New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 ...New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 5 Figure 2.1 Representative

Record 2015/20 | GeoCat 83855

New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, New South WalesArmistead, S. E. and Fraser, G. L.

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New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, New South Wales GEOSCIENCE AUSTRALIA RECORD 2015/20

Armistead, S. E. and Fraser, G. L.

Department of Industry and Science Minister for Industry and Science: The Hon Ian Macfarlane MP Parliamentary Secretary: The Hon Karen Andrews MP Secretary: Ms Glenys Beauchamp PSM

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ISSN 2201-702X (PDF)

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GeoCat 83855

Bibliographic reference: Armistead, S. E. and Fraser, G. L. 2015. New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, New South Wales. Record 2015/20. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2015.020

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http://dx.doi.org/10.11636/Record.2015.020

Contents

Executive Summary .................................................................................................................................. 1

1 Introduction ............................................................................................................................................ 2 2 F1 prospect granite (drillhole F1DD02) ................................................................................................. 5

2.1 Sampling details and geological relationships ................................................................................. 5 2.2 Petrography ..................................................................................................................................... 6 2.3 Zircon description ............................................................................................................................. 7 2.4 U-Pb isotopic results ........................................................................................................................ 8 2.5 Geochronological interpretation ....................................................................................................... 8

3 F1 prospect granitic dyke (drillhole F1DD01) ......................................................................................12 3.1 Sampling details and geological relationships ...............................................................................12 3.2 Petrography ...................................................................................................................................13 3.3 Zircon description ...........................................................................................................................14 3.4 U-Pb isotopic results ......................................................................................................................15 3.5 Geochronological interpretation .....................................................................................................15

4 Quartz diorite (drillhole CUTACD02) ...................................................................................................18 4.1 Sampling details and geological relationships ...............................................................................18 4.2 Petrography ...................................................................................................................................19 4.3 Zircon description ...........................................................................................................................19 4.4 U-Pb isotopic results ......................................................................................................................20 4.5 Geochronological interpretation .....................................................................................................21

5 Sandstone (drillhole F03D02) ..............................................................................................................24 5.1 Sampling details and geological relationships ...............................................................................24 5.2 Petrography ...................................................................................................................................25 5.3 Zircon description ...........................................................................................................................25 5.4 U-Pb isotopic results ......................................................................................................................26 5.5 Geochronological interpretation .....................................................................................................27

Acknowledgements ................................................................................................................................31

References .............................................................................................................................................32

Analytical procedures ..........................................................................................................34 Appendix AA.1 Analytical procedures ....................................................................................................................34

A.1.1 Sample acquisition and crushing .............................................................................................34 A.1.2 Mineral separation ...................................................................................................................34 A.1.3 Mount preparation ....................................................................................................................34 A.1.4 Instrument setup and data acquisition .....................................................................................34

A.2 Data reduction and presentation ...................................................................................................35 A.2.1 Calibration procedures .............................................................................................................35 A.2.2 Propagation of uncertainties ....................................................................................................36 A.2.3 Discordance .............................................................................................................................37

A.3 Session-specific calibrations and data processing ........................................................................37

New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW iii

iv New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

Executive Summary

SHRIMP U-Pb zircon ages are presented from four samples from the vicinity of the Cuttaburra and F1 mineral prospects in the southern Thomson Orogen of New South Wales. The work reported here represents part of Geoscience Australia’s contribution towards a collaborative project in the southern Thomson Orogen, conducted under the auspices of National Collaborative Framework (NCF) agreements between Geoscience Australia, the Geological Survey of New South Wales and the Geological Survey of Queensland.

Magmatic crystallisation ages from two samples of intrusive igneous rocks from the F1 prospect, each of which host sulfide-bearing veins, represent the first radiometric ages obtained from this prospect. The F1 prospect granite (drillhole F1DD02; GA SampleNo: 2167675) yields an age of 428.2 ± 3.1 Ma (uncertainties are quoted at the 95% confidence level), and a fine- to medium-grained granitic dyke from the same prospect (drillhole F1DD01; GA SampleNo: 2167701) yields an age of 424.5 ± 4.9 Ma. These two ages are indistinguishable from one another at the 95% confidence level.

A quartz diorite from the Cuttaburra prospect (drillhole CUTACD02; GA SampleNo: 2167668) yields a magmatic crystallisation age of 429.0 ± 8.5 Ma, indistinguishable from a previously-published age of 428.3 ± 2.8 Ma from a granite from a different drillhole at the Cuttaburra prospect (Chisholm et al., 2014).

Together, these ages suggest that intrusive magmatism occurred contemporaneously, and over a relatively short time interval, at the Cuttaburra and F1 prospects. These ages also provide a maximum constraint on the timing of sulfide mineralisation hosted within these magmatic rocks.

A sandstone from a drillhole (F03D02; GA SampleNo: 2167713) located between the Cuttaburra and F1 prospects was sampled as representative of regional metasedimentary rocks into which the magmatic rocks at the Cuttaburra prospect intruded. Detrital zircons from this sandstone were dated to provide a maximum depositional age constraint, and also to characterise the provenance of this metasedimentary rock. The detrital zircon age spectrum from this sample is dominated by relatively euhedral zircon grains with a weighted mean age of 498.7 ± 3.9 Ma, suggesting a relatively proximal igneous source. Smaller proportions of Neoproterozoic (c. 600 Ma), Mesoproterozoic (c. 1250–1000 Ma), Paleoproterozoic and Mesoarchean ages are also present in this sample.

New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 1

1 Introduction

This Record contains new zircon U-Pb geochronological data obtained via Sensitive High-Resolution Ion Micro Probe (SHRIMP) from three samples of intrusive igneous rock and one sample of sedimentary rock. All four samples were acquired from drillcore in the vicinity of the Cuttaburra and F1 mineral prospects in the southern Thomson Orogen, New South Wales (Figure 1.1 and Figure 1.2).

The work reported here represents part of Geoscience Australia’s contribution towards a collaborative project in the southern Thomson Orogen, conducted under the auspices of National Collaborative Framework (NCF) agreements between Geoscience Australia, the Geological Survey of New South Wales and the Geological Survey of Queensland.

The Cuttaburra and F1 prospects are spaced approximately 40 km apart and both are located slightly north of the Olepoloko Fault, which is interpreted as the major boundary between the Lachlan and Thomson Orogens (Stevens and Crawford, 1992; Gray and Foster, 2004; Glen et al., 2007; Glen et al., 2013). Preliminary drilling results in the area have yielded anomalous values of Au, Mo, W and base metals, suggested to be associated with local granitic intrusions (Rothery, 2013).

Due to the presence of relatively thick sedimentary cover of the Eromanga Basin, the regional basement geology in the vicinity of the Cuttaburra and F1 prospects is poorly constrained, but is proposed to be dominated by early Paleozoic sedimentary rocks intruded by granites of probable Silurian-Devonian age. The only previously-published radiometric age from these prospects comes from a porphyritic granodiorite intersected in drillhole CUTAD01, which yielded a U-Pb SHRIMP zircon magmatic crystallisation age of 428.3 ± 2.8 Ma (Chisholm et al., 2014).

The geochronological study reported here was aimed at providing further age constraints on the magmatic rocks from the Cuttaburra and F1 prospects, and testing whether both prospects contain magmatic rocks of similar age. In addition to the magmatic rocks, detrital zircons from a sample of metasedimentary basement rock from a drillhole located between the Cuttaburra and F1 prospects were analysed to (i) provide a maximum depositional age constraint on the regional metasedimentary rocks which host the granitic intrusions and mineralisation, and (ii) to characterise the detrital zircon age spectrum to allow comparison with other metasedimentary rocks of the southern Thomson and northern Lachlan Orogens.

The results of this study are summarised in Table 1.1 and the underlying isotopic data are available via Geoscience Australia’s online Geochronology Delivery System (www.ga.gov.au/geochron-sapub-web/). A description of sample acquisition and processing procedures, preparation and analysis of SHRIMP mounts, and data reduction and presentation methods is included in the Appendix, along with analytical session-specific details of the calibration data collected on the reference 238U/206Pb and 207Pb/206Pb zircons.

Table 1.1 Summary of new U-Pb SHRIMP zircon ages reported in this Record.

SampleNo Sample ID Sample Name (drillhole) Interpreted Age Geological attribution

2167675 2013831005B F1 prospect granite (F1DD02) 428.2 ± 3.1 Ma Magmatic crystallisation

2167701 2013831006J F1 prospect granitic dyke (F1DD01) 424.5 ± 4.9 Ma Magmatic crystallisation

2167668 2013831003B Quartz diorite (CUTACD02) 429.0 ± 8.5 Ma Magmatic crystallisation

2167713 2013831009B Sandstone (F03D02) 498.7 ± 3.9 Ma Maximum deposition age

2 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

http://www.ga.gov.au/geochron-sapub-web/

(a)

(c)

(b)

Figure 1.1 (a) Map of eastern Australia with orogens labelled; study area for this Record is shown in red; (b) Geophysical-geological interpretation map of basement lithologies of the Cuttaburra and F1 prospects in the southern Thomson Orogen region. Map is presented as a transparency over a greyscale 1VD TMI RTP image. Drillholes and prospects in the region are labelled. Map data from Hegarty (2010); (c) Legend for map in b (Hegarty, 2010).


Figure 1.2 Schematic cross-section of the F1 prospect drillholes which intersect Eromanga Basin sediments and underlying granite. Locations of samples collected for U-Pb geochronology are shown on drillholes. Profile is from west to east (looking north).


2 F1 prospect granite (drillhole F1DD02)

Table 2.1 Summary of results: F1 prospect granite (drillhole F1DD02; GA SampleNo: 2167675).

GA SampleNo 2167675

Sample ID 2013831005B

Parent Unit -

Stratigraphic Unit -

Informal Identifier -

Lithology Medium-grained, biotite-rich granite

Drillhole name & depth (downhole) F1DD02 148.1–149.05 m

Province Thomson Orogen

1:250 000 Sheet White Cliffs (H5412)

1:100 000 Sheet Yantabangee (7636)

Location (GDA94) -30.50621, 143.87473

Location (MGA94) Zone 54, 775900 mE, 6621605 mN

SHRIMP mount ID GA6273

Analytical Session No 140039, 8–14 April 2014

Interpreted Age 428.2 ± 3.1 Ma (95% confidence; 31 analyses of 31 zircons)

Geological Attribution Magmatic crystallisation

Isotopic Ratio used 238U/206Pb (204Pb-corrected)

2.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole F1DD02 (downhole depth 148.1–149.05 m), drilled in 2013 at the F1 prospect.

Drillhole F1DD02 contains undeformed shale and sandstone of the Eromanga Basin from the surface to ~130 m (downhole depth). Biotite-rich granite unconformably lies below the Eromanga Basin sediments.

