Geologists, students search for former lead mines

ALTOONA >> Cold wind blew across a Tyrone Township farm field Saturday as a handful of geologists and Juniata College students gathered atop mysteriously bare patches of ground.

To the untrained eye, the patches might just look like the sites of a poor harvest.

But the geology students, led by Professor Ryan Mathur, see something else: the possible sites of long-abandoned lead mines, perhaps going back to the 1770s.

Now a county park and education site, Fort Roberdeau was built in 1778 to protect strategically important lead supplies in Sinking Valley.

Miners pulled the lead from the earth, then shipped it east toward the Susquehanna River, where it was turned into musket balls for the Continental Army.

“The question becomes, ‘Where are those lead mines?’” Mathur said.

George Pedlow, a retired geologist, had researched the old mine sites for a talk last year at the fort. But 18th-century mapmakers, lacking global positioning systems and precision equipment, often left the mine locations vague.

“Some maps just said ‘lead’ in all of Sinking Valley,” Mathur said.

He and his students — with help from Pedlow, geologist and Juniata College alumnus Jim Stuby and representatives from Fort Roberdeau — used electrical equipment Saturday to detect the locations of decades- or centuries-old mines on county-owned farmland near the fort.

The geologists stretched lengths of cable along the bare patches, then used an underground electrical charge to seek holes miners might have dug. The electrical readout would show points of greater or lesser resistance underground, possibly pointing to soilfilled gaps in the limestone.

There’s little doubt lead remains in the ground, Mathur said. Students could easily see galena, a mineral form of lead, in the surface rocks.

That’s how revolutionary-era miners would have detected it: Without advanced equipment, they simply had to look for lead ore in the soil and rocks and begin digging, he said.

The underground metal was likely responsible for the bare patches, which seem to have lingered in the farm field for decades, said Pedlow, who provided research for the work.

“The bare spots show up year after year after year at the exact same place,” he said. “What is here in the soil just doesn’t allow plants to grow.”

The students prepared days earlier by plotting out possible sites for the search. Displaying a map on her cellphone, geology student Tara Fowler of York pointed out spots where mineral evidence suggests old mines.

Using those clues, the researchers were set to spend Saturday moving from place to place, exploring each likely site before gathering the data for analysis.

If they find evidence of mines, archaeologists could one day follow up and search for physical remains. Miners often leave equipment behind, Mathur said, and researchers might find further evidence of the 18th-century settlement there.

Even if they find lead deposits or old holes, there’s no guarantee they will be traced to the revolution, said Karen Morrow, a historian and staff assistant at the fort. Another wave of lead mining followed in the 1800s, and miners sought zinc in the area a few decades ago.

Nevertheless, scientific evidence could be a step forward for Fort Roberdeau — long called “the lead mine fort” even as its namesake mines remain unidentified.

“We have always wondered where the original mines were,” Morrow said. “To pinpoint those mines has been a challenge.”