Hydrothermal alteration is a complex geological process that can later serve as an indicator of gold deposits for mineral explorers. The process sees hot and metal-rich fluids interact with surrounding rocks, causing chemical and mineralogical changes.

Potassic (K) alteration is a common geological feature of many gold deposits worldwide, particularly lode gold deposits. In these, gold occurs in veins alongside quartz and sulfides within the rock. This alteration is shown by the presence of potassium-rich minerals, such as K-feldspar and muscovite, with gold accumulating within the alteration zone.

This phenomenon occurs when fluids containing potassium, sulfur and gold interact with surrounding rocks. Such alteration is easily visualized, often showing a light pink color on a rock surface. It can be used as an indicator of nearby gold mineralization.

Despite this well-documented relationship, it was previously unknown whether potassium has played a role in the process of gold formation.

Innovative methods fill key knowledge gaps

Dr. Yuan Mei and Dr. Siyu Hu are researchers in our Mineral Resources team. To help address the knowledge gap, they co-supervised a visiting Early Career Researcher Dr. Gao-Hua Fan. The latter drove this work in collaboration with his primary supervisor, Professor Jian-Wei Li, from the China University of Geosciences, Wuhan.

Together, the team developed a novel geochemical model that sheds new light on the fundamental mechanism of potassium in gold mineralization. Their work is grounded in ab initio (from inception) molecular dynamics simulations. It explored the behavior of potassium in Au-bearing hydrothermal fluids at the point of lode gold formation. The research was recently published in Geochimica et Cosmochimica Acta.

Our computational geochemist Dr. Yuan Mei said ab initio molecular simulation allows us to explore early metal behaviors under extreme conditions.

“These tests would be impossible without supercomputers. Thanks to the Pawsey Supercomputing Research Center, we utilized over a million CPU hours through parallel computing to simulate the interaction between gold and potassium ions at the atomic scale,” Yuan said.

“That’s equivalent to more than 100 years on a single CPU. We can simulate reaching temperatures up to 1,000ºC and pressures of 2,500 bar—conditions that are difficult to physically achieve experimentally.”

The results provided compelling evidence that ion pairing between K⁺ and Au(HS)₂⁻ is very weak in both vapor-like and liquid-like fluids. This finding indicates that potassium plays a minimal role in transporting gold within lode gold-mineralization systems.

A significant contribution to hydrothermal geochemistry

In addition to molecular simulations, the team investigated fluid evolution. They were particularly interested in how the transition from early K-feldspar to later muscovite influences gold deposition.

They identified that gold mineralization and K-minerals transition (from K-feldspar to muscovite) occur simultaneously during the cooling of fluids. Decreases in pH and oxygen fugacity play secondary roles in this process.

These findings underscore that the genetic relationship between potassic alteration and gold mineralization arises from the impact of fluid evolution on gold precipitation. It is not due to a direct influence of potassium on gold transport.

Our economic geologist Siyu explained how potassic alteration is an important indicator for gold deposits.

“By better understanding the genetic association between this type of alteration and gold mineralization, gold explorers can confidently use this alteration as a robust indicator,” Siyu said.

“This will enhance their ability to identify and target gold deposits with greater precision.”