The unit sampled is a biotite-rich granite with weak patchy chlorite replacement of biotite (Figure 2.1). The granite contains small enclaves of slightly finer grained and more mafic hornblende-bearing granite. The granite hosts minor sulfide veins and disseminated pyrrhotite.

No radiometric ages from the F1 prospect have been published prior to this study. This sample was analysed to provide an age for granitic magmatism at the F1 prospect. The magmatic age will provide a maximum age for the sulfide mineralisation hosted within the granite. The age from this sample will also provide a useful comparison with magmatic ages from the Cuttaburra prospect, located ~40 km to the east.


Figure 2.1 Representative photograph of the F1 prospect granite (drillhole F1DD02; GA SampleNo 2167675). Field of view is ~15 cm wide.

2.2 Petrography This sample consists of quartz, plagioclase with minor sericite replacement, biotite with minor replacement by bright green chlorite and clear muscovite, minor disseminated pyrrhotite, and accessory zircon and ilmenite (Figure 2.2). The plagioclase commonly exhibits concentric zoning in cross-polarised light, often overprinted by albite twinning. Biotite is strongly pleochroic, with colours including pale-brown, khaki, orange and dark brown. This rock has been interpreted as a medium-grained, biotite-rich granite.

(a) (b)

Figure 2.2 Representative photomicrographs of the F1 prospect granite (drillhole F1DD02; GA SampleNo: 2167675). (a) Plane-polarised light; beige to brown biotite (top right of image) with green chlorite replacement and minor clear muscovite replacement, abundant quartz and feldspar; (b) Cross-polarised light; weakly zoned plagioclase crystals, high birefringent muscovite replacing biotite/chlorite.


2.3 Zircon description The mounted crystals are characterised by long axes spanning the range 50–250 μm (typically 80–150 μm), and aspect ratios (length:width) as high as 7:1, but more commonly between 2:1 and 3:1 (Figure 2.3). Crystal forms are predominantly euhedral to subhedral and the majority of grains preserve facets. The external morphologies of unbroken crystals are dominated by elongated prisms with pyramidal terminations. In transmitted light, most crystals are transparent to translucent, and colourless to mid-brown, and some grains are cracked and iron-stained (Figure 2.3). Some of the crystals host small rounded inclusions (less than 10 μm in diameter) of dark coloured minerals; there are also lesser pale inclusions which are typically larger (up to 15 μm in diameter).

Cathodoluminescence (CL) images reveal widely varied CL emission intensities and zoning patterns. Many crystals contain rounded to irregular-shaped central domains, with low to moderate CL emission; although some have high CL emission. Many crystals contain concentric oscillatory zoning, while others preserve a banded or ill-defined core which is disconformably overgrown by zircon with low to moderate CL emission and well-defined oscillatory zoning parallel to the grain margins.

Figure 2.3 Representative zircons from the F1 prospect granite (drillhole F1DD02; GA SampleNo: 2167675).Transmitted light image is shown in the upper half, cathodoluminescence image in the lower half. SHRIMP analysis sites are labelled ‘sample.grain.area’, where ‘sample’ is the final three digits of the GA SampleNo.


2.4 U-Pb isotopic results Forty-two analyses were collected from 40 different zircon grains. The results are presented in Table 2.2 and displayed in Figure 2.4. The analysed zircons contain widely varied U concentrations, between 91 and 1324 ppm, with a median value of 456 ppm. Th/U ratios vary between 0.26 and 1.52 with a median value of 0.62. Common Pb (206Pbc) values range between 0.00 and 0.85%. The 42 analyses can be divided into four groups based on textural, chemical and isotopic criteria:

• Group 1 comprises 31 analyses derived predominantly from oscillatory-zoned zircon with medium to low CL response, with many of the analyses positioned within pyramidal terminations of euhedral crystals. Analyses in this group contain U concentrations ranging between 117 ppm and 1324 ppm, with a median value of 586 ppm, and Th/U between 0.40 and 1.38, with a median value of 0.62. Their individual 238U/206Pb ages range between c. 445 Ma and c. 414 Ma, and combine to form a statistically coherent weighted mean age of 428.2 ± 3.1 Ma (95% confidence, MSWD = 1.26, P = 0.15). Probability of equivalence is herein referred to as ‘P’.

• Group 2 comprises six analyses from rounded zircon cores with medium to bright CL response that are disconformably overgrown by oscillatory-zoned and lower CL response zircon characteristic of Group 1. The zircon cores of Group 2 contain U concentrations between 91 ppm and 326 ppm, with a median value of 230 ppm, and Th/U between 0.31 and 1.45, with a median value of 0.95. Analyses from this group yield individual 238U/206Pb ages between c. 1031 Ma and c. 561 Ma.

• Group 3 comprises four analyses from zircon cores or anhedral to subhedral, relatively equant grains, with varied CL response. U concentrations vary from 95 ppm to 786 ppm, with a median value of 139 ppm, and Th/U ranges from 0.26 to 0.65, with a median value of 0.48. Three analyses from this group yield near-concordant individual 207Pb/206Pb ages of c. 3512 Ma, c. 2840 Ma, c. 1706 Ma, and the fourth analysis is 35% discordant with a 207Pb/206Pb age of c. 1990 Ma.

• Group 4 consists of a single analysis (675.14.1) from zircon that is morphologically and chemically similar to those in Group 1, but yields a younger 238U/206Pb age of c. 324 Ma.

2.5 Geochronological interpretation The weighted mean 238U/206Pb age of 428.2 ± 3.1 Ma derived from the 31 analyses in Group 1 is interpreted as the magmatic crystallisation age of this granite. The single analysis in Group 4 (675.14.1) comes from a relatively high U (964 ppm) and low CL portion of a grain from which a second analysis (675.14.2) from lower U (117 ppm), oscillatory zoned zircon yielded an age of c. 419 Ma, forming part of the Group 1 mean age. Consequently, the anomalously young age of c. 324 Ma from the Group 4 analysis is interpreted as a result of partial Pb-loss, likely induced by crystal damage arising from the relatively high U content, and is regarded as geologically meaningless.

The 238U/206Pb ages from the zircon cores in Group 2, are interpreted as inherited zircon of Neoproterozoic age. Similarly, the cores and anhedral grains of Group 3 are interpreted as inherited zircon of Paleoproterozoic to Archean age, one of which has experienced partial Pb-loss resulting in significant discordance and rendering its 207Pb/206Pb age a minimum constraint on the true crystallisation age of this inherited grain.


2200

18001400

1000600

0.0

0.1

0.2

0.3

0.4

0 4 8 12 16 20 24238U/206Pb

207 Pb

/206 Pb

1σ error ellipses

Group 1: magmatic crystallisation (n = 31)Mean 238U/206Pb age = 428.2 ± 3.1 Ma

95% conf., MSWD = 1.26, P = 0.15

Drillhole F1DD02GA Sample No: 2167675GA Sample ID: 2013831005Bn = 42 of 42 analyses

(a)

500 480 460 440 420 400 380

0.04

0.05

0.06

0.07

0.08

12 13 14 15 16 17238U/206Pb

207 Pb

/206 Pb

1σ error ellipses

Group 1: magmatic crystallisation (n = 31)Mean 238U/206Pb age = 428.2 ± 3.1 Ma

95% conf., MSWD = 1.26, P = 0.15

Drillhole F1DD02GA Sample No: 2167675GA Sample ID: 2013831005Bn = 31 of 42 analyses

(b)

Figure 2.4 SHRIMP U-Pb data for zircons from the F1 prospect granite (drillhole F1DD02; GA SampleNo: 2167675). (a) Tera-Wasserburg concordia diagram showing all analyses; (b) Tera-Wasserburg concordia diagram showing analyses from the interpreted magmatic zircon population. Yellow fill denotes Group 1 (magmatic crystallisation); green fill denotes Group 2 (Mesoproterozoic–Neoproterozoic inheritance); purple fill denotes Group 3 (Pre-Mesoproterozoic inheritance); white fill denotes Group 4, the single analysis of c. 324 Ma.


Table 2.2 SHRIMP U-Pb zircon data from the F1 prospect granite (drillhole F1DD02; GA SampleNo: 2167675). All analyses were collected in session 140039.

Grain.area 206Pbc

(%) U

(ppm) Th

(ppm) 232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

Group 3: Pre-Mesoproterozoic inheritance (n = 4; 207Pb/206Pb dates tabulated)

32.1 0.09 95 37 0.41 1.471 2.00 0.30827 0.62 3512.3 9.6 +6

38.1 0.05 112 59 0.54 1.801 1.92 0.20174 0.73 2840.3 11.9 -0

23.1 0.09 786 200 0.26 4.274 1.79 0.12229 0.54 1989.8 9.6 +35

37.1 0.05 166 104 0.65 3.332 1.74 0.10452 1.04 1705.8 19.1 +1

Group 2: Mesoproterozoic–Neoproterozoic inheritance (n = 6; 238U/206Pb dates tabulated)

31.1 0.41 304 165 0.56 5.764 1.55 0.07341 1.65 1031.4 14.7 -1

40.1 0.00 326 96 0.31 9.372 1.55 0.06244 1.59 653.6 9.6 +5

39.1 -0.30 208 118 0.59 10.122 1.68 0.06329 2.74 607.3 9.7 +16

6.2 0.43 168 236 1.45 10.777 1.72 0.05918 3.55 572.0 9.4 +0

30.1 0.53 253 323 1.32 10.951 1.59 0.05686 3.20 563.3 8.6 -17

29.1 -0.31 91 133 1.52 10.994 2.02 0.06384 3.98 561.2 10.9 +25

Group 1: Magmatic crystallisation (n = 31; 238U/206Pb dates tabulated)

