This document discusses developing a new metallogenic framework to aid mineral exploration in the Cobar Basin region of New South Wales, Australia. It involves creating metallogenic maps to better understand the timing, sources, and conditions of mineralization. This includes commodity studies, mineral potential studies, and developing mineral system models from the state to regional scale. Broken Hill and Cobar metallogenic syntheses projects are underway at 500k scales. The Cobar project involves new basement interpretations, metamorphic mapping with over 11,000 petrographic observations, and HyLogger studies on 9,000m of core to better understand alteration associated with mineralization.

1. A new metallogenic framework to aid
mineral exploration in the Cobar Basin
Phil Blevin
Joel Fitzherbert
Peter Downes

2. Metallogenic mapping, commodity and
mineral potential studies
 Metallogenic maps >> need to understand mineral system drivers
 Timing of mineralisation
 Source of metals/fluids
 Temperature of fluid and fluid sources
 Traps >> redox, temperature etc
 Mineral system models (process based)
 Commodity studies >> better understand metal endowment vs
deposit models and metal/fluid sources
 Mineral potential studies >> define realistic mineral potential tracts
that are geologically defensible for Tier 1 and 2.
 Develop a series of mineral system models from state to regional scale.
Where When Why Where else?

3. 500k scale Metallogenic Syntheses
 Broken Hill 250k – done
 Cobar – underway
 New England – preliminaries
 Macquarie Volcanic Province
 S.E. LFB

4. Broken Hill Metallogenic Map
 New synthesis including all
elements of Broken Hill geology
(Willyama, Adelaidean & regolith),
 First complete time-space plot for
BH including mineralising events,
 Used NSW mineral system
schema,
 239 deposits & mines shown
although ~3500 sites reviewed
 Inserts showing metamorphic
isograds for both Olarian and
Delamerian events,
 Two supporting Quarterly Notes
with back of map aimed at general
public.

5. Yanco Glen (W)
Waukeroo (Sn)
Euriowie (Sn)
Kantappa (Sn)
Stratigraphic control has been inferred
Lower sill complex (W) Hores Gneiss
Upper pegmatite field (Sn) Paragon Group
Lower layered sill complex (W)
Amphbolite facies
Upper pegmatite field (Sn)
Greenschist facies
Pegmatite/quartz
vein hosted
Olarian Orogeny (1600-1580 Ma)
Example: Sn-W-bearing pegmatites

6. Syn to post D1
Lower sill complex in
amphibolite facies
Upper pegmatite field
(upper greenschist facies)
Metamorphic field gradient is essentially stratabound
Intrusive phases are essentially stratabound
Yanco Glen (W)
Waukeroo (Sn)
Euriowie (Sn)
Kantappa (Sn)
BUT… Stevens 2006
Olarian Orogeny (1600-1580 Ma)
Example: Sn-W-bearing pegmatites

7. Sillimanite + K-feldspar (+ partial melt) isograd
Thermal death at or close to wet solidus
Helps to explain lower sill complex, what about upper pegmatite field?
Olarian Orogeny (1600-1580 Ma)
Example: Sn-W-bearing pegmatites

8. Sawyer (1998)
Fitzherbert (1998)
Lower sill complex = pooling
small volume melt batches at
or below solidus.
Level of the Hores Gneiss and
sill-Kspar-partial melt isograd
Small fractionated melt
batches, enriched in fluxing
elements (F, Li, B)
Amblygonite (Li, F)
Flouroapatite (F)
Lepidolite (Li)
Tourmaline (B)
Depressed solidus promotes
intrusion at considerably
higher levels in the Paragon
Group
Olarian Orogeny (1600-1580 Ma)
Example: Sn-W-bearing pegmatites
Li

9. Cobar Metallogenic Project
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10. New Cobar 500K basement interpretation
• New Basement interpretation
– Incorporates new GSNSW mapping from Sussex-
Byrock, Coolabah, Cargelligo, Nymagee
• Focus on:
– basement subdivisions/faults
– middle Silurian stitching plutons and
– controls on Cobar Basin opening & inversion.
• Combine with metamorphic facies/isograd and
lithostratigraphic maps to help refine
prospective areas through the basin.
Peperitic rhyolite margin
with sphalerite-rich
replacement on its
margins. Mallee Bull

11. Cobar – metamorphic map
Over 11 000 petrographic observations
available.
Can query these to make maps of primary
and secondary mineral assemblages,
metamorphic textures (e.g. granoblastic,
hornfels)
Collate all historical temperature control
(CAI, mica crystallinity, mica chemistry,
fluid inclusion), field observations and
past metamorphic mapping for the area.

12. Cobar – metamorphic map
Color coded points highlighting distinctive
secondary minerals

13. Cobar – metamorphic map
Reassessed all historical GSNSW thin sections
from Mount Hope Group, Rast Group, Kopyje
Group, Amphitheatre Group, Nurri Group,
Mouramba Group, Ootha Group.
Plagioclase-phyric dacitic lava -
Babinda Volcanics (Ettamogah Tuff
Member).
Rhyolite with flow foliation -
Florida Volcanics
Compelling evidence that the rhyolites were erupted first
with a change to dacitic composition occurring at a higher
stratigraphic level.

