The Henderson Mine is in the heart of the Colorado Rockies. (Image: Flickr/Ed Ogle)
Just outside the small mountain town of Empire, Colorado, highway 40 begins its climb up and over Berthoud Pass, toward the ski resort promised land of Winter Park. But before the 11,300-foot summit and before the hotel billboards, a narrow road snakes off the highway and toward the Henderson Mine.
The understated sign and rows of pine trees mask what has been a massive extractive operation for decades. The Henderson mine is the continent’s largest producer of molybdenum, an important strengthening additive in steel alloys and a useful industrial catalyst. Over a billion pounds of the element have been recovered, but unlike similarly sized projects, there is no external tailings pile; instead, a 17 mile-conveyor belt takes waste material toward the town of Kremling.
The true scale of the mine only becomes apparent underground. Industrial machinery moves along the 330 miles of road, and geologists and miners pursue ore rich veins of rock while engineers keep the place from flooding with groundwater. As geologist John Spear puts it, “entering the mine is like going to a gigantic city that just happens to be 3000 feet below the surface.”
Spear is a Professor of civil and environmental engineering at the Colorado School of Mines in nearby Golden, an outsider not directly tied to the Henderson’s primary raison d’être. And yet he has spent a lot of time underground in the name of fundamental research, working to understand the distribution and roles of microorganisms that inhabit Earth’s interior, the intraterrestrials.
Reflecting on years of mine-based microbiological work at the International Society of Subsurface Microbiology conference, Spear showed that the human presence in the mine has pervasively altered the Henderson’s geochemical and geobiological reality. The lake at the bottom of the mine – where fluid from throughout the operation collects – contained abundant nitrate and nitrite chemicals, which Spear attributes to episodes of TNT blasting.
The anthropogenic impact on mine microbiology was also apparent when the team of scientists examined the array of species inhabiting the mine’s rock walls. At one collection site, 10% of the recovered organisms – a relatively large number for a site of moderate diversity – belonged to the Ascomycota fungal phylum, which is a common stowaway on human skin. The fungal prevalence in such a remote location was surprising, as microbiologists tend to focus on Bacteria and Archaea rather than the more complicated eukaryotic organisms. “When we look for life in the subsurface,” Spear cautioned, “we can’t forget about the Eukaryotes. They’re around, but we just don’t hear much about them.”
That said, a whopping 56% of the mine’s microbial life was made up of a previously undiscovered species Spear’s team labeled “Henderson Group 1.” Through a concerted program of sequencing and geochemical studies, the team is working to understand what this microbe could be doing in the mine, and how it has been so successful.
Much of Spear’s initial characterization came when the National Science Foundation was considering converting the Henderson Mine into the Deep Underground Science and Engineering Laboratory – an integrated subsurface facility for biology and physics experiments. The distinction ultimately went to the Homestake Mine in South Dakota, but the experience informed Spear’s view of the relationship between microbiologists and mine managers. “We need to help them understand their resource,” he urged, noting that researchers tend to attract suspicion and guarded cautiousness. “They think that our being there will expose a pollutant issue or bring more environmental regulations.”
“But really we’re after the same goal – we just want to understand what’s happening underground, and we have useful ways of figuring that out.”
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