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Arizona is known as the Copper State. One listener wanted to know where all of that copper came from. It turns out it all started with a bang.
When certain stars explode, they create copper and other heavy elements and scatter them into space, where they later combine to form planets.
Copper is fairly abundant in Earth's crust; what sets Arizona apart is its wealth of mineable copper, which it owes to a copper-rich granite formed in ancient volcanoes.
That copper either had lingered there since the Arizona crust formed around 1.7 billion years ago, or had arrived when the Pacific tectonic plate subducted underneath North America 50-80 million years ago.
Water weathering removed the volcanoes and exposed the copper minerals to the surface, but it also enriched deposits by leaching copper and redepositing it in more concentrated forms.
"Many of many of the deposits in Arizona would not have been able to be mined easily if they didn't have this upper level of this enriched copper," said Stephen Reynolds, a professor in the School of Earth and Space Exploration at Arizona State University.
Arizona produced nearly 830,000 metric tons of copper in 2018 according to the Arizona Geological Survey.
