@misc{ Solr-6812363, title = {Statistical summary.}, editor = {United States. Bureau of Mines}, address = {Washington, D.C.}, publisher = {[U.S. Dept. of the Interior, Bureau of Mines]}, year = {1994}, note = {Description based on last issue; title from PDF caption (viewed Nov. 21, 2007).}, url = {https://purl.fdlp.gov/GPO/LPS88131} }