203702: Metadacite, Golden Grove Mine (Scuddles Member, Gossan Hill Formation, Murchison Supergroup, Murchison Domain, Youanmi Terrane, Yilgarn Craton)

203702.1.pdf Geochronology Record 1259

203702: metadacite, Golden Grove mine (Scuddles Member, Gossan Hill Formation, Murchison Supergroup, Murchison Domain, Youanmi Terrane, Yilgarn Craton)

Location and sampling Petrographic description Yalgoo (SG 50-2), Badja (2240) The sample is a porphyritic metadacite, consisting MGA Zone 50, 496097E 6816582N of about 65–70% aphanitic matrix, 20% plagioclase, 10% actinolite, and accessory chlorite, epidote, and Sampled on 18 December 2012 iron–titanium oxide minerals. The matrix is crypto- to microcrystalline (grain size up to 0.05 mm), and composed This sample was collected from the 804.40 – 808.77 m mainly of sericite, quartz, and feldspar. Plagioclase depth interval of diamond drillhole G12/501, at MMG’s (andesine, An30–34) forms subhedral to euhedral lath- Golden Grove copper–lead–zinc mine, located about shaped phenocrysts, up to 0.8 mm long, that are clouded 230 km east of Geraldton and 56 km southeast of Yalgoo. by saussurite and rimmed by albite. Actinolite occurs as The drillhole is located on the west side of a track, about sheaves of acicular, microcrystalline to fine-grained (up 4.1 km northeast of Minjar Well, 2.4 km north-northeast to 0.1 mm long) crystals. Minor resorption of plagioclase of Minjar Hill, and 2.2 km southwest of the southeast end phenocrysts suggests they were entrained in the magma of Golden Grove airstrip. prior to crystallization of the melt.

Tectonic unit/relations Zircon morphology The unit sampled is a metadacite assigned to the Zircons isolated from this sample are colourless and Scuddles Member of the Gossan Hill Formation of the subhedral to euhedral. The crystals are up to 250 µm long, Murchison Supergroup (Van Kranendonk et al., 2013). The and equant to elongate, with aspect ratios up to 5:1. In 3000– 2700 Ma Murchison Supergroup consists mainly cathodoluminescence (CL) images, concentric zoning is of metabasalt, felsic metavolcanic and metavolcaniclastic ubiquitous, and many crystals exhibit sector zoning. A CL image of representative zircons is shown in Figure 1. rocks, and clastic and chemical metasedimentary rocks (Van Kranendonk et al., 2013). The 2963–2947 Ma Gossan Hill Formation consists of rhyolitic to dacitic Analytical details metavolcanic and metavolcaniclastic rocks, locally hosting economic massive sulfide mineralization (e.g. Sharpe This sample was analysed on 31 May – 1 June 2013, using and Gemmell, 2001). The Scuddles Member consists of SHRIMP-B, and 10–11 June 2013, using SHRIMP-A. porphyritic metadacite with lesser rhyodacite and felsic Analyses 1.1 to 17.1 (spot numbers 1–17) were obtained volcaniclastic rocks, and overlies felsic metavolcanic during the first session, together with 11 analyses of the rocks of the Golden Grove and Gossan Valley Members BR266 standard, of which eight analyses indicated an of the Gossan Hill Formation. Volcanic rocks of the external spot-to-spot (reproducibility) uncertainty of 0.55% (1σ) and a 238U/206Pb* calibration uncertainty of Gossan Hill Formation were coeval with metatonalite and 207 206 metagranodiorite of the 2964–2945 Ma Bunnawarra Suite, 0.26% (1σ). Isotopic mass fractionation of Pb/ Pb which consists of deformed rafts within plutons of the ratios during the first session was corrected by reference to the OGC1 standard; measured ratios were increased c. 2750 Ma Rothsay Suite of the 2820–2735 Ma Annean by 0.71%. Analyses 18.1 to 35.1 (spot numbers 18–35) Supersuite (Van Kranendonk et al., 2013; Chen et al., in were obtained during the second session, together with prep.). The Gnows Nest Granodiorite of the Thundelarra 12 analyses of the BR266 standard, which indicated an Supersuite intrudes the base of the Gossan Hill Formation external spot-to-spot (reproducibility) uncertainty of and may be subvolcanic to the Scuddles Member (Chen 0.50% (1σ) and a 238U/206Pb* calibration uncertainty of et al., in prep.). Metarhyolite of the underlying Golden 0.20% (1σ). Isotopic mass fractionation of 207Pb/206Pb Grove Member, sampled at approximately 596–600 m ratios during the second session was corrected by depth in drillhole G12/501, yielded a crystallization age reference to the OGC1 standard; measured ratios were of 2963 ± 6 Ma (GSWA 203703, Wingate et al., 2015a). increased by 0.24%. Calibration uncertainties are included A metarhyolite of the Gossan Valley Member, sampled at in the errors of 238U/206Pb* ratios and dates listed in approximately 8–10 m depth in drillhole G12/501, yielded Table 1. Common-Pb corrections were applied to all a crystallization age of 2959 ± 5 Ma (GSWA 203704, analyses using contemporaneous isotopic compositions Wingate et al., 2015b). determined according to the model of Stacey and Kramers (1975).

