Compressor mining originated in the mid-1990s in Camarines Norte, an impoverished coastal province about 200 miles southeast of Manila.
Divers dig down as far as 60 feet while breathing through a tube connected to a homemade compressor, typically fashioned from a San Miguel beer keg. They dig in rice paddies, rivers, and bays, and stay underground for hours at a time. Their job is to fill bucket after bucket with soil for a fellow miner to haul up to the surface. Some miners wear a diving mask; many just keep their eyes shut.
The job is hazardous, the returns are paltry, and they say their work is illegal. But that doesn't stop the miners - mostly adults and some children - from diving into the mud to find gold.
"We have no choice," said Rafael Ramorez, 16, who dropped out of high school in his freshman year to work as a miner. "There is no other job."
Rafael spoke as his cousin Jonathon Ramorez, 12, stood waist-deep in the murky bay with a wide wooden pan he uses to separate gold from sediment. In his teeth, he held a plastic bag containing a small lump of mercury and gold, the product of the crew's work for the day.
Jonathon, Rafael, and Brian are among a million children worldwide who work in the hazardous occupation of mining, according to an estimate by the International Labor Organization, a United Nations agency.
The Philippines banned compressor mining in 2012. The crews operate outside the law by employing children and using highly toxic mercury. At Mambulao Bay, miners say they stay in business by paying police agencies the equivalent of $11 a month for each worker. Local officials say the miners are issued permits.
More than 400 miners work from 40 rafts of wood and bamboo anchored on the bay near the village of Santa Milagrosa. Typhoon Haiyan, which ripped across the Philippines in November and left thousands dead, had little effect on these miners. The center of the storm passed more than 260 miles south, halting the mining for only a day.
Most of the miners' rafts have a blue plastic tarp stretched overhead to block the tropical sun, giving the place the look of a floating encampment. The workers get around in wooden canoes, which double as tubs for breaking up the sediment.
Inspired by fishermen
Boys and girls as young as 10 work alongside adults in crews of about a dozen. Children usually do the less strenuous jobs, such as panning for gold while standing for hours in the filthy water.
The $5 the miners make in a typical day is more than they could earn at other unskilled jobs in the impoverished region - if they could find jobs.
Compressor mining was inspired by Filipino fishermen who use compressors to breathe underwater while catching reef fish. The beer-keg compressor is connected to a small motor designed for pumping well water. Miners loop the air hose around their shoulders and hold the end in their teeth.
At the surface, the tunnel opening is small - barely three feet square. After the divers descend into the hole, it is impossible for them to see. Operating by feel, they shovel dirt into a rice bag.
Once they reach a layer of dirt where there might be gold, they dig sideways, heightening the danger of a collapse.
Compressor mining poses a range of health risks, especially to children who dive.
When a diver is underwater, nitrogen bubbles can form in the bloodstream and travel to the brain and lungs, causing many small patches of damage. The problem is worsened if the compressor motor unexpectedly stops and the diver rushes to the surface for air.
Diesel fumes, carbon monoxide, and other pollutants can enter the hose and foul the air the divers breathe, sometimes with deadly effect. Miners on Mambulao Bay say the man who thought up compressor mining died from inhaling oil through his hose.
Divers can suffer skin infections or maladies such as leptospirosis from immersion in the dirty water, which often is tainted with animal waste and teeming with bacteria, said Julie Hall, World Health Organization representative to the Philippines.
"For somebody to be spending a lot of time breathing poor-quality air, under pressure, under the water, and exposed to all of these bacteria and other bugs in that dirty water, this clearly poses a significant health risk," Hall said during an interview at her Manila office. "And particularly for young people, if they are doing this repeatedly, it is likely to affect their development."
Compounding the risk to miners, the mercury they use to extract gold from the sediment is highly toxic and is known to cause tremors, memory loss, and brain damage, among other symptoms.
"You can't reverse mercury poisoning," said Richard Gutierrez, executive director of Ban Toxics, an environmental group seeking to end mercury use in the Philippines. "Brain cells are destroyed and can't be replaced."
Divers say their greatest fear is a tunnel cave-in. They tell of two men who were crushed that way.
The biggest disaster was in November 2012 in Paracale, a coastal town east of Mambulao Bay where miners had dug about 100 shafts on the beach and offshore. Some tunnels collapsed, and seawater rushed in. Three bodies were recovered, but some accounts suggest the toll was higher.
Government investigators concluded a miner working illegally had used explosives and caused the collapse. The deaths drew national attention, and authorities banned all mining at Paracale. But compressor mining continues elsewhere.
About five miles inland from central Paracale, in the farming village of Tawig, an extended family of 16 miners has set up operations in the waterlogged soil between a rice paddy and the Bacung River. The crew includes cousins Edlyn Ortiz, 12, and Elias Delima, 15.
The group has been mining for several days in a grove of nipa, a small, sturdy palm common to riverbanks. The ground is pockmarked with holes brimming with brown water. They look like puddles but are as deep as 40 feet.
Two divers send up buckets of dirt. Family members shovel the dirt into a tub, break it up with their feet, run it through a sluice box, and pan the sediment for gold dust.
A family business
Five-year-old Ernie Delima plays in the mud and helps by hauling water and moving dirt.
Older brother Elias, who left school in fourth grade to work in the family business, said he occasionally takes the hose in his teeth and dives. "I just want to go in and help," he said.
Still, he said, the muddy tunnel is unnerving.
"I feel scared," he said. "I am afraid because maybe the tunnel will collapse. It is very hard to breathe."
The diver gets a double share of the earnings, and Elias said he once earned the equivalent of about $23 in a day. But, he concedes, "I'd like to find another job."
Dindo Leche, 20, married into the family of miners. He said he began diving at 14. "I had no choice," he said. "We needed to support the family."
He said he was afraid at first. His longest stay underground was six hours.
"I don't feel anything inside the hole, just cold," he said, adding: "I feel a little afraid that it will collapse. A lot of the time, the soil collapses."
At day's end, Leche takes the gold-laden sediment they have all collected, mixes it with mercury, and swirls it in a wooden pan. Squeezing out the excess mercury through a piece of nylon, he ends up with a lump of metal smaller than a wad of chewed gum. Later, he will burn it with a blowtorch to vaporize the mercury.
It is one last hazard the family faces in a long day of mining.
Journalists Larry C. Price and Sol Vanzi, in Manila, contributed to this article.
This story was produced by the Center for Investigative Reporting ( www.cironline.org) in collaboration with the Pulitzer Center on Crisis Reporting in Washington ( www.pulitzercenter.org). Price, an Inquirer photographer from 1983 to 1989, is documenting child labor in developing countries as part of a long-term project funded by grants from the Pulitzer Center. Price has won two Pulitzer Prizes, the second for his Inquirer photographs from Angola and El Salvador.