@inproceedings{sgem2001paper,
  title = {ORIGIN OF SULFUR IN BALKAN COAL BASIN AND SOME RELATED ENVIRONMENTAL PROBLEMS},
  author = {Irena Kostova},
  booktitle = {1st International Scientific Conference - SGEM2001},
  year = {2001},
  pages = {41-50},
  publisher = {SGEM Scientific GeoConference},
  doi = {}
}