2015 broken hill resources investment symposium - geological survey of south australia - liz...
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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
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Bulletin 56
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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.
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STRATHEARN GROUP Mount Howden Subgroup
SUNDOWN GROUP
SALTBUSH 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
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Bulletin 56
Ameroo
11 rectified maps showing the spatial location and geological context of
the geochronology samples
Mulga
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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 have been reprocessed with the same software package: SQUID 1.
• 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
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%)
84 SHRIMP sessions of OG1 on GA’s SHRIMP IIe compared (Feb 2008-2010)
Rod’s QGNG standards for the BHEI project
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
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Results: Saltbush Group
1. Plumbago Formation - inferred volcaniclastic psammite immediately overlying the Bimba Formation. Zircons consistently yield 1697 Ma when normalised
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Plumbago Formation volcaniclastic psammite (1693 Ma)
graphitic metasiltstone near Mt Howden Co mine
Pb loss
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2. Detrital zircons in sandy facies of the Bimba Formation define a maximium depositional age of 1706 ± 4 Ma
Saltbush Group
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1706±4 Ma
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Saltbush Group
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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
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• Ages on felsic volcanics range between 1712 and 1721 Ma.
Results: Curnamona Group
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• 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 differen
ce
('*' if significan
t)
Conclusion
Whereas SHRIMP dating could delineate broad stratigraphic variations at the Group level, stratigraphic differences of < 10 m.y. can not be resolved.
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
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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
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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
Where to find our publications
hUp://minerals.statedevelopment.sa.gov.au/geoscience/geological_survey/geoscienEfic_data/geochronology
Where to find our publications
hUps://www.researchgate.net/profile/Elizabeth_Jagodzinski
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: [email protected]