A new study led by Prof. XIAO Wenjiao from the Xinjiang Institute of Ecology and Geography of the Chinese Academy of Sciences sheds light on the ore-forming process and key mechanisms of the gold deposit in the South Tianshan of northwest China.

The study was published in Geological Society of America Bulletin on Jan. 20.

The Tianshan Orogenic Belt is the world's second-largest gold-rich region. The researchers focused on a massive gold deposit known as Sawayaerdun. The region is estimated to contain a staggering 3.7 million ounces of gold, though it is spread thinly, averaging about 1.38 grams per ton.

However, how the gold formed, where it came from, and how it was concentrated remained scientific puzzles.

To solve this puzzle, the researchers used advanced tools to identify microscopic changes in the elements and isotopes of the gold-bearing minerals.

They discovered that the initial "pre-gold" stage, during which gold became concentrated in the early-formed pyrite minerals within the dark rocks, was crucial. This early enrichment set the stage for the massive gold deposit seen today.

The researchers also identified a critical process in which fluids carrying gold underwent a type of "phase separation," similar to how oil and water separate. This phase separation helped concentrate gold in these "orogenic" deposits.

This fluid phase separation process has a lower average gold grade, averaging 0.66 parts per million. However, it accounts for over 80% of the total ore volume and makes up approximately 38% of the total gold resources in the region.

"Our findings provide critical guidance for gold exploration in the Tianshan Orogenic Belt and elsewhere," said MA Guoxiong, the study's first author.