34.1 0.10 1217 593 0.50 13.990 1.81 0.05767 1.11 445.1 7.8 +14

26.1 0.30 311 191 0.63 14.198 1.53 0.05370 2.81 438.8 6.5 -23

27.1 -0.58 232 147 0.65 14.212 1.61 0.05815 3.65 438.3 6.8 +19

19.1 0.31 537 248 0.48 14.228 1.42 0.05318 2.08 437.9 6.0 -31

22.1 0.15 222 131 0.61 14.303 1.58 0.05514 2.64 435.6 6.6 -4

2.1 0.00 1324 750 0.58 14.333 1.33 0.05510 0.82 434.8 5.6 -5

11.1 0.16 377 226 0.62 14.332 1.44 0.05496 1.94 434.8 6.1 -6

35.1 0.10 400 476 1.23 14.353 1.49 0.05474 2.07 434.2 6.3 -8

12.1 0.74 728 529 0.75 14.428 1.49 0.05334 2.40 432.0 6.2 -27

4.1 0.50 1216 796 0.68 14.424 1.41 0.05637 1.52 432.1 5.9 +8

24.1 0.16 592 229 0.40 14.415 1.42 0.05497 1.77 432.4 5.9 -5

17.1 0.23 586 394 0.69 14.490 1.40 0.05267 1.76 430.2 5.8 -38

18.1 0.13 593 296 0.52 14.499 1.40 0.05433 1.58 430.0 5.8 -12

25.1 0.39 405 185 0.47 14.539 1.48 0.05342 3.79 428.8 6.2 -24

13.1 0.04 889 411 0.48 14.525 1.36 0.05708 1.09 429.2 5.6 +14

7.1 0.01 1069 619 0.60 14.515 1.34 0.05655 0.88 429.5 5.6 +10

3.1 0.26 732 683 0.96 14.532 1.52 0.05457 1.54 429.0 6.3 -9

10.1 0.28 512 465 0.94 14.567 1.81 0.05436 2.01 428.0 7.5 -11

28.1 0.15 1151 800 0.72 14.615 1.36 0.05490 1.30 426.6 5.6 -5

9.1 0.31 876 406 0.48 14.649 1.36 0.05620 1.48 425.7 5.6 +8

1.1 0.06 1073 733 0.71 14.663 1.35 0.05647 1.00 425.3 5.5 +10

15.1 0.06 1767 908 0.53 14.706 1.33 0.05552 0.85 424.1 5.4 +2


Grain.area 206Pbc

(%) U

(ppm) Th

(ppm) 232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

6.1 0.08 1046 704 0.70 14.722 1.36 0.05523 1.78 423.7 5.6 -1

33.1 0.09 224 298 1.38 14.780 2.14 0.05604 3.82 422.0 8.8 +7

36.1 0.28 507 196 0.40 14.769 1.45 0.05454 2.25 422.3 5.9 -8

20.1 0.14 350 207 0.61 14.805 1.50 0.05539 2.07 421.4 6.1 +2

8.1 0.44 354 217 0.63 14.888 1.46 0.05397 2.71 419.1 5.9 -14

14.2 -0.87 117 86 0.75 14.878 1.90 0.06728 5.35 419.3 7.7 +52

16.1 0.62 195 132 0.70 14.918 1.62 0.05408 4.33 418.3 6.5 -12

5.1 0.85 145 69 0.49 14.954 1.70 0.05405 5.29 417.3 6.9 -12

21.1 0.18 615 279 0.47 15.079 1.42 0.05537 1.86 413.9 5.7 +3

Group 4: Pb-loss (n = 1; 238U/206Pb date tabulated)

14.1 0.25 964 777 0.83 19.429 1.51 0.05488 1.49 323.5 4.8 +21


3 F1 prospect granitic dyke (drillhole F1DD01)

Table 3.1 Summary of results: F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: 2167701).

GA SampleNo 2167701

Sample ID 2013831006J

Parent Unit -



Lithology Fine- to medium-grained, leucocratic granitic dyke

Drillhole name & depth (downhole) F1DD01 237.5–238.5 m




Location (GDA94) -30.50623, 143.87578







3.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole F1DD01 (downhole depth 237.5–238.5 m), drilled in 2013 at the F1 prospect.

This drillhole is located ~100 m to the east of drillhole F1DD02 and, similar to that drillhole, intersected Eromanga Basin sedimentary rocks overlying granite (Figure 1.2). The unit sampled is a fine- to medium-grained leucocratic granite dyke (Figure 3.1) that is ~1 m wide, and intrudes the main phase granite as dated and described in F1DD02 – see Section 2 of this Record. This dyke hosts molybdenite and other sulfides, and is surrounded by greisen alteration.


Figure 3.1 Representative photograph of the F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: 2167701). Field of view is ~15 cm wide.

3.2 Petrography This fine- to medium-grained sample consists of quartz, plagioclase and sericite (Figure 3.2). Quartz grains are equant and subhedral. Plagioclase commonly exhibits concentric zoning in cross-polarised light. The cores of plagioclase grains are commonly replaced with sericite; often remnant plagioclase grains have been completely replaced by sericite.

(a) (b)

Figure 3.2 Representative photomicrographs of the F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: 2167701). (a) Plane-polarised light; quartz and feldspar crystals with grey sericite alteration; (b) Cross-polarised light; fine-grained sericite replacement within zoned plagioclase cores (lower centre-left).


3.3 Zircon description The mounted crystals are characterised by long axes spanning the range 60–150 μm (typically 80–100 μm), and aspect ratios (length:width) as high as 3:1, but more commonly between 1:1 and 2:1 (Figure 3.3). Crystal forms are predominantly subhedral and broken, although there are fewer euhedral, unbroken grains. In transmitted light, most crystals are transparent to translucent and colourless to mid-brown, and several grains are cracked and iron-stained. Some of the grains host small rounded inclusions (less than 10 μm) of dark coloured minerals.

Cathodoluminescence (CL) images reveal widely varied CL emission intensities and zoning patterns. Crystals commonly contain ill-defined zoning within the central domains which is disconformably overgrown by concentric oscillatory zoning parallel to the grain boundary. Some grains contain rounded central domains surrounded by concentric oscillatory zoning and others contain parallel banding. The well-defined oscillatory zoned grains are interpreted as representative of magmatic crystallisation. The ill-defined zoning and parallel banding textures are interpreted as inherited zircon.

Figure 3.3 All zircons analysed from F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: 2167701). Transmitted light image is shown in the upper half, cathodoluminescence image in the lower half. SHRIMP analysis sites are labelled ‘sample.grain.area’, where ‘sample’ is the final three digits of the GA SampleNo.


3.4 U-Pb isotopic results A total of 27 analyses were collected from 22 different zircon grains, and the results are presented in Table 3.2 and displayed in Figure 3.4. The analysed zircons contain U concentrations ranging between 94 ppm and 1563 ppm, with a median value of 370 ppm. Th/U ratios vary between 0.01 and 1.94 with a median value of 0.74. Common Pb (206Pbc) contents are all less than 0.55%, with the majority of analyses less than 0.25%. The 27 analyses can be divided into four groups based on textural, chemical and isotopic characteristics:

• Group 1 comprises 13 analyses from faceted grains and fragments that exhibit low to medium CL response and either fine-scale oscillatory zoning that is concentric to grain margins, or planar internal zoning. Analyses in this group contain U concentrations between 172 ppm and 1027 ppm, with a median value of 406 ppm. Th/U of zircon in this group ranges between 0.53 and 1.94, with a median value of 0.70. Their individual 238U/206Pb ages range between c. 435 Ma and c. 412 Ma, and combine to form a statistically coherent population with a weighted mean age of 424.5 ± 4.9 Ma (95% confidence, MSWD = 1.50, P = 0.12).

• Group 2 comprises four analyses. Three of these come from the interior of grains from which the pyramidal tips form part of Group 1 analyses. These four analyses combine to yield a statistically coherent weighted mean 238U/206Pb age of 444.2 ± 10.0 Ma (95% confidence, MSWD = 0.03, P = 0.99).

• Group 3 comprises nine analyses derived predominantly from zircon with subhedral or anhedral morphology or fragments, some of which show surface pitting or irregularities. Zircon in this group exhibits a wide range of CL response, from relatively bright to dark. Several of the grains show internal zoning patterns that are truncated by the grain margins. Analyses from this group yield individual 238U/206Pb ages ranging from c. 1197 Ma to c. 504 Ma.

• Group 4 consists of a single analysis from a rounded, equant grain with moderate CL response that yields a 207Pb/206Pb age of c. 2858 Ma and is 18% discordant.

3.5 Geochronological interpretation The weighted mean 238U/206Pb age of 424.5 ± 4.9 Ma of the 13 analyses in Group 1 is interpreted as the magmatic crystallisation age of this granitic dyke, and is indistinguishable at the 95% confidence level from the age of 428.2 ± 3.1 Ma obtained from the host granite, as reported in Section 2 of this Record. The four analyses of Group 2, with a mean age of c. 444 Ma, are interpreted as inherited zircon based on zircon morphology and age.

The ages of subhedral to anhedral zircons in Group 3 are interpreted as inherited zircon of Mesoarchean to Cambrian age. Similarly, the single analysis of Group 4 is interpreted as inherited zircon, and its Mesoarchean 207Pb/206Pb age of c. 2858 Ma is regarded as a minimum constraint on the crystallisation age of this grain due to at least one episode of Pb-loss, as indicated by its discordance.


2600

2200

1800

1400

1000600

0.04

0.08

0.12

0.16

0.20

0.24

0 4 8 12 16 20238U/206Pb

207 Pb

/206 Pb

1σ error ellipses

Group 1: magmatic crystallisation (n = 13)Mean 238U/206Pb date = 424.5 ± 4.9 Ma

95% conf., MSWD = 1.50, P = 0.12

Group 2: inherited zircon (n = 4)Mean 238U/206Pb date = 444.2 ± 10.0 Ma

95% conf., MSWD = 0.03, P = 0.99

F1 prospect granitic dyke (drillhole F1DD01)GA Sample No: 2167701GA Sample ID: 2013831006Jn = 27 of 27 analyses

(a)

490 470 450 430 410 390

0.04

0.05

0.06

0.07

12 13 14 15 16238U/206Pb

207 Pb

/206 Pb


95% conf., MSWD = 1.50, P = 0.12

Group 2: inherited zircon (n = 4)Mean 238U/206Pb date = 444.2 ± 10.0 Ma

95% conf., MSWD = 0.03, P = 0.99

F1 prospect granitic dyke (drillhole F1DD01)GA Sample No: 2167701GA Sample ID: 2013831006Jn = 17 of 27 analyses

1σ error ellipses

(b)

Figure 3.4 SHRIMP U-Pb data for zircons from the F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: 2167701). (a) Tera-Wasserburg concordia diagram showing all analyses; (b) Tera-Wasserburg concordia diagram showing analyses of Paleozoic age. Yellow fill denotes Group 1 (magmatic crystallisation); red fill denotes Group 2 (Ordovician inheritance); green fill denotes Group 3 (Cambrian–Mesoproterozoic inheritance); purple fill denotes Group 4 (c. 2858 Ma single inherited zircon).


Table 3.2 SHRIMP U-Pb zircon data from the F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: 2167701). All analyses were collected in session 140039.

