Climate helps drive the erosion process that exposes economically valuable copper deposits and shapes the pattern of their global distribution, according to a new study from researchers at the University of Idaho and the University of Michigan. Nearly three-quarters of the world's copper production comes from large deposits that form about 2 kilometers (1.2 miles) beneath Earth's surface, known as porphyry copper deposits. Over the course of millions to tens of millions of years, they are exposed by erosion and can then be mined.

Brian Yanites of the University of Idaho and Stephen Kesler of the University of Michigan examined data on the age and number of exposed porphyry copper deposits worldwide. When they compared those data to the climate in each region, they noticed a pattern: The youngest deposits are in areas of high rainfall, such as the tropics, where erosion was rapid. Deposits are older in dry areas that have low rates of erosion.

Then they counted the number of deposits in the different regions and found something striking. Where erosion is rapid, there were relatively few deposits, but locations with low erosion rates contain lots of deposits. Such regions include the Atacama Desert in the Andes Mountains and the American Southwest -- both places where porphyry copper mining is important to the economy.

By using porphyry copper deposits as a marker of a specific depth (2 kilometers) beneath Earth's surface, Yanites and Kesler were able to determine how rapidly the overlying crust had been eroded. The results showed that climate-driven erosion influenced the age and abundance of exposed copper porphyry deposits around the world.

Their findings are scheduled for online publication May 11 in Nature Geoscience.