2015 broken hill resources investment symposium - geology survey of south australia - steve hill
TRANSCRIPT
Using the Cover to Uncover the Curnamona Steve Hill Director, Geological Survey of South Australia
May 2015
www.statedevelopment.sa.gov.au
The Cover Impediment… • The greatest impediment for future discoveries in the Curnamona – Ignore it – Punch or look through it – Use it to help guide explora;on
The prize…. • Broken Hill and nearly all other Curnamona mineral occurrences were found because they stuck out of the ground
• Notable excep;ons: – Sedimentary uranium (Beverley, Four Mile…) – Geophysical targe;ng under the Mundi Mundi Plain
• The reason we haven’t had more discoveries is that they are under cover
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White dots = Major mineralisa;on discoveries = Bias towards areas with outcrop / shallow basement
INSPIRATION: new exploraGon search space beyond shallow cover
Australian Discoveries under cover…
Geology of the Cover • We need our geological brains working in the cover … its not the domain that geology forgot
Geological Processes in the Cover: • Weathering / erosion / sediment and element
accumula;on • Element mobility – source, transport, accumula;on,
preserva;on • Supergene enrichments • Biogeochemical processes • Placer concentra;on and recycling • Geochemical footprint enlargement • -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ • Dilu;on • Barren cover (‘blind” deposits) • Erosion / poor preserva;on
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Weathering
Erosion SedimentaGon
Preserva;on Leaching
Denuda;on Physical Dispersion
Burial Re-‐accumula;on (“False anomaly”)
Dynamic Equilibrium
Mapping Through and within Transported Cover
(From James Cleverley, CSIRO)
How does cover geology work? (e.g. Tunkillia)
However…. • Perhaps the cover in itself is not the real impediment to discovery?
• Could it be that our knowledge and aNtude to the geology of the cover that is our biggest hurdle?
Key points 1. A becer geological context for the
Curnamona’s cover 2. Cover penetra;on: some ways to see
through it 3. Enlarged mineral system footprints in the
cover
A becer geological context for the cover • Geological type sections and their associated data have received diminished
attention, particularly since the GSSA work in basin areas in 1970s and 1980s
• These are important reference sections, particularly as exploration moves into surrounding covered areas.
• Modern data for these sections can include: • GPS coordinates • Lithological logging • Biostratigraphy • HyLogger mineralogy • Lithogeochemistry • Detrital zircon dating • et al……
Trinity Well type sec;on, Marree 1:250k mapsheet
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Trinity Well Reference Section
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Deep cover atlas of SA (DET CRC) …
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5 other components • Detailed palaeodrainage and palaeosurface reconstruc;on and history?
• Regional regolith geochemistry – hydrogeochemistry has best coverage so far
• Regional depth of cover? • Links between geophysics and cover? • Cover expressions of key mineral systems?
Cover penetra;on: some ways to see through it
• Geophysics • Mineralogy • Geochemistry • Biogeochemistry
White Dam Cu-‐Au, Curnamona Province, SA
Cu Topsoil
Cu BSB
Aier R E Smith & B Singh, 2007
Enlarged mineral system footprints in the cover
Enlarged mineral system footprints in the cover
Scale of the distal footprint of the Broken Hill mineral system
• Lateral dispersion for >100 km – High grade garnets in beach sands
at Menindee Lakes (>100 km to SE) – Staurolite and other high grade
metamorphic minerals in sediments overlying low-‐grade metamorphic rocks in the Fowlers Gap and Bancannia Basin (>100 km to N)
– Lateral dispersion onto Mundi Mundi Plains (30-‐50 km to W and NW)
Catchment headwaters within Barrier Ranges
Mundi Mundi Plains
Umberumberka Reservoir
Umberumberka Creek -‐ Broken Hill (Charloce Mitchell, DET CRC)
Catchment headwaters within Barrier Ranges
Mundi Mundi Plains
Umberumberka Reservoir
Umberumberka Creek -‐ Broken Hill (Charloce Mitchell, DET CRC)
Mundi Mundi Plain • Lateral dispersion and reaccumula;on
Tibooburra Au provenance...
Tors of Tibooburra Granodiorite (photo S.Hill)
Au hosted in basal Mesozoic sediments
Tibooburra: Mesozoic palaeoflow model in rela;on to historic Au diggings (Hill et al 2009)
Emergent
.The Granites . Easter Monday . Tunnel Hill
. Six Mile
Think about the cover • Ignore it at your peril • We known a licle about it (probably just enough to be dangerous)
• Huge rewards to change our explora;on success in the region
Disclaimer The informaGon contained in this presentaGon has been compiled by the Department of State Development and originates from a variety of sources. Although all reasonable care has been taken in the preparaGon and compilaGon of the informaGon, it has been provided in good faith for general informaGon only and does not purport to be professional advice. No warranty, express or implied, is given as to the completeness, correctness, accuracy, reliability or currency of the materials. The Department of State Development and the Crown in the right of the State of South Australia does not accept responsibility for and will not be held liable to any recipient of the informaGon for any loss or damage however caused (including negligence) which may be directly or indirectly suffered as a consequence of use of these materials. The Department of State Development reserves the right to update, amend or supplement the informaGon from Gme to Gme at its discreGon.
www.statedevelopment.sa.gov.au