@misc{indiciaef5025f6309c4,
  title = {A simplified economic filter for open-pit gold-silver mining in the United States},
  author = {Donald A. Singer and W. David Menzie and Keith R. Long},
  year = {1998},
  doi = {10.3133/ofr98207},
  url = {https://pubs.usgs.gov/publication/ofr98207},
  note = {Source identifier: ofr98207}
}