Diamonds are a rare and valuable commodity, but finding them can be a daunting task. However, a new method developed by geologists from ETH Zurich and the University of Melbourne could make it easier and cheaper to locate diamond deposits. The method relies on the chemical composition of kimberlites, the volcanic rocks that carry diamonds from the depths of the earth to the surface.
Kimberlites and Olivine
Kimberlites are formed when magma from the earth’s mantle rises rapidly and erupts on the surface. They are the main source of natural diamonds, as they can transport the precious stones from more than 150 kilometers below the surface, where they are formed under high pressure and temperature. Kimberlites occur only on very old continental blocks that have remained geologically unchanged for billions of years, predominantly in Canada, South America, central and southern Africa, Australia, and Siberia.
The new method is based on analyzing the mineral olivine, which makes up around half of kimberlite rock. Olivine consists of varying proportions of magnesium and iron. The more iron olivine contains, the less magnesium it has, and vice versa.
The researchers found that there is a direct link between the iron-to-magnesium ratio of olivine and the diamond content of the kimberlite. In rock samples where the olivine was very rich in iron, there were no diamonds or only very few. On the other hand, in samples where the olivine had more magnesium, the diamonds were preserved.
The Role of Metasomatism
The researchers explained that the key factor that affects the iron-to-magnesium ratio of olivine and the presence of diamonds is the process of metasomatism, which takes place in the earth’s interior. In metasomatism, hot liquids and melts attack the rock. The minerals present in the rock react with the substances dissolved in the fluids to form other minerals.
The researchers discovered that olivine becomes richer in iron in the places where melt penetrates the lithospheric mantle, the layer where diamonds are present, and changes the composition of mantle rocks significantly. The infiltration of the melt that makes olivine richer in iron destroys diamonds.Â
The researchers also found that kimberlites don’t normally reach the earth’s surface in one go. Rather, they begin to rise as a liquid mass, pick up fragments of the mantle on the way, cool down, and then get stuck. In the next wave, more melt swells up from the depths, entrains components of the cooled mantle, rises higher, cools, and gets stuck. This process can happen multiple times.
“It’s a real stop-and-go process of melting, ascent, and solidification. And that has a destructive effect on diamonds,” said Andrea Giuliani, the lead author of the study, who has been studying the formation and occurrence of the gemstones since 2015. “If, on the other hand, conditions prevail that allow kimberlites to rise directly to the surface, then this is ideal for the preservation of the gemstones.”
A Simpler and Faster Way to Prospect for Diamonds
The new method is as reliable as previous prospecting methods, which are mainly based on the minerals clinopyroxene and garnet. However, the new method is easier and faster: it takes only a few analyses to get an idea of whether a given kimberlite field has diamonds or not.
“The great thing about this new method is not only that it’s simpler, but also that it finally allows us to understand why the previous methods worked,” Giuliani said. “De Beers is already using this new method.”
The study was published in the journal Nature Communications and received financial support from De Beers. The researchers hope that their method will help the diamond industry recover from the recent downturn caused by the global pandemic and the rise of lab-grown diamonds.
Diamonds are not only a symbol of love and luxury, but also a potential source of clean energy. Scientists are exploring the possibility of using diamonds as batteries, as they can store large amounts of energy and last for thousands of years. With the new method, finding diamonds could become easier and more sustainable, paving the way for a brighter future.
Source: Mining.com
