Australia opalised fossil sites

Introduction

White Cliffs sits in the far northwest of New South Wales, roughly 290 kilometres northeast of Broken Hill, and it holds two overlapping records: Australia’s oldest continuously operated commercial opal field, established in 1889, and one of the few places in the world where Cretaceous marine fossils have been converted entirely to precious opal. The same geological process that produced the gem-quality opal here also replaced the shells, bones, and bodies of creatures that lived in the shallow Eromanga Sea 110 million years ago. The result is fossil material that is both scientifically significant and visually striking.

Visitors come to White Cliffs to fossick in the public opal fields, explore the underground dugout homes that residents carved into the hillsides to escape the extreme heat, and examine the opalised specimens on display and for sale in the town’s opal shops. This guide covers access to the fossicking areas, what types of opalised fossils occur here, the geological setting that produced them, the rules that apply to public fossicking, and the practical information needed to visit safely.

Location and Directions

Address

White Cliffs, New South Wales 2836. The town sits in Unincorporated Far West NSW, administered by the Far West Regional Council. The fossicking areas are scattered around the town on Crown Land leased for mining.

Directions

From Broken Hill, drive northeast along the Silver City Highway for approximately 90 kilometres to Wilcannia, then continue east on the Barrier Highway briefly before turning north onto the White Cliffs Road. The total distance from Broken Hill is approximately 290 kilometres. From Bourke, travel west along the Mitchell Highway to Cobar, then northwest via the Barrier Highway to Wilcannia, and north to White Cliffs — approximately 450 kilometres in total.

The road from Wilcannia to White Cliffs (approximately 100 kilometres) is sealed but narrow and single-lane in sections. Drive carefully and give way to road trains. A conventional two-wheel-drive vehicle is adequate for the main road, but accessing individual mining leases around town may require care on rough tracks. Fill your fuel tank in Broken Hill or Cobar before departing, as fuel availability at White Cliffs can be limited. Parking is informal around town on the open red earth; there are no designated car parks at the fossicking areas.

What Fossils You’ll Find

The fossils at White Cliffs occur within the Cretaceous Griman Creek Formation and the Finch Clay Member, marine sediments laid down in the Eromanga Sea. What makes them unusual is that the original fossil material — shell, bone, and organic structure — has been partially or wholly replaced by precious opal through a process of silicification. This opalisation is the same process that created the gem opal mined commercially here.

Bivalve shells are the most commonly encountered opalised fossils. Species of Inoceramus (a large ribbed clam widespread in Cretaceous seas) and smaller bivalves appear as opalised casts and moulds in the clay sediments. Many show the characteristic blue, green, and gold colour play associated with White Cliffs potch opal.

Belemnites — the internal guards of extinct squid-like cephalopods — occur as cylindrical opalised rods within the sediment. Their cigar-shaped form makes them recognisable even when the original calcite has been completely replaced.

Ammonites are less common but do occur. These coiled cephalopods appear as flat spiral forms, often showing the original suture pattern of the shell partitions as dark lines through the opal replacement material.

On rare occasions, miners have uncovered fragments of opalised vertebrate material — fish bones, and in exceptional cases, portions of marine reptile remains. These significant specimens are typically sold to museums or private collectors rather than remaining accessible in the public fossicking areas.

When fossicking in the public areas, look for opalised material in the spoil heaps left by previous mining activity. Freshly turned earth after rain sometimes exposes new material on the surface. Most fossils here are found as loose pieces in disturbed sediment rather than in bedrock.

Geologic History

The Ancient Environment

The fossils at White Cliffs formed in the Cretaceous period, approximately 100 to 115 million years ago, during the Albian and Cenomanian stages. At this time, a vast shallow inland sea — the Eromanga Sea — covered much of inland Australia, stretching from the present Gulf of Carpentaria in the north to the present Murray-Darling Basin in the south. The sea was warm, shallow, and highly productive, supporting abundant bivalves, cephalopods, fish, and larger marine reptiles including plesiosaurs and ichthyosaurs.

The sediments accumulated as fine muds and sands on the seafloor. The Griman Creek Formation, which hosts the opal deposits, represents these shallow marine and marginal marine environments. Organisms that died in the sea settled into the soft seafloor sediment and were buried.

The opalisation process occurred much later, during the weathering of the rock sequence. Silica-rich groundwater percolated through the buried sediments and slowly replaced the original calcium carbonate of shells and bones with hydrated silica — opal. This replacement was sometimes complete and sometimes partial, resulting in fossils that range from pure gem opal to opal-replaced bone with original structure still visible under magnification.

How White Cliffs Became a Fossil Fossicking Site

Commercial opal mining began at White Cliffs in 1889 following the discovery of gem-quality stones by kangaroo hunters. Miners worked the shallow Cretaceous sediments with picks and shovels, cutting drives and shafts through the soft rock. As mining expanded across the landscape, opalised fossils emerged alongside the gem material as an inevitable by-product. For most of the field’s early history, fossils were either discarded or sold informally through the opal trade. Over time, scientific attention to the opalised vertebrate specimens in particular grew, and a number of significant finds entered museum collections. Today the public fossicking areas designated around the town allow visitors to search the disturbed ground and spoil heaps from earlier mining operations without requiring a mining lease of their own.

Visiting Rules and Regulations

Is Fossil Collecting Allowed?

Public fossicking at White Cliffs is permitted in designated fossicking areas on Crown Land under the NSW Fossicking Act 1998. A NSW Fossicking Licence is required for anyone aged 18 or over. Licences are available online through the NSW Resources Regulator or from Service NSW. The licence costs a small annual fee and authorises fossicking for minerals and gemstones — including opalised fossils — using hand tools only. You may keep what you find in the fossicking areas.

You must not fossick on active mining leases without the lease holder’s written permission. The boundaries of leases are marked with pegs; do not cross into a leased area. Under the NSW National Parks and Wildlife Act, significant vertebrate fossil material (particularly opalised marine reptile bones) may be subject to additional protection. If you find what appears to be a significant vertebrate specimen, contact the Australian Museum or the NSW NPWS for guidance before removing it.

Recommended Equipment

For surface fossicking in the spoil heaps, a small trowel or hand pick, a stiff brush for cleaning specimens, and a container for your finds are all you need. A magnifying glass helps identify opalised material against plain potch. Wear sturdy footwear — old mining shafts can be hidden beneath surface rubble, and collapses have occurred. A hat, high-SPF sunscreen, and a long-sleeved shirt are essential; the White Cliffs area receives intense UV radiation year-round. Carry at least two litres of water per person at all times. A basic first aid kit is recommended for any remote NSW fossicking trip.

Safety

White Cliffs is genuinely remote. The nearest hospital with emergency services is in Wilcannia, 100 kilometres south, or Broken Hill, 290 kilometres southwest. Avoid fossicking on hot days — summer temperatures regularly reach 45°C and above. The greatest physical hazard at White Cliffs is old, unmarked mine shafts. These shafts can be as deep as 15 metres and may not be visible from the surface. Never walk on ground that appears recently disturbed unless you can clearly see what is beneath your feet. Do not enter any mine shaft. Keep children within close sight at all times. Mobile coverage exists in town but is patchy in the surrounding field areas. Tell someone your plans before heading out.

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White Cliffs Opal Fossicking: Opalised Marine Fossils in Outback New South Wales