2015 broken hill resources investment symposium - geological survey of new south wales - joel...
TRANSCRIPT
Broken Hill 1:250 000 metallogenic special &
Refined metamorphic facies-‐isograd maps
Joel Fitzherbert Peter Downes, Phil Blevin and David Forster
This talk • Current series of GSNSW metallogenic maps
• Broken Hill 1:250 000 – Concept and components
• Refined metamorphic facies/isograd maps
• ApplicaEon of isograd maps to mineral systems
• Current and future GSNSW work in the Broken Hill
Current metallogenic map series
Each map to highlight key aspects of the geology relevant to that area. e.g. Bathurst – Ord volcanism Review data on individual deposits to beNer classify them. New data acquired and integrated into the deposit datasets Mineral deposits classified according to the mineral systems of New South Wales Updated Eme space plot that includes the main mineralising events Back of the map to highlight mining history and geology
Broken Hill 1:250 000 Concept and components
Broken Hill 1:250 000 Concept
Detailed mapping, but lack of a summary map
Recent daEng/straEgraphic relaEons in posters/papers
Broken Hill 1:250 000 Concept
DiagrammaEc representaEon ReproducEon of Phillips (1978)
• Complex geology at 1:250 000 – Highlights the Purnamoota Subgroup
• Hores Gneiss • Silver King Metadolerites • Olarian intrusive phases removed
• Simplified version of: – Broken Hill StraEgraphic. Willis (1989) – InterpretaEon of Broken Hill 1:25 000 map
series Stevens (2009) – 1:100 000 scale interpreEve Proterozoic
geology GSNSW (2009) – Includes undercover interpretaEon – Cover sequences GA 1 million
• Transparent, sEppled
Broken Hill 1:250 000 components
• First complete Eme-‐space plot
• Updated geology and daEng – Stevens (2008) – Dutch et al (2006) – GSNSW (2009)
• AddiEon of mineral deposits against Eme
• AddiEon of tectonic interpretaEon against Eme
Broken Hill 1:250 000 components
• Two 1:500 000 scale insets for Olarian and Delamerian Isograd/facies maps
• Commodity plots for mineral occurrences interpreted to be associated with each orogenic event
• Olarian inset includes • Olarian intrusive phases
• Delamerian – Post Olarian dykes and intrusions – Delamerian structure
Broken Hill 1:250 000 components
Broken Hill 1:250 000 components
Broken Hill 1:250 000 SupporEng info
Metamorphic facies/isograd maps
Olarian c. 1600 Ma
Delamerian c.500 Ma Isograds/facies broadly parallel to straEgraphy
In a broad sense isograds are rotated around regional F2 structures.
Higher-‐T zones broadly reflect higher-‐T zones in the Olarian Isograds crosscut straEgraphy
Mineral zones: Staurolite
Staurolite+chloritoid
Chloritoid
Facies maps: Upper-‐greenschist Amphibolite Granulite Isograds: BioEte Sillimanite Sillimanite+Kspar Othopyroxene
Key aspects
Drill Core
Metamorphic facies/isograd maps ConstrucEon
Field Traverses
Petrographic re-‐evaluaEon
Previous work
Petrographic database
Polymetamorphism/deformaIon • MulEply deformed terrane
– At least 2 peak and 2 retrograde events
• MulEple thermal highs – Up to four generaEons of aluminosilicate
• MulEple retrograde events – At least two at similar P-‐T condiEons
Stratabound nature of the field gradient & composiIonal heterogeneity • Increased grade ocen corresponds with
changing mineralogy • Group-‐scale heterogeneity
– albite rocks, pelite, psammite, granite, dolerite, felsic volcanic, carbonaceous
• Within-‐group heterogeneity – Example of basic rocks
• EvoluEon to high FeO-‐type • Control on index minerals
Metamorphic facies/isograd maps ConstrucEon issues
Orthopyroxene isograd (metabasite composiEon)
High FeO Broken Hill Group
High MgO+CaO Thackaringa Group
VariaEon between two main composiEonal types
Metamorphic facies/isograd maps
Metamorphic facies/isograd maps (Sillimanite + K-‐feldspar isograd)
Hardest isograd to map Phillips (1978) Sillimanite+K-‐feldspar Burton (2001) Sillimanite+parEal melt
Applying facies/isograd maps to mineral systems Commodity Versus Metamorphic grade
Commodity over metamorphic grade
AddiEon of Olarian intrusive phases -‐ PegmaEte (D1) -‐ Mundi Mundi granite
AssociaEon with metamorphic facies zones and isograds -‐ Amphibolite facies -‐ Between orthopyroxene and sillimanite-‐K-‐feldspar isograds
Apparent straEgraphic control on pegmaEte -‐ Stevens (1978)
But….
