Equipped with rock picks and hand lenses, a team of geoscientists deployed to the Mojave Desert recently to investigate a tantalizing “fingerprint” detected by a NASA sensor. Their target: a cache of topaz hiding in plain sight.
The geologists weren’t searching for gem-grade treasure. Rather, the presence of topaz could hint at a more valuable deposit below of something known as porphyry copper.
One of the world’s primary sources of copper, these deposits are left behind when magma and hot water from deep underground course through Earth’s crust, chemically transforming the surrounding rock. This tends to occur where one tectonic plate dives below another, known as a subduction zone, such as the North American Cordillera, which stretches from the Canadian Rockies to western Mexico.
In addition to copper — the third most used metal in the world after steel and aluminum — the deposits can hold other critical minerals like molybdenum and tellurium, which are used in everything from steelmaking to solar panels. Finding the deposits isn’t easy. Geologists look for topaz because it forms under the same volcanic conditions.
For the team in the Mojave, the goal was to collect more evidence. That would require boots on the ground and a heavy bag of samples. The scientists who converged on the site included three experts from the U.S. Geological Survey (USGS) and Robert Green of NASA’s Jet Propulsion Laboratory in Southern California.
