Tertiary sediments are widespread throughout South Australia with the Cainozoic a time of marked climatic and sea-level fluctuations.

Mainly fluvial and lacustrine sediments occur in small basins such as the Willochra and Walloway Basins. In contrast, thicker marine and nonmarine sediments accumulated along the subsiding southern continental margin basins such as the Eucla, Pirie, St Vincent, Murray and Gambier Basins.

Increasing marine influence, with relative sea level rises and a subsequent increase in marine influence in southern Australia resulted in a succession of non-marine clastic sediments passing upwards to marginal marine sediments and widespread temperate marine limestones. Along the coast, extensive deposits of carbonate dune sand accumulated during sea-level highstands.

Relative sea-level falls in the Late Eocene and Early Pliocene resulted in the deposition of extensive coastal sand in the Eucla and Murray Basins.

In the interior, widespread sand deserts of longitudinal dunes formed during arid phases that alternated with periods of moister climate when fluvial and lacustrine sedimentation was more extensive.

The Cainozoic basins of South Australia contain important resources of sedimentary uranium, heavy mineral sand, coal, construction materials (sand, clay, aggregate, building stone), dolomite and limestone, and gypsum.

Eucla Basin

Age

?Late Paleocene to Holocene.

Prospective commodities

Placer gold, heavy mineral sand, placer gold, uranium

Major exploration models

• Beach/barrier placer,
• Channel-hosted placer gold,
• Channel-hosted roll-front uranium,
• Channel-hosted palygorskite,
• Fluvial-estuarine coal.

The Eucla Basin covers a large area of southwestern South Australia, extending east from Western Australia to western Gawler Craton. A large and well-preserved palaeodrainage system, extending from South Australia into Western Australia, flowed from the Gawler Craton, Musgrave Province and Yilgarn Block into the Eucla Basin.

A series of well-preserved, Middle and Late Eocene, as well as Neogene, coastal barrier landforms occurs along the inland margin of the eastern Eucla Basin including the 800km long Ooldea barrier.

The onshore Eucla Basin comprises of marine limestones that pass into shallow marine, coastal and non-marine terrigenous sediments towards the basin margin. Onshore, the Eucla Basin sediments overlie Mesozoic sediments of the Bight and Polda Basins, Neoproterozoic sediments of the southern Officer Basin, and basement rocks of the Gawler Craton.

Tertiary sediments are relatively thin (<150 m) on the onshore platform but thicken up to 1500 m offshore.

Exploration has revealed basement gold mineralisation in the area of the Garford, Anthony and Kingoonya palaeodrainage networks such as Challenger, Campfire Bore, Golf Bore, Birthday, South Hilga, Tarcoola.

Heavy Mineral Sands

Recent exploration success in the Jacinth, Ambrosia and Tripitaka deposits suggests that anomalous mineralisation extends across an extensive area and the mineralisation detected occurs in unconsolidated sands above the water table, containing very high zircon contents (up to 63%) by world standards. Given this significant discovery, the prospectivity of the Barton Range region farther to the east has also increased.

Gold

Like the goldfields of Western Australia, sediments of the Eucla Basin may provide a host for placer mineralisation in the palaeovalleys and their tributaries. For instance, traces of placer gold have been found in channel sediments located near the South Hilga and Tarcoola gold prospects/deposits.

Detrital gold may have been carried in streams as bedload or suspended/saltating load in the case of fine particles. A change in flow velocity would have resulted as the palaeoriver narrowed and then widened again, or changed flow direction at point bars, or joined other palaeorivers.

Placer gold deposits have not yet been recognised but it is likely that they exist in the Middle Eocene channels (Pidinga Formation), particularly in tributaries close to basement mineralisation.

Murray Basin

Age

Late Paleocene to Holocene.

Prospective commodities

Heavy mineral sands, gypsum, coal, uranium.

Major exploration models

·  Strandline-hosted heavy mineral sand.

The Murray Basin is an intracratonic basin of Cainozoic freshwater, shallow marine, coastal and continental sediments covering an area of ~330 000km². The Tertiary sequence is up to 600m thick in the west–central Renmark Trough area, but generally 200–300m elsewhere in the basin.

The Cainozoic sediments overlie the Permian Nadda Basin and Cretaceous Berri Basin.

The South Australian portion of the Murray Basin is flanked to the west by Adelaidean to Cambrian rocks of the Adelaide Geosyncline and Kanmantoo Trough, and Proterozoic rocks of the Curnamona Province to the north.

Murray Basin Basement

The Murray Basin Basement consists of an extensive area of poorly outcropping to deeply covered Neoproterozoic and Cambrian Kanmantoo Group metasediments, and Cambro-Ordovician syn- to post-tectonic felsic to mafic volcanics and granitic, mafic and ultramafic intrusives. This area can be divided into several broad zones including the shallow, Cainozoic-covered basement area of the Padthaway Ridge, and the more deeply covered Pinnaroo, Glenelg River and Stavely Zones (Fig. 1).