14. Cobar – metamorphic map
New petrographic and hyperspectral work
conducted on selected prospects and deposits,
(e.g. Nymagee, Hera, Lowan, Mount Allen,
Browns Reef, Mallee Bull, May Day, Manuka,
Yellow Mountain, Mineral Hill, Great Central,
Mount Solar). Reassessment of all historic
GSNSW thin sections from many of the other
deposits.
actinolite/biotite. Nymagee stilpnomelane. Nymagee

15. Cobar – metamorphic map
Secondary information also obtained
from over 15 000 field observations

16. Cobar – metamorphic map
Example of color coding for textural
information from GSNSW field
observations.
For example blue dots are recorded
cordierite.
Cupiferous shingleback

17. Cobar – metamorphic map
The basin has experienced mostly diagenetic to
anchizonal, very low grade metamorphic conditions
during burial and inversion, with the exception of Glen’s
Zone 1, which is the high strain zone through Cobar
itself).
There is a disconnect between the highest grades of
overprinting metamorphism and deformation. Highest
grade alteration systems (pre-fabric, high-T potassic ,
calc-potassic to calcsilicate alteration) are actually
preserved in the lesser deformed sequences.
Where high hydrothermal grades have been attained
they are extremely localised (except around intrusions)
and there is a strong thermal contrast between the host
rocks and the metasomatic mineral associations. e.g 10’s
to 100’s of meters away have sub greenschist facies
(~200oC) basinal rocks. Strongly suggestive of a hot,
proximal heat source.
Thermal highs very much spatially associated with
Devonian intrusions.

18. The basin rocks…
Detrital biotite and muscovite are very well
preserved and the effects of deformation are
weak. All noted by Pogson (Nymagee 100K)
Some sandstones preserve diagenetic textures and
primary porosity

19. Approaching mineralisation…
(but only tens of metres away)
Biotite flooding of sandstone/siltstones and crosscutting
biotite veins (note they are subsequently deformed).
Early biotite porphyroblasts enveloped by
chloritic foliation
Hera

20. Mineralisation…
Calcsilcate alteration (garnet-tremolite (retrogressed to
chlorite-plagioclase) intimately associated with
mineralisation.
Also identified from Nymagee using Hylogger.
Garnet-rich veins from Hera, along with
abundant garnet with sulfide.
(courtesy of Adam McKinnon, Aurelia)

21. The high temperature connection
In the pipeline:
 Hylogging for CSA, Peak,
Endeavor, followed by new
petrographic work.
 Sm-Nd dating of garnet from
high-T alteration systems at
Nymagee and Hera.
 δO-δD of tremolite in high-T
alteration zones from
Nymagee and Hera.
 Possible garnet fluid inclusion
work for Nymagee and Hera.Stegman, 2000, Cobar conf. vol.

22. ● Canbelego-Mineral Hill Belt
● Kopyje Shelf
● Cobar Basin
● Mount Hope Trough
● Winduck Shelf
Pb-isotopes: mineralisation related data
Notes — data sources
• 2012/14 = this study
• pmdcrc
• CSIRO (selected only)
2012/14 and pmdcrc studies have higher
precision than older analyses
Background: LFB major metallogenic events
from Carr et al (1995)
Ordovician (basement)-dominant
signature: Mallee Bull, Mineral Hill,
Blind Calf, Bobadah
mid-late Silurian-dominant
signature: Hera, Nymagee,
Wagga Tank, Shuttleton, part
Manuka
Early Devonian
signature
Sandy Creek, part
Manuka, Wagga Tank

23. S-isotopes: mineralisation related data
W E
Pb & S
Pb & S
Pb & S
Basinal Fluids
Basement Fluids
Fluid mixing
zones
siliciclastics
greywackes &
mafics
Cobar
Basin
Girilambone
Basement
Hera Nymagee
ShuttletonMallee Bull Sandy Creek
δ34S >8
δ34S <~8
Pb Zn Ag
Cu Au
Cu Au

24. Suppel DW, 1984 A study of mineral deposits in the Cobar Supergroup, Cobar region, New South Wales. MSc. UNSW (unpubl).

25. Aims
 Build a virtual core library for mineral deposits in the Cobar district;
 Document regional metamorphism & changes to host rock mineralogy
distal to mineralised zones;
 Document alteration associated with mineralising event(s);
 Support other big picture projects e.g. deep seismic;
Cobar HyLogger project FY15/16

26. The Cobar HyLogger project
NCRIS funding for 9,000m of core from Cobar

27. Cobar Map Progress

28. Neodymium Map of NSW
Nd two-stage depleted mantle model age map for eastern Australia (Champion, 2013, GA record 2013/44)

29. Charlotte Barry and Michael Nelson
Neodymium Map of NSW