@misc{indiciae82a27e5726f3,
  title = {Grade and Tonnage Relationships Among Copper Deposits},
  author = {D.A. Singer and Dennis P. Cox and Lawrence J. Drew},
  year = {1975},
  doi = {10.3133/pp907a},
  url = {https://pubs.usgs.gov/publication/pp907A},
  note = {Source identifier: pp907A}
}