1 203702.1.pdf Geochronology Record 1259

Figure 1. Cathodoluminescence image of representative zircons from sample 203702: metadacite, Golden Grove mine. Numbered circles indicate the approximate positions of analysis sites.

0.24 203702 3100 35 analyses of 35 zircons

0.23 3050 *

Pb 0.22 206 Pb*/ 207 0.21 2900

2850 0.20 2800

0.19 1.31.4 1.51.6 1.71.8 1.92.0 2.1 238U/206Pb*

Figure 2. U–Pb analytical data for sample 203702: metadacite, Golden Grove mine. Yellow squares indicate Group I (magmatic zircons).

2 203702.1.pdf Geochronology Record 1259 1. 6 1. 2 1. 9 1. 8 1. 6 1. 2 3.4 3.1 2.1 0.2 2.5 0.2 -1.5 -1.5 -1.3 -1.8 -0.7 -3.8 -6.7 -6.5 -2.5 -2.0 -4.0 -2.7 -0.2 -2.1 -3.5 -2.1 -0.3 -0.1 -0.4 -4.1 -6.8 -4.6 -3.0 (%) Disc.

σ 9 6 8 9 6 9 7 6 9 8 11 11 11 11 11 11 11 10 10 10 10 10 10 10 10 13 15 12 13 14 12 12 12 13 64 Pb* 206 Pb*/ 2974 2976 2976 2938 2942 2948 2948 2949 2950 2952 2953 2954 2956 2956 2956 2958 2959 2959 2959 2960 2961 2964 2965 2966 2966 2967 2967 2970 2970 2975 2977 2977 2977 2979 2991 207 date (Ma) ±1 date

σ 33 25 23 26 25 23 33 26 39 42 41 29 33 27 33 24 29 27 32 31 35 26 29 24 38 32 44 32 29 37 27 34 32 48 101 Pb* 206 U/ 238 3117 3016 2901 3146 2917 3145 3076 2914 3179 2958 3054 2994 2850 2902 2996 3030 2900 2868 3040 2896 2967 3024 3067 3027 2975 2969 2980 2963 3008 3027 3097 2927 2972 2942 3080 date (Ma) ±1 date 0.00115 Pb* 0.00108 0.00137 0.00126 0.00123 0.00140 0.00144 0.00130 0.00136 0.00177 0.00195 0.00163 0.00141 0.00130 0.00141 0.00128 0.00152 0.00144 0.00170 0.00120 0.00156 0.00190 0.00157 0.00164 0.00123 0.00158 0.00152 0.00134 0.00156 0.00184 0.00083 0.00086 0.00871 0.00097 0.00087

σ 206 ± 1 Pb*/ 207 0.21767 0.21814 0.21912 0.21422 0.21483 0.21561 0.21563 0.21567 0.21583 0.21606 0.21621 0.21632 0.21661 0.21661 0.21669 0.21686 0.21706 0.21708 0.21709 0.21721 0.21732 0.21791 0.21799 0.21804 0.21809 0.21856 0.21857 0.21925 0.21934 0.21936 0.21948 0.21950 0.21956 0.21979 0.22143 0.017 0.015 0.019 0.019 0.017 0.018 0.018 0.017 0.018 0.018 0.017 0.019 0.024 0.024 0.025 0.028 0.030 0.020 0.065 0.025 0.025 0.020 0.022 0.022 0.025 0.020 0.027 0.022 0.029 0.023 0.022 0.023 0.024 0.020 0.032 Pb* σ 206 ± 1 U/ 238 1.711 1.748 1.740 1.718 1.760 1.676 1.763 1.714 1.760 1.650 1.590 1.692 1.799 1.759 1.690 1.590 1.667 1.636 1.785 1.660 1.671 1.641 1.668 1.705 1.750 1.709 1.702 1.682 1.669 1.622 1.569 1.707 1.729 1.608 1.632 0.00119 0.00112 0.00176 0.00108 0.00125 0.00135 0.00123 0.00139 0.00143 0.00129 0.00136 0.00177 0.00195 0.00162 0.00140 0.00129 0.00140 0.00125 0.00152 0.00143 0.00168 0.00154 0.00188 0.00157 0.00162 0.00123 0.00156 0.00149 0.00130 0.00155 Pb 0.00082 0.00085 0.00868 0.00096 0.00086

σ 206 ± 1 Pb/ 207 0.21749 0.21747 0.21740 0.21448 0.21556 0.21566 0.21581 0.21547 0.21623 0.21634 0.21630 0.21632 0.21661 0.21638 0.21687 0.21725 0.21720 0.21690 0.21736 0.21732 0.21788 0.21960 0.21802 0.21787 0.21892 0.21881 0.21898 0.21902 0.21934 0.21858 0.21893 0.21868 0.21872 0.22005 0.22035 0.017 0.015 0.019 0.019 0.017 0.018 0.018 0.017 0.018 0.018 0.017 0.019 0.024 0.024 0.025 0.028 0.030 0.020 0.065 0.025 0.025 0.020 0.022 0.022 0.025 0.020 0.026 0.022 0.029 0.023 0.022 0.023 0.024 0.020 0.032

