Jorge Galleguillos, a veteran miner at the San José Mine in Chile’s Atacama Desert, was working 2,000 feet below the Earth’s surface when he saw what he thought was a butterfly. His co-worker, Franklin Lobos, disagreed.

“It was white rock,” he said, referring to the “translucent, milky quartz that glimmers when it catches the light.”

It was also a harbinger.

Because as they drove not 65 feet (20 meters) past that spot, that one falling rock became “a massive explosion,” and the area around them “filled with dust.”

Unknown to them, this was but one part of an incredible collapse occurring throughout the mine. The men, along with 31 others, were about to undergo an ordeal the likes of which few suffer, and fewer survive. The next time they saw daylight, they would be global heroes, and their lives would never be same.

The collapse of the San José Mine on Aug. 5, 2010, became international news, as 33 men were trapped underground for 69 days, battling starvation and hopelessness as the world waited anxiously for news of their rescue.

Héctor Tobar, author of the new book “Deep Down Dark: The Untold Stories of 33 Men Buried in a Chilean Mine, and the Miracle That Set Them Free” (Farrar, Straus and Giroux), was the only journalist given access to the men and their families, and returns with a riveting account of a remarkable disaster.

Translation: ‘We’re f—ed’

The San José Mine was more than 100 years old, and a century of “digging and blasting” had all but worn away its internal structure. The mine was known for “primitive working conditions and perfunctory safety practices,” including escape tunnels that were “useless in an emergency because they lack the ladders necessary for the miners to use them.”

On the afternoon of the 5th, the miners heard the explosion, and were enveloped in dust, as the ramps leading to the surface collapsed.

It sounded like “a massive skyscraper was crashing down behind them.”

“A single block of diorite, as tall as a 45-story building, has broken off from the rest of the mountain and is falling through the layers of the mine … causing a chain reaction as the mountain above it collapses, too.” This piece, the men would later learn, was about 550 feet tall and weighed 770,000 tons — “twice the weight of the Empire State Building.”

In the ensuing quake, several men were “knocked off their feet by a blast wave” as “the walls began to shake and stones the size of oranges [began] falling around them.”

When the quaking was done, the men found themselves trapped and one miner uttered, “Estamos cagados.” “Loose translation,” writes Tobar, “We’re f—ed.”

A quick inspection showed that “all the connections to the surface have been cut: the electricity, the intercom system, the flow of water and compressed air.”

The men, not yet knowing the extent or cause of the devastation and believing they’d be rescued in a few hours or days at most, retreated to the Refuge, a classroom-size, steel-reinforced safe room that holds provisions meant to feed 25 men for two days.

The inventory of the food included “1 can of salmon, 1 can of peaches, 1 can of peas, 18 cans of tuna, 24 liters of condensed milk (8 of which are spoiled), 93 packages of cookies,” not counting a few that some of the men ate on the sly, “and some expired medicines.”

There were also “a mere 10 bottles of water,” although there were thousands of liters keeping the engines of their machinery cool. While dirty, oily and occasionally used for bathing, it was drinkable enough to keep them alive.

Smell of the grave

Food rationing, they soon learned, would be harsh, since, “If each man eats one or two cookies and a spoonful of tuna each day, the provisions might stretch out a week.”

A miner named Mario Sepúlveda, one of the leaders throughout the ordeal, would line up “37 plastic cups in rows and spoon one teaspoon of canned fish into each cup, then pour in some water, making a broth. He [then passed] out two cookies to each man. ‘Enjoy your meal,’ he says. ‘This is delicious stuff. Make it last.’ That single meal, at noon, likely contains fewer than 300 calories and is meant to hold them all until the next noon.”

They’ll soon broaden the menu to include soup they’ll cook, using the industrial water, “in a truck’s air filter from a single can of tuna, with . . . no salt and only a few peas and some motor oil for flavoring.”

In time, the rumbling of their collective stomachs will grow so loud that, in the echo of the mine, some will mistake it for the sound of the mountain collapsing.

Most of the men slept in the Refuge, where, after several days, “the fetid scent begins to gather and cook, transforming the air into a stew of body odor,” leading one miner to later say, “I’ve smelled corpses before, and after a while, it smelled worse than that.”

As days pass, a society develops. The men hold daily prayer meetings. They play checkers using a board made from cardboard, and dominoes one miner created by “pulling apart and cutting up the white plastic frame of the reflective traffic-hazard triangle in his truck.” They occasionally think they hear drilling, but no rescue appears.

Sometimes, the humor turns gallows, as when one miner tells the sole Bolivian in the group, “You better hope they come for us. Because if they don’t, since you’re Bolivian, you’ll be the first one we’re going to eat.”

Some men (including, reportedly, the joke’s subject) appreciated the levity. Others could not, realizing that if one of them died, they might have to consider such action.

Slice of peach for 33

Above ground, meanwhile, several potential rescuers descended 2.8 miles (4.5 kilometers) into the mine, only to be stopped by the monolith. Seeing it, one veteran miner wept, knowing that his colleagues were doomed.

