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

Transcription

1 Record 2015/20 GeoCat New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, New South Wales Armistead, S. E. and Fraser, G. L. APPLYING GEOSCIENCE TO AUSTRALIA S MOST IMPORTANT CHALLENGES

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3 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.

4 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 Geoscience Australia Chief Executive Officer: Dr Chris Pigram This paper is published with the permission of the CEO, Geoscience Australia Commonwealth of Australia (Geoscience Australia) 2015 With the exception of the Commonwealth Coat of Arms and where otherwise noted, this product is provided under a Creative Commons Attribution 4.0 International Licence. ( Geoscience Australia has tried to make the information in this product as accurate as possible. However, it does not guarantee that the information is totally accurate or complete. Therefore, you should not solely rely on this information when making a commercial decision. Geoscience Australia is committed to providing web accessible content wherever possible. If you are having difficulties with accessing this document please clientservices@ga.gov.au. ISSN X (PDF) ISBN (PDF) GeoCat Bibliographic reference: Armistead, S. E. and Fraser, G. L New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, New South Wales. Record 2015/20. Geoscience Australia, Canberra.

5 Contents Executive Summary Introduction F1 prospect granite (drillhole F1DD02) Sampling details and geological relationships Petrography Zircon description U-Pb isotopic results Geochronological interpretation F1 prospect granitic dyke (drillhole F1DD01) Sampling details and geological relationships Petrography Zircon description U-Pb isotopic results Geochronological interpretation Quartz diorite (drillhole CUTACD02) Sampling details and geological relationships Petrography Zircon description U-Pb isotopic results Geochronological interpretation Sandstone (drillhole F03D02) Sampling details and geological relationships Petrography Zircon description U-Pb isotopic results Geochronological interpretation...27 Acknowledgements...31 References...32 Appendix A Analytical procedures...34 A.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

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

7 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: ) yields an age of ± 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: ) yields an age of ± 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: ) yields a magmatic crystallisation age of ± 8.5 Ma, indistinguishable from a previously-published age of ± 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: ) 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 ± 3.9 Ma, suggesting a relatively proximal igneous source. Smaller proportions of Neoproterozoic (c. 600 Ma), Mesoproterozoic (c 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

8 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 ± 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 ( 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 sessionspecific details of the calibration data collected on the reference 238 U/ 206 Pb and 207 Pb/ 206 Pb 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 B F1 prospect granite (F1DD02) ± 3.1 Ma Magmatic crystallisation J F1 prospect granitic dyke (F1DD01) ± 4.9 Ma Magmatic crystallisation B Quartz diorite (CUTACD02) ± 8.5 Ma Magmatic crystallisation B Sandstone (F03D02) ± 3.9 Ma Maximum deposition age 2 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

9 (a) (b) (c) 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). New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 3

10 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). 4 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

11 2 F1 prospect granite (drillhole F1DD02) Table 2.1 Summary of results: F1 prospect granite (drillhole F1DD02; GA SampleNo: ). GA SampleNo Sample ID B Parent Unit - Stratigraphic Unit - Informal Identifier - Lithology Drillhole name & depth (downhole) Province Medium-grained, biotite-rich granite F1DD m Thomson Orogen 1: Sheet White Cliffs (H5412) 1: Sheet Yantabangee (7636) Location (GDA94) , Location (MGA94) Zone 54, me, mn SHRIMP mount ID GA6273 Analytical Session No , 8 14 April 2014 Interpreted Age Geological Attribution Isotopic Ratio used ± 3.1 Ma (95% confidence; 31 analyses of 31 zircons) Magmatic crystallisation 238 U/ 206 Pb ( 204 Pb-corrected) 2.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole F1DD02 (downhole depth 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. New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 5

12 Figure 2.1 Representative photograph of the F1 prospect granite (drillhole F1DD02; GA SampleNo ). 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 mediumgrained, biotite-rich granite. (a) (b) Figure 2.2 Representative photomicrographs of the F1 prospect granite (drillhole F1DD02; GA SampleNo: ). (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. 6 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

