Mining for dark matter in Lead, South Dakota

 

Updated 6/17/13

In the 1870s, gold fever struck South Dakota's Black Hills. Mining camps like the infamous Deadwood sprung from the mud, supporting bustling trade in opium and liquor. The gold seams went deep, and hundreds of miners and their families settled into a stable and prosperous living in the nearby, larger town of Lead (pronounced "leed"). From 1879 until 2000, Homestake Mining Company carved 370 miles of tunnels as deep as 8,000 feet, creating one of the deepest mines in the country. But in 2000, the ore vein exhausted, Homestake shut down and Lead tumbled into decline.

Today, not miners but scientists don hard hats and neon-yellow vests and descend Homestake's mineshaft elevators to nearly a mile underground. They are drawn to the mine's extraordinary depth for a different reason: it provides a quiet environment for detecting faint but earth-penetrating signals from space. The experiments could give scientists insight into the fundamental workings of the universe. And they are breathing a new sense of purpose into Lead, which has struggled to redefine itself since Homestake left.

The Sanford Underground Research Facility is a collaboration between the State of South Dakota, the Department of Energy's Lawrence Berkeley National Laboratory and dozens of top research universities. After years of planning and construction, the lab opened last year, and scientists are readying their experiments.

For decades, physicists have pried into a realm of tiny, elusive particles millions of times smaller than atoms in order to understand the building blocks of the universe. Much of this research has made use of particle accelerators -- giant, underground magnetic tubes like the Large Hadron Collider in Switzerland -- to smash atoms together and observe the results. But another method involves observing particles hurling through space. On the surface of the earth, it's difficult to detect these particles because of the background noise of celestial and human-caused radiation. But deep underground, buffered by a mile-thick mass of earth, most of that background noise is absent, making places like Homestake prime real estate for research. Only a few such facilities exist in the world; one major one is in Italy.

One riddle the scientists are trying to resolve is the discord between their celestial observations and textbook theories of gravity. The discord suggests that the universe is hiding "dark matter," which hasn't been observed but is estimated to be five times more abundant than the stuff of galaxies. Scientists hypothesize that dark matter is made up of Weakly Interacting Massive Particles, or WIMPS. An experiment in the Sanford lab is designed to produce a flash of light when a cosmic particle hits it, and the intensity and pattern of the light can be used to infer whether or not the collision was caused by a WIMP.

LUX dark matter detector

Homestake has a history of this kind of experimentation. In the 1960s, Ray Davis became the first physicist to observe the sun's neutrinos -- another kind of tiny, penetrating particle. The mining company carved out a cavern for Davis to install his massive detector. Davis's work was famous in the physics community (he received the Nobel Prize in physics in 2002). So when Homestake announced the mine's closure in 2000, it took only two weeks for physicists to propose converting the mine into a laboratory.

Construction of Davis's neutrino experiment at Homestake mine, 1966.

Some of Lead's residents thought that the transition would be seamless, and were actually counting on the lab to save the town's economy. But figuring out who would own and operate the facility took time, and funding was tenuous. Meanwhile, the mine shafts were filling with groundwater. And the loss of mining jobs was so severe that Lead passed a special ordinance to deal with vacant and abandoned homes.

The state of South Dakota stepped in, and formed the South Dakota Science and Technology Authority in 2004 to handle the project. South Dakota had long tried to gain a foothold in science research, and Homestake's closure looked like a prime opportunity. Homestake donated the mine to South Dakota in 2006, and the state kicked in $40 million to start the retrofit. The lab's namesake benefactor, Denny Sanford, donated $70 million. The money has been used to refurbish mineshafts, excavate new areas and construct special rooms to clean and store scientific equipment.

"The Lab," as it's known in Lead, hasn't made up completely for the economic loss of the mine, but it's become a "very significant" part of the community, says Mike Stahl, Lead's city administrator. The influx of scientists and construction contractors has helped to prop up tax revenue. The lab employs about 130 people -- 70 of them former Homestake employees -- with an annual payroll of $8 million.

Meanwhile, Homestake crews are reclaiming parts of the old mine on the surface, dealing with tailings piles and open mine cuts. The memories of Lead's mining days linger on the landscape, but the town is reshaping itself, not just around the lab, but with hopes of attracting tourists and offering a family-friendly atmosphere to complement Deadwood's gambling scene. "Lead learned that the era of being a company town was over," writes Melissa Johnson, director of Lead's Chamber of Commerce, in The Western Planner, "and more importantly that it was a good thing."

Marshall Swearingen is a High Country News intern.

First image, courtesy City of Lead; second, third and fifth images, courtesy of Sanford Underground Research Facility; fourth image, Brookhaven National Lab.

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