This sequence of images captures some of the work I have undertaken in underground mines across four continents.

Photographing underground mines is incredibly difficult. For starters, it's dangerous. It's usually very hot — the closer you get to the centre of the earth the hotter it gets. Lighting is tremendously difficult, particularly in artisanal underground mines where completely black is a better description than dark. Silicosis, lung cancer, rock falls, deadly gases, dodgy ladders, open voids and moving equipment are constant hazards. Add to that the potential for crushing accidents, regular blasts — some errant — and in the high mountains, altitude sickness and avalanche risk.

For many years my underground mining photos were ordinary and I wondered why clients continued to persist with me. But then in 2016, facing three weeks of ebola quarantine in West Africa, I made a sudden trip to Potosí in Bolivia instead. There, on one of the world's most dangerous mountains, I spent six weeks photographing the underground silver and tin miners of Cerro Rico. A place where some four to eight million people are said to have been killed since mining began in 1545.

Cerro Rico was the darkest, most inhospitable place you could possibly imagine. Even when I was there, some three to five miners a month were perishing in their quest for silver and tin. The mountain sits high on the Andes Altiplano at an altitude of 4,782 metres.

I said to a photographer friend in the US at the time that "the smell of death here is everywhere" — to which he replied "wouldn't it be great to photograph the smell of death." Which is what I then set about doing.

But first I had to learn how to photograph some of the most difficult underground mines in one of the most remote parts of the world.

For two weeks I struggled. I tried different techniques with flash but they were ultimately limited and could not accommodate the feeling I wanted to capture. Until one day my fixer, Helen — who was brilliant — showed me the work of a Swiss photographer, Jean-Claude Wicky, who had produced the most exquisite images of underground mining I had ever seen.

I sent him an email asking whether he might have time to share some of his techniques. To my surprise he wrote back saying yes — his techniques were hard earned and he owed me nothing. A few days later we spoke for about ninety minutes while he talked me through how he had made certain of the images in his book.

When I put down the phone I had a list of things to chase up. I spent a day or two away from the mine accumulating the gear — not always easy in remote Potosí. And then I got stuck in.

Over the following weeks I finally started to get some flow in my work. And some good images. The work was still very difficult and very dangerous but the images started to work.

Often I found myself deep inside the mountain, crawling through gaps of maybe fifty centimetres with camera gear in tow — forever hoping we would not succumb to rockfalls or other hazards. Or even the mountain collapsing, as 471 years of underground mining had turned it into something resembling Swiss cheese, constantly collapsing in on itself. Every day I woke wondering whether we would come home alive. Just as the miners had been doing every day for the past 471 years.

These images show the results of the techniques Jean-Claude was so generous to share with me. But it was not until five weeks later — when I reached out for a final conversation — that I learned he had passed away. A pioneer in his field. He had succumbed to lung cancer.

I felt very sad. But also deeply grateful. A person I had never met had been so generous with his time and hard-earned knowledge.

It is something I also hope to be able to do with what remains of my own time here on this planet.