13 2.3 Zircon description The mounted crystals are characterised by long axes spanning the range μm (typically 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: ).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. New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 7

14 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 Common Pb ( 206 Pb c ) 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 Their individual 238 U/ 206 Pb ages range between c. 445 Ma and c. 414 Ma, and combine to form a statistically coherent weighted mean age of ± 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 Analyses from this group yield individual 238 U/ 206 Pb ages between c 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 Three analyses from this group yield near-concordant individual 207 Pb/ 206 Pb ages of c Ma, c Ma, c Ma, and the fourth analysis is 35% discordant with a 207 Pb/ 206 Pb age of c Ma. Group 4 consists of a single analysis ( ) from zircon that is morphologically and chemically similar to those in Group 1, but yields a younger 238 U/ 206 Pb age of c. 324 Ma. 2.5 Geochronological interpretation The weighted mean 238 U/ 206 Pb age of ± 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 ( ) comes from a relatively high U (964 ppm) and low CL portion of a grain from which a second analysis ( ) 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 238 U/ 206 Pb 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 207 Pb/ 206 Pb age a minimum constraint on the true crystallisation age of this inherited grain. 8 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

15 (a) Drillhole F1DD02 GA Sample No: GA Sample ID: B n = 42 of 42 analyses 207 Pb/ 206 Pb Group 1: magmatic crystallisation (n = 31) Mean 238 U/ 206 Pb age = ± 3.1 Ma 95% conf., MSWD = 1.26, P = σ error ellipses U/ 206 Pb (b) Drillhole F1DD02 GA Sample No: GA Sample ID: B n = 31 of 42 analyses 207 Pb/ 206 Pb Group 1: magmatic crystallisation (n = 31) Mean 238 U/ 206 Pb age = ± 3.1 Ma 95% conf., MSWD = 1.26, P = σ error ellipses U/ 206 Pb Figure 2.4 SHRIMP U-Pb data for zircons from the F1 prospect granite (drillhole F1DD02; GA SampleNo: ). (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. New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 9

16 Table 2.2 SHRIMP U-Pb zircon data from the F1 prospect granite (drillhole F1DD02; GA SampleNo: ). All analyses were collected in session Grain.area 206 Pb c U (ppm) Th (ppm) 232 Th / 238 U 238 U / 206 Pb 207 Pb / 206 Pb Date (Ma) (Ma) Disc Group 3: Pre-Mesoproterozoic inheritance (n = 4; 207 Pb/ 206 Pb dates tabulated) Group 2: Mesoproterozoic Neoproterozoic inheritance (n = 6; 238 U/ 206 Pb dates tabulated) Group 1: Magmatic crystallisation (n = 31; 238 U/ 206 Pb dates tabulated) New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

17 Grain.area 206 Pb c U (ppm) Th (ppm) 232 Th / 238 U 238 U / 206 Pb 207 Pb / 206 Pb Date (Ma) (Ma) Disc Group 4: Pb-loss (n = 1; 238 U/ 206 Pb date tabulated) New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 11

18 3 F1 prospect granitic dyke (drillhole F1DD01) Table 3.1 Summary of results: F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: ). GA SampleNo Sample ID J Parent Unit - Stratigraphic Unit - Informal Identifier - Lithology Drillhole name & depth (downhole) Province Fine- to medium-grained, leucocratic granitic dyke F1DD m Thomson Orogen 1: Sheet White Cliffs (H5412) 1: Sheet Yantabangee (7636) Location (GDA94) , Location (MGA94) Zone 54, me, mn SHRIMP mount ID GA6273 Analytical Session No , 8 14 April 2014 Interpreted Age Geological Attribution Isotopic Ratio used ± 4.9 Ma (95% confidence; 13 analyses of 11 zircons) Magmatic crystallisation 238 U/ 206 Pb ( 204 Pb-corrected) 3.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole F1DD01 (downhole depth 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. 12 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

19 Figure 3.1 Representative photograph of the F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: ). 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: ). (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). New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 13

