supergiant Olympic Dam deposit: Links with regional tectonothermal - PowerPoint PPT Presentation

1 Post-1590 Ma modification of the supergiant Olympic Dam deposit: Links with regional tectonothermal events Alexander Cherry, Vadim Kamenetsky, Jocelyn McPhie, Maya Kamenetsky School of Physical Sciences, University of Tasmania Kathy Ehrig BHP Billiton Olympic Dam John Keeling Geological Survey of South Australia

2 Granite Olympic Dam Breccia N Granite breccia Low Fe breccia Fe-rich breccia Complex (ODBC) Volc. breccia Clastic facies • Unconformably overlain by 350m of post- glacial cover. • Breccias – Primarily derived from granite. – Lesser felsic volcanics and clastic facies. 2 km • Most prior workers regard the ODBC (and deposit) forming in a “ geologically brief magmatic-hydrothermal event at ca. 1590 Ma ” (e.g. Johnson and Cross, 1995). schematic

3 Clastic facies in the ODBC • Most are interbedded sandstone, mudstone and conglomerates. – Contain same hydrothermal/ore minerals as the hematite-rich breccia. – Provenance exclusively ca. 1590 Ma. • One facies, however, is distinct. All core is HQ

4 Quartz-rich sandstone • Not interbedded with the other clastic facies. • HQ core Much more strongly brecciated. • Contains few of the hydrothermal/ore minerals in the hematite-rich breccia. • Contains non-1590 Ma provenance components. Is the quartz-rich sandstone instead part of a much younger sedimentary succession?

RD1628 RD2751 5 • Intersected in only 300 300 a few drill holes. Unconformity Depth (m) – Appears to be a 500 single domain. 400 – Faulted or brecciated 700 contacts with breccia and other clastic facies. 500 900 1100 600 1300 EOH EOH 685m 1390m

Sandstone 6 • Sandstone fragments and red- brown matrix contains the same components. – Primarily quartz (granitic and metamorphic), minor lithic clasts, Fe oxide. • And same detrital zircon age populations. 200 µm Matrix 1.0 1.4 1.8 2.2 2.6 3.0 200 µm 207 Pb/ 206 Pb age (Ga)

7 Potential correlates 134 ° E 136 ° E 138 ° E • Candidates need to be stratigraphically intermediate 30 ° S to basement and the cover sequence above OD. • Two candidate successions are 32 ° S present: 150 km – Pandurra Formation Olympic Dam Whyalla Sandstone – Whyalla sandstone 34 ° S Pandurra Formation Gawler Range Volcanics (GRV) Hiltaba Suite Palaeoproterozoic - Archaean units

8 134°E 136°E 138°E Pandurra Formation • 30°S Extensive red-bed succession. – Fluvial quartz-rich sandstones, lesser lithic sandstones and shales. 34°S – Occurs within the Cariewerloo Basin. 150 km Olympic Dam • Olympic Dam Minimum depositional age - ca. Hiltaba Suite 1400 Ma (Fanning et al., 1983). GRV 32°S >1.6 Ga basement Pandurra Formation Acropolis Excess details Oak Dam 25 km After Skirrow et al. (2007)

9 138°E 134°E 136°E Whyalla Sandstone • Similar extent to Pandurra 30°S Formation. – Comprises aeolian quartz-rich sandstone. 34°S 150 km • Deposited during the Cryogenian Olympic Dam Hiltaba Suite glaciation. Olympic Dam GRV – > 630 Ma (Williams et al., 2011). >1.6 Ga basement Whyalla Sandstone Acropolis Oak Dam Emmie Bluff 25 km After Skirrow et al. (2007) Dep. State Dev., Gov. South Australia (2017)

10 Quartz-rich sandstone (OD) Whyalla Sandstone Pandurra Formation 1 mm 1 mm 1 mm Quartz overgrowths Carbonate cement 100 µm 100 µm 200 µm 100 µm 200 µm Authigenic illite/dickite

11 Quartz-rich sandstone (OD) Detrital zircon n = 289 comparison • LA-ICPMS of over 3000 detrital Relative Probability Pandurra Formation zircons and comparison of n = 991 most concordant analyses. • Multiple common age populations. Whyalla Sandstone n = 81 – Whyalla Sandstone has additional younger zircon populations. – Younger maximum depositional 1.0 1.4 1.8 2.2 2.6 3.0 age. 207 Pb/ 206 Pb age (Ga)

12 Timing of deposition Apatite • Quartz-rich sandstone (OD) – Euhedral authigenic apatite occurs in the cement. – LA-ICPMS U-Pb age of apatite ( 1441 ± 15 Ma ) = minimum timing 40 µm Illite of deposition. 0.105 1700 0.100 207 Pb/ 206 Pb • Pandurra Formation 1600 0.095 1500 – Whole rock Rb-Sr 1424 ± 51 Ma 0.090 1400 (Fanning et al., 1983). 0.085 1300 – Illite Ar-Ar 1426 ± 6 & 1458 ± 11 Ma 0.080 (P. Polito, unpub. data). 3 4 5 6 238 U/ 206 Pb

13 Quartz-rich sandstone (OD) = Pandurra Formation • The Pandurra Formation once extended over OD. • Brecciation and incorporation occurred after lithification of the = sandstone. • Implications for post- 1590 Ma tectonic activity at OD.

