LEAD | For the past 17 years, shovels, safety goggles, tramway cars and other remains of the defunct Homestake gold mine lingered in a closed-off tunnel under the city of Lead, growing brownish-orange and crusty with rust.
Now the tunnel is alive with activity again, thanks to preparations for an internationally coordinated science experiment that will be conducted deep underground.
To make room for the experiment, several expansive caverns will be excavated nearly a mile deep in the former mine.
The excavated rock will be hauled up a shaft, crushed into smaller pieces, and dumped onto a conveyor belt in the tunnel, which is 200 feet underground at its deepest point.
The conveyor will run 2,000 feet through the old tunnel, and then poke out of a hillside and run nearly another 2,000 feet through an above-ground tube that will pass over U.S. Highway 85 in Lead. At the edge of the half-mile-wide historical mining pit known as the Open Cut, the crushed rock will tumble out of the conveyor into the pit’s 1,250-foot depths.
About 800,000 tons of rock will be excavated, which sounds like a lot, except when compared to the 170 million tons that was excavated to create the Open Cut. David Vardiman, a project engineer at the site, said the visual impact of the new pile of rocks in the massive pit will be negligible.
“You won’t even hardly notice any difference whatsoever,” Vardiman said. “As a matter of fact, you’ll have to get pretty high on the high wall to even see that pile at the bottom.”
A contractor, Kiewit-Alberici Joint Venture, has been rehabilitating the old tramway tunnel since April and is nearly finished with the work, which has included pouring a concrete floor and stabilizing the rock walls. The activity at the tunnel’s opening — just south of Lead’s Gold Run Park — is a visible sign of progress after several years of less-visible work toward the eventual installation of the Deep Underground Neutrino Experiment (known by the acronym “DUNE”).
While the rehabilitation of the tunnel wraps up this fall, the conveyor system will be fabricated for installation next year.
After that, drilling and blasting to excavate the huge caverns underground will commence at a depth of 4,850 feet in the mine. The excavation is expected to take about four years. Three caverns will be carved, the biggest being about two football fields long, 70 feet wide and 95 feet tall.
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During the excavation phase, the crushed rock tumbling out of the conveyor and into the Open Cut will be visible to the public from the nearby Sanford Homestake Lab Visitor Center. The conveyor will run only during weekdays, not during nights or weekends, and the design includes features to make the noise of the conveyor minimally noticeable to people nearby.
Construction is underway to convert an old tramway tunnel at the old Homestake Mine into a conveyor tunnel for the removal of excavated rock f…
The use of the old tunnel to transport crushed rock will mimic its historical purpose. The tunnel was created by miners who drilled and blasted into the hard rock under Lead during the 1930s. Gold-bearing ore was hauled up from the depths of the Homestake Mine, crushed, and dumped into tramway cars in the tunnel. The tram carried the crushed ore on railroad tracks through the tunnel to a mill in Lead, where the ore was processed to extract the gold.
The rock that will be excavated from the mine in future years will be from a geologic unit known as the “Poorman Formation,” for its lack of valuable minerals. Instead of producing gold, the excavation’s purpose is the creation of space for DUNE, which will study little-understood but abundant subatomic particles called neutrinos.
Installation of DUNE’s equipment will take several more years after the excavation. When the experiment begins, possibly around 2028, Fermilab in Chicago will shoot a beam of neutrinos through the earth toward a gargantuan set of liquid-argon containers that will be installed in the underground caverns at the old Homestake Mine (the caverns housing the experiment will be called the Long-Baseline Neutrino Facility, or LBNF), where the depth of the containers will protect them from cosmic rays and other kinds of interference. The argon will act as a neutrino detector, giving scientists their best-ever opportunity to gauge the mass of neutrinos, probe the role of neutrinos in the universe, and perhaps even detect neutrinos escaping an exploded star or black hole.
There is a lot of work to be done between now and then. A U.S. Department of Energy 2020 budget request to Congress cites a preliminary 2016 estimate saying that U.S. contributions to the LBNF/DUNE project could be up to $1.86 billion by the time it’s finished, with additional contributions expected from international partners. Congress is providing its share in phases, including up to $175 million for the project in a pending 2020 spending bill.
The project has brought heightened economic activity to Lead, which was a town on life support after the closing of the Homestake Mine in 2002. Roughly 200 people are now buzzing around the state-run Sanford Underground Research Facility — the overall name of the former Homestake complex — on any given day, including facility staff, employees of Fermilab helping to prepare for DUNE, construction workers, and scientists working on multiple underground experiments and projects other than DUNE that are already in progress or being installed.
Activity at the old mine has coincided with rising sales tax collections in Lead. Compared to the same month of 2018, Lead’s 2019 collections were up 23 percent in July and 20 percent in August, according to state sales-tax reports.
Patrick Weber is the head of the South Dakota Services Division for Chicago-based Fermilab, which is leading the DUNE project. Weber said the bustle of pre-excavation activity is a welcome sight in Lead, where the economy suffered greatly after Homestake’s closure and the colossal neutrino experiment has been a subject of long anticipation.
“To see those guys doing that work, to see these yellow trucks driving around town, that’s really encouraging and I think heartening to people that this is really happening,” Weber said.