20 3.3 Zircon description The mounted crystals are characterised by long axes spanning the range μm (typically 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: ). 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. 14 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

21 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 Common Pb ( 206 Pb c ) 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 Their individual 238 U/ 206 Pb ages range between c. 435 Ma and c. 412 Ma, and combine to form a statistically coherent population with a weighted mean age of ± 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 238 U/ 206 Pb age of ± 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 238 U/ 206 Pb ages ranging from c Ma to c. 504 Ma. Group 4 consists of a single analysis from a rounded, equant grain with moderate CL response that yields a 207 Pb/ 206 Pb age of c Ma and is 18% discordant. 3.5 Geochronological interpretation The weighted mean 238 U/ 206 Pb age of ± 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 ± 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 207 Pb/ 206 Pb age of c 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. New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 15

22 (a) F1 prospect granitic dyke (drillhole F1DD01) GA Sample No: GA Sample ID: J n = 27 of 27 analyses 207 Pb/ 206 Pb Group 1: magmatic crystallisation (n = 13) Mean 238 U/ 206 Pb date = ± 4.9 Ma 95% conf., MSWD = 1.50, P = 0.12 Group 2: inherited zircon (n = 4) Mean 238 U/ 206 Pb date = ± 10.0 Ma 95% conf., MSWD = 0.03, P = σ error ellipses U/ 206 Pb (b) 0.07 F1 prospect granitic dyke (drillhole F1DD01) GA Sample No: GA Sample ID: J n = 17 of 27 analyses Group 1: magmatic crystallisation (n = 13) Mean 238 U/ 206 Pb date = ± 4.9 Ma 95% conf., MSWD = 1.50, P = Pb/ 206 Pb Group 2: inherited zircon (n = 4) Mean 238 U/ 206 Pb date = ± 10.0 Ma 95% conf., MSWD = 0.03, P = σ error ellipses U/ 206 Pb Figure 3.4 SHRIMP U-Pb data for zircons from the F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: ). (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 Ma single inherited zircon). 16 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

23 Table 3.2 SHRIMP U-Pb zircon data from the F1 prospect granitic dyke (drillhole: F1DD01; GA SampleNo: ). All analyses were collected in session Grain.area 206 Pb c U (ppm) Th (ppm) 232 Th / 238 U 238 U / 206 Pb 207 Pb / 206 Pb Date (Ma) (Ma) Disc Group 4: Pre-Mesoproterozoic inheritance(n = 1; 207 Pb/ 206 Pb dates tabulated) Group 3: Mesoproterozoic Cambrian inheritance (n = 9; 238 U/ 206 Pb dates tabulated) Group 2: Ordovician inheritance (n = 4; 238 U/ 206 Pb dates tabulated) Group 1: Magmatic crystallisation (n = 13; 238 U/ 206 Pb dates tabulated) New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 17

24 4 Quartz diorite (drillhole CUTACD02) Table 4.1 Summary of results: quartz diorite (drillhole CUTACD02; GA SampleNo: ). GA SampleNo Sample ID B Parent Unit - Stratigraphic Unit - Informal Identifier - Lithology Drillhole name & depth (downhole) Province Medium- to coarse-grained, biotite-rich quartz diorite CUTACD m Thomson Orogen 1: Sheet Louth (H5509) 1: Sheet Thoolabool (7736) Location (GDA94) , Location (MGA94) Zone 55, me, mn SHRIMP mount ID GA6273 Analytical Session No , 8 14 April 2014 Interpreted Age Geological Attribution Isotopic Ratio used ± 8.5 Ma (95% confidence; six analyses of six zircons) Magmatic crystallisation 238 U/ 206 Pb ( 204 Pb-corrected) 4.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole CUTACD02 (downhole depth m), drilled in 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 ± 2.8 Ma (Chisholm et al., 2014) obtained from granite from the CUTAD01 drillhole approximately 10 km to the west of CUTACD New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

25 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: ). (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 μm (typically 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 ironstaining 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. New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 19