14 Post-1590 Ma tectonic activity • Faults likely Cariewerloo Basin (Pandurra Formation) Propagation of faults propagated up from up from the ODBC the ODBC. unconformity • And brecciated overlying lithified granite ODBC Pandurra Formation. schematic

15 Post-1590 Ma tectonic activity • Faulting was on a scale Cariewerloo Basin sufficient to drop (Pandurra Formation) sandstone 100s of meters into the ODBC. unconformity • Likely occurred between: – ca. 1400 Ma (diagenesis/ granite ODBC lithification) and, schematic – ca. 600 Ma (max age of current cover).

16 The Cariewerloo Basin as a Xt conduit for fluid access Qz Zr • Evidence of fluid movement in the Cariewerloo Basin (Pandurra Formation). 20 µm 0.10 – 1260-1180 Ma K-Ar ages of illite 0.09 crystallisation throughout the 1400 207 Pb/ 206 Pb Basin (Keeling et al., 2016). 0.08 1200 – Late authigenic xenotime growth 0.07 1000 in quartz-rich sandstone 800 0.06 (Pandurra Fm) at OD - LA-ICPMS 600 U-Pb age of 1081 ± 13 Ma . 0.05 3 5 7 9 11 13 238 U/ 206 Pb

• No recorded events in the 17 Musgrave Gawler Craton correlate with Stuart Shelf Province (includes these ages. Whyalla Sandstone) • But are coincident with thermal events in the Olympic Musgrave Province. Dam Cariewerloo Basin – e.g. Musgrave Orogeny and (Pandurra Formation) Giles Event. Gawler Craton • Suggests distal event(s) caused fluid movement in the Cariewerloo Basin. Adelaide – including at OD.

18 Potential resource modification • Post-1590 Ma ages of uraninite has been recorded Potential for U- in OD. bearing(?) fluids Permeability likely – 1400-1150 Ma (Trueman et to discharge into increased by faults al., 1986; Johnson, 1993; ODBC Ehrig, 2016). • Corresponds with ages recorded in the Pandurra Formation and Musgrave granite ODBC Province. • Fluids from the overlying Pandurra Formation may have contributed to modification or upgrading of the U resource.

Thank you for your attention For more information Cherry et al., 2017, Linking Olympic Dam and the Cariewerloo Basin: Was a sedimentary basin involved in formation of the world’s largest uranium deposit ?, Precam. Res , 300C, 166-180. doi:10.1016/j.precamres.2017.08.002. Contact Alexander Cherry PhD Candidate Department of Earth Sciences/CODES University of Tasmania T: +61 416 217 892 E: alexander.cherry@utas.edu.au

References • Ehrig, K., 2016, The Olympic Dam Fe-oxide Cu-U-Au-Ag deposit: 40 years since discovery, Australian Earth Sciences Convention, Adelaide, Australia. • Fanning, C. M., Flint, R. B., and Preiss, W. V., 1983, Geochronology of the Pandurra Formation: Geological Survey of South Australia Quarterly Geological Notes, v. 88, p. 11-16. • Johnson, J. P., 1993, The geochronology and radiogenic isotope systematics of the Olympic Dam copper- uranium-gold-silver deposit, South Australia., PhD thesis (unpublished), Australian National University. • Johnson, J. P., and Cross, K. C., 1995, U-Pb geochronological constraints on the genesis of the Olympic Dam Cu-U-Au-Ag Deposit, South Australia: Economic Geology & the Bulletin of the Society of Economic Geologists, v. 90, no. 5, p. 1046-1063. • Keeling, J., Wilson, T., Zwingmann, H., van der Wielen, S., and Mauger, A., 2016, Mesoproterozic Cariewerloo Basin, South Australia: spectral approach to mapping mineral diagenesis as a guide to fluid flow and unconformity uranium potential, Australian Earth Sciences Convention, Adelaide, Australia. • Polito, P. A., The uranium potential of Proterozoic South Australian basins, unpublished presentation. • Trueman, N. A., 1986, Lead-uranium systematics of the Olympic Dam deposit and Stuart Shelf mineralisation: Summary report of U-REE mineralisation, Adelaide, Australia: Western Mining Corp., internal memo, XPSA86/1, 13 January 1986, 7p. • Skirrow, R. G., Bastrakov, E. N., Baroncii, K., Fraser, G. L., Creaser, R. A., Fanning, C. M., Raymond, O. L., and Davidson, G. J., 2007, Timing of iron oxide Cu-Au-(U) hydrothermal activity and Nd isotope constraints on metal sources in the Gawler craton, south Australia: Economic Geology, v. 102, no. 8, p. 1441-1470.

19 Was there an upgrade? • Uraninite of different ages/generations in OD have been found to have different REE compositions (Macmillan et al., 2016). – i.e. Early and late generations have REE patterns indicating high- and low-T formation, respectively. • Insufficient Pb is present in the deposit relative to the amount of radiogenic Pb that should be present if all of the U was present at 1590 Ma (Trueman, 1986; Reeve et al., 1990).