Apr 30, 2019

New Research Says Diamonds Can Give Clues to the Formation of the Continents

A new study published recently in the journal Science, led by a research scientist at GIA, says that looking at the composition of tiny mineral elements trapped in a diamond during its formation billions of years ago can give scientists significant clues to better understanding the process of formation of continents.

The article Sulfur Isotopes in Diamonds Reveal Differences in Continent Construction has GIA research scientist Karen Smit as the lead writer; with Steven B. Shirey and the late Erik H. Hauri of the Department of Terrestrial Magnetism of the Carnegie Institution for Science; and Richard A. Stern, a research scientist at the University of Alberta, as co-authors.

“Diamonds are one of the most valuable gems, not only as jewellery but also in geoscience,” said GIA research scientist Dr. Karen Smit. “The mineral inclusions in diamonds let us study the inaccessible depths of Earth – somewhere that today’s science cannot otherwise reach.”

The study is based on the fact that mineral inclusions in diamonds are the most direct geological samples from the inaccessible depths of Earth. They provide information about water in the earth’s interior, mineralogy of the deep earth and metallic phases in the deep earth. They have also been used as the only method to date diamonds.

The researchers examined diamonds from the Zimmi mining area near the Liberia-Sierra Leone border, which is known for producing yellow diamonds. The Zimmi diamonds are classified as Type Ib diamonds because they have rare nitrogen impurities. Type Ib diamonds are exceptionally rare in nature, accounting for less than 0.1% of natural diamonds mined worldwide. By laser-cutting and polishing very thin plates from the Zimmi diamonds, the researchers were able to isolate and study sulphide inclusions, extracting chemical isotopes that offered clues to when the diamonds – and the deepest and oldest parts of the continents – formed.

The researchers specifically examined the sulphur and rhenium-osmium isotopes in sulphide inclusions in these diamonds and compared the results to diamonds from southern Africa and northern Canada.

They found that as in the case of Zimmi diamonds, diamonds from the Jwaneng and Orapa mines in southern Africa do contain MIF sulfur1,7. On the other hand diamonds mined in northern Canada do not show the same sulphur chemistry. These results gave some valuable insights into the geological processes involved in the formation of continents.

 “This kind of insight is possible only because of the unique characteristics of diamonds,” said Dr. Wuyi Wang, GIA vice president of research and development. “GIA’s significant investment in research, unique access to rare diamonds and the outstanding collaboration with the Carnegie Institution and the University of Alberta made this significant discovery possible.”

Pic caption: Rough diamond from Zimmi in West Africa, near the Sierra Leone-Libera border. It contains a sulfide inclusion with compositions that give clues to how the West African continent formed.

Pic courtesy: Karen Smit/GIA