A review of the cover geology and regolith in the central Gawler Craton region

…from legacy to reality…

Dr Carmen Krapf Geological Survey of South Australia Legacy regolith and cover data for central Gawler

. 13 CRC LEME/GSSA Open file reports including Regolith Benchmark Atlas (Sheard, 2008)  http://crcleme.org.au/Pubs/index.html . Central Gawler Exploration Guide (Sheard et al., 2008) . six regolith maps at various scale (incl. Lake Harris, Tunkillia, Jumbuck, …) . GA Record Hydrogeology and Hydrogeochemistry of the Kingoonya Palaeovalley (Lewis et al., 2012) . DET CRC Geological and Hydrological Atlas of Gawler Craton (van der Hoek & Forbes eds., 2013)

. PhD theses (Normington, van der Hoek, Dart, etc.) . and much more ………. Geological framework from basement to cover

. Archean‐Palaeoproterozoic basement mostly high‐grade metamorphic rocks, granitoids, felsic volcanics, greenstones and meta‐siliciclastics

. Mesoproterozoic basement Hiltaba Suite granites, GRV, mineralising systems and younger siliciclastics  deformation during Sleafordian, Kimban and Kararan orogenies  intruded by Neoproterozoic mafic dykes

(Lewis et al, 2012) Cover ‐ Mesoproterozoic

Carriewerloo Basin (Pandurra Fm.)

. fluvio‐lacustrine redbed sediments

. c. 1500‐1450 Ma Cover ‐ Neoproterozoic

Stuart Shelf and Officer Basin

. terrestrial to marine argillaceous, arenaceous and calcareous‐dolomitic sediments

. two glacial intervals (Sturtian and Marinoan)

. c. 850‐540 Ma Cover ‐ Cambrian

Arrowie Basin and Officer Basin

. marine argillaceous, arenaceous and calcareous‐dolomitic sediments

. c. 540‐500 Ma Cover –Late Carboniferous to Triassic

Arckaringa Basin and Mulgathing Trough

. glacigene and post glacial sediments locally overlying crystalline basement and infilling glacial valleys and troughs

. c. 300‐250 Ma Cover ‐ Mesozoic

Eromanga Basin

. terrigenous to marine sediments

. c. 150‐70 Ma Cover ‐ Cenozoic

Palaeocene (c. 65‐50 Ma) . Australia‐Antarctica break‐up . deep weathering, uplift, erosion . palaeovalley formation

Eocene to Pliocene (c. 50‐5 Ma) . palaeovalleys infill with variable assemblage of fluvial, estuarine, deltaic and marine sediments over several major depositional cycles

Quaternary (c. 2.5 Ma to 2019) . ice ages with associated windy and arid climate, aeolian, fluvial and lacustrine sedimentation, weathering and erosion Cover Thickness –Depth to Basement

 resulted in a complex interplay of variably thick in‐situ weathered basement overlain by a relatively thin layer of transported regolith in the central part

 and areas of thick basin cover in the northwest, north and east Regolith materials

. in situ weathering profiles ‐ display progression from fresh rock – saprock – saprolite – pedolith +‐ ‐ profiles can exceed 100m in thickness ‐ multiple weathering phases resulting in complex regolith profiles ‐ + ‐ + Regolith materials

. surface lags ‐ composed of chemically resistant materials ‐ derived by erosion of various source materials ‐ in many cases have been recycled and widely dispersed across the landscape ‐ provenance may be difficult to establish Regolith materials

. transported regolith ‐ widespread and variable in character ‐ includes glaciogene, alluvial, fluvial, lacustrine, aeolian and colluvial deposits ‐ mostly less than 25m thick, but can exceed 100m in palaeochannels and glacial valleys . indurated regolith ‐ includes siliceous, ferruginous, calcareous and gypseous cements ‐ marks intervals of landscape stability ‐ present at various levels within landscape ‐ calcrete widely used as sample material Regolith architecture and typical profiles

Regolith architecture is a reflection of the combination of deep weathering, profile truncation, cementation and transported cover

Sheard et al., 2008 Integrating regolith/cover knowledge & exploration

. Regolith knowledge is simply another mineral DEM over MrVBF exploration tool focused on surface materials  most accessible to sample and study  will assist in choice of sampling medium

. Regolith/cover studies underpin landscape evolution models through geological time and assist with interpretation of past climate, neotectonics and unconformities  fundamental for developing models for mineral dispersion and accumulation

However, factors that limit or facilitate movement of elements through the unsaturated zone and cover sediments are poorly understood Where to from here?

Central Gawler has a large amount of regolith/cover data in comparison to other part of SA

. regolith‐landform map coverage of the central Gawler is limited to small, widely separated areas and existing maps provide limited information in relation to cover/in‐situ interface

. good understanding of cover and regolith variation and preservation is needed

. mapping regolith and cover in 3D with emphasis on palaeotopography, unconformities, positon within in‐situ regolith profile and neotectonic structures

 DATA INTEGRATION Contacts

Dr Carmen Krapf Senior Geologist Geological Survey of South Australia Department for Energy and Mining 11 Waymouth Street, Adelaide, South Australia 5000 GPO Box 320, Adelaide, South Australia 5001

T: +61 8 8429 2544 E: [email protected] DISCLAIMER

The information contained in this presentation has been compiled by the Department for Energy and Mining (DEM) and originates from a variety of sources. Although all reasonable care has been taken in the preparation and compilation of the information, it has been provided in good faith for general information 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. DEM 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 information for any loss or damage however caused (including negligence) which may be directly or indirectly suffered as a consequence of use of these materials. DEM reserves the right to update, amend or supplement the information from time to time at its discretion.