Grain.area 206Pbc

(%) U

(ppm) Th

(ppm) 232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

Group 4: Pre-Mesoproterozoic inheritance(n = 1; 207Pb/206Pb dates tabulated)

7.1 0.23 231 68 0.30 2.190 1.51 0.20393 0.50 2857.9 8.1 +18

Group 3: Mesoproterozoic–Cambrian inheritance (n = 9; 238U/206Pb dates tabulated)

2.1 0.36 94 132 1.46 4.901 1.81 0.07865 2.05 1197.0 19.7 -3

14.1 0.04 123 170 1.42 5.004 1.74 0.08232 1.47 1174.4 18.7 +7

20.1 0.07 370 334 0.93 5.071 1.49 0.07983 0.96 1160.2 15.8 +3

22.1 0.10 310 85 0.28 6.203 3.19 0.07567 1.29 963.5 28.5 +12

21.1 0.04 407 120 0.31 6.375 2.43 0.07212 1.95 939.3 21.3 +5

23.1 0.03 995 419 0.44 9.920 1.37 0.05983 0.92 619.1 8.1 -4

16.1 -0.14 221 352 1.64 9.947 1.56 0.06326 1.89 617.5 9.2 +15

18.1 0.32 127 1 0.01 10.488 1.80 0.05911 3.60 587.1 10.1 -3

4.1 0.06 1140 885 0.80 12.299 1.34 0.05715 0.88 503.9 6.5 -1

Group 2: Ordovician inheritance (n = 4; 238U/206Pb dates tabulated)

15.2 -0.02 1563 1472 0.97 13.974 1.33 0.05578 0.81 445.6 5.7 -0

1.1 0.05 1366 361 0.27 14.029 1.33 0.05539 0.83 443.9 5.7 -4

5.2 0.21 434 356 0.85 14.018 1.68 0.05793 1.90 444.2 7.2 +16

9.2 0.13 370 336 0.94 14.057 1.47 0.05464 1.93 443.0 6.3 -12


13.1 -0.02 1027 1113 1.12 14.322 1.35 0.05564 0.97 435.1 5.7 +1

8.1 0.09 826 596 0.74 14.387 1.36 0.05510 1.25 433.2 5.7 -4

15.1 0.02 833 560 0.70 14.441 1.37 0.05655 2.03 431.6 5.7 +9

17.1 0.00 627 942 1.55 14.532 1.59 0.05615 1.26 429.0 6.6 +7

3.1 0.31 323 515 1.65 14.574 1.45 0.05388 2.32 427.8 6.0 -17

3.2 -0.05 319 599 1.94 14.590 1.88 0.06026 3.09 427.4 7.8 +31

5.1 0.23 406 267 0.68 14.720 1.44 0.05363 2.15 423.7 5.9 -20

9.1 0.37 354 271 0.79 14.720 1.46 0.05176 3.54 423.7 6.0 -56

11.1 0.00 287 191 0.69 14.741 1.49 0.05595 1.80 423.1 6.1 +6

12.1 0.17 580 325 0.58 14.864 1.40 0.05449 1.71 419.7 5.7 -8

11.2 0.53 172 104 0.63 15.015 2.23 0.05633 4.33 415.6 9.0 +11

10.1 0.34 334 206 0.64 15.063 1.47 0.05330 2.67 414.4 5.9 -22

6.1 0.19 1010 520 0.53 15.140 1.35 0.05473 1.34 412.3 5.4 -3


4 Quartz diorite (drillhole CUTACD02)

Table 4.1 Summary of results: quartz diorite (drillhole CUTACD02; GA SampleNo: 2167668).

GA SampleNo 2167668


Parent Unit -



Lithology Medium- to coarse-grained, biotite-rich quartz diorite

Drillhole name & depth (downhole) CUTACD02 404.7–406.5 m


1:250 000 Sheet Louth (H5509)

1:100 000 Sheet Thoolabool (7736)

Location (GDA94) -30.64254, 144.33094




Interpreted Age 429.0 ± 8.5 Ma (95% confidence; six analyses of six zircons)



4.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole CUTACD02 (downhole depth 404.7–406.5 m), drilled in 2011.

This drillhole predominantly intersected metasedimentary psammite, with intervals of diorite to granodiorite dykes or sills up to several metres wide, which host mineralised carbonate and quartz veins. The veins contain thin alteration selvedges of white mica.

The sample was selected from one of the igneous bodies for the purpose of U-Pb geochronology to provide the timing of magmatic crystallisation of these intrusions. This in turn provides a maximum constraint on timing of intrusion-related sulfide mineralisation. An age from this sample will also be of interest for comparison with the age of 428.3 ± 2.8 Ma (Chisholm et al., 2014) obtained from granite from the CUTAD01 drillhole approximately 10 km to the west of CUTACD02.


4.2 Petrography This fine-grained sample consists of quartz, sericite, biotite with minor alteration to chlorite, plagioclase, muscovite and accessory pyrrhotite, pyrite and zircon. Quartz is relatively equant, subhedral to anhedral and commonly exhibits undulose extinction in cross-polarised light. The biotite commonly exhibits very diffuse grain boundaries although some grains show distinct planar cleavage and grain boundaries. The plagioclase commonly occurs as relatively large grains (4 mm long) and shows concentric zoning in cross-polarised light. The majority of plagioclase cores have undergone some degree of sericite replacement; often the whole grain has been replaced. Minor disseminated pyrrhotite and pyrite occurs within the sericite alteration of large plagioclase grains.

(a) (b)

Figure 4.1 Representative photomicrographs of quartz diorite (drillhole CUTACD02; GA SampleNo: 2167668). (a) Plane-polarised light; abundant brown biotite with diffuse grain boundaries, minor clear to pale green chlorite alteration and clear muscovite alteration. Clear quartz grains and light beige plagioclase; (b) Cross-polarised light; moderate to highly birefringent biotite, chlorite and muscovite; concentrically zoned plagioclase crystals, some with sericite replacement in cores.

4.3 Zircon description The mounted crystals are characterised by long axes spanning the range 50–180 μm (typically 60–150 μm), and aspect ratios (length:width) as high as 3:1, but more commonly between 2:1 and 3:2 (Figure 4.2). Crystal forms are predominantly euhedral to subhedral, with many grains preserving facets. External morphologies of unbroken crystals commonly contain equant or rounded central regions upon which pyramidal terminations are superimposed. In transmitted light, most crystals are transparent to translucent and colourless to pale brown, although widespread cracking and iron-staining gives a mottled texture to some grains. Dark mineral inclusions up to 25 μm in diameter are common.

Cathodoluminescence (CL) images reveal varied CL emission and zoning patterns. Commonly grains contain large ill-defined central regions with low to moderate CL emission which are disconformably overgrown by weakly-defined concentric oscillatory zoning parallel to the grain boundary. Some grains contain oscillatory banding parallel to the long axis.


Figure 4.2 Representative zircons from quartz diorite (drillhole CUTACD02; GA SampleNo: 2167668). Transmitted light image is shown in the upper half, cathodoluminescence image in the lower half. SHRIMP analysis sites are labelled ‘sample.grain.area’, where ‘sample’ is the final three digits of the GA SampleNo.

4.4 U-Pb isotopic results Forty-two analyses were collected from 41 different zircon grains. The results are presented in Table 4.2 and displayed in Figure 4.3. The analysed zircons contain U concentrations ranging from 58 ppm to 1737 ppm, with a median value of 250 ppm. Th/U ratios vary between 0.01 and 3.08 with a median value of 0.58. Eleven analyses contain >0.70% common Pb (206Pbc) and have been excluded from geological interpretation on that basis. The remaining 31 analyses can be divided into three groups based on textural, chemical and isotopic criteria:

• Group 1 comprises six analyses derived from faceted, euhedral grains, with analyses positioned within oscillatory-zoned pyramidal tips, or within planar zoned zircon. Analyses in this group contain U concentrations between 212 ppm and 547 ppm, with a median value of 337 ppm, and Th/U between 0.54 and 1.76 with a median value of 1.13. Their individual 238U/206Pb ages range between c. 446 Ma and c. 421 Ma, and group to form a statistically coherent weighted mean age of 429.0 ± 8.5 Ma (95% confidence, MSWD = 1.43, P = 0.21).

• Group 2 comprises 20 analyses from cores of grains which have narrow, faceted overgrowths, or from grains with subhedral to anhedral grain shapes, and a range of internal zoning patterns and CL responses. Analyses in this group contain U concentrations between 90 ppm and 1737 ppm, with a median value of 340 ppm, and Th/U between 0.01 and 1.26, with a median value of 0.51. Their individual 238U/206Pb ages range between c. 497 Ma and c. 1175 Ma.

• Group 3 comprises five analyses from grain cores, or from rounded, relatively equant grains with internal zonation that is truncated by the grain surface. Analyses in this group contain U concentrations between 58 ppm and 371 ppm, with a median value of 230 ppm, and Th/U between 0.27 and 3.08, with a median value of 0.74. Individual 207Pb/206Pb ages within this group range between c. 2827 Ma and c. 1378 Ma.


4.5 Geochronological interpretation The weighted mean 238U/206Pb age of 429.0 ± 8.5 Ma of the six analyses in Group 1 is interpreted as the magmatic crystallisation age of this quartz diorite. The limited number of analyses obtained to define this age reflects the fact that oscillatory-zoned, magmatic zircon forms a relatively small volumetric proportion of all zircon obtained from this rock, and typically forms as narrow rims on older, inherited zircon. The age from this sample is indistinguishable at 95% confidence level from the age of 428.3 ± 2.8 Ma obtained by Chisholm et al. (2014) from a granite within the CUTAD01 drillhole ~10 km to the west.

The 238U/206Pb ages from the zircon cores and subhedral to anhedral, rounded grains of Group 2 are interpreted as inherited zircon of Cambrian to late Mesoproterozoic age. Similarly, the cores and rounded grains of Group 3 are interpreted as inherited zircon of Mesoproterozoic to Archean age.

2600

2200

1800

1400

1000600

0.02

0.06

0.10

0.14

0.18

0.22

0 4 8 12 16238U/206Pb

207 Pb

/206 Pb


95% conf., MSWD = 1.43, P = 0.21

1σ error ellipses

Quartz diorite (drillhole CUTACD02)GA Sample No: 2167668GA Sample ID: 2013831003Bn = 42 of 42 analyses

Figure 4.3 SHRIMP U-Pb data for zircons from quartz diorite (drillhole CUTACD02; GA SampleNo: 2167668). Tera-Wasserburg concordia diagram showing all analyses. Yellow fill denotes Group 1 (magmatic crystallisation); green fill denotes Group 2 (Mesoproterozoic–Cambrian inheritance); purple fill denotes Group 3 (Pre-Neoproterozoic inheritance); white fill denotes analyses rejected on the basis of relatively high common Pb (206Pbc > 0.70%).


Table 4.2 SHRIMP U-Pb zircon data from quartz diorite (drillhole CUTACD02; GA SampleNo: 2167668). All analyses were collected in session 140039.

