THE national tourism agency calls the Mexican mountain town of Angangueo a “Pueblo Mágico.” If so, it is a dark magic.

In recent years, Angangueo’s 5,000 inhabitants have been cursed by calamities natural and manufactured. Snowstorms, mudslides and flash floods have terrorized the town. Hulking piles of mine tailings line the main road, barren reminders of the silver, gold and copper mining that petered out a quarter-century ago after defining the community for 200 years.

Even the monarch butterflies that are the focus of the “magic town” tourism campaign are suffering. Millions still roost on nearby mountains, a wintertime spectacle that attracts the visitors from “El Norte” who are the town’s economic lifeline. But the overwintering population of monarchs has fallen by almost two-thirds over the past dozen years, and this year’s better-than-usual aggregation was abruptly devastated in March by another freak snowstorm, the worst in years.

Now those monarchs are facing another potential calamity. One of ’s largest corporations is close to winning government approval to reopen a sprawling mine in Angangueo, right next to the most important winter habitat of North America’s most iconic insect. In a region where butterfly tourism isn’t doing much to ease pervasive poverty, the mining proposal has plenty of local support, even as it alarms biologists.

I spent a few days recently in Angangueo, about 75 miles west of Mexico City, doing research for a book about monarchs. Many people know the outlines of their plight: Monarchs are under extreme pressure from , deforestation in Mexico and the elimination of milkweed — almost the only food monarch caterpillars will eat — from Midwestern farm fields (hastened by the use of genetically modified corn and soybeans).

At risk is one of the most wondrous migrations on earth, where tens of millions of monarchs, each weighing only about as much as a paper clip, flutter south from Canada and the northern United States for as far as 3,000 miles. Catching rides on thermal air currents, they cross mountains and deserts, somehow arriving at the same forested mountainsides in south-central Mexico where their great-great-grandparents spent the previous winter.

But even amid so much public concern about monarchs, very few people are aware that Mexico’s largest mining conglomerate, Grupo México, wants to use a legal loophole to revive mining in the Monarch Butterfly Biosphere Reserve, a protected region where most industrial activity is supposed to be banned, said Felipe Martínez Meza, the acting director of the reserve.

Amazingly, the Mexican environmental authorities and a global conservation group that has an active program in the reserve have said almost nothing publicly about the proposal, which local scientists say poses a clear threat to the beleaguered butterflies. The plan also raises difficult questions about what’s best for the long suffering people of Angangueo, where jobs are so scarce that on some mornings the mere rumor that the shuttered mine might need a few temporary laborers generates a stampede to the mine’s front gate — all for the privilege of earning about $8 for a long shift pumping water out of cramped, dank tunnels.

Grupo México has already gotten most of the permits it needs to reopen the mine, but is still negotiating with the Mexican government over an ore-processing plant it needs. The company argues that it should be allowed to go forward because the mine never technically closed, and thus predates the creation of the biosphere reserve and its accompanying restrictions, Mr. Martínez said.

The proposal is avidly supported by Angangueo’s local government and most of its residents, who would benefit most directly from the low-wage jobs the mine would bring — at first a few hundred jobs, and ultimately perhaps several thousand.

Elsewhere in the region, however, many are wary. Silvestre Chávez Sánchez, the elected leader of another community near the monarch reserve, told me, “We know that no mining project in Mexico has ever brought lasting development for local people, but has always had problems associated with natural resource destruction.”

Grupo México’s track record is not encouraging. In 2014, a huge copper mine it operates in the northern state of Sonora was the site of one of the worst environmental disasters in Mexican history. About 10 million gallons of toxic copper sulfate acid breached a dam at the mine and spilled into two rivers that supply water to more than 24,000 people.

In Angangueo, Grupo México wants to process up to 1,200 tons of ore daily, and says it will do so in an environmentally sensitive way, said María Isabel Ramírez, a geographer who studies monarchs at the National Autonomous University of Mexico in Morelia. But the company has been frustratingly vague on some key issues, including how much water and acid will be needed to extract copper, zinc, lead, silver and gold from all that ore, and where the resulting waste will be dumped. Nor has Grupo México fully explained where and how it plans to expand the old tunnel network that snakes beneath nearby mountains — the same mountains where monarchs roost every winter.

Ms. Ramírez worries that the huge volumes of water used by the mine will dry up mountain springs and threaten the viability of the oyamel fir trees where the butterflies roost. “We have many concerns about it,” she said, noting that the firs are already stressed by climate change and illegal logging, which persists despite years of efforts to stop it.

You might think that the World Wildlife Fund for Nature, which operates an active program within the reserve, would be leading the opposition. But the organization, which actively seeks corporate contributions, has been quiet so far, though the W.W.F.’s chief local representative gave me a blunt assessment. “My professional and personal position, W.W.F. aside, is that opening up the mine could have terrible implications ecologically and economically,” said Eduardo Rendón-Salinas, who heads W.W.F.-Mexico’s Monarch Butterfly Program.

The W.W.F. and other nonprofits, with some support from the Mexican government, are trying to develop alternate economic models for the region based on ecotourism, sustainable farming and logging, and native crafts, but funding has been limited and progress slow in a region where poverty is all but inescapable. The mine proposal, by contrast, offers a faster route — but to where, exactly? As Mr. Martínez told me: “It will provide work for a small group of people, but the cost may not be worth the benefit. We feel strongly that something like this may be catastrophic for the reserve.”

In Angangueo, memories are still fresh from the last catastrophe: the floods of 2010, when three days of heavy rain and hail produced mud slides and caused the local river to overrun its banks. After hours of gradual flooding, something suddenly gave way — no one is sure what — and sent a wall of water hurtling down the town’s main street. At least 30 people were killed, and hundreds were left homeless. Some locals blamed the honeycomb of mine tunnels above the town, but an official investigation absolved the mine and blamed the heavy rain — just another calamity for a community that has endured so much for so long.