Researchers have confirmed the existence of a previously unknown meteorite impact crater near the historic gold mining district of Ora Banda in the Eastern Goldfields of Western Australia. The discovery, based on geological surveys and drilling analysis, was reported in the journal Meteoritics & Planetary Science.
Discovery and Characteristics
The crater, heavily eroded and partially buried, was initially identified by geologists surveying for gold deposits who detected a circular gravity anomaly—a zone of denser rock beneath the desert surface. Subsequent analysis by a team including researchers from Curtin University and led by Raiza Quintero of the University of Puerto Rico confirmed the structure's origin.
Reports differ on the crater's diameter, with some sources stating it is approximately 4 km wide and others reporting it as 5 km wide. The impact event is believed to have occurred before the Early Cretaceous period. The structure is currently referred to as the Ora Banda impact structure; researchers are working with the Goldfields Aboriginal Language Centre to establish an Indigenous name for the site.
Key Evidence for Impact
Confirmation of the impact was based on several diagnostic lines of evidence:
- Gravity anomaly: A circular feature of denser rock detected beneath the desert surface.
- Shatter cones: Distinctive conical fractures in rocks, formed by shock waves, found in surface outcrops and drill cores.
- Impact breccias: Rocks shattered and mixed by the impact, including suevite (breccia containing glassy melt particles) and rocks composed of angular fragments welded together, found in drill cores.
- Shocked quartz: Quartz grains with microscopic deformation features that form only under extreme pressures.
- Meteorite residue: Extraterrestrial material dissolved within glassy melt particles. Elevated levels of siderophile elements—including nickel, cobalt, iridium, platinum, palladium, and rhodium—were detected in glass blobs, consistent with an iron-rich meteorite impactor.
Impact Event and Geological Context
The impact occurred in ancient greenstone rocks, which are metamorphosed volcanic rocks. The Ora Banda structure is one of few known impact craters on Earth where the target rocks are greenstones, and it is the second confirmed impact structure formed entirely in Archaean greenstone.
Gold particles and nuggets were found within the breccias, suggesting the impact ejected gold-bearing material that later fell back into the crater. The study suggests that the impact may have locally mobilized gold in the surrounding rocks, though the rocks examined did not contain economic concentrations. The findings contribute to evidence that asteroid impacts can influence mineral systems and redistribute metals in the Earth's crust.
Significance
With this discovery, Australia now has 34 confirmed meteorite impact craters.
The structure provides new insight into the geological history of the Goldfields, a major mining district, and offers an analog for studying impacts on early Mars. The discovery suggests that other impact structures may be hidden in greenstone formations.