Grain.area 206Pbc

(%) U

(ppm) Th

(ppm) 232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

Group 3: Pre-Neoproterozoic inheritance (n = 5; 207Pb/206Pb dates tabulated)

41.1 0.09 116 346 3.08 1.840 1.91 0.20004 0.78 2826.5 12.8 +1

32.1 0.05 230 128 0.57 2.002 1.62 0.18483 0.93 2696.7 15.3 +4

38.1 0.38 58 41 0.74 3.481 2.38 0.09685 3.40 1564.4 63.7 -5

31.1 0.05 258 199 0.80 3.947 1.57 0.09060 0.94 1438.2 17.9 -1

17.1 0.06 371 96 0.27 4.130 1.47 0.08779 0.80 1377.9 15.4 -2

Group 2: Mesoproterozoic–Cambrian inheritance (n = 20; 238U/206Pb dates tabulated)

1.1 0.05 350 195 0.57 5.001 1.46 0.07936 0.86 1175.1 15.7 +1

26.1 0.19 417 69 0.17 5.298 1.48 0.07492 1.10 1114.7 15.1 -5

8.1 0.25 90 38 0.43 5.397 1.87 0.07686 2.20 1095.7 18.8 +2

24.1 0.05 279 195 0.72 5.518 1.55 0.07452 1.17 1073.7 15.3 -2

23.1 0.03 796 458 0.59 5.521 1.38 0.07627 0.65 1073.1 13.6 +3

30.1 0.28 169 68 0.41 5.821 1.72 0.07288 2.05 1021.9 16.2 -1

35.1 0.54 591 372 0.65 5.895 2.47 0.07651 3.25 1010.0 23.1 +10

7.1 0.39 175 95 0.56 6.390 2.74 0.07382 4.03 937.2 23.9 +10

36.1 0.22 243 64 0.27 6.697 2.13 0.07076 1.71 897.2 17.8 +6

14.1 0.19 759 193 0.26 10.166 1.38 0.05979 1.20 604.8 7.9 -2

33.1 0.02 537 6 0.01 10.189 1.43 0.06195 1.21 603.5 8.3 +11

2.1 0.25 331 403 1.26 10.276 1.46 0.06035 1.82 598.6 8.3 +3

29.1 0.28 192 197 1.06 10.339 1.67 0.06099 2.78 595.1 9.5 +7

27.1 0.15 315 72 0.24 10.854 1.54 0.06003 2.05 568.1 8.4 +6

22.1 0.23 1737 9 0.01 11.203 1.45 0.05840 0.91 551.2 7.7 -1

3.1 -0.02 508 340 0.69 12.171 1.40 0.05876 1.16 509.0 6.8 +9

6.1 0.70 154 121 0.82 12.424 1.67 0.05610 4.35 499.0 8.0 -10

18.1 0.24 496 117 0.24 12.417 1.42 0.05700 1.81 499.3 6.8 -2

16.2 0.20 349 156 0.46 12.442 1.51 0.05877 2.26 498.3 7.3 +11

9.1 0.49 208 191 0.95 12.482 1.56 0.05613 3.21 496.8 7.5 -9


20.1 -0.16 343 425 1.28 13.971 1.85 0.05766 2.16 445.7 8.0 +14

10.1 0.17 314 397 1.31 14.420 1.47 0.05592 2.05 432.2 6.2 +4

28.1 0.61 212 124 0.61 14.443 2.21 0.05768 4.32 431.6 9.2 +17

11.1 0.04 415 216 0.54 14.556 1.44 0.05790 1.60 428.3 6.0 +19

19.1 0.38 547 932 1.76 14.696 1.42 0.05457 2.19 424.4 5.8 -8

25.1 0.32 331 314 0.98 14.829 1.53 0.05661 2.83 420.7 6.2 +12

Not considered: 206Pbc >0.70% (n = 11; 238U/206Pb dates tabulated)


Grain.area 206Pbc

(%) U

(ppm) Th

(ppm) 232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

34.1 0.80 82 54 0.68 5.570 2.10 0.07332 3.80 1064.4 20.6 -4

39.1 2.15 395 104 0.27 6.070 1.51 0.07971 3.37 983.0 13.8 +19

21.1 1.27 91 85 0.96 8.569 1.98 0.06075 5.97 711.5 13.3 -14

37.1 0.76 151 78 0.54 9.973 1.80 0.05537 4.77 616.0 10.6 -46

12.1 0.93 200 85 0.44 10.734 2.07 0.05345 4.31 574.2 11.4 -68

40.1 0.81 236 127 0.56 12.488 1.63 0.05155 4.58 496.6 7.8 -90

5.1 1.09 144 108 0.77 12.536 1.68 0.05092 5.54 494.8 8.0 -113

4.1 1.32 88 84 0.98 12.560 1.89 0.05097 7.59 493.9 9.0 -111

15.1 13.56 232 123 0.55 12.776 4.85 0.06853 42.29 485.8 22.7 +47

16.1 5.32 84 46 0.57 14.236 2.23 0.09385 13.86 437.6 9.4 +73

13.1 10.35 145 105 0.75 14.265 2.84 0.08238 23.53 436.8 12.0 +67


5 Sandstone (drillhole F03D02)

Table 5.1 Summary of results: sandstone (drillhole: F03D02; GA SampleNo: 2167713).

GA SampleNo 2167713


Parent Unit -



Lithology Sandstone

Drillhole name & depth (downhole) F03D02 481.4–482 m




Location (GDA94) -30.63214, 143.98371



Analytical Session No 140039, 8–14 April 2014; 150033, 15–16 April 2015


Geological Attribution Maximum deposition age


5.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole F03D02 (downhole depth 481.4–482 m), drilled in 2011. This drillhole is located ~30 km west of the Cuttaburra mineral prospect, and between the Cuttaburra and F1 prospects.

This drillhole contains predominantly pelitic and psammitic rocks with abundant quartz veins, and was sampled for geochronology as representative of the regional metasedimentary basement rocks which are intruded by mineralised granites at the Cuttaburra prospect. The sampled sandstone is comprised of rounded to sub-angular quartz grains within a fine-grained matrix of quartz, feldspar and sericite. The age of the youngest detrital zircons from this sample will provide a maximum age constraint on the timing of deposition of this sedimentary rock. The detrital zircon age spectrum will also be of interest for comparison with age spectra from other regional metasedimentary rocks of the southern Thomson and northern Lachlan Orogens.


5.2 Petrography This fine- to medium-grained sample consists of quartz grains, supported by a relatively fine-grained matrix comprised of quartz, feldspar and sericite (Figure 5.1). There is also minor rutile and Ti-oxides. The quartz grains are rounded to sub-angular with some exhibiting undulose extinction in cross-polarised light. There is a weak alignment of long axes of quartz grains that could be representative of bedding. This sample is cross-cut by several quartz veins.

(a) (b)

Figure 5.1 Representative photomicrographs of sandstone (drillhole: F03D02; GA: 2167713). (a) Plane-polarised light; rounded to sub-angular fractured quartz grains in a fine-grained matrix; minor oxides and opaque minerals; (b) Cross-polarised light; matrix consists of fine-grained quartz, feldspar and white mica.

5.3 Zircon description The mounted crystals are equant to moderately elongate, with long axes spanning the range 40–250 μm (typically 70–150 μm), and aspect ratios (length:width) as high as 4:1, but more commonly between 2:1 and 3:1 (Figure 5.2). Crystal forms are generally either euhedral or well-rounded, with preservation of facets on euhedral crystals. External morphologies of euhedral crystals are dominated by equant central regions upon which prominent pyramidal terminations are commonly superimposed. In transmitted light, most crystals are transparent to translucent, and colourless to pale brown. Inclusions up to 10 μm are common in both the euhedral and well-rounded grains.

Cathodoluminescence (CL) images reveal varied CL emission and zoning patterns. Some grains display broad banding parallel to their long axes, others contain low- to high-contrast oscillatory zoning and some display ill-defined zoning. Many grains contain low CL emission cores surrounded by low- to moderate-contrast oscillatory zoning. The euhedral grains are interpreted to represent a relatively proximal source of detrital zircon whereas the well-rounded grains appear to have been subject to more abrasion during sedimentary transport, possibly in more than one sedimentary cycle.


Figure 5.2 Representative zircons from sandstone (drillhole: F03D02; GA SampleNo: 2167713). Transmitted light image is shown in the upper half, cathodoluminescence image in the lower half. SHRIMP analysis sites are labelled ‘sample.grain.area’, where ‘sample’ is the final three digits of the GA SampleNo.

5.4 U-Pb isotopic results Isotopic data for this sample were collected over two analytical sessions. Forty-two analyses were collected during an initial session (140039), concurrently with analyses of the three magmatic samples from the Cuttaburra and F1 prospects presented earlier in this report. A subsequent analytical session (150033) collected an additional 29 analyses to augment the detrital zircon spectrum from this metasedimentary sample. In total, 71 analyses were collected from 71 different zircon grains and the results are presented in Table 5.2 and displayed in Figure 5.3.

The analysed zircons contain U concentrations ranging between 33 ppm and 1699 ppm, with a median value of 267 ppm. Th/U ratios vary between 0.07 and 2.22 with a median value of 0.57. Common Pb (206Pbc) contents for 68 of the 71 analyses are less than 0.5%; three analyses containing greater than 1.2% common Pb are excluded from geological interpretation. The remaining 68 analyses can be divided into three groups based on textural, chemical and isotopic characteristics:

• Group 1 comprises 23 analyses from faceted grains that exhibit low to medium CL response and either fine-scale oscillatory zoning that is concentric to grain margins, or low-contrast planar internal zoning. Analyses in this group contain U concentrations between 128 ppm and 888 ppm, with a median value of 329 ppm. Th/U of zircon in this group ranges between 0.21 and 1.12 with a median value of 0.50. The individual 238U/206Pb dates range between c. 515 Ma and c. 489 Ma, and combine to form a statistically coherent population with a weighted mean date of 498.7 ± 3.9 Ma (95% confidence, MSWD = 1.03, P = 0.42).

• Group 2 comprises 33 analyses derived from faceted zircon with either faceted or anhedral grains or fragments. Zircons in this group exhibit a wide range of CL response and zoning patterns, from relatively bright to dark, parallel banding, concentric oscillatory zonation and poorly defined CL emission. Analyses from this group yield individual 238U/206Pb dates ranging from c. 1252 Ma to c. 518 Ma.


• Group 3 comprises 12 analyses derived from predominantly well-rounded zircon grains, some of which show surface pitting or irregularities. Zircons in this group exhibit a wide range of CL response, from relatively bright to dark. Some grains show weakly-defined oscillatory zoning while others display irregular zoning patterns. Analyses from this group yield individual 207Pb/206Pb dates ranging from c. 3342 Ma to c. 1625 Ma.

