Download - SA Garwin Epithermal Vein Presentation April2011

8/10/2019 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



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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



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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


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



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Hydrothermal Alteration


Associated with near-neutral H acid H 3ores

Mineral illite sericite alunite, kaolinite,assemblage interstratified clays

(illite-smectite)

zoned higher T

pyrophyll ite, diaspore,zoned acid neutral pH



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Geochemical Associations


High Au, Ag,As, Sb,

Au, Ag,

As, Sb, Bi,

, , ,

Se, K, Ag/Au

, , ,

Te, Sn, Mo,

Low Cu, Te/Se (unless alkaline) K, Zn, Ag/Au



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Noel C. White

SEGEG-MGEI WorkshopGEI Workshop Mataramataram IndonesiaIndonesia

November 2010ovember 2010


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Boilin of H drothermal FluidsSinterlithostatic

200

400

th

,m more

gasmoresalt

600

De

hydrostatic+

800

Hedenquist et al., 1998

100 200 300

Temperature, oC


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Boiling of Hydrothermal FluidsBoiling is a powerful and complexmechanism. It is associated with

Lowering of temperature and pressure

Loss of gases (mostly H2O, CO2, H2S)

Increase in oxidation state (slight)

Champagne Pool, Waiotapu, New Zealand


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yAu(HS)2

- + 2H+ + e- Auo + 2H2Sreduction

Porgera, Zone 7Papua New Guinea

Sleeper, Nevada


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Adularia de osition b boilinHS- + H+ H2S

HCO3- + H+ CO2 + H2O

Adularia crystals, Mexico



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Ca(HCO3)2 CaCO3 + H2O + CO2

Lattice textureHedenquist et al., 1998


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Silica de osition b coolin



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Silica depositionis affected by pH

Neutral pHQuartz, chalcedony

and amorphous sil icadeposit

Acid pH

suppressed

No siliceous veins

Low sulfidation vein texture, McLaughlin, California, USA


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Manganese Minerals in

Epithermal Veins Some epithermal veins contain manganese

minerals, mainly rhodochrosite, manganoancalcite or rhodonite (look for pink colour)

s s a yp ca ea ure o n erme a esulfidation deposits (discussed more later)

base metals and commonly have high Ag

Mn minerals weather to black oxides that

cause hydrogen peroxide solution to fizz

Rhodochrosite, Capillitas, Argentina


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Significance of Alunite

1. Acid conditions.

3. Available alkalis

These conditions can occur from1. magmatic gases (HS)

2. near-surface condensation of boiled offgases (HS, IS, LS)

.

rich rock)

LS settings onlyLithocap ( HS) settings only( )


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g y(steam-heated blanket possible) H2S + 2O2 H2SO4

Steam-heated waters,LS, IS, HS possible

2. STEAM-HEATED

(HCl, SO2)1. MAGMATIC

Any sulfide-rich setting

Sill itoe, 1993

.


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Significance of Pyrophyllite

BUT , ~

If supersaturated w.r.t. quartz, T low

In practice

Pyrophyll ite + chalcedony or amorphoussilica means T low

Temperature oC


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Alunite

Mineral 100 200 300

pH

Temperature oC

MineralStabilityJarositeHalloysite

Kaolinite

Dickite

Pyrophylliteidic

StabilityDiaspore

Zunyite, topaz

Anatase

Rutile

Ac

Mineral assemblagesallow us to estimate

Quartz

Pyrite

Marcasite

Smectitetral

temperature and acidity

Sinter

lithostatic

Chlorite/smectite

Illite

Chlorite

Epidote

Ne

400

200

th,m

Biotite

Adularia

Calcite

Mordenitelkaline

800

600

De

hydrostatic(water + 1 wt% CO )22

Hedenquist et al., 1998after Reyes, 1990

Wairakite

Epithermal ore deposition

100 200 300Temperature, oC


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Structure and Epithermal Deposits

y ro erma epos s are con ro e yhydrology (i.e., permeability)

os ep erma epos s are nocontrolled by major faults

Most attempts to relate epithermal deposits

Think about permeability and fluid flow


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Low- and Intermediate-Sulfidation

oe . e

SEGEG-MGEI WorkshopGEI Workshop Mataramataram IndonesiaIndonesia

November 2010ovember 2010


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Form of Deposits

Low-Sulfidation Intermediate-Sulfidation

High-Sulfidation

pen-space ve nsdominant

pen-space ve nsdominant

e ns su or na e,locally dominant

Stockwork ore Stockwork ore Stockwork orecommon common minor

Disseminated ore Disseminated ore Disseminated ore

Replacement ore Replacement ore Replacement ore


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Veins are the commonest form for

There are many variations, including oc wor s comp ex ve n arrays Vein breccias breccia zones with

the form of veins Most veins show complex histories

re-opening, more deposition, etc

Cl i l


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Classical

Model

Buchanan, 1981

This enduring model wasproduced before thedistinction between

different deposit typeswas recognised.

