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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

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SLIDE 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

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SLIDE 2

Olympic Dam Breccia Complex (ODBC)

  • Unconformably overlain by 350m of post-

glacial cover.

  • Breccias

– Primarily derived from granite. – Lesser felsic volcanics and clastic facies.

  • 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

  • Volc. breccia

Fe-rich breccia Low Fe breccia Granite breccia Granite Clastic facies N

2 km

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SLIDE 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

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SLIDE 4
  • Not interbedded with the other clastic

facies.

  • Much more strongly brecciated.
  • Contains few of the hydrothermal/ore

minerals in the hematite-rich breccia.

  • Contains non-1590 Ma provenance

components.

Quartz-rich sandstone

Is the quartz-rich sandstone instead part of a much younger sedimentary succession?

HQ core

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SLIDE 5
  • Intersected in only

a few drill holes.

– Appears to be a single domain. – Faulted or brecciated contacts with breccia and other clastic facies.

300 700 900 1100 1300 Depth (m) EOH 1390m 300 600 400 500 EOH 685m 500

RD2751 RD1628

Unconformity

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SLIDE 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.

3.0 2.6 2.2 1.8 1.4 1.0

207Pb/206Pb age (Ga)

200 µm 200 µm Sandstone Matrix

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SLIDE 7

Potential correlates

  • Candidates need to be

stratigraphically intermediate to basement and the cover sequence above OD.

  • Two candidate successions are

present:

– Pandurra Formation – Whyalla sandstone

134°E 138°E 30°S 136°E 32°S 34°S 150 km Whyalla Sandstone Pandurra Formation Hiltaba Suite Palaeoproterozoic - Archaean units Olympic Dam Gawler Range Volcanics (GRV)

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Pandurra Formation

  • Extensive red-bed succession.

– Fluvial quartz-rich sandstones, lesser lithic sandstones and shales. – Occurs within the Cariewerloo Basin.

  • Minimum depositional age - ca.

1400 Ma (Fanning et al., 1983).

Excess details 150 km 30°S 138°E 136°E 134°E 34°S >1.6 Ga basement Pandurra Formation 32°S Hiltaba Suite GRV Olympic Dam

After Skirrow et al. (2007)

25 km Olympic Dam Acropolis Oak Dam

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SLIDE 9

Whyalla Sandstone

  • Similar extent to Pandurra

Formation.

– Comprises aeolian quartz-rich sandstone.

  • Deposited during the Cryogenian

glaciation.

– > 630 Ma (Williams et al., 2011).

Hiltaba Suite GRV 150 km 30°S 138°E 136°E 134°E 34°S Olympic Dam >1.6 Ga basement Whyalla Sandstone 25 km Olympic Dam Acropolis

After Skirrow et al. (2007)

  • Dep. State Dev., Gov. South Australia (2017)

Emmie Bluff Oak Dam

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SLIDE 10

Pandurra Formation

Quartz-rich sandstone (OD) Whyalla Sandstone

1 mm 1 mm 200 µm 100 µm 200 µm 100 µm 100 µm 1 mm

Quartz overgrowths Authigenic illite/dickite Carbonate cement

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Detrital zircon comparison

  • LA-ICPMS of over 3000 detrital

zircons and comparison of most concordant analyses.

  • Multiple common age

populations.

– Whyalla Sandstone has additional younger zircon populations. – Younger maximum depositional age.

Relative Probability

3.0 2.6 2.2 1.8 1.4 1.0

207Pb/206Pb age (Ga)

Quartz-rich sandstone (OD) n = 289 Pandurra Formation n = 991 Whyalla Sandstone n = 81

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Timing of deposition

0.080 0.085 0.090 0.095 0.100 0.105 3 4 5 6

207Pb/206Pb 238U/206Pb

1600 1700 1500 1300 1400

Illite Apatite 40 µm

  • Quartz-rich sandstone (OD)

– Euhedral authigenic apatite occurs in the cement. – LA-ICPMS U-Pb age of apatite (1441 ± 15 Ma) = minimum timing

  • f deposition.
  • Pandurra Formation

– Whole rock Rb-Sr 1424 ± 51 Ma (Fanning et al., 1983). – Illite Ar-Ar 1426 ± 6 & 1458 ± 11 Ma (P. Polito, unpub. data).

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Quartz-rich sandstone (OD) =

  • The Pandurra Formation
  • nce extended over OD.
  • Brecciation and

incorporation occurred after lithification of the sandstone.

  • Implications for post-

1590 Ma tectonic activity at OD.

Pandurra Formation =

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SLIDE 14

Post-1590 Ma tectonic activity

  • Faults likely

propagated up from the ODBC.

  • And brecciated
  • verlying lithified

Pandurra Formation.

Cariewerloo Basin (Pandurra Formation) granite ODBC unconformity Propagation of faults up from the ODBC

schematic

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SLIDE 15

Post-1590 Ma tectonic activity

  • Faulting was on a scale

sufficient to drop sandstone 100s of meters into the ODBC.

  • Likely occurred

between:

– ca. 1400 Ma (diagenesis/ lithification) and, – ca. 600 Ma (max age

  • f current cover).

Cariewerloo Basin (Pandurra Formation) granite ODBC unconformity

schematic

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SLIDE 16

20 µm

The Cariewerloo Basin as a conduit for fluid access

  • Evidence of fluid movement in

the Cariewerloo Basin (Pandurra Formation).

– 1260-1180 Ma K-Ar ages of illite crystallisation throughout the Basin (Keeling et al., 2016). – Late authigenic xenotime growth in quartz-rich sandstone (Pandurra Fm) at OD - LA-ICPMS U-Pb age of 1081 ± 13 Ma.

0.05 0.06 0.07 0.08 0.09 0.10 3 5 7 9 11 13

207Pb/206Pb 238U/206Pb

600 800 1000 1200 1400 Zr Xt Qz

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SLIDE 17
  • No recorded events in the

Gawler Craton correlate with these ages.

  • But are coincident with

thermal events in the Musgrave Province.

– e.g. Musgrave Orogeny and Giles Event.

  • Suggests distal event(s) caused

fluid movement in the Cariewerloo Basin.

– including at OD.

Gawler Craton Cariewerloo Basin

(Pandurra Formation)

Stuart Shelf

(includes Whyalla Sandstone)

Musgrave Province Olympic Dam Adelaide

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Potential resource modification

  • Post-1590 Ma ages of

uraninite has been recorded in OD.

– 1400-1150 Ma (Trueman et al., 1986; Johnson, 1993; Ehrig, 2016).

  • Corresponds with ages

recorded in the Pandurra Formation and Musgrave Province.

granite ODBC Potential for U- bearing(?) fluids to discharge into ODBC Permeability likely increased by faults

  • Fluids from the overlying Pandurra Formation

may have contributed to modification or upgrading of the U resource.

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SLIDE 19

Contact

Alexander Cherry PhD Candidate Department of Earth Sciences/CODES University of Tasmania T: +61 416 217 892 E: alexander.cherry@utas.edu.au

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.

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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.

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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).

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