The Genesis book/project started in 2004. As to how much is from digital, this might help:
"Up until about 2009 Sebastião worked exclusively with film, it got to a point where his assistants would be carrying 50+lb bags of film while travelling, and in a post-9/11 world, TSA screenings had begun to make this rather difficult for Salgado. He recalls a friend suggesting he try switching to digital, which he was reluctant to do, but he did ultimately embrace the new technology. His process involves digital capture of his images which are then printed onto contact sheets, and then, just like he would do in a traditional darkroom setting, they are processed digitally to mimic the film stock he had mastered so well (Kodak Tri-X) and finally sent to a lab which converts the digital image into a medium format film negative and prints them using a traditional darkroom. (Man; Evening with Salgado) To my knowledge, this process is not widely used and is almost unique to him."
This is from