Short interview with actress on the shoot:

“Salt and Fire,” set in South America, was a challenging production. “We were shooting for six weeks in Bolivia at 13,000 feet,” she says. Ferres spent six weeks preparing at a camp in Europe, where she slowly acclimatized to the conditions at that altitude. “Michael Shannon, Werner Herzog and me, we had no problems. But a lot of the crew members were bleeding, fainting, couldn’t see,” she recalls.

http://variety.com/2015/film/global/veronica-ferres-pay-the-ghost-salt-and-fire-1201611907/#respond