Uranium deposit types: a systems perspective

Transcription

1 Uranium deposit types: a systems perspective Roger Skirrow Onshore Energy & Minerals Division roger.skirrow@ga.gov.au

2 Outline 1. A new view of U deposit types: 3 families of mineral systems 2. Concepts and data for exploration targeting of uranium ore systems: Magmatic-related U we should have more! Basin-related U Australia s hidden potential Results from Onshore Energy Security Program (OESP, )

3 Uranium deposit classification Most widely used: IAEA RED BOOK Breccia complex (Iron Oxide Cu-Au) Unconformity-related Sandstone Surficial Metasomatite Metamorphic Volcanic Intrusive Vein Quartz-pebble conglomerate Collapse breccia pipe Phosphorite Lignite Black shale Based on host-rock or deposit morphology Links between deposit types not clear Four Mile Beverley

4 An alternative U deposit framework: 3 families of uranium mineral systems Three end-member fluids Continuum of deposit styles Hybrids are expected MAGMATIC- RELATED U SYSTEMS Volcanic Intrusive Vein Magmatichydrothermal fluids Volcanic mixing mixing Meteoric, seawater (1) Shallow U-bearing hematite IOCG HYBRID U SYSTEMS Deep (mgt) IOCG Calcrete U Groundwaters Sandstone U (V, Cu) Formation waters / connate waters Metasomatic Vein Unconformity U (PGE, Au) Diagenetic fluids mixing BASIN- and SURFACE-RELATED U SYSTEMS METAMORPHIC - RELATED U SYSTEMS Metamorphic fluids (incl. metamorphic rock-buffered) From Skirrow et al., Uranium mineral systems: Processes, exploration criteria, and a new deposit framework, Geoscience Australia Record 2009/20.

5 Why is this systems scheme important? Exploration for clones of standard deposit types could overlook important variants/hybrids E.g. Hematite breccia type was not a known U deposit type prior to 1975 discovery of OD E.g. Four Mile deposit is likely a hybrid of sandstone U (and is higher grade than Beverley).

6 What and where is Aust s U potential? 10 Uranium grade / tonnage resources of Australian vs global deposits 239,000 t, 17.8% U % t U 0.1 t U 10 t U 100 t U Australia underrepresented in: Magmatic-related U? Basin-related U ( sandstone )? 1,000 t U 10,000 t U 100,000 t U McA RIVER 1,000,000 t U KAZAKHSTAN TOTAL t U Kazakhstan total: Fyodorov (1999) Other data: IAEA (2009) ROSSING STRELTSOVKA 0.01

7 Magmatic-related U systems: Key mappable criteria ( ingredients ): Peralum, peralk, or A- and hi-t I-types Highly fractionated (Rb/Sr) High U solubility (peralkaline, Cl, F) Volcanic vs plutonic High U content Chem gradients for U deposition (ph etc) Orthomagmatic U systems Magmatichydrothermal U systems Secondary magmatic-related U systems

8 GA national datasets for exploration: Magmatic U and other mineral systems Digital Surface Geology Gravity Anomaly Radiometrics Magnetic Anomaly + Mineral deposits and occurrences database + Geochemical analysis (whole rock) database + Geochronology database

9 Magmaticrelated uranium Potential for magmatic-related uranium systems in Australia Schofield (2010) Uranium content of igneous rocks of Australia 1:5m scale maps: Explanatory notes and discussion Schofield (2009)

10 Basin-related uranium systems Lakewater Bittern Basinal / connate brine Meteoric water Metamorphic fluid Oil / gas / H 2 S Different deposit styles: related processes tabular sandstone U styles: paleochannel rollfront SCALE: 1 to 50 km weathered granite 1 to 5 km aquiclude aquifer mafic unconformityrelated U (basement hosted style) basement (meta-sedimentary, meta-igneous) Westmoreland U style radiogenic heat Source: Skirrow et al. (2009)

11 Uranium content of fluid controlled by redox and temperature U, ppm OXIDISED surface-related ( calcrete ) sandstone-hosted & Westmoreland style 10 ppm 1 ppm 10 ppb BASIN- AND SURFACE- RELATED U SYSTEMS Continuum of fluid characteristics All involve highly oxidised fluids U depositional conditions differ but reduction is key in most systems unconformity-related Log fo 2 REDUCED Temperature Source: Bastrakov et al. (in press) and Skirrow et al. (2009) 1M Cl fluid buffered by K-feldspar-muscovite-bearing granite

12 GA datasets for basin-related U exploration: National datasets + regional seismic, AEM & 3D data OESP data co-funded by GA, State & NT surveys, and universities Seismic AEM OESP Completed Pre-OESP AuScope In progress

13 Examples from Paterson AEM survey, WA Mapping resistive basement (blue) 3D paleovalley maps Deep paleochannels 400 m m LEI depth slice 100 m TEMPEST depth of penetration Source: Williams et al. (in press)

14 Legend Springs Deposits (OZMIN) Uranium Occurrences Redox Drill Holes Lake Frome region, SA: Paleochannel and redox mapping in 3D beneath cover Four Mile Pepegoona Beverley Neogene Paleochannels Paleogene Paleochannels Oxidised Mixed Redox State Reduced Drill hole logs interrogated Reduced zones = Fe 2+ minerals, reduced-c, reduced-s, black, etc Oxidised zones = Fe 3+ minerals, red, etc Gridded in 3D North-south paleovalleys in Namba Fm as well as Eyre Fm? (in Eyre Fm) Top of Namba Formation Source: Skirrow (ed., 2009)

15 FROME URANIUM PROVINCE EVOLUTION: 3 potential U systems since Mesozoic Uranium ore-forming systems of the Lake Frome region, South Australia From Skirrow (ed., 2009) Probable hybrid U deposit style (Four Mile)

16 Eromanga Basin 3D model A framework for uranium & geothermal exploration, and groundwater studies Mesozoic stratigraphic units displayed from old to young, as 3D voxet model. Vertical Exaggeration = 50 times Source: van der Wielen et al. (2009 & in press)

17 Conclusions 3 families of U mineral systems in ternary scheme, based on fundamental fluid types and settings: Basin- and surface-related Magmatic-related hybrids Metamorphic-related GA (+State/NT) OESP datasets and new concepts available for U targeting & exploration Australia has the right geology for discovery of giant basin-related and magmatic-related U deposits

18 Acknowledgements Geoscience Australia: Evgeniy Bastrakov, Allison Britt, Andrew Cross, Subhash Jaireth, Alison Kirkby, Aden McKay, Terry Mernagh, Anthony Schofield, Simon van der Wielen, John Wilford, Nick Williams, Andy Barnicoat Steven Hore (PIRSA), Steven Hill (Uni of Adelaide)