High-resolution aeromagnetics has revealed tight, upright- folded metasediments and extensive felsic to mafic, syn- to post-tectonic intrusives. Drilling of these folded metasediments has revealed quartz-biotite-feldspar metasandstone and pyritic, pyrrhotitic, black, carbonaceous siltstones and shales.

Drilling of the Murray Basin Basement has also revealed a variety of rock types. These include meta-argillites resembling Kanmantoo Group units, porphyroblastic schist, pyroclastic tuffaceous sandstone, black carbonaceous mudstone, impure limestone and dolomite, amygdaloidal basalt lavas, gabbro-norite plutons, syn-volcanic basalt and micro gabbro intrusives. Other felsic to intermediate extrusives and syn- to post-tectonic S-, I- and A-type granitoid plutons have been intersected.

Heavy Mineral Sands

Heavy mineral sand in the Murray Basin has become a major exploration focus with numerous discoveries throughout the basin in the last few years.

Initial exploration in the South Australian portion of the Murray Basin focused on stranded coastal dunes of Bridgewater Formation formed during Pleistocene sealevel highstands. Later exploration concentrated on strandlines of the Pliocene Loxton and Parilla Sands.

Heavy mineral sand exploration in the South Australian portion of the basin outlined several deposits in beach facies of the Loxton and Parilla Sands, including the Mindarie,, Oakvale, Perponda and Mercunda prospects

The majority of prospects to date are located on uplifted areas, probably related to Cainozoic movement The Loxton and Parilla Sands are near or at he surface on this ridge, thus increasing its prospectivity.

Presently, Australian Zircon has moved into the construction phase with its Mindarie HMS Project. All construction is expected to be completed in the first quarter of 2007 and commissioning by the end of May, at which time production will begin.

The Mindarie deposit has proven and probable reserves of 59 Mt containing 4.3% HMs, mainly zircon and titanium, and with resource drilling continuing an increase in reserves is expected.

Lake Eyre Basin

Age

Late Paleocene to Holocene.

Prospective commodities

Uranium, heavy mineral sands

Major Exploration models

• Palaeochannel-hosted roll-front uranium.
• Palaeochannel-hosted palygorskite
• Palaeochannel-hosted placers (heavy mineral sand)

The Lake Eyre Basin in SA consists of a thick (>400 m) sedimentary succession in a northeastern depocentre that thins and becomes discontinuous towards the southwest. The basin is separated into the Tirari and Callabonna Sub-basins by the Birdsville Track Ridge, which is expressed at the surface by silcrete-capped (Cordillo, Gason and Cooryanna) domes of Mesozoic sediments.

Uranium

The Callabonna Sub-basin contains economic palaeochannel-hosted sedimentary uranium deposits including Beverley and Honeymoon together with numerous other prospects defined within the associated Tertiary palaeochannels such as East Kalkaroo, Goulds Dam, Oban and Yarramba

Heavy Mineral Sands

Heavy minerals (including zircon) have been recorded in Eyre Formation palaeochannels in the southern Callabonna Sub-basin and there is potential for heavy mineral placer deposits in favourable depositional settings within this system.

Gambier Basin

Age

Late Paleocene to Holocene.

Prospective commodities

Limestone, dolomite, coal, heavy mineral sand.

Cainozoic tectonic movements divided the onshore Tertiary sediments of southeastern South Australia and southern Victoria into separate basins, the westernmost of which is the Gambier Basin.

The Tertiary sediments reach a maximum onshore thickness of ~1000m in the Port MacDonnell area, thinning southwards offshore.

The Tertiary sediments unconformably overlie Cretaceous Otway Basin sediments except on the northern basin margin, where they rest on Palaeozoic basement of the Padthaway Ridge.

The Padthaway Ridge was a partial barrier between the Gambier and Murray Basins, and there was interbasinal connection especially during periods of high sea level.

In the area southeast of Naracoorte, the Kanawinka Fault forms the basin margin

Coal

The Kingston coal deposit, on the northern margin of the Gambier Basin, contains 985 Mt of lignite, mainly as a single seam up to 12 m thick in Dilwyn Formation.

Dolomite

In the southern Gambier Basin, dolomite has been formed by metasomatic replacement of Gambier Limestone adjacent to faults. Dolomitisation is irregular and unpredictable, and dolomite passes vertically and laterally into typical white, bryozoal Gambier Limestone.

Limestone

Gambier Limestone is quarried extensively for building stone. The limestone is exceptionally white, contains a significant silt-sized and finer carbonate fraction and is low in deleterious noncarbonate materials such as sand, silt, clay, dolomite, flint, iron and manganese.