26 Figure 4.2 Representative zircons from quartz diorite (drillhole CUTACD02; GA SampleNo: ). 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 Eleven analyses contain >0.70% common Pb ( 206 Pb c ) 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 Their individual 238 U/ 206 Pb ages range between c. 446 Ma and c. 421 Ma, and group to form a statistically coherent weighted mean age of ± 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 Their individual 238 U/ 206 Pb ages range between c. 497 Ma and c 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 Individual 207 Pb/ 206 Pb ages within this group range between c Ma and c Ma. 20 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

27 4.5 Geochronological interpretation The weighted mean 238 U/ 206 Pb age of ± 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 ± 2.8 Ma obtained by Chisholm et al. (2014) from a granite within the CUTAD01 drillhole ~10 km to the west. The 238 U/ 206 Pb 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 Quartz diorite (drillhole CUTACD02) GA Sample No: GA Sample ID: B n = 42 of 42 analyses Pb/ 206 Pb Group 1: magmatic crystallisation (n = 6) Mean 238 U/ 206 Pb date = ± 8.5 Ma 95% conf., MSWD = 1.43, P = σ error ellipses U/ 206 Pb Figure 4.3 SHRIMP U-Pb data for zircons from quartz diorite (drillhole CUTACD02; GA SampleNo: ). 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 ( 206 Pb c > 0.70%). New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 21

28 Table 4.2 SHRIMP U-Pb zircon data from quartz diorite (drillhole CUTACD02; GA SampleNo: ). All analyses were collected in session Grain.area 206 Pb c U (ppm) Th (ppm) 232 Th / 238 U 238 U / 206 Pb 207 Pb / 206 Pb Date (Ma) (Ma) Disc Group 3: Pre-Neoproterozoic inheritance (n = 5; 207 Pb/ 206 Pb dates tabulated) Group 2: Mesoproterozoic Cambrian inheritance (n = 20; 238 U/ 206 Pb dates tabulated) Group 1: Magmatic crystallisation (n = 6; 238 U/ 206 Pb dates tabulated) Not considered: 206 Pb c >0.70% (n = 11; 238 U/ 206 Pb dates tabulated) 22 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

29 Grain.area 206 Pb c U (ppm) Th (ppm) 232 Th / 238 U 238 U / 206 Pb 207 Pb / 206 Pb Date (Ma) (Ma) Disc New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 23

30 5 Sandstone (drillhole F03D02) Table 5.1 Summary of results: sandstone (drillhole: F03D02; GA SampleNo: ). GA SampleNo Sample ID B Parent Unit - Stratigraphic Unit - Informal Identifier - Lithology Drillhole name & depth (downhole) Province Sandstone F03D m Thomson Orogen 1: Sheet White Cliffs (H5412) 1: Sheet Yantabangee (7636) Location (GDA94) , Location (MGA94) Zone 54, me, mn SHRIMP mount ID GA6273 Analytical Session No , 8 14 April 2014; , April 2015 Interpreted Age Geological Attribution Isotopic Ratio used ± 3.9 Ma (95% confidence; 23 analyses of 23 zircons) Maximum deposition age 238 U/ 206 Pb ( 204 Pb-corrected) 5.1 Sampling details and geological relationships This sample is from diamond drillcore obtained from Thomson Resources Ltd. drillhole F03D02 (downhole depth m), drilled in 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. 24 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW

31 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 crosspolarised 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: ). (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 μm (typically 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. New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW 25

32 Figure 5.2 Representative zircons from sandstone (drillhole: F03D02; GA SampleNo: ). 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 Common Pb ( 206 Pb c ) 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 The individual 238 U/ 206 Pb dates range between c. 515 Ma and c. 489 Ma, and combine to form a statistically coherent population with a weighted mean date of ± 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 238 U/ 206 Pb dates ranging from c Ma to c. 518 Ma. 26 New SHRIMP U-Pb zircon ages from the Cuttaburra and F1 prospects, southern Thomson Orogen, NSW