@misc{indiciae676876445e7d,
  title = {A simplified economic filter for underground mining of massive sulfide deposits},
  author = {D.A. Singer and W. D. Menzie and Keith R. Long},
  year = {2000},
  doi = {10.3133/ofr00349},
  url = {https://pubs.usgs.gov/publication/ofr00349},
  note = {Source identifier: ofr00349}
}