"Curnamona Proterozoic Geochronology". Liz Jagodzinski, Geochronologist, Geological Survey of South Australia. Technical presentation at 2015 Broken Hill Resources Investment symposium.

1. GEOCHRONOLOGY IN THE
CURNAMONA PROVINCE
Elizabeth A. Jagodzinski and Wolfgang V. Preiss
Geological Survey of South Australia
Broken Hill Resources Investment Symposium, 24-27 May, 2015
www.statedevelopment.sa.gov.au

2. 2Department of State Development
Bulletin 56

3. 3Department of State Development
Revision of Geochronology
• Work was initially carried out at Geoscience Australia as part of the
Broken Hill Exploration Initiative by Rod Page.
• The aim was to establish a time framework for the stratigraphy of
the Curnamona Province, to accompany the mapping program, in
both Broken Hill and Olary Domains.

4.
4Department of State Development
STRATHEARN GROUP
Mount Howden Subgroup
SUNDOWN GROUPSALTBUSH
GROUP BROKEN HILL GROUP
Larry Macs Sgp: Plumbago, Bimba Ettlewood Calc-silicate Member
THACKARINGA GROUP
RANTYGA GROUP
CURNAMONA GROUP
Ethiudna Subgroup: Peryhumuck Fm v v v v v
Cathedral Rock Formation
Tommie Wattie Formation v v v v v v
Wiperaminga Subgroup v v v v v v v
15 m.y. hiatus
~1655-1640
~1685
~1705
~1710
~1715-
1720
~1720
Purnamoota Subgp: Hores Gneiss
PARAGON GROUP
?15 m.y. hiatus
Allendale Metasediments
OLARY DOMAIN BROKEN HILL DOMAIN Ma
~1695-1700
Walparuta Formation
Raven Hill Subgroup

5. 5Department of State Development
Bulletin 56
Ameroo
11 rectified maps showing the spatial
location and geological context of
the geochronology samples
Mulga

6. 6Department of State Development
Revision of Geochronology 1
• SHRIMP data were collected between 1998 and 2006, using many
different versions and generations of software
• Rod used earlier software (PRAWN) written by RSES, which allowed
user bias to creep in to the data processing
• In the late 1990’s Ken Ludwig (Berkeley) developed a ‘black box’
processing package that removed this user bias by identifying outliers
on a statistical basis, called SQUID.
• In order to compare all data on a level playing field, all the analyses
havebeen reprocessed with the same software package: SQUID 1.

7. • Rod Page used the standard QGNG to monitor the 207Pb/206Pb ratio:
for each session, he compared the measured SHRIMP age of QGNG
to its TIMS-determined age of 1851.6 ± 0.6 Ma
• Measured ages for QGNG ranged from 1844 to 1856 Ma
• Rod Page normalised some of the sample data to the correct
reference age, but not all
• A correction has now been applied to all samples, which normalises the
ages to the TIMS reference age of QGNG, so these session differences
are eliminated. This is called an IMF correction (instrumental mass
fractionation (Stern et al. 2007)
Revision of Geochronology 2

8. 50 SHRIMP sessions of QGNG compared
• All
4
instruments
means
lower
than
TIMS
mean
~
1849.1
Ma
• instruments
1,3,4
show
excess
session-­‐session
dispersion,
with
a
range
up
to
.5%
between
highest
and
lowest
• Isoplot
2σ
external
error
required
for
all
sessions
=
±
4.1
Ma
(.22%)

9. 84 SHRIMP sessions of OG1 on GA’s SHRIMP IIe compared
(Feb 2008-2010)

10. Rod’s QGNG standards for the BHEI project

11. Rod’s QGNG standards for the BHEI project
Tommie
Wa)e
Fm
quartz-­‐phyric
granofels
(volcanic)
North
Walparuta
region
original
processing normalised
data
sets
2092274 1719 4 1719 3
480533 1713 2 1717 2

12. 12
Results: Saltbush Group
1. Plumbago Formation - inferred volcaniclastic psammite
immediately overlying the Bimba Formation. Zircons
consistently yield 1697 Ma when normalised
1
Plumbago Formation volcaniclastic psammite
(1693 Ma)
graphitic metasiltstone near
Mt Howden Co mine
Pb loss

13. 13
2. Detrital zircons in sandy facies of the Bimba Formation
define a maximium depositional age of 1706 ± 4 Ma
Saltbush Group
2
1706±4 Ma

14. 14
Saltbush Group
3
3. The Portia Formation has been proposed
for the mineralised section above the
Curnamona Group in the Mulyungarie
Domain. A thin tuff in two drillholes gives
ages ranging from 1697 to 1704 Ma but
within error, so contemporary with the
Bimba Formation
Cu-­‐Au
and
Pb-­‐Zn
mines
and
prospects
e.g.
PorEa,
Kalkaroo,
Hunters
Dam,
McBrides,
Polygonum,
Thunderdome

15. 15Department of State Development
• Ages on felsic volcanics range between 1712 and 1721 Ma.
Results: Curnamona Group

16. 16
• Ages on felsic volcanics range between 1712 and 1721 Ma.
• Analysis of Variance test (or ANOVA) compares all pairs of dates for the
Curnamona Group
• It indicates a significant difference in age between only a few of the dates
obtained for volcanics in the Peryhumuck Formation and the George Mine
Formation; these are coloured yellow in the table.
Results: Curnamona Group
Tukey-­‐Kramer
minimum
significant
difference
Actual
difference
('*'
if
significant)

17. Conclusion
Whereas SHRIMP dating could
delineate broad stratigraphic
variations at the Group level,
stratigraphic differences of
< 10 m.y. can not be resolved.

18. Curnamona: where next?
• Future research: key volcanic horizons will be selected for dating by
Thermal Ionisation Mass Spectroscopy (TIMS), which has a resolution
of < 1 m.y.
• Hf isotopes on metasedimentary rocks of the Willyama Supergroup

19. 19
TIMS dating
• We have a collaborative research partnership with the University of Idaho to
provide TIMS dating for the GSSA. Successful projects so far:
1. Early Cambrian stratigraphy, tectonics, biostratigraphy and Timescale study
2. GRV/Hiltaba Suite
1
2

20. 2020
Mount Howden Subgroup: 1657±7 Ma
Plumbago Formation: 1697±4 Ma
Bimba Formation: max dep age 1706± 4 Ma
tuff mean age 1701±6 Ma
SUMMARY
Curnamona Group: ages on felsic
volcanics range between 1712 and
1721 Ma
Denotes samples selected for TIMS dating

21. Where to find our publications

22. hUp://minerals.statedevelopment.sa.gov.au/geoscience/geological_survey/geoscienEfic_data/geochronology
Where to find our publications

23. hUps://www.researchgate.net/profile/Elizabeth_Jagodzinski

24. www.statedevelopment.sa.gov.au
Geological Survey of South Australia
Level 4, 101 Grenfell Street
Adelaide, South Australia 5000
GPO Box 320
Adelaide, South Australia 5001
T: +61 8 8463 3081
E: liz.jagodzinski@sa.gov.au