Sulfidation High-Sulfidation

    Open-space veinsdominant

    Veins subordinate, locallydominant

    Disseminated ore mostlyminor

    Disseminated oredominant

    ep acement ore m nor ep acement ore common

    White and Hedenquist, 1995

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    Stockwork, Golden Cross Vein, La Guitarra

    Vein, Golden CrossVein, Hishikari

    FORM

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    Chinkuashih La Coipa

    Akeshi Sul fide vein, El Indio

    FORM

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    Characteristic Textures

    Neutral-pH, meteoricLow-Sulfidation

    Acid-pH, magmaticHigh-Sulfidation

    banded veins

    breccia veins

    vuggy quartz

    massive quartzdrusy cavities

    crustification

    massive sulfide veins

    crudely banded veins

    White and Hedenquist, 1995

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    La Guitarra Golden Cross

    TEXTURES Dealul Crucii, Baia Mare Aginsky

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    Vuggy quartz

    TEXTURES

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    Ore Minerals in Au-rich Oresrequency o occurrence a un ance

    Low-Sulfidation High-Sulfidation

    Pyrite ubiquitous (abundant) ubiquitous (abundant)

    Sphalerite common (variable) common (very minor)

    Galena common (variable) common (very minor)

    Chalco rite common ver minor common minor

    Enargite-Luzonite rare (very minor) ubiquitous (variable)

    Tennantite-Tetrahedrite common (very minor) common (variable)

    Covellite uncommon ver minor common minor

    Stibnite uncommon (very minor) rare (very minor)

    Orpiment rare (very minor) rare (very minor)

    Arsenopyrite common (minor) rare (very minor)

    Cinnabar uncommon (minor) rare (very minor)

    Native Gold common (very minor common (minor)

    Tellurides-Selenides common (very minor uncommon (variable)

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    Min r l f nfrequency of occurrence (abundance)Low-Sulfidation Hi h-Sulf idation

    Quartz ubiquitous (abundant) ubiquitous (abundant)Chalcedony common (variable) uncommon (minor)

    Adularia common (variable) absent

    Illite common (abundant) uncommon (minor)

    Pyrophyllite-Diaspore absent (except overprint) common (variable)

    Alunite absent (except overprint) common (minor)

    ar e common very m nor common m nor

    White and Hedenquist, 1995

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    Hydrothermal Alteration

    Low-Sulfidation High-Sulfidation

    Associated with near-neutral H acid H 3ores

    Mineral illite