1. Asturiana de Zinc S.A., Spanish Patent No. 304,601; application lodged 12th October, 1964. Equivalent U.S. Patent No. 3,434,798 granted 25th March, 1969.
2. Electrolytic Zinc Company of Australasia Limited, Australian Patent No. 401,724; application lodged 31st March, 1965. Equivalent U.S. Patent No. 3,493,365 granted 3rd February, 1970.
3. Det Norske Zinkkompani A/S Norwegian Patent No. 108,047; application lodged 30th April, 1965, Equivalent U.S. Patent No. 3,434,947 granted 25th March, 1969.
4. C. J. Haigh and R. W. Pickering:World Symposium on the Mining and Metallurgy of Lead and