Inspiration for the song is said to be from Chan’s visit to South Africa where she met children orphaned by the diamond trade. However, she didn’t write the song until later. From Wikipedia (emphasis mine):
Marshall wrote “Cross Bones Style,” along with five other songs from Moon Pix, one night in the fall of 1997, after awaking from a hallucinatory nightmare while alone in the South Carolina farmhouse she shared with then-boyfriend, Bill Callahan. “My nightmare was surrounding my house like a tornado,” she explained. “So I just ran and got my guitar because I was trying to distract myself. I had to turn on the lights and sing to God. I got a tape recorder and recorded the next sixty minutes. And I played these long changes, into six different songs. That’s where I got the record.”
Oh to be struck by such a muse.