Applying facies/isograd maps to mineral systems An example: Hores-‐type W and Waukeroo-‐type Sn
Yanco Glen (W) Waukeroo (Sn) Euriowie (Sn) Kantappa (Sn)
PegmaEte/quartz vein hosted
Stratabound
W Hores Gneiss Sn Paragon
Euriowie 1582 +/-‐ 16 Ma (Cassiterite)
Applying facies/isograd maps to mineral systems An example: Hores-‐type W and Waukeroo-‐type Sn
Stevens (2006)
Sill/dyke complex in amphibolite facies
Yanco Glen (W) Waukeroo (Sn) Euriowie (Sn) Kantappa (Sn)
Upper pegmaEte field (upper greenschist facies)
Metamorphic field gradient is essenIally stratabound Intrusive phases are essenIally stratabound
Pooled at/close to the wet solidus
Syn to post D1
Applying facies/isograd maps to mineral systems An example: Hores-‐type W and Waukeroo-‐type Sn
Sawyer (1998) Fitzherbert (1998)
Pooling small volume melt batches at or below solidus. Level of the Hores Gneiss
Small fracEonated melt batches, enriched in fluxing elements (F, Li, B) Amblygonite (Li, F) FlouroapaEte (F) Lepidolite (Li) Tourmaline (B) Depressed solidus rises considerably higher levels in the Paragon Group
Applying facies/isograd maps to mineral systems An example: Hores-‐type W and Waukeroo-‐type Sn
Applying facies/isograd maps to mineral systems An example: Hores-‐type W and Waukeroo-‐type Sn
Blevin (1998)
Applying facies/isograd maps to mineral systems Further applicaEon
Mundi Mundi Suite (1590-‐1580 Ma) Equivalents of Bimbowrie Supersuite rocks Iron Duke Type breccias Fe +/-‐ U Amphibolite facies and shallower Larger plutons greenschist facies In Broken Hill, just see the eastern edge of the extensive late syn-‐ to post-‐Olarian magmaEc event (1590-‐1580 Ma).
Applying facies/isograd maps to mineral systems Curnamona wide
Isograds of Webb and Crooks (2005)
Mundi equivalent Bimbowrie Supersuite
Located in the amphibolite facies and above. Main zone straddles the andalusite sillimanite isograd
IOCG associaEon
Applying facies/isograd maps to mineral systems What’s lec? Other possibiliEes
Melts and volaEle phase separaEon, prograde metamorphic fluids, retrograde metamorphic fluids
ParEal melEng
DehydraEon
Retrograde H2O addiEon
Applying facies/isograd maps to mineral systems Retrograde isograds
• ExhumaEon of Palaeoproterozoic • Weathering • Focused hydraEon along pre-‐exisEng
faults/shears OR Neoproterozoic basinal faults
• ?Neoproterozoic burial metamorphism – Under as much as ?15 km of Neoproterozoic. – Isogads developed – Dutch, Hand, Clark, Raimondo et al… – Staurolite isograd ~500oC
• Delamerian Orogeny – ReacEvaEon of hydrous zones as schist zones. – Further shortening
– ExhumaEon?
Dutch et al (2006)
Applying facies/isograd maps to mineral systems Example: Moderate-‐T retrograde fluids
Retrograde fluids? Appear to be replacement of a granulite facies fabric
Applying facies/isograd maps to mineral systems Low –T retrograde (Thackaringa) CommodiEes over
Delamerian isograds. Thackaringa Type siderite-‐quartz veins Arcuate zone of shear zone hosted veins centered around Broken Hill Broadly parallel, but transgress Delamerian field gradient to south AlteraEon and fluid inclusions 150-‐200°C (Dong et al (1987) Reid et al (2009). Not stratabound – low metamorphic grade
Aim: -‐ Characterise the thermal response of
medium-‐ to high-‐grade regional metamorphism.
-‐ BeNer characterise mineralisaEon and alteraEon in the Broken Hill area.
SelecIon criteria: -‐ Cover all of peak Olarian metamorphic
zones -‐ Focus on short holes that have similar, but
variable rock types. -‐ Cover the straEgraphic variaEon. -‐ Represent or sample areas of known
mineralisaEon -‐ Sample the Delamerian retrograde schist
zones.
Current & future studies in Broken Hill GSNSW Broken Hill core hylogger project
Visible and near infrared (VNIR) 400 -‐ 1000 nm Iron oxides e.g. hemaEte, goethite, jarosite REE oxide minerals Shortwave Infrared (SWIR) 1000 -‐ 2500 nm OH bearing minerals Clays, phyllosilicates, amphiboles, sulphates Carbonates Mid or Thermal Infrared (MIR or TIR) 8000 -‐ 12000 nm Silicates e.g. quartz, feldspar, garnet, pyroxene
Spectral regions relevant to geology (& Hylogger) Thermal (TIR)
Broken Hill required addiEon of new minerals to the spectral library e.g. kyanite, sillimanite, staurolite
Current & future studies in Broken Hill GSNSW Broken Hill core hylogger project
5000m of core has been hylogged and will be complimented by a petrographic study including mineral chemistry:
-‐ Style of mineralisaEon/alteraEon
-‐ Timing of mineralisaEon/alteraEon
-‐ RelaEonship to metamorphism? If not can we see through the effects of metamorphism?
Black Prince
Current & future studies in Broken Hill GSNSW Broken Hill hylogger project
Future Work
Pb/S Isotopes • CollecEon of samples from
areas peripheral to the main line
• Any well located samples would be appreciated
DaEng
• DaEng of metamorphism/alteraEon/mineralisaEon
• Early metamorphic assemblages