5.5 Geochronological interpretation The weighted mean 238U/206Pb date of 498.7 ± 3.9 Ma derived from the 23 analyses in Group 1 is interpreted as the magmatic crystallisation age of zircon from a relatively local magmatic source and represents a maximum constraint on the timing of deposition of this sedimentary rock.

The 238U/206Pb dates between c. 1205 Ma and c. 518 Ma obtained from the 33 analyses in Group 2 are interpreted as detrital grains of Mesoproterozoic to Cambrian age. The 207Pb/206Pb dates between c. 3342 Ma and c. 1625 Ma obtained from the seven analyses in Group 3 are interpreted as pre-Mesoproterozoic detrital zircon.

3000

2600

2200

1800

14001000

600

0.02

0.06

0.10

0.14

0.18

0.22

0.26

0.30

0 4 8 12 16238U/206Pb

207 Pb

/206 Pb

1σ error ellipses

Group 1: Maximum deposition age (n = 23)Mean 238U/206Pb date = 498.7 ± 3.9 Ma

95% conf., MSWD = 1.03, P = 0.42

Sandstone (drillhole F03D02)GA Sample No: 2167713GA Sample ID: 2013831009Bn = 71 of 71 analyses

Figure 5.3 SHRIMP U-Pb data for zircons from the sandstone (drillhole: F03D02; GA SampleNo: 2167713). Tera-Wasserburg concordia diagram showing all analyses. Dark green fill denotes Group 1 (analyses used to calculate the maximum deposition age); light green fill denotes Group 2 (Mesoproterozoic–Neoproterozoic detrital zircon); purple fill denotes Group 3 (Pre-Mesoproterozoic detrital zircon); white fill denotes analyses rejected on the basis of relatively high common Pb (206Pbc > 1.2%).


0 500 1000 1500 2000 2500 3000 3500

Age (Ma)

Rel

ativ

e pr

obab

ility

Sandstone (drillhole F03D02)GA Sample No: 2167713GA Sample ID: 2013831009Bn = 68 of 71 analyses

Figure 5.4 Probability density diagram for SHRIMP U-Pb data from detrital zircons from sandstone (drillhole: F03D02; GA SampleNo: 2167713). Three analyses with relatively high common Pb content are not shown. Analyses younger than 1300 Ma are plotted as 238U/206Pb ages; analyses older than 1300 Ma are plotted as 207Pb/206Pb ages.

Table 5.2 SHRIMP U-Pb zircon data from sandstone (drillhole: F03D02; GA SampleNo: 2167713). Preceding ‘grain. area’, superscript ‘a’ indicates analyses collected in session 140039, superscript ‘b’ indicates analyses collected in session 150033.

sessionGrain.area

206Pbc (%)

U (ppm)

Th (ppm)

232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

Group 3: Pre-Mesoproterozoic detrital zircon (n = 12; 207Pb/206Pb dates tabulated) a39.1 0.10 130 177 1.41 1.549 1.85 0.27636 0.58 3342.5 9.1 +5 b47.1 0.01 282 88 0.32 1.973 2.09 0.27333 0.26 3325.2 4.0 +25 b56.1 0.01 346 322 0.96 2.204 0.89 0.16559 0.59 2513.6 9.9 +5 a40.1 0.09 34 38 1.16 2.204 2.96 0.15012 5.26 2347.3 90.0 -3 a34.1 0.06 261 191 0.76 2.337 1.59 0.14514 0.63 2289.4 10.8 -0 a37.1 -0.31 71 36 0.52 2.891 2.21 0.12865 1.56 2079.6 27.5 +9 a31.1 0.13 152 96 0.65 2.705 1.75 0.12860 0.95 2078.9 16.8 +3 b45.1 -0.02 242 133 0.57 2.969 1.45 0.12305 0.89 2000.9 15.8 +7 a32.1 0.22 180 135 0.77 2.806 1.70 0.12233 0.95 1990.4 16.8 +1 b61.1 -0.15 77 27 0.36 3.020 1.23 0.11528 0.88 1884.3 15.8 +2 b46.1 -0.02 314 315 1.04 3.033 0.90 0.11397 0.40 1863.7 7.3 +2 a38.1 0.07 137 92 0.69 3.528 1.82 0.10005 1.26 1624.9 23.4 +1


sessionGrain.area

206Pbc (%)

U (ppm)

Th (ppm)

232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

Group 2: Mesoproterozoic–Cambrian detrital zircon (n = 33; 238U/206Pb dates tabulated) b57.1 0.00 83 76 0.95 4.666 1.20 0.08100 1.10 1251.9 13.6 -3 b64.1 0.08 254 132 0.54 4.832 0.93 0.07956 0.71 1212.5 10.3 -2 b60.1 0.13 155 84 0.56 4.858 2.01 0.07912 0.95 1206.7 22.1 -3 a42.1 0.03 829 174 0.22 4.867 3.89 0.07430 4.79 1204.6 42.8 -16

a3.1 0.42 107 67 0.65 4.958 1.77 0.07901 2.03 1184.5 19.1 -1 a36.1 0.29 96 68 0.73 5.340 2.01 0.07683 2.50 1106.5 20.4 +1 b71.1 -0.03 311 155 0.51 5.422 0.90 0.07694 0.65 1091.1 9.1 +3 b63.1 -0.01 178 105 0.61 5.485 1.00 0.07531 0.94 1079.6 9.9 -0 b70.1 0.05 267 147 0.57 5.547 0.97 0.07570 0.73 1068.5 9.5 +2 b59.1 0.00 508 230 0.47 5.548 0.85 0.07606 0.50 1068.2 8.3 +3 a33.1 0.35 195 77 0.41 5.605 1.67 0.07273 1.97 1058.3 16.3 -6 b62.1 0.05 385 191 0.51 5.860 0.87 0.07340 0.62 1015.6 8.2 +1 a10.1 0.15 194 33 0.17 5.973 1.58 0.07267 1.49 997.9 14.7 +1 b53.1 0.02 184 165 0.93 6.056 1.83 0.07929 3.13 985.3 16.8 +18 b65.1 0.00 177 143 0.84 6.115 1.82 0.07183 1.94 976.4 16.5 +1 b66.1 -0.01 1699 316 0.19 6.493 0.79 0.07248 0.74 923.4 6.8 +8 b44.1 0.07 277 130 0.48 6.548 6.52 0.05902 6.95 916.2 55.7 -66

a5.1 0.10 340 91 0.28 8.001 1.76 0.06889 1.15 759.2 12.6 +16 b69.1 -0.05 187 124 0.69 9.022 2.07 0.06454 2.37 677.7 13.3 +11 a35.1 -0.14 323 356 1.14 9.995 1.54 0.05970 1.95 614.7 9.0 -4 b48.1 0.00 266 166 0.64 10.023 0.92 0.06037 1.03 613.0 5.4 +1 b52.1 0.18 182 108 0.61 10.091 1.34 0.05964 1.54 609.1 7.8 -3 a26.1 -0.30 130 71 0.56 10.159 1.80 0.06400 3.20 605.3 10.4 +19 b51.1 0.02 431 472 1.13 10.241 0.86 0.05953 0.83 600.6 4.9 -2 b50.1 0.11 131 110 0.87 10.383 1.06 0.06211 1.66 592.8 6.0 +13 b54.1 0.00 540 114 0.22 10.533 0.85 0.06094 1.31 584.7 4.7 +9 b49.1 0.06 176 83 0.49 10.606 0.99 0.06063 1.39 580.9 5.5 +8 a41.1 -0.04 866 58 0.07 10.734 1.39 0.05938 1.08 574.2 7.6 +1 b68.1 0.03 388 255 0.68 11.418 0.88 0.05790 0.97 541.2 4.6 -3 a14.1 0.17 536 134 0.26 11.853 1.40 0.05555 1.53 522.1 7.0 -21 a15.1 0.61 167 112 0.70 11.903 1.73 0.05286 4.34 520.0 8.6 -64 a25.1 -0.44 173 79 0.47 11.903 2.43 0.06020 4.47 520.0 12.1 +15 b55.1 -0.06 358 138 0.40 11.952 0.88 0.05736 1.07 518.0 4.4 -3


sessionGrain.area

206Pbc (%)

U (ppm)

Th (ppm)

232Th /238U

238U /206Pb

±1σ (%)

207Pb /206Pb

±1σ (%)

Date (Ma)

±1σ (Ma)

Disc (%)

Group 1: Cambrian detrital zircon, maximum depositional age (n = 23; 238U/206Pb dates tabulated) a9.1 0.31 299 78 0.27 12.021 1.48 0.05535 2.24 515.1 7.3 -22

a13.1 0.17 337 69 0.21 12.082 1.48 0.05480 2.06 512.6 7.3 -28 a18.1 0.05 354 173 0.50 12.088 1.48 0.05823 1.75 512.4 7.3 +5 a28.1 0.00 148 60 0.42 12.154 1.76 0.05962 2.59 509.7 8.6 +14 a11.1 -0.04 333 226 0.70 12.318 1.47 0.05856 1.64 503.2 7.1 +9 a21.1 0.03 547 364 0.69 12.338 1.42 0.05822 1.32 502.4 6.8 +7 a24.1 0.15 329 169 0.53 12.339 1.52 0.05627 2.17 502.3 7.3 -9

a7.1 0.00 200 168 0.87 12.372 1.56 0.05787 1.86 501.0 7.5 +5 a23.1 0.11 576 368 0.66 12.413 1.41 0.05656 1.49 499.5 6.8 -5 a16.1 0.34 316 191 0.62 12.435 1.49 0.05627 2.40 498.6 7.1 -8 a19.1 0.09 888 890 1.03 12.442 1.55 0.05784 1.17 498.4 7.4 +5

a4.1 -0.19 128 59 0.48 12.450 1.72 0.06205 2.81 498.1 8.2 +27 a6.1 0.10 645 269 0.43 12.452 1.38 0.05597 1.28 497.9 6.6 -11

a29.1 -0.06 281 85 0.31 12.457 1.88 0.05865 2.07 497.8 9.0 +11 b58.1 0.20 172 155 0.93 12.459 1.00 0.05552 1.87 497.7 4.8 -15 a20.1 0.20 393 263 0.69 12.470 1.46 0.05683 1.99 497.3 7.0 -3 a22.1 0.16 468 112 0.25 12.493 1.44 0.05568 1.77 496.4 6.9 -13 a17.1 0.43 472 193 0.42 12.495 1.43 0.05354 2.28 496.3 6.8 -43 b67.1 0.04 178 193 1.12 12.533 1.00 0.05630 1.61 494.9 4.8 -7 a30.1 0.26 288 71 0.25 12.559 1.57 0.05621 2.73 493.9 7.5 -7 a27.1 0.29 318 205 0.67 12.615 1.53 0.05902 2.69 491.8 7.2 +14 b43.1 0.09 275 98 0.37 12.648 0.92 0.05704 1.34 490.5 4.3 +1 a12.1 0.16 340 156 0.47 12.687 1.46 0.05803 1.89 489.1 6.9 +8

Not considered: 206Pbc >0.70% (n = 3; 238U/206Pb dates tabulated)

a2.1 2.72 65 140 2.22 10.474 2.10 0.04105 14.18 587.8 11.8 +321 a1.1 1.22 37 24 0.69 11.344 2.54 0.05766 9.95 544.6 13.3 -6 a8.1 1.58 33 23 0.72 12.254 2.69 0.05590 13.11 505.7 13.1 -13


Acknowledgements

Roger Skirrow, Michael Doublier, David Huston and David Champion collected the samples reported here, and are thanked for various discussions regarding the geological context. The Geoscience Australia mineral separation team of David DiBugnara, Ben Linehan and Jo Tubby are acknowledged for their attention to detail and skill in producing high quality zircon mounts and associated images, upon which this work is critically dependant. Patrick Burke was responsible for maintaining the GA SHRIMP instrument, and assisted greatly with instrument tune-up and troubleshooting. We thank Keith Sircombe for his ongoing support of the GA SHRIMP facility, and Les Sullivan for maintaining the laboratory information management system (LIMS). Natalie Kositcin and Jane Thorne provided thorough reviews which improved this Record.