Low sulf idation schematic


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Low-sulf idation schematicmodel

Silicified blanket

Illite adularia



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Central Taupo Volcanic Zone New Zealand


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Taupo Volcanic Zone

Meteoric water


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Meteoric water

Water table

Silica sinter

Ore body

argillic alteration

200

2

00

2

50

asement

30

Intrusion1 km

1 km

New Zealand low sulfidation model

Silli toe and Hedenquist, 2003Geothermal (and LS) setting


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Geothermal (and LS) setting


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Low-Sulfidation epithermal gold deposits

fluids Fluids dominantl near-neutral Hmeteoric water (possible small magmatic component)

Deposits occur in zones of highpermea y (mostly open fractures) Characteristic vertical and lateral

Characteristic textures


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Vent area enriched- - -

Steam-heated alt'n(HgAu-Ag) Overprint

uartz-illite adularia

- Au A As Sb Tl H

Brecciazones

chlorite

Berger and Eimon, 1983


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Depth Tempo Alteration Vein textures/Mineralo

100

1000

150Smectite

Illite-chalcedonymassive

banded

200200

smectite quartz-

chalcedony

300 225

gold

400 Illitequartz

600 calcite

att ce

700

250

adularia

OhaakiN Z l d

Early Carboniferous sinterN th Q l d


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New Zealand North Queensland

Rotorua

New Zealand

Modern and Ancient


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sinter

El Salvador

sinter

Lattice textureLattice texture


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Calcite scale, geothermal bore, New Zealand

Quartz after lattice calcite, Bimurra, Queensland

Lattice calci te, Martha, New Zealand

Golden Cross, New Zealand


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Sleeper USA


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Sleeper, USA

Gold/electrumlattice texture

colloform-crustiform banding

Hishikari, Southern Kyushu5 5 MT @ 55 g/t Au (1996)


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500 m5.5 MT @ 55 g/t Au (1996)

IlIl--SmSmQzQz--SmSm

rr-- mm

AndesiteAndesite

AndesiticAndesitic PyroclasticsPyroclastics

DaciteDaciteMine Section

NW SERegional Section

Izawa et al., 1990


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Cross-Section B-BW SE

Gravity High

AndesiteAndesite

--

QzQz--SmSmrr-- mm ac teac te

ChCh--SeSe

Izawa et al. 1990

BasementBasement SiliciclasticSiliciclastic RocksRocks


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Honko

vein

systemGreywacke

basement

High > 100 g/t Au

Medium / Low =

confidential

Hishikari, Japan


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Intermediate-Sulfidation Epithermal Deposits


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Intermediate Sulfidation Epithermal Deposits

Silver-Gold-Base metals e.g., Fresnillo, Pachuca, Comstock Lode, Creede

Ag or Au dominant economic metal; Au minor in

some. Ag/Au commonly X000-X0000 Zn and Pb typically ~1%; Cu and minor Sn may

increase at depth

Veins typically quartz and calcite with minor

chalcedony; some adularia, Mn carbonate, fluorite,gypsum, anhydrite

Textures diverse, may not be so well developed

Vein strike len th variable can be ver lon >20 km

Not likely to have formed in geothermal systems liketodays

Vein rhodochrosite, Capillitas, Argentina

These can be Giant deposits!

Acupan, Baguio, Philippines


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~ 8 Moz Au mined from Acupan veinsbetween 1931 and 1993

~ 3 Moz bulk minable resource defined inmid 1990s

Diatreme volcanism around 1 Ma >460 IS epithermal Au-Ag-(Te) veins

formed after 0.7 Ma (av. 1 m width)

Quartz-carbonate-base metal veins hostedin granodiorite, diatreme and andesite

Modified from Cooke and Bloom(1990)

Modif ied from Cooke et al (1996)

Balatoc Diatreme

Virac Granodiorite

Ampucao Dacite Porphyry

Zig-Zag Formation

Baguio, Philippines


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Weak surface ex ression of

veins mined below in Acupanmine. Outcrop 200 m belowsurrounding hills, 200 m

.

Acupan Epithermal Au Veins


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p p

Colloform bands of quartz, calcite, rhodochrosite and base metal sulfidesClast of Au-rich grey quartz breccia overgrown by colloform calcite

Potassic and propylitic-altered Virac GranodioriteBrecciated qz-pyrite vein

Fresnillo, Mexico


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Santo Nio vein

425 m Level

Siliceous veinZacatecas, Mexico

Rhodochrosite vein with sphaleriteCapill itas, Argentina


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LS IS

Creede IS


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Creede IS

10 km

HS IS

Simmons et al., 2005

HS w/ IS to NIS w/ lithocap HS


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.,

w adv arg

LSa, VIILS


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p t erma e n epos t eometry

and Mineralization Styles

- Ex loration Im lications

Fresnillo, MexicoMajor IS deposit, Ag-Au veins 3,600 t Ag, 22 t Au

Ore outcro s onl at Co. Proao


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Ore outcro s onl at Co. Proao

Co. ProaoSan Luis shaft


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Fresnillo, Mexico


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Surface expression of major veins at depth

Fresnillo, Mexico


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Santo Nio vein

425 m Level


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Gosowong Kencana Vein System


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Gosowong Kencana Vein System


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Kencana Longitudinal Section


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Kencana Deposit


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Kencana Mineralization Stages


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Kencana Mineralization Stages


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Kencana: Vein Types and Zoning

-

1000 - 3000100 - 1000

Au (g x m)

0 -1010 - 50


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Kencana: Distal Calcite Veins


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Kencana: Distal Quartz Veins


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Stockworks and Breccia


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and Sheeted Veins

Way Lingo Longitudinal Section


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N40oWS40oE

Augxm:

20

50

1001065mRL

VeinA

Dacite

Andesite

200

Predicted

oreshoot

1020mRL70o

?45o

??

VeinB?

100m


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N40oWS40oE

1065mRL

VeinA

Ag/Au:

20

15

10Dacite

Andesite

1020mRL

5

?

open

?open

VeinB?

100m

open

Ag/Au~1500(valuesupto3390Agand2.0AuinDDHLL05)


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