1. R. L. Stanton: ‘Ore petrology’, 713; 1972, New York, McGraw-Hill Book Company.
2. R. K. Duncan and G. C. Willett: In ‘Geology of mineral deposits of Australia and Papua New Guinea’, (ed. F. E Hughes), 591-597; 1990, Melbourne, The Australasian Institute of Mining and Metallurgy.
3. C. K. Gupta and A. K. Sun: ‘Extractive metallurgy of niobium’, 254; 1994, Boca Raton, FL, CRC Press.
4. Anon:Mining 1, 1999, 332, (8532), 376.
5. R. Ring, K. Soldenhoff, A. Bellingham, S. Brown, D. Collier, A. Day, D. Levins, C. Quan, R. Secomb, G. Tapsell, D. Kingsnorth and M. Chan: Proc. 18th Int. Mineral Process. Cong., Sydney, Australia, May 1993, AusIMM, 5, 1239-1244.