Each time I arrived in Hongjun village after a 12-hour journey by plane, bus, and motorbike, I took deep breaths of the crisp mountain air—as if that could clean out my Beijing-polluted lungs.

It did not take long for the irony to hit me. This alpine landscape in central China is home to hundreds—perhaps thousands—of men too sick to breathe normally.

View Images Photographer Sim Chi Yin has made portraits of more than 30 former gold miners suffering from silicosis. Pictured holding their chest x-rays, clockwise from top left: Song Dengfa, died 2013; He Quangui, diagnosed with silicosis in 2004; Wang Yiyin, died 2011; She Faxue, died 2012. ALL PHOTOGRAPHS BY SIM CHI YIN

Once farmers, these men left en masse in the late 1990s to work in gold mines—part of the army of migrant workers who powered China’s economic boom in recent decades. They dug deep into the mountains for treasures. Years later, they came back with the lung disease silicosis, and now wait in their homes for death.

View Images Former gold miner He Quangui at home in Shaanxi province, China. He is suffering from silicosis—an incurable, but preventable, lung disease that scars and hardens the lungs.

For years, I’ve been a regular visitor to one of those former gold miners: a man named He Quangui, who lives in an old earthen house with his wife, Mi Shixiu. Mr. He has been struggling with silicosis for over ten years—surviving longer than most in his area. He keeps a notebook to record the names of those who’ve succumbed to silicosis. Flipping through it, he tells me: “I’ve watched them die, one by one. I know one day it will happen to me too.”

This is the unseen cost of gold mining in China—the world’s top gold producer. In China, silicosis is considered a form of pneumoconiosis, which affects an estimated six million workers who toil in gold, coal, or silver mines or in stone-cutting factories. It’s the country’s most prevalent occupational disease.

View Images Mi Shixiu prepares an injection for He Quangui as a lung infection and fever persist into a fourth week. She is wife, confidante, and nurse to him. It turned out to be severe tuberculosis.

What the statistics can’t capture are the miners’ slow deaths. The men waste away, their lungs gradually scarring or becoming hardened from the dust they breathed years earlier. The disease is irreversible—a lung transplant is the only known cure—but is preventable with protective gear and ventilation while drilling. Mr. He says the type of mines he worked in lacked such safety measures.

In recent years, mining conditions have improved, but out here in hardscrabble rural China, most workers cannot track down mine owners to cover medical bills and don’t get treatment until it is too late. Most just give up as costs mount. Some commit suicide.

View Images Seen in 2012, four months after surgery on both lungs, He Quangui, jokes around with his wife, Mi Shixiu, while she plays the Chinese flute. They have been married 19 years.

I wanted to try to tell one deep, personal story, in the hope of showing what the disease does to a person and family in its final stages. Like most documentary photographers, I hope that Mr. He’s story might move people to action.

When I first met Mr. He, I thought I had come to document his slow death, but I soon realized I was shooting a love story. I watched him and his wife kid around like teenagers freshly in love—tactile and affectionate in a way I’ve rarely seen in Chinese couples. When he could still sing, I sat by them as they belted out their favorite songs, in hearty, loving duet. I watched her tend to his needs as he lay in bed fearing to do more than just breathe. He calls her Xiao Mi—“Little Rice”; she calls him Guazi—“Idiot.” Seeing them together, it’s easy to believe Mr. He when he says her love has kept him alive.

View Images When He Quangui is too sick to walk, his wife carries him. They have a very close relationship, and according to a relative, are “still like two teenagers who just fell in love.”

But he confided to me—out of her earshot—his multiple attempts and plans to kill himself, by electrocution (submerging his hands and electric wires in water), by drinking pesticides, and while he could still walk, by jumping into a nearby river.

“If you die in a work accident, it’s quick, short pain. If you get this disease, it’s like you can’t die and you can’t live,” he tells me. “If there was a medicine I could take that would make me not feel anything, I would take it, pay anything for it.”

View Images Collapsing a second time in the same day, Mr. He struggles to breathe, while his son, He Jingbo, fans him with a piece of cardboard. His wife and his father, He Decheng, hold him, crying. That night he tried to kill himself.

Through months of getting to know one another and after being by his side through a traumatic hospital stay, the He family granted me a rare bedside view of an ordinary Chinese family going through a long emotional crisis. I did what I could to document it. I took notes, recorded sound, and eventually turned on the video mode on my camera and made this film (top of page), trying to do justice to the story of the final years of this unusually articulate and musically talented miner who has become a friend.

Over the past three years, I have watched Mr. He, once a healthy 143 pounds, deteriorate to a mere 88 pounds. I witnessed his repeated collapses, and one suicide attempt in the middle of the night. He has said good-bye to me many times, and then miraculously fought off severe tuberculosis and other ailments, living through another winter—the season silicosis patients fear most.

View Images A shadow of his former self, He Quangui once weighed 143 pounds and is now a skeletal 88 pounds. It is tradition in rural China that a person die in their own home.

The wooden coffin he built for himself sits under a dusty plastic shroud in the attic. For five years, his wife has been preparing the hand-sewn cloth shoes, five shirts, and three pairs of trousers he will wear to his grave as dictated by custom. After one of his many collapses, I watched him whisper instructions in her ear: Buy thick white paper to line the coffin, do not spend too much money on religious rites or he will come back and haunt her, and wash his favorite faux leather jacket so he can wear it in death.

This project was supported by a grant from the Pulitzer Center on Crisis Reporting.

Sim Chi Yin is a photographer based in Beijing, and is a member of VII photo agency. She was a reporter and foreign correspondent for the Straits Times for nine years before quitting to shoot photos. She sometimes dreams in mute, black-and-white mode, but in real life is fascinated by color and light.