References

Black, L. P., Kamo, S. L., Allen, C. M., Davis, D. W., Aleinikoff, J. N., Valley, J. W., Mundil, R., Campbell, I. H., Korsch, R. J. and Williams, I. S., 2004. Improved 206Pb/238U microprobe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, ID–TIMS, ELA–ICP–MS and oxygen isotope documentation for a series of zircon standards. Chemical Geology 205, 115–140

Chisholm, E. I., Blevin, P. L., Downes, P. M. and Simpson, C. J., 2014. New SHRIMP U–Pb zircon ages from the central Lachlan Orogen and Thomson Orogen, New South Wales: July 2011–June 2012. Record 2014/32 Geoscience Australia, Canberra. Report GS2013/1837, Geological Survey of New South Wales, Maitland.

Claoué-Long, J. C., Compston, W., Roberts, J. and Fanning, M., 1995. Two Carboniferous ages: a comparison of SHRIMP zircon dating with conventional zircon ages and 40Ar/39Ar analysis. In Berggren, W.A., Kent, D.V., Aubry, M.-P. and Hardenbol, J., eds., Geochronology, Time Scales and Global Stratigraphic Correlation. SEPM Special Publication 54, pp. 3–21. Society for Sedimentary Geology, Tulsa, Oklahoma, USA.

Compston, W., Williams, I. and Meyer, C., 1984. U-Pb geochronology of zircons form lunar Breccia 73217 using a sensitive high mass-resolution ion microprobe. Journal of Geophysical Research 89 (Supplement), B525–B534. 14, 525.

Glen, R. A., Korsch, R. J., Hegarty, R., Saeed, A., Djomani, Y. P., Costelloe, R. D. and Belousova, E., 2013. Geodynamic significance of the boundary between the Thomson Orogen and the Lachlan Orogen, northwestern New South Wales and implications for Tasmanide tectonics. Australian Journal of Earth Sciences 60, 371–412.

Glen, R. A., Poudjom-Djomani, Y., Korsch, R. J., Costello, R. D., Dick, S. and Lewis, P. C., 2007. Thomson-Lachlan seismic project–results and implications. Mines and Wines conference NSW, 2007, 73–78.

Gray, D. R. and Foster, D. A., 2004. Tectonic evolution of the Lachlan Orogen, southeast Australia: historical review, data synthesis and modern perspectives. Australian Journal of Earth Sciences 51, 773–817.

Hegarty, R., 2010. Preliminary geophysical-geological interpretation map of the Thomson Orogen. Thomson Orogen Release of Provisional and Preliminary Information June. Geological Survey of New South Wales, Maitland.

Ludwig, K., 2003. User’s manual for Isoplot 3.6: Geochronological toolkit for Microsoft Excel (revised 2008). Berkeley Geochronology Center, Special Publication 4.

Ludwig, K., 2009. Squid 2.50: A User's Manual. Berkley Geochronology Center, Special Publication 5. Nasdala, L., Hofmeister, W., Norberg, N., Mattinson, J. M., Corfu, F., Dörr, W., Kamo, S. L., Kennedy,

A. K., Kronz, A. and Reiners, P. W., 2008. Zircon M257‐a Homogeneous Natural Reference Material for the Ion Microprobe U‐Pb Analysis of Zircon. Geostandards and Geoanalytical Research 32, 247–265.

Nelson, D., 1997. Compilation of SHRIMP U–Pb zircon geochronological data, 1996. Western Australia Geological Survey Record (1997/2).

Rothery, E., 2013. A new intrusion-related gold field in the Thomson Fold Belt, NSW. AIG Bulletin 55. Stacey, J. S. and Kramers, J. D., 1975. Approximation of terrestrial lead isotope evolution by a two-

stage model. Earth and Planetary Science Letters 26, 207–221. Stern, R. A., Bodorkos, S., Kamo, S. L., Hickman, A. H. and Corfu, F., 2009. Measurement of SIMS

instrumental mass fractionation of Pb isotopes during zircon dating. Geostandards and Geoanalytical Research 33, 145–168.

Stevens, B. P. J. and Crawford, A. J., 1992. Early to Middle Cambrian geochemistry and tectonics of northwestern NSW. Geological Society of Australia Abstracts 32, 25.


Williams, I., Buick, I. and Cartwright, I., 1996. An extended episode of early Mesoproterozoic metamorphic fluid flow in the Reynolds Range, central Australia. Journal of Metamorphic Geology 14, 29–47.

Williams, I. S., 1998. U-Th-Pb geochronology by ion microprobe. In McKibben, M.A., Shanks III, W.C. and Ridley, W.I., eds., Applications of Microanalytical Techniques to Understanding Mineralizing Processes. Reviews in Economic Geology 7, 1–35. Society of Economic Geologists, Littleton, Colorado, USA.


Analytical procedures Appendix A

A.1 Analytical procedures All isotopic analyses reported in this Record were undertaken using the SHRIMP IIe at Geoscience Australia (GA), Canberra. A summary of key parameters from individual analytical sessions is shown in Appendix Table A.1. The analytical procedures adopted (and outlined below) for zircon follow those published by Compston et al. (1984), Claoué-Long et al. (1995), Nelson (1997), and Williams (1998).

A.1.1 Sample acquisition and crushing

All samples documented in this Record were collected from diamond drillcore, typically as ~1 m intervals of half-core. In the mineral separation laboratory at Geoscience Australia samples were split to ~2.5 cm pieces which were then washed and dried before being crushed and milled.

A.1.2 Mineral separation

Mineral density separation was undertaken using a Wilfley table, with multiple iterations employed to successively deslime the rock flours and decant bulk low-density minerals such as quartz and feldspar, thereby reducing the sample to about 5% of its post-milling weight. Strongly paramagnetic grains were successively removed from this heavy fraction using a ferrous magnet and a rare-earth element magnet, before the remainder underwent a series of magnetic separations using a Frantz barrier separator. This typically involved 6–8 separations in total, progressively increasing the strength of the magnetic field then decreasing the tilt of the ramp to remove successively less paramagnetic minerals. The resultant zircon concentrate was then handpicked under optical microscope to separate the clearest and least metamict grains for mounting.

A.1.3 Mount preparation

Handpicked zircons from all four samples documented in this Record were mounted in epoxy together with about 100 grains of the 238U/206Pb reference zircon Temora-2 (Black et al., 2004), about 40 grains of the 207Pb/206Pb reference zircon OG1 (Stern et al., 2009), and a fragment of the uranium concentration standard M257 (840 ppm U; Nasdala et al., 2008). Epoxy mounts were polished to expose the zircon grains in cross section before being photographed in transmitted and reflected light, then coated with ~20 Å of gold for cathodoluminescence imaging using a JEOL JSM-6490LV scanning electron microscope (SEM). After SEM imaging the gold coat was removed and the mount cleaned before recoating with ~150 Å of gold in preparation for SHRIMP isotopic analyses.

A.1.4 Instrument setup and data acquisition

A 20–30 μm-diameter primary beam of O2- ions at 10keV was employed to sputter secondary ions from the surface of the target minerals. Before each analysis, the surface of the analysis site was pre-cleaned by rastering of the primary beam for four minutes, in order to reduce the amount of common Pb on the mount surface. Data acquisition involved cycling the magnetic field through a run-table


comprising the following 10 mass-stations, each shown with the relevant counting times in seconds: 196Zr (2 s), 204Pb (20 s), background 204.05 (20 s), 206Pb (15 s), 207Pb (40 s), 208Pb (5 s), 238U (5 s), 248ThO (2 s), 254UO (2 s), and 270UO2 (2 s). A full cycle through the mass-stations in termed a scan, and each analysis comprised either 5 (session 150033) or 6 scans (session 140039).

Analyses were collected in a sequence that typically involved collecting one analysis of the Temora-2 reference zircon after every third or fourth sample analysis, and one analysis of the OG1 reference zircon after every second Temora-2 analysis. For session 140039, where multiple igneous samples were being analysed, these samples were analysed in round-robin fashion, with one analysis of each sample being collected in a repeating cycle. Session 150033 involved only analyses of detrital zircon from a single sample, together with Temora-2 and OG1 reference zircon.

Analysis labels shown in the data tables in this Record take the format X.Y, where X is the grain number, and Y is the spot number within the grain.

A.2 Data reduction and presentation Data reduction and presentation used the SQUID2 (Ludwig, 2009) and Isoplot (Ludwig, 2003) software. Concentration of U was calibrated using the M257 reference zircon (840 ppm U; Nasdala et al., 2008), 206Pb/238U ratios were calibrated using concurrent measurements of the Temora-2 reference zircon (206Pb/238U age = 416.8 Ma; Black et al., 2004), and 207Pb/206Pb mass fractionation was monitored using the OG1 reference zircon (207Pb/206Pb age = 3465.4 ± 0.6 Ma; Stern et al., 2009). Session-specific details of calibration parameters are provided in the section below.

For analyses of the Temora-2 reference zircons the presence of any common Pb was corrected for by using the measured 204Pb and assuming a default Pb isotopic composition calculated via the model of Stacey and Kramers (1975) at an age of 416.8 Ma. For analyses of zircons of unknown age, the measured 204Pb was used together with a Pb isotopic composition calculated using the Stacey and Kramers (1975) model at a preliminary age calculated by assuming the default Pb isotopic composition. Common Pb is reported in the data tables in this Record as 206Pbc, which denotes the percentage of total measured 206Pb that has been attributed to common Pb.

