1. 1. HM Mikami . Industrial minerals and rocks , 5th edn. , Vol. 1 . AIME, New York, 1983 : 567 -584 .
2. 2. BA Kennedy . Surface mining , 2nd edn , Society for Mining Metallurgy and Exploration, Maryland, 1990 : 126 -130 .
3. 5. WB Lauder, and WH Hartford . US Patent No. 3,095,266, 1963 .