Officials also discovered that the building-size slab was still shifting, making “a new collapse possible at any moment.” Mining and drilling experts sought to figure out where they could drill without collapsing the already weakened mountain. In time, drilling experts from around the world would join the effort.

Just outside the mine entrance, the miners’ families set up a camp — calling it Camp Esperanza, or “Hope” — where they could stay while awaiting word of their loved ones and keeping pressure on government officials.

For some of the miners, this led to complications. Yonni Barrios, a “paunchy, soft-spoken Romeo,” lived with his girlfriend, except when they were fighting. Then, he stayed with his wife, who lived less than a block away. Both women planted their flags at the camp, and their battle for Barrios’ heart went public. (The girlfriend won.)

The story quickly went global, and the Chilean media put the miners’ chances for survival at “less than 2%.”

After two weeks underground, many of the miners were having trouble walking, and their ribs began sticking through their skin. The sound of daily drilling was by now unmistakable, but the miners had no idea how long rescue would take. They would eventually hear over a dozen drills fail to find their target, disappointments that came to feel like “a second death.”

By now, there was just enough food to give each man one cookie every two days. In time, they stretched that out to three days to make the food last longer. At one point, “a single slice of peach, about the size of a thumb” was found, and meticulously divided into 33 slivers “about the size of a fingernail.”

Another time, one of the men experienced temporary blindness, “the first signs of a common side effect of hunger, caused by vitamin-A deficiency.”

On day 17, a drill that had been growing louder suddenly stopped, the sound replaced by “a whistle of escaping air” — one of the drills had broken through. The miners ran to see and began banging on it furiously with wrenches “like little kids hitting a piñata.”

The men, “laughing and cheering,” celebrated by “passing around a plastic bottle filled with dirty water as if it were champagne.”

They tied notes to the drill bit, informing those on the surface that all 33 of them were still alive. After 17 days of hell, the men finally had hope. But the end of their ordeal was still far away.

Animals in a cage

As food, clean water, a phone line and other supplies were passed down the 4.5-inch hole, the men’s joy was dashed when they learned that getting them to the surface, including finding a way to reach them and bring them up that didn’t risk collapsing the already fragile mine, could take as long as four months.

“If they are indeed stuck until Christmas,” writes Tobar, “they will have been trapped underground twice as long as any human being in history.”

While the men managed to support each other during their times of dire starvation, there was a greater danger in strong, healthy men dealing with this collective frustration in the pits of hell, and their confrontations grew increasingly heated. With their fortunes in the hands of the mystery people above, one miner wrote, “Now I know how an animal in captivity feels, always depending on a human hand to feed it.”

Above ground, meanwhile, they were becoming international celebrities, as media around the world interviewed their families, and a Chilean millionaire began an effort to raise funds ensuring that all the men were millionaires by the time they reached the surface. (While they all received gifts from many donors, their fortunes never became that grand.)

There was also trouble brewing regarding press coverage of individual miners, including the braggings of Sepúlveda, who mentioned in a letter to his family that he was “the absolute leader,” causing bitterness among the men. Sepúlveda also raised suspicions by joking about eating each other, jokes that, as the men’s strength increased, took on a violent edge, leading some to fear for their safety.

While the surreal nature of knowing they were rich and famous while still trapped underground messed with their heads, they did keep it together in one crucial area, making a pact that the rights to their tale would be owned by all of them, in 33 equal parts. This pact would lead to some disagreements down the road, but ultimately it would hold.

The rescue couldn’t take place through the hole already drilled, but required a new hole 28 inches in diameter. The problems faced in drilling the first hole were now multiplied, since this hole needed to be wide enough for the men to fit through.

In time, many nations would send help, including the US, with a special 26,000-pound drill coming from a company in Pennsylvania, and a top American driller participating in the final rescue effort. It was agreed that three separate drilling efforts would proceed simultaneously, in an effort to rescue the men as quickly as possible.

Finally, daylight

On Sept. 17, one of the drills broke through to the men via a 17-inch hole, and that was widened over the next several weeks to the required 28 inches. From there, a few days were needed to remove the drill bit from the hole, and then a rescuer was sent down in a tube, dubbed the Fenix, built specially for this purpose.

The first man, Florencio Avalos, began his ascent a little before midnight on Oct. 12. He reached the top around 30 minutes later, met by his family, news cameras from around the world, and the president and first lady of Chile.

Around 24 hours later, Luis Urzua became the last man to hit the surface. As he did, the 69-day nightmare of the San José Mine officially reached its end.

Many of the miners struggled to readjust, feeling withdrawn and suffering flashbacks and nightmares. After darkness fell, Barrios, for one, would sometimes wake “in the middle of the night and put on his old helmet,” just sitting there with his helmet lamp on, suddenly screaming and punching the couch cushions.

For several, such as Alex Vega, the cure was surprising. After two years of “emotional suffering” including “nightmares about being buried alive,” Vega realized he needed to “confront this fear” head on — which for him meant returning to the mines.

Every day for a week, he drove 980 feet (300 meters) deep, “wandering about the stone passageways, and then back up and out of those dank caverns and into the sunshine.”

His nightmares never returned.