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Overview of the geology and mineral potential of
the Entia Dome, Eastern Arunta region Jo Whelan
Dorothy Close Chris Carson Mike Baker
Geoscience Australia
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Location
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Tectonothermal Events

• Seven tectonothermal
• Events have been
• recognised in the Arunta,
• three of these effect the
• Palaeoproterozoic Entia
• Dome.

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Quartz 1100 000 Map sheet
The Bruna Granitic Gneiss structually detaches
the Palaeoproterozoic basement rocks of the Entia
dome from the Cabro-Ordovician Harts Range
Metamorphic Complex.
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Palaeoproterozoic Basement Rocks
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Harts Range Metamorphic Complex
Lithostratigraphy of the Harts Range Metamorphic
Complex (modified from Hand Maidment 2007)
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Palaeozoic Pegmatites

• The Entia Pegmatite Field
• Multiple generations based on
• Mineralogy
• Geochemistry
• Orientation
• Degree of deformation

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Deformation

• Strain partitioning in the basement rocks during
  the Alice Springs Orogeny
• Entia orthogneisses are high strain equivalents
  of the granodiorites
• Multiple compression and extension events
• Local examples of vertical and upright, inclined
  folding
• Map scale examples of isoclinal folding

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Metamorphism

• Majority of ages from zircon rims and metamorphic
  monazite give Alice Springs ages
• New age data from zircon rims in the north
  eastern Entia dome preserve Strangways age
  metamorphism in granulite facies rocks 1717 10
  Ma
• 2 ages for metamorphic monazite (1719 9 Ma) and
  zircon (1731 Ma) preserve Strangways age
  metamorphism in amphibolite facies rocks
• Evidence of Strangways aged metamorphism in the
  eastern Albarta Metamorphics in amphibolite grade
  rocks 1729 Ma
• No evidence of Ordovician Larapinta Event
  preserved in the basement rocks in the Entia Dome

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GeochronologyIgneous rocks

• Yambah 1770 Ma - - Intrusion of the Ambulbinya
  Igneous Complex and correlatives
• 1750 Bruna Granitic Gneiss
• Stanovos Event (Maidment 2005) 520 derived from
  in-situ partial melting of the Upper Stanovos
  Gneiss
• Larapinta Event 475 - 460 Ma - Mafic magmatism in
  an extensional environment
• Alice Springs Orogeny - Intrusion of voluminous
  pegmatites related to extension

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GeochronologyMetasediments
1813
1770
2460
1770
1770
Maximum deposition age
1770
2474
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GeochemistryMafic Rocks

• Entia gneisses, Huckitta and
• Inkamulla rocks are I-type
• metaluminous rocks with
• ASI 1.1
• Correlate well on Harker
• variation diagrams which
• extend towards at least some
• of the Entia amphibolites,
• scatter in some mafic rocks
• is attributed to cumulous nature
• of some rocks
• 2 types of amphibolite
• 1. Continental tholeiite-type rocks formed in a
  continental rift environment, high, Ce/YbN
• 2. Massive amphibolites high La/Nb and Zr/Nb
  typical of subduction related magmas
• Massive amphibolites 1770 Ma
• Continental tholeiite-type rocks ??

Entia Dome
Casey Inlier
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GeochemistryFelsic Rocks

• Some of the EGC orthogneisses
• have same geochemistry as Huckitta
• and Inkamulla granodiorites
• The felsic rocks of the Entia
• Dome are consistent with the
• CAT suite of Zhao McCulloch
• (1995).
• Equivalents in the Albarta
• Metamorphics and the Atneequa
• Granitic Complex, south of the
• Entia Dome
• Fractionation of arc-type
• magmas and/or partial melting of
• arc related intrusions or
• underplates

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Revised Geological Framework for the Entia Dome

• Pink is the new yellow!!
• Ambulbinya Igneous Complex
• Comprises most of the Entia Dome
• Potential correlatives in the Albarta
  Metamorphics, the Atneequa Granite Complex and
  the central zone of the Casey Inlier
• Two packages of metasediments
• Locally derived 1780-1760 Ma signature
• Unknown protolith with 2470-2460 Ma signature

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Mineral Occurrences In the Arunta Region

• U
• REEs
• Ni
• W, Mo
• Au

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Pegmatite associated U and REE

• Form eastern extent of a corridor of elevated U
  and REE that extends north west to the Nolan's
  REE, U, Th deposit.
• Anomalous U generally associated with HREE
• Anomalous Th generally associated with LREE
  anomalies
• Thor Mining recently reported U grade of 7.7 for
  a pegmatite from Daicos prospect in the Entia
  Dome

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Mineral Potential of the Entia Dome Magnetite
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Conclusions

• Multiple magmatic events spanning from
  Palaeoproterozoic to Carboniferous.
• Entia Dome is large magmatic system incorporating
  small rafts of metasedimentary packages
• Possible correlations between intrusive rocks
  from the Entia, Albartas, Atneequa and Central
  Casey
• Voluminous pegmatite intrusions - potential for
  U, Th, REEs, Ta and Nb.
• More work needs be done!