IOCG Depos posit its s – The Expl xplor ora ati tion on and Resea sear halle eng nges es s ear ear ch c h Chall Dr Tim Baker , Manager, Manager, Geolog Geological ical Sur vey Prim rimary ary Indust IIndu ndustr r ies and and Resources Resources South Australia alia stries So So uth Austr
[email protected]
IOCG Depos posit its s – The Expl xplor ora ati tion on and Resea searr ch Chall halle eng nges es
• IOCG Dep Depo osits – Expl plo orat atiion Chal allleng nges es • Ev Eval alua uatting the Cr Criitical Ing ngrred ediien entts • Co Com mpa parrison ons s of IOCG Ter Terrran anes es an and d System ems s • Ex Expl plor orat atiion Impl Impliica cati tions ons and Res Resear earch ch Di Dire rect ctiions
Why Exploring for IOCG’s Is Difficult •
Vast alteration systems – hard to drill unaltered rocks
•
Numerous occurrences
•
Alteration and geochemical vectors to ore systems not well constrained
•
More than one way to form the deposits – Form from fluid mixing, multiple fluid sources – difficult to predict
•
Deposits form at a wide range of crustal depths
•
Wide variety of deposit styles
•
Good geophysical models; can we use alteration/geochemistry more smartly?
IOCG – The Critical Ingredients
• Evaluated Proterozoic terranes with major deposits (Cloncurry) and less endowed terranes (Wernecke’s) • Evaluated barren regional alteration, magmaticenvironments and IOCG deposits (Cloncurry)
Global IOCG Terranes
(Williams et al., 2005)
IOCG Terrane Endowment Terrane Feature
Cloncurry
Wernecke
Mineral Occ urrences
Numerous including several economic deposits
Numerous but no economic deposits
Host Rocks
Abundant, long lived mafic and felsic magmatism; meta-evaporites; abundant Fe stone
No known felsic intrusives; minor mafic magmatism; meta-evaporites
Deformation and Metamorphic History
Complex, long lived, structural history; med- to high grade metamorphism
Complex structural history; dominantly greenschist facies
Fluid Types and Conditions
Abundant high T ultra-saline Abundant moderate salinity brines and CO2; widespread brines; minor CO2 moderate salinity brines
Fluid Origins
Magmatic abd basinal/metamorphic
Basinal/metamorphic (possible hint of magmatic)
Cloncurry Mineral Occurrences
(Mustard et al., 2005)
Deposit
Size (Mt)
Cu (%)
Au (g/t)
Ernest Henry
166
1.1
0.5
Osborne
15.2
3.0
1.1
Eloise
3.2
5.8
1.5
Mt Elliot Starra
275 7
0.6 1.7
0.4 4.8
Rocklands
59
2.0* (Cu eq. inc. Co)
Wernecke Mineral Occurrences
(Hunt et al., 2005)
Wernecke Mineral Occurrences Spatially associated with Fe oxide-Cu-Au, significant U Veins, breccias, and replacement
(Hunt et al., 2005)
Cloncurry Host Rocks: Abundant Mafic and Felsic Rocks
Terrane Scale Structures and Stratigraphic Architecture
Wernecke Host Rocks: Meta-Evaporites and Minor Mafic Magmatism
(Hunt et al. 2005)
Critical Ingredients IOCG Terrane Endowment Ore System Analysis
Contributing Factors
Cloncurry/Wernecke
Source Metals and Sulphur
Cu: direct magmatic exsolution and leaching of mafics; S: multiple sources
Cloncurry: abundant, long lived mafic history including major mafic-felsic intrusives; Wernecke leaching host rocks
Transport of Metals
High T and high salinity critical factors in metal transport
Cloncurry: long lived high T thermal history, evaporite and magmatic Cl and CO2 phase separation; Wernecke basinal
Major regional structures with Trap Sites: Structural splays, jogs and intersections Redox changes, reactive host Chemical rocks (carbonate, Fe stones); mixing of multiple fluid types
Both have favourable structural sites Cloncurry: variable redox states to deposits (hem-mag to mag-po); fluid mixing between magmatic-non-magmatic fluids Wernecke: carbonaceous horizons in WSG; lacks major magmatic, possible deep fluid U?
IOCG – The Critical Ingredients
• Evaluated Proterozoic terranes with major deposits (Cloncurry) and less endowed terranes (Wernecke’s) • Evaluated barren regional alteration, magmaticenvironments and IOCG deposits (Cloncurry)
System Scale IOCG Evaluation: A Fluids Perspective IOCG deposits
Ernest Henry
• Osborne • Starra • Eloise • Ernest Henry • Mt Dore • Greenmount Regional alteration
• Cloncurry fault • Barren breccias • Snake Ck • Mary Kathleen Cloncurry granites
• Mt Angelay • Lightning Ck • Saxby
IOCG Deposits
Osborne
Starra
1cm
Eloise
1cm
Ernest Henry
Barren Regional Alteration and Granite-Hosted Magmatic-Hydrothermal Systems
Cloncurry Fluid Types Type 1: Ultra saline Multisolid – L+V+nS (n > 1)
10um
Type 2: Highly saline Halite-bearing – L+V+S
10um
Type 4 Carbon dioxide-rich
Type 3: Moderately saline Liquid-rich – L+V 10um
(Baker et al., 2008)
Fluid Types in IOCG Deposits Multisolid Halite-bearing Liquid-rich
(Baker et al., 2008)
Fluid Types in Barren Regional Alteration Multisolid Halite-bearing Liquid-rich
Fluid Types in Barren Magmatic-Hydrothermal Systems
Multisolid Halite-bearing
Evaluating Fluid and Metal Sources in IOCG
Raster-scanned proton beam
Depth d
Proton beam
PIXE Analysis X-ray
Detector
m
Thickness T Absorption path-length
Fluid inclusion Vapour bubble
(Ryan, 2001)
PIXE Analysis of Fluid Inclusions: Cu and Halogens
(Baker et al., 2008)
Fluid Sources Using Halogens • Origin of fluid salinity: – Halite dissolution (low Br/Cl) – Bittern brine (high Br/Cl) – Seawater – Magmatic fluids (non-unique but restricted ranges)* • Halogens potential provide a way of tracking salinity sources in hydrothermal systems • Halogens signature conserved in the fluid • Combine with metal content of fluid to provide insights to fluid-metal source
PIXE Analysis of Fluid Inclusions: Cu and Halogens >300ppm multisolid only (mostly IOCG and granite-hosted)
Multisolid Halite-bearing Liquid-rich
(Baker et al., 2008)
Exploration Implications and Future Research Directions • Distinct signature of IOCG fluids • Alteration and geochemical footprint poorly constrained • Need improved zonation models • Need to put the GU in IOCGU (i.e. where does Au and U fit)
Research within the GSB • The Hylogger has arrived • Key holes through known IOCG deposits • Developing alteration vectors to ore • Combining with geochemistry
• Geochemical vectors around IOCG’s • Identifying possible near misses – unsuccessful gravity/magnetic targeted drilling and linking with alteration/geochemistry
• Linking into GIS prospectivity • Alteration mapping • Capturing mineral data in SAGEODATA
