@misc{indiciae6a76cbe14d77,
  title = {Porphyry gold; a supplement to U.S. Geological Survey bulletin 1693},
  author = {J. J. Rytuba and D. P. Cox},
  year = {1991},
  doi = {10.3133/ofr91116},
  url = {https://pubs.usgs.gov/publication/ofr91116},
  note = {Source identifier: ofr91116}
}