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For a long time it was thought metal uranium did not exist in nature. This latest study has proved the contrary.

The latest issue of Geology (English version) published a cover story saying that researchers from China have discovered naturally occurring uranium. The results not only provide important essentials that reveal the nature of hydrothermal uranium mineralization, but are also of great significance to study the origin of the uranium, the formation and evolution of the Earth's heat.

Uranium is both the basic element of the nuclear arms industry and the civilian use of nuclear energy. And it is widely distributed on Earth, but because of its instability, science hitherto assumed that uranium does not occur in nature in pure form but only in oxygen-containing minerals.

The research team, led by president of the Beijing Institute of Geology, Li Ziying, conducted a systematic study of the composition and the valence of uraninite in hydrothermal uranium deposits. The study found that the uranium uraninite was not only in tetravalent and hexavalent form, but also existed as uranium metal (zero valence).

Due to the strong reduction environment inside the Earth, uranium remains in a metallic state or low valence state. When the uranium fluids are transported to near the Earth’s surface, due to the continuous increase of contact with oxygen, most of the uranium combines with oxygen to form tetravalent or hexavalent compounds.

The samples for Li’s research were collected from two famous mineral deposits in China: "Guidong 330" and "Zhuguang 302" in the northeast of Guangdong province in the far south of China. The research team has analyzed the samples by X-ray photoelectron spectroscopy.

Only a portion of the uranium remains in its metallic state. Li Ziying considers that the proportion of pure uranium, tetravalent and hexavalent in the field of hydrothermal uranium ore may reflect the depth of the ore formation.

This important discovery provides important fundamentals in understanding the nature of hydrothermal uranium mineralization and the basic elements for ore control, and thus has an important practical value.