Location of the world’s oldest ochre mine detected

University of Cologne

 

image: 

Ochre mine in the Lion Cavern in Eswatini, a country in southern Africa

view more 

Credit: Jörg Linstädter

In a recent study, an international team of researchers used luminescence dating and geochemical analyses to confirm the location of the oldest ochre mine in the world. It is located in the Lion Cavern in Eswatini, a country in southern Africa. Not only have the researchers dated the mine to an age of around 48,000 years, but they were also able to show how the ochre spread from the mine to nearby areas. The researchers analysed 173 samples from 15 Stone Age sites and reconstructed the methods of ochre extraction, use and transport networks. The study ‘Ochre communities of practice in Stone Age Eswatini’ was published in Nature Communications.

Ochre is a naturally occurring pigment made from iron-rich materials. It has been used by people for thousands of years – for cave paintings and to decorate symbolic objects and personal ornaments. Ochre has cultural, historical and spiritual significance in many societies and therefore offers researchers valuable insights into the growth of human society and human self-expression.

For this study, the researchers created a geochemical fingerprint of the ochre from the Lion Cavern region. For this purpose, small samples of ochre artefacts are safely made radioactive by neutron irradiation. Some of the resulting products can be radioactive. When these radioactive materials begin to decay, they emit characteristic energies. These can be measured and can thus provide information on where the material comes from and how it was created. In this way, the origin and transport routes of the artefacts can be reconstructed. In addition to this method, the researchers used an advanced laser technology, which makes the sample’s molecular bonds vibrate. This vibration indicates the mineral composition of the ochre. 

Dr Svenja Riedesel from the Cologne Luminescence Laboratory at the University of Cologne’s Institute of Geography contributed to the dating of the samples. Luminescence dating is based on the fact that materials such as quartz or feldspar absorb small amounts of energy from their surroundings over the course of time. The main source of this energy is the natural radiation in the ground, which is all around us. Small defects in the crystal structure of the material store this energy. “To determine the age of a material, we take a sample and expose it to light or heat in the laboratory,” said Riedesel. “In this way, the stored energy is released again and a weak light – known as luminescence – is produced.” The amount of light released indicates how long the material has not been exposed to sunlight or heat.

Riedesel used quartz grains to date the materials inside of the now abandoned mining caves of Lion Cavern. The results of the luminescence samples show that the caves were created by mining at least 42,000 years ago. This confirms earlier geochronological findings suggesting that ochre was mined in the Lion Cavern 48,000 years ago. “With the help of Optically Stimulated Luminescence dating, we were able to prove that this is the oldest known ochre mine in the world,” summarized the geographer.

---

Journal

Nature Communications

DOI

10.1038/s41467-024-53050-6 

Article Title

Ochre communities of practice in Stone Age Eswatini