In the coastal areas of the Philippines, much of the clay containing the gold ore is below the water table. This means most mining activity must take place under water. In modern times, successful mining involves cheating the sea with low-tech techniques borrowed from local fisherman.
They call the practice compressor mining. It's the most deadly gold extraction method on earth and is unique to this part of the Philippines. Compressor mining is considered illegal under Philippine law, but the law is largely ignored.
Miners work underwater, breathing through a slender tube attached to a compressor on the surface--hence the name. Fishermen breathed through tubes such as these for generations, but even in relatively shallow waters, the practice is extremely dangerous. Drownings, accidents and carbon monoxide poisoning from faulty compressors are common.