Geologists from ETH Zurich and the University of Melbourne have introduced a groundbreaking method for detecting diamond deposits, linking the occurrence of diamonds to the presence of the mineral olivine.
Published in the journal Nature Communications, their research explains how this new method will streamline the detection process for diamond deposits. The technique relies on the chemical composition of kimberlites, geological formations found predominantly in ancient continental blocks across regions including Canada, South America, central and southern Africa, Australia, and Siberia.
Lead author of the study, Andrea Giuliani, highlights olivine as a key mineral component of kimberlite rock, comprising varying proportions of magnesium and iron. Giuliani explains that the iron-to-magnesium ratio in olivine directly correlates with the diamond content of kimberlite. Through extensive sampling and analysis, the researchers consistently observed that samples with olivine rich in iron either lacked diamonds or contained very few.
These findings prompted further investigation into the relationship between olivine composition and diamond presence. Supported by the Swiss National Science Foundation, Giuliani and his team explored how the process of metasomatism—where hot fluids interact with rock in the Earth’s interior—affects diamonds. Their analysis revealed that olivine becomes enriched in iron in areas where melt from deeper layers alters the composition of mantle rocks, typically found around 150 kilometers below the Earth’s surface—the depth at which diamonds are formed.
The infiltration of melt, which enriches olivine in iron, is detrimental to diamonds, leading to their destruction. Conversely, when minimal or no melt penetrates the lithospheric mantle, preserving olivine’s magnesium content, diamonds remain intact.
Giuliani emphasizes that kimberlites ascend to the Earth’s surface in a multi-stage process, picking up mantle fragments along the way. This “stop-and-go” ascent, accompanied by repeated melting and solidification, poses a risk to diamond preservation. However, if conditions allow kimberlites to ascend directly to the surface, the likelihood of preserving diamonds is higher.
The new olivine analysis method offers a simpler and faster alternative to traditional prospecting techniques, providing insights into whether a kimberlite field contains diamonds. Giuliani notes that De Beers is already employing this method, recognizing its efficiency and reliability compared to previous approaches based on minerals like clinopyroxene and garnet.