206

U/ ± 1

238 1.747 1.747 1.740 1.710 1.717 1.761 1.676 1.763 1.713 1.761 1.649 1.590 1.692 1.799 1.758 1.690 1.590 1.667 1.635 1.785 1.660 1.671 1.642 1.669 1.705 1.709 1.702 1.681 1.669 1.622 1.570 1.709 1.730 1.608 1.634 0.174 0.083 0.010 0.016 0.017 ƒ204 (%) 0.029 0.006 0.021 0.045 0.031 0.000 0.000 0.020 0.043 0.044 0.000 0.040 0.027 0.000 0.029 -0.013 -0.016 -0.121 -0.023 -0.026 -0.021 -0.023 -0.058 -0.008 -0.030 -0.025 -0.088 -0.061 -0.093 -0.094 Th U 1.04 1. 11 1. 01 1. 12 1. 19 1.24 1.31 1.40 1.23 1.30 1.03 1.37 232 0.97 0.84 0.98 0.90 0.58 0.54 0.75 0.88 0.58 0.59 0.60 0.94 0.66 0.71 0.59 0.80 0.61 0.62 0.67 0.60 0.77 0.64 0.63 238 Table 1. Ion microprobe analytical results for zircons from sample 203702: metadacite, Golden Grove mine sample 203702: metadacite, Golden Grove from zircons for analytical results 1. Ion microprobe Table Th 76 49 24 32 96 59 66 71 83 70 71 42 48 42 83 59 57 35 111 115 117 101 157 109 131 136 182 186 132 214 146 246 396 320 207 232 (ppm) U 55 43 63 91 96 54 82 70 93 57 111 111 157 110 115 107 105 102 102 123 168 312 167 132 128 137 219 122 170 125 128 147 156 229 254 238 (ppm) 7. 1 1. 1 3.1 6.1 5.1 8.1 4.1 2.1 9.1 11. 1 1 7. 1 27.1 31.1 21.1 10.1 18.1 13.1 19.1 12.1 14.1 15.1 16.1 28.1 33.1 29.1 32.1 20.1 35.1 23.1 24.1 30.1 26.1 34.1 25.1 22.1 spot Grain.

3 6 5 7 8 4 2 9 1 11 10 18 13 19 12 17 14 15 16 28 33 29 32 20 35 31 21 23 24 30 26 34 25 27 22 no. Spot I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ID Group

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Results Recommended reference for this Thirty-five analyses were obtained from 35 zircons. Results publication are listed in Table 1, and shown in a concordia diagram Wingate, MTD, Kirkland, CL, Ivanic, TJ and Wyche, S 2015, 203702: (Fig. 2). metadacite, Golden Grove mine; Geochronology Record 1259: Geological Survey of Western Australia, 4p. Interpretation Data obtained: 11 June 2013 The analyses are concordant to strongly discordant Data released: 30 June 2015 The analyses are concordant to moderately discordant (Fig. 2), and define a single coherent group, based on their 207Pb*/206Pb* ratios. Group I comprises 35 analyses (Table 1), which yield a weighted mean 207Pb*/206Pb* date of 2962 ± 4 Ma (MSWD = 1.4). The date of 2962 ± 4 Ma for the 35 analyses in Group I is interpreted as the magmatic crystallization age of the dacite.

References

Chen, SF, Zibra, I, Ivanic, TJ et al. in prep., Badja, WA Sheet 2240: Geological Survey of Western Australia, 1:100 000 Geological Series.

Sharpe, R and Gemmell, JB 2001, Alteration characteristics of the Archean Golden Grove Formation at the Gossan Hill deposit, Western Australia: Induration as a focusing mechanism for mineralizing hydrothermal fluids: Economic Geology, v. 96, no. 5, p. 1239–1262.

Stacey, JS and Kramers, JD 1975, Approximation of terrestrial lead isotope evolution by a two-stage model: Earth and Planetary Science Letters, v. 26, p. 207–221.

Van Kranendonk, MJ, Ivanic, TJ, Wingate, MTD, Kirkland, CL and Wyche, S 2013, Long-lived, autochthonous development of the Archean Murchison Domain, and implications for Yilgarn Craton tectonics: Precambrian Research, v. 229, p. 49–92.

Wingate, MTD, Kirkland, CL, Ivanic, TJ and Wyche, S 2015a, 203703: metarhyolite, Golden Grove mine; Geochronology Record 1260: Geological Survey of Western Australia, 4p.

Wingate, MTD, Kirkland, CL, Ivanic, TJ and Wyche, S 2015b, 203704: metarhyolite, Golden Grove mine; Geochronology Record 1261: Geological Survey of Western Australia, 4p.