Molybdenum or Mo is a metallic element that does not occur naturally as a free metal on Earth; it is found only in various oxidation states in minerals. Mo readily forms hard, stable carbides in alloys, and for this reason about 80% of world production of the element is used in steel alloys, including high-strength alloys and superalloys. 

Molybdenum deposits are found and mined on almost every continent. China has one of world’s richest molybdenum reserve bases, distributed mainly in the intra-continent areas, especially orogenic belt such as the Qinling Orogenic Belt and the Central Asian Orogenic Belt. 

A recent research by scientists in the Xinjiang Institute of Ecology and Geography (XIEG) of the Chinese Academy of Sciences summarize the geological, geochemical and geochronological characteristics of the Mo deposits, and discuss their geneses and tectonic settings. 

The team led by ZHOU Kefa collected 27 Mo deposits in northwest China. Their analysis showed that the majority of the deposits are porphyry type, followed by the skarn and quartz vein types. The deposits, represented by giant Donggebi and Baishan, were formed in syn- to post-collisional tectonic setting.  

“The types of porphyry Mo deposits and their contrasting geological and geochemical characteristics are a powerful indicator of the tectonic settings,” said ZHOU. “Available data indicate a Late Carboniferous-Permian transformation from subduction-related accretionary orogeny to continental collision orogeny.” 

Scientists found that Mo deposits in the northwest China were formed from the Devonian to Triassic periods. Porphyry Cu-Mo deposits appeared during the Devonian-Early Carboniferous, while Mo-only, Mo-dominated and W-Mo and Be-Mo deposits associated with crust-sourced granitic rocks were formed in the Triassic period.  

Further study showed that the Late Carboniferous-Permian had seen the development of both the porphyry-type Mo-only and Cu-Mo de-posits, due to its connection of Devonian-Early Carboniferous and Triassic period, two constrasting tectonic regimes in time.

The research was published recently in Ore Geology Reviews entitled “Mo deposits in Northwest China: Geology, geochemistry, geochronology and tectonic setting”.