How an Electron Microprobe Helps Find Minerals (and Makes Pretty Pictures!)

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Today’s high-end electronics increasingly rely on mineral commodities...and research into those mineral commodities is increasingly using high-end electronics too!

Image shows a scan of a grain of pyrite rimmed with stibnite, with varying levels of arsenic shown in a color gradient.
Image shows a scan of a grain of pyrite rimmed with stibnite, with varying levels of arsenic shown in a color gradient. Image produced by Erin Marsh, USGS. (Public domain.)

The image above may look like one of those brilliant NASA portraits of a far-away nebula, but it’s actually the opposite in terms of scale. This is an image of a single grain of pyrite, also known as Fool’s Gold, rimmed with stibnite.

USGS scientists Erin Marsh, David Adams, and Heather Lowers created this image using a tool called an electron microprobe. As its name implies, it probes things using a beam of electrons, which interact with the sample and provide the instrument with information regarding sample chemistry. In this case, the scientists were interested in the amounts of arsenic in the pyrite grain. White and red indicate high amounts, blue and purple indicate low amounts.

Marsh and her colleagues are trying to learn more about how the Yellow Pine deposit of central Idaho formed. The Yellow Pine deposit has people’s attention, because it’s rich in stibnite, an important source of the critical element antimony, as well as gold, silver, and tungsten. The image, also known as an electron microprobe elemental map, will help Marsh by shedding light on the conditions that led to the Yellow Pine deposit’s formation.

That information will be important both in the development of the Yellow Pine deposit, but also in finding other deposits rich in important mineral resources. Many of the minerals critical to the U.S. economy are not as well-understood, requiring more research to understand how they form, where they occur, and how they can be produced.

In fact, although antimony is critical for lead storage batteries and fire retardants, the United States imports more than 70 percent of the antimony it uses, primarily from China. As China reduces production, understanding the origins of the Yellow Pine deposit, the largest known antimony deposit in the United States, is critical for future exploration for undiscovered deposits of this type.

So, although maps like this one are quite beautiful, they are also proof of how USGS research geologists like Erin Marsh and her colleagues deploy cutting-edge research to help meet the critical mineral needs for the Nation’s economy and security.