LSU Geologist Helps Develop New Method to Date Copper Ore Formation

Copper, a critical mineral, is essential to modern society. Its primary use is conducting electricity, from cell phones to national electrical grids. Meeting the demand for copper is vital to supporting the technologies that power our everyday lives.

Like most critical minerals, copper is mined from rocks. Determining when copper mineralization occurred is key to understanding how ore deposits form and evolve. Yet relatively few copper-bearing ore minerals can be dated directly using established techniques.

To address this challenge, a new study by LSU geologist Darrell Henry dates minerals that formed alongside copper minerals, helping establish the timing of ore formation.

Tourmaline is a common accessory mineral in many hydrothermal ore deposits, which form from hot, mineral-rich fluids. It is also widely used as an indicator mineral in critical mineral exploration. Where tourmaline can be shown to have formed during copper mineralization, determining its age can help pinpoint when the ore deposit formed.

In the September issue of Geology, Emily Mixon of the University of Wisconsin–Madison, Henry of LSU, Brian Jicha of the University of Wisconsin–Madison and Christopher Beckett-Brown of the Ontario Geological Survey report ages for tourmaline associated with copper mineralization at sites in Yukon, Canada. One of these sites, the Casino deposit, is a major porphyry copper-gold-molybdenum system. The team measured argon isotope ratios directly in tourmaline to determine the timing of mineralization. The results indicate that copper mineralization occurred approximately 75 million years ago.

This first-of-its-kind study demonstrates that dating tourmaline can accurately establish the timing of copper ore formation. The approach offers a potentially powerful new tool for understanding how mineral deposits evolve and for guiding critical-mineral exploration.