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2. A.M. Bateman:Economic Mineral Deposits, John Wiley and Sons, New York, NY, 1955, pp. 274–89.
3. P.J. McGauley and E.S. Roberts: U.S. Patent No. 2,568,963, Sept. 25, 1951.
4. E.S. Roberts, F.A. Schaufelberger, and P.J. McGauley: U.S. Patent No. 2,662,009, Dec. 8, 1953.
5. P.J. McGauley, F.A. Schaufelberger, and E.S. Roberts: U.S. Patent No. 2,755,172, July 17, 1956.