SA fossils – Go Fossil Hunting

Introduction

Andamooka is a small, rough-edged opal mining town about 600 kilometres north of Adelaide in outback South Australia. While Coober Pedy gets most of the publicity, Andamooka has its own extraordinary fossil record, including the Addyman Plesiosaur, described by palaeontologists as the finest opalised skeleton on Earth, and Opallionectes andamookaensis, a newly described plesiosaur species that provided new insights into plesiosaur evolution when it was formally named in 2012. South Australia’s only confirmed dinosaur, the theropod Kakuru kujani, was also recovered from opal country near Andamooka. Unlike Coober Pedy, Andamooka still allows members of the public to fossick on mullock heaps outside registered mining claims, making it one of the few places in Australia where you can legally search for opalised invertebrate fossils with your own hands. This guide covers how to get there, what you can legally fossick for, the geological history that made it all possible, and the practical rules you need to follow before you pick up a tool.

Location and Directions

Address

Andamooka township is located at Andamooka, South Australia 5722. The Post Office and Opal Museum, which serves as the main visitor contact point, is on Andamooka’s main street in the town centre.

Directions

From Adelaide, drive north on the Stuart Highway for approximately 560 kilometres to Pimba, then turn right (east) onto the Olympic Dam Access Road toward Roxby Downs. Continue through Roxby Downs and follow the signposted road north for approximately 30 kilometres to Andamooka. The total drive from Adelaide is roughly 600 kilometres and takes around six hours. Most of the road is sealed, but the final stretch into Andamooka includes sections of unsealed road that can become impassable after heavy rain. A standard two-wheel drive vehicle is suitable in dry conditions. Check road conditions with the South Australian Department for Infrastructure and Transport before travelling. Fuel is available in Roxby Downs; Andamooka’s fuel supply is limited and more expensive. Parking is unrestricted throughout the township.

What Fossils You’ll Find

The fossils at Andamooka come from the same Bulldog Shale marine sediments as those at Coober Pedy. Opalised bivalves are the most common finds on the mullock heaps and are what most fossickers are likely to encounter. These are the discarded heaps of rock and matrix removed from active and historical mining operations. Sorting through mullock is unpredictable but genuinely productive, and small opalised shell material is a realistic find for a patient visitor.

Opalised gastropods and fragments of opalised wood also occur in the heaps. Belemnites, the solid guard sections of ancient squid-like cephalopods, sometimes turn up as small, cigar-shaped opals.

The scientifically important material, including plesiosaur specimens, is found deep in active mining operations and is not accessible to the public. The Addyman Plesiosaur, a long-necked elasmosaurid plesiosaur discovered in 1968 and measuring between six and ten metres in length, is held at the South Australian Museum in Adelaide. Opallionectes andamookaensis, described in 2012 from material recovered near Andamooka, belongs to the family Polycotylidae and had a shorter neck than elasmosaurids, with long, needle-like teeth suited for catching fish. Kakuru kujani, South Australia’s only dinosaur, is known from a single opalised tibia recovered from the Andamooka area and is also held at the South Australian Museum.

The Post Office and Opal Museum in Andamooka provides equipment hire and can assist visitors in identifying finds. Any material you believe may be scientifically significant should be reported to the South Australian Museum.

Geologic History

The Ancient Environment

The fossils at Andamooka are preserved in the Bulldog Shale, a marine sedimentary formation of Early Cretaceous age deposited approximately 110 to 115 million years ago during the Albian stage. During this period, a large shallow sea called the Eromanga Sea flooded the centre of Australia, connecting the present-day Carpentaria Basin in the north with the Murray Basin in the south. Andamooka’s position in what is now South Australia placed it within the southern portion of this sea, which at the time was at approximately 70 degrees south latitude, well within polar latitudes. The water was cold and the light was seasonal, with extended polar winters alternating with long summer days. Despite these conditions, the sea supported diverse marine life including fish, molluscs, cephalopods, and large marine reptiles.

When organisms died, their remains sank to the fine sediment on the sea floor and were buried by ongoing clay deposition. Over tens of millions of years, silica-rich groundwater percolated through the lithified sediment and progressively replaced the original calcite and bone material of the fossils with amorphous hydrated silica, producing the precious opal that defines the region today.

How Andamooka Became a Fossil Fossicking Site

Opal mining at Andamooka began in the 1930s and has continued in the same general area for nearly a century. Mining methods involve drilling shafts and tunnelling horizontally through the opal-bearing horizon within the Bulldog Shale. The waste rock and matrix removed during this process is piled on the surface, creating the mullock heaps that now dot the landscape around the township. It is on and around these heaps that legal public fossicking takes place. Because the heaps have already been processed for opal, miners have no objection to hobbyist fossickers sorting through the discarded material. The combination of a long mining history and a cooperative community culture has made Andamooka one of the most accessible opal-fossicking destinations in Australia.

Visiting Rules and Regulations

Is Fossil Collecting Allowed?

Yes, with conditions. Under South Australian law, you need a Miner’s Right to fossick anywhere in the state. A Miner’s Right costs $12.45 (as of recent reporting) and is valid for 12 months. You can purchase one online through the South Australian Department for Energy and Mining, or in person at relevant government offices. With a Miner’s Right, you may fossick on mullock heaps outside registered mining claims. Registered claims are marked by four corner posts defining an area of 50 metres by 100 metres up to 100 metres by 200 metres. You must stay outside these marked areas. The Andamooka fossicking area at the main camping ground has a specific heap set aside for visitors, which is the most appropriate starting point. Opalised invertebrate fossils that you find on mullock heaps may be kept. Opalised vertebrate fossils (including any bones or teeth) are the property of the South Australian Crown under state heritage legislation and must be reported to the South Australian Museum. The Post Office and Opal Museum hires tools and can provide up-to-date guidance on current regulations.

Recommended Equipment

The Post Office and Opal Museum hires fossicking tools including sieves and small picks. If you bring your own equipment, a coarse-mesh sieve, a small hand pick, and sturdy gloves are the most useful items. Sunscreen, a wide-brimmed hat, and at least two litres of water per person are essential on any visit. Closed-toe boots with ankle support are recommended because mullock heaps are uneven and contain sharp rock fragments.

Safety

Andamooka is in the South Australian outback and the same hazards as other remote outback destinations apply. Open mine shafts are present throughout the town and surrounding mining areas. Do not walk across unmapped ground at night, and keep children supervised at all times. Summer temperatures can exceed 45°C; visiting between May and September is strongly recommended. Mobile phone coverage in Andamooka is limited. The road from Roxby Downs can become impassable after rain. Always carry sufficient water, food, and a means of communication before leaving the main sealed highway network.

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Andamooka Opal Fossils: Fossick for Opal and Find Cretaceous Marine Life, SA