Diamonds reveal first natural evidence of deep mantle metal alloys

Two diamonds from the Voorspoed mine in South Africa have provided the first direct natural evidence of nickel-iron metallic alloys and nickel-rich carbonates existing deep within Earth’s mantle, at depths between 280 and 470 kilometers. Researchers from Hebrew University of Jerusalem analyzed tiny nano- and micro-inclusions trapped inside these diamonds, which act as “time capsules” preserving chemical reactions and mantle conditions that would otherwise be lost. This discovery confirms long-standing geological models predicting the formation of nickel-rich metal alloys at these depths and reveals a rare coexistence of nickel-iron alloy and nickel-rich carbonate minerals, which typically would react and not coexist. The study explains this coexistence through a metasomatic redox-freezing reaction, where an oxidized, carbon-rich melt infiltrates a reduced, metal-bearing mantle rock, producing nickel-rich carbonates and oxidizing the surrounding mantle. This process also supports the theory that natural diamonds can form from reactions between carbonate fluids and reduced metals deep in the mantle, particularly as