A.2.1 Calibration procedures

Elemental U concentrations in the unknowns are calibrated using the power-law relationship proposed by Claoué-Long et al. (1995), using the equation:

[196Zr2O+/238U+] = A x [254UO+/238U+]0.66 [1]

Where A is a session-dependent constant determined from measurements on M257 zircon. All U concentration data tabulated for unknowns have uncertainties on the order of 15–20%, based on the extent of known variations in the U abundance of M257 zircon.

The values of 232Th/238U in the unknowns are calculated using the relationship proposed by Williams et al. (1996):

232Th/238U = [248ThO+/254UO+] x ((0.03446 x [254UO+/238U+]) + 0.868) [2]


The values of 206Pb/238U in the unknowns are calibrated using analyses of Temora-2 for zircon, and the power-law relationship proposed by Claoué-Long et al. (1995):

[206Pb+/238U+] = B x [254UO+/238U+]2 [3]

Where B is a session-dependent constant determined from measurements on the TEMORA-2 reference material.

The accuracy of 207Pb/206Pb in unknown zircons is monitored using the OG1 reference zircon (207Pb/206Pb = 0.29907, corresponding to an age of 3465.4 Ma; Stern et al., 2009). In this report, no correction to 207Pb/206Pb values of unknowns, on the basis of the co-analysed OG1, has been made.

A.2.2 Propagation of uncertainties

In each session, a ‘calibration constant’ value is determined for each individual analysis of Temora-2 zircon (e.g. bi = [206Pb+/238U+]i/[

254UO+/238U+]i2, following equation 3). Uncertainties associated with

each of these individual ‘calibration constants’ (i.e. ± bi) are governed primarily by the counting statistics associated with constituent isotopic ratio(s). The value of the session ‘calibration constant’ (B; see equation 3) is calculated as the error-weighted mean of the session-specific population of individual calibration constants. These populations commonly display significant excess scatter, manifested by an MSWD value for B that far exceeds unity, despite the fact that most reference zircons are (by definition) characterised by 206Pb/238U homogeneity at a range of scales. This indicates that the values of ± bi are usually underestimated in going from analysis to analysis. Consequently, SQUID calculates the constant additional uncertainty per spot (expressed as a percentage) that must be added in quadrature to each ± bi in order to produce MSWD ~1 for the population of bi values used to calculate B (Ludwig, 2009). This constant additional uncertainty is termed the ‘spot-to-spot error’ (or ‘reproducibility’), and its session-specific 2σ values are presented in Appendix Table A.1 and Appendix Table A.2. The spot-to-spot error is added in quadrature to the other sources of error (principally related to counting statistics and the magnitude of the common-Pb correction) for each value of 206Pb/238U in the unknowns, and thus is incorporated in the uncertainties for all individual 206Pb/238U values presented in the data tables.

SQUID also calculates the uncertainty associated with the session-specific calibration constant (i.e.± B). This uncertainty is termed the ‘session-to-session error’ (or ‘calibration uncertainty’), and its session-specific 2σ value is presented in Appendix Table A.1 and Appendix Table A.2. The session-to-session error is not included in the uncertainties of individual 206Pb/238U values presented in the data tables, and it should be neglected when comparing pooled 206Pb/238U ages for unknown samples co-analysed in a single analytical session. The session-to-session errors must, however, be included when comparing pooled 206Pb/238U ages more widely (e.g. between datasets obtained in different analytical sessions, or by independent analytical methods). Consequently, pooled ages reported here incorporate (via quadratic addition) the session-to-session errors of the analytical sessions contributing to that mean age.

Dates derived from the pooling of multiple individual analyses are error-weighted means unless otherwise specified. Each error-weighted mean has an associated Mean Square of Weighted Deviates (MSWD) value, which is a measure of the degree of scatter of the constituent analyses relative to the assigned uncertainties (Ludwig, 2003), and a ‘probability of equivalence’ (P) value, which is the probability that all of the constituent analyses are equivalent within their uncertainties. By convention, scatter beyond the assigned uncertainties is assumed to be present when P is less than 0.05. Uncertainties on dates derived


from the pooling of multiple individual analyses are quoted at the 95% confidence level, unless otherwise indicated. For weighted means, the 95% confidence level is defined as t-sigma (where t is Student’s t for n – 1 degrees if freedom, and n is the number of individual analyses in the population) when the MSWD of the population is less than unity. When MSWD exceeds unity, but P is equal to or greater than 0.05, the 95% confidence level is defined as t-sigma multiplied by the square root of the MSWD. Ellipses depicting results from individual analyses are plotted on Concordia plots at the 1σ level.

A.2.3 Discordance

Discordance is a measure of the agreement between 206Pb/238U and 207Pb/206Pb dates from the same analysis and is calculated in this Record using the default equation in SQUID2 (Ludwig, 2009):

Discordance (%) = 100 x [(207Pb/206Pb date) – 206Pb/238U date)]/(206Pb/238U date)

Discordance provides an indication of the extent to which the analysed zircon has remained closed to Pb loss since the time of its crystallisation, and is thus a useful criterion to assess the geological reliability of the ages from any particular analysis. It is worth noting, however, that the relatively poor precision in 207Pb/206Pb ages for samples younger than c. 1000 Ma, in turn related to the relatively low abundance of 207Pb, means that discordance is of limited use as a reliability criteria for Neoproterozoic and Phanerozoic zircons.

A.3 Session-specific calibrations and data processing The data reported in this Record were collected over the course of two analytical sessions, each with its own calibration and data reduction parameters, as described below.

Appendix Table A.1 Session 140039: Mount GA6273, 8–14 April 2014

Session Number 140039

Mount GA6273

Session Date 8–14 April 2014

Calibration Batch No. 1 of 1 238U/206Pb reference zircon: Temora-2 (416.8 ± 1.3 Ma; Black et al., 2004)

Analyses Used 60 of 60 238U/206Pb uncertainty (2σ) 0.43% 238U/206Pb reproducibility (2σ) 2.57% 207Pb/206Pb date (95% confidence) 380 ± 37 Ma

204 overcount correction applied No 207Pb/206Pb reference zircon: OG1 (3465.4 ± 0.6 Ma; Stern et al., 2009)

Analyses used 28 of 28 207Pb/206Pb date (95% confidence) 3468.0 ± 2.3 Ma

Mass fractionation correction applied No

Number of samples analysed 6

GSNSW SiteID (GA SampleNo) 2167675


2167701

2167668

2167713

2169065 (not reported here)

2169078 (not reported here)

This session included analyses from six samples, four of which are reported in this Record. Analyses of each of the six samples were collected in round-robin fashion over the six days of the analytical session.

A total of 60 analyses of the 206Pb/238U reference zircon Temora-2 were acquired during session 140039. All 60 of these analyses yield a slope of 1.72 +0.25/-0.23 on a plot of ln[206Pb+/238U+] versus ln[(238U16O)+/238U. This slope is only marginally different to the canonical value of 2, and consequently a calibration exponent of 2 was applied in processing data from the unknowns in this session. The weighted mean 206Pb/238U value has a session-to-session uncertainty of 0.43% (2σ), and 206Pb/238U reproducibility is 2.57% (2σ). The session-to-session uncertainty is included via quadratic addition in the uncertainty of each calculated weighted mean 206Pb/238U age, and the reproducibility is included in the uncertainty associated with 206Pb/238U for each individual analysis in this session.

The robust mean of the 207Pb/206Pb age for the 60 Temora-2 analyses used in the 206Pb/238U calibration is 380 ± 37 Ma (95% confidence), which is within uncertainty of the reference age of 416.8 Ma (Black et al., 2004), indicating no apparent overcounts at mass 204Pb and thus no 204 overcount correction was applied.

In addition to the Temora-2 reference zircon, a total of 28 analyses of the OG1 reference zircon were acquired during Session 140039, collectively yielding a weighted mean 207Pb/206Pb age of 3468.0 ± 2.3 Ma (95% confidence). No correction for instrumental fractionation of 207Pb/206Pb was applied.

Appendix Table A.2 Session 150033: Mount GA6273, 15–16 April 2015

Session Number 150033

Mount GA6273

Session Date 15–16 April 2015

Calibration Batch No. 1 of 1 238U/206Pb reference zircon: Temora-2 (416.8 ± 1.3 Ma; Black et al., 2004)

Analyses Used 14 of 14 238U/206Pb uncertainty (2σ) 0.26% 238U/206Pb reproducibility (2σ) 1.50% 207Pb/206Pb date (95% confidence) 437 ± 39 Ma

204 overcount correction applied No 207Pb/206Pb reference zircon: OG1 (3465.4 ± 0.6 Ma; Stern et al., 2009)

Analyses used 7 of 7 207Pb/206Pb date (95% confidence) 3466.5 ± 3.1 Ma

Mass fractionation correction applied No

Number of samples analysed 1

GSNSW SiteID (GA SampleNo) 2167713


This session included analyses of a single sample, and was aimed at providing additional analyses of detrital zircon from sample 2167713 to augment those previously collected during session 140039 (see above). The analytical session was conducted over a 20 hour period.

A total of 14 analyses of the 206Pb/238U reference zircon Temora-2 were acquired during session 150033. All 14 of these analyses yield a slope of 1.82 +0.17/-0.23 on a plot of ln[206Pb+/238U+] versus ln[(238U16O)+/238U. This slope is not distinguishably different from the canonical value of 2 and consequently a calibration exponent of 2.0 was applied in processing data from the unknowns in this session. The weighted mean 206Pb/238U value has a session-to-session uncertainty of 0.26% (2σ), and 206Pb/238U reproducibility used was the minimum default value of 1.50% (2σ). The session-to-session uncertainty is included via quadratic addition in the uncertainty of each calculated weighted mean 206Pb/238U age, and the reproducibility is included in the uncertainty associated with 206Pb/238U for each individual analysis in this session.

The robust mean of the 207Pb/206Pb age for the 14 Temora-2 analyses used in the 206Pb/238U calibration is 437 ± 39 Ma (95% confidence), which is within uncertainty of the reference age of 416.8 Ma (Black et al., 2004), indicating no apparent overcounts at mass 204Pb and thus no 204 overcount correction was applied.

In addition to the Temora-2 reference zircon, a total of seven analyses of the OG1 reference zircon were acquired during Session 150033, collectively yielding a weighted mean 207Pb/206Pb age of 3466.5 ± 3.1 Ma (95% confidence), within uncertainty of the OG1 reference age of 3465.4 ± 0.6 Ma (Stern et al., 2009), thus no correction for instrumental fractionation of 207Pb/206Pb was applied.


New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 ...New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 5 Figure 2.1 Representative

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