Yilgarn 3/MERIWA Projectpmd CRC Yilgarn 3/MERIWA Project Hydrothermal Alteration Footprints Peter...

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YilgarnYilgarn 3/MERIWA Project3/MERIWA ProjectHydrothermal Alteration FootprintsHydrothermal Alteration Footprints

Peter Neumayr1, Steffen G. Hagemann1, John Walshe2, Leo Horn2

1 Centre for Global Metallogeny, UWA2 CSIRO, Division of Exploration and Mining

pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery

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Outline of presentationOutline of presentation

• Camp-scale geological overview• Camp-scale redox variations• Deposit-scale alteration variation

– Paragenetic studies– Whole-rock geochemical analyses– Magnetite compositions

• Exploration implications


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mapmapGeological map of Geological map of the St. Ives gold the St. Ives gold campcamp

Cross-section

Geochemical traverse

Perth

KalgoorlieKambalda

Modified after Watchorn (1998)Geological OverviewGeological Overview


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CrossCross--section through section through IntrepideIntrepide

After Karen Connors (2002)

Geological OverviewGeological Overview


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Detailed GravityDetailed GravityPlaya Fault

Victory Defiance

NorthOrchin

Revenge

After Ned Stolz, SIG (2002)


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0 5 km

MagnetitePyritePyrrhotite

Playa Fault

Victory Defiance

NorthOrchin

Revenge

Delta Fault

CampCamp--scale scale redoxredox variationsvariations

AB

Oxidized– Hematite– Magnetite– Pyrite– Arsenopyrite– Pyrrhotite– Loellingite

Reduced


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DCB

KSL

DFDDFD

PBS

PBS

W E

DCB

KSL

KSL?

FP

FP

SC

X-SECTION

A B

Geological OverviewGeological Overview


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Mount Blanc Fault

Gamma West Fault

Playa Fault

Victory Defiance

NorthOrchin

Revenge

0 5 km

MagnetiteMagnetite/Pyrite

Detailed gravity data: SIG CampCamp--scale scale redoxredox variationsvariations


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kilometres0 1 2

FelsicFelsic Porphyries Porphyries -- MagnetiteMagnetite

VictoryVictory--DefianceDefiance

RevengeRevenge



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PBS

PBS DFD CND BFL BFLDCB

DCB

PBSPBSKAM

KSL

KSLBFL

NautilusBrittania

Repulse

ConquerorFoster

Boulder Lefroy

South AfricaSirius

Intense PorphyryIntrusionsDCB

SN

SN

1km

1000m

Magnetite Alt.Pyrrhotite Alt.

Gold

DFD

KSL

DCB

KSLDCB DFD

DCB


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1 km

Empirical background for Te after Eilu and Mikucki(1996)

LD7114

X-section modified after Phung (1997)

Dispersion of Te around RevengeDispersion of Te around RevengeGeochemical traverseGeochemical traverse


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1 km

-10.00

-9.00

-8.00

-7.00

-6.00

-5.00

-4.00

-3.00

-2.00

-1.00

0.00

8.00 10.00 12.00 14.00

del18O

del13

C

LD70426 Playa LD70449 Playa LD7114 Revenge T effect Poly. (T effect)

400C 350C 300C 250C

Fluid composition:18O is +5 and13C is -2

Zonation on Zonation on 1313C and C and 1818OOcomposition of carbonate composition of carbonate

Geochemical traverseGeochemical traverse


pmd CRCDifferent generations of Different generations of magnetite:magnetite:•• epidote-magnetite

• magnetite

EpMag

Magnetite pre-dates gold

Mag

Ep bands, qtz-mag-

chpy veins

Hbl-btporphyry



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Revenge Gold Mine Revenge Gold Mine –– Ore PyriteOre Pyrite

Redox switches are important for gold mineralization LD7114 181.6 m

Magnetite

Hematite

10 um10 um



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Magnetite chemistryMagnetite chemistry

