@misc{indiciae459846912488,
  title = {A simplified economic filter for open-pit mining and heap-leach recovery of copper in the United States},
  author = {Keith R. Long and Donald A. Singer},
  year = {2001},
  doi = {10.3133/ofr01218},
  url = {https://pubs.usgs.gov/publication/ofr01218},
  note = {Source identifier: ofr01218}
}