This summer, and through the fall, residents of Telluride have noticed a periodic buzz in the skies above town. That buzz was coming from helicopters sent out by the federal government to take a birds-eye look at the minerals below earth’s surface.

Tien Grauch — a research geophysicist with the US Geological Survey — says if you spotted one of these helicopters, you might’ve noticed it carried a sort of nose.

“It is a sensor that sticks out from the front of the helicopter like a big boom, or stinger. And at the end of the stinger is a magnetometer,” Grauch explains.

Different rocks in the subsurface affect the magnetic field in the atmosphere, “and this sensor looks at those subtle variations and from that we can — by doing a bunch of analysis — understand what rock types lie below the surface, and where they extend,” Grauch continues.

So from above, the helicopter reads magnetic variations in the earth below with that big bee stinger wand. But wait, says Grauch, there’s more: “the other instrument is inside the helicopter, and this is the second method. It’s called Gamma-Ray spectrometery. It’s a crystal pack inside the helicopter, and it’s detecting gamma rays.”

Gamma rays come wafting off rocks as they slowly decompose — losing little particles — isotopes and atoms and sending them floating off into the air. If this all sounds high tech? Grauch says it’s nothing new. “These methods have been around for quite a while, especially the magnetic method. It started up in the 1940s. The mining industry has been using these methods for that many years to help them explore for minerals,” Grauch says.

However, Grauch explains, in the mid 20th century when companies were monitoring Colorado for mining assets, they were flying at high elevations, which compromised the data.

“The closer you get to the ground the better resolution you have of what’s there,” says Grauch. “Because it was so long ago, people flew up high, so the data we have is not very good. So the big push with the Earth MRI Program is to get these big data sets. So we start with places that might have some critical resources, and look in a big region around these areas to try to focus our efforts.”

So, that search for critical mineral resources has brought the US Geological Survey to the Colorado mining belt, with its rich and documented history of mineral claims — and the potential for untapped resources.

Those critical minerals range from the metals vital to manufacturing computer chips, solar panels, issues of national security, and so on. Funds flowing from congress are supporting the survey, which someday aims to create an updated map of mineral resources across the US.

And, with exploration, comes mining. Depending on what they find, could Southwest Colorado and Telluride see a revival of its mining past? Grauch says the information once collected, will be made public. Then, she says,“it will be up to the private sector to decide what they might pursue in terms of mineral exploration.”

The skies have quieted above Telluride in recent weeks, and the survey work over Southwest Colorado has been completed. Next spring, the USGS will move on to flights farther north, in the Crested Butte area. It will be a couple years before final data is released, but says Grauch:

“I have seen some of the preliminary results from the area and there are some bigger features we haven't seen before which we’re seeing in a regional sense. I don't know what it means in terms of mineral potential, it’s just interesting we’re seeing geology that we hadn't seen before,” Grauch notes.

Interesting, indeed — perhaps for mining companies and certainly for Coloradans hearing the buzz of not-so distant helicopters.