@misc{indiciae503a67672bb6,
  title = {Revised grade and tonnage model of carbonatite deposits},
  author = {D.A. Singer},
  year = {1998},
  doi = {10.3133/ofr98235},
  url = {https://pubs.usgs.gov/publication/ofr98235},
  note = {Source identifier: ofr98235}
}