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

V2O3

Al2

O3

LD7114 198.5 LD7114 142.6_1 LD7114 315.1 LD51356 104 LD51356 147.6

V2O3/Al2O3=1

V2O3/Al2O3=10

V2O3/Al2O3=0.05

OxidizedOxidized

Red

uced

Red

uced



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Temporal and spatial integrationTemporal and spatial integration

• Most magnetite pre-dates gold• Minor hematite-magnetite present at the time of gold

deposition in the central corridor• Oxidized fluids present at the time of gold deposition• Regionally magnetite focused around gravity lows• Oxidized fluids are spatially, and most likely

genetically, related to felsic to intermediate magmaticintrusions

• Reduced fluids present in domains subjacent to magnetite

• Gold mineralization occurs preferentially in zones of greatest redox gradient

IntegrationIntegration


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Translate preliminary results Translate preliminary results into exploration criteriainto exploration criteria

Exploration criteriaExploration criteria


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Exploration criteriaExploration criteriaShear zones

Ox. Fluid conduits

Reduced fluid zones?

Gravity Low

Te anomaly

Magnetite halo



pmd CRCLocal exploration criteriaLocal exploration criteria

Po domain

Mag anomalies

Redox gradient

Overlay on “traditional” exploration criteria (e.g., structure)



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Project Review 3-4 Dec. 2002, Canberra

Major HighlightsMajor Highlights

• St. Ives camp is zoned with respect to redox conditions of ore fluid

• Hydrothermal alteration forms at different times– seafloor alteration (epidote)– porphyry-related alteration (epidote-magnetite-chalcopyrite) – carbonate alteration (regional fault zone)– pre-gold dispersed magnetite – gold-related alteration (chlorite, biotite, carbonate, feldspar, pyrite)

• Hydrothermal magnetite rims gravity lows on camp scale and has a strong spatial association with abundant porphyries



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Project Review 3-4 Dec. 2002, Canberra


• Zones of gold mineralization coincide with zones of greatest redox gradients

• Some faults (e.g., Conqueror) separated reduced from oxidized fluids

• Reduced fluids are diffused whereas oxidized fluid are highly focussed

• Pathfinder elements dispersed >100m around lodes• Te dispersion marks size of hydrothermal footprint

which can be traced to about 3km away from the deposit

• Methodology currently incorporated in the St. Ives targeting strategy



pmd CRCProgress on Y3 DeliverablesProgress on Y3 Deliverables

Mineral- and geochemical database

50% completed

Alteration geochemical plots 40% completed

Digital maps of alteration footprints

60% completed

Database of magm.-hydroth. history

Ph.D. project by MherdadHeydari

4D structural-hydrothermal models

50% completed

Microanalytical database of hydrothermal fluids

20% completed

Numerical and chemical models

commenced

Generic chemical and structural targeting criteria

40% completed


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Y3 / MERIWA Y3 / MERIWA Exploration Impact at St IvesExploration Impact at St Ives

• A working group established to maximize impact of research results on exploration targeting – research team integral part

• Working group utilising results generated by Y3/MERIWA in exploration targeting

• Expect drilling of targets identified by working group in 2004


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Y3 Y3 –– MERIWA Progress MERIWA Progress Additional PhDs / PostAdditional PhDs / Post--doc!!doc!!

• Integration of alteration/geochemical data at deposit to district scale

• Defining the relative / absolute timing of chemical events at district scale

• Relating chemical events to deformation events

• Sources of fluids??? – radiogenic isotopes

☺


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Ongoing/Future Research and Ongoing/Future Research and Exploration TasksExploration Tasks

• Determine extent of hydrothermal magnetite in other lithologies; specified structures

• Distinguish different magnetite types using microanalysis• Identify reduced and oxidized fluid conduits along fault zones

using mineralogy and whole-rock geochemistry• Fingerprint the geochemical characteristics of reduced and

oxidized fluids in the different structural corridors• Integrated geochemical/structural models with real fluid

compositions• Construct 3D/4D geochemical and structural model (Pathfinder

Elements)• Identify exploration targets in 2D/3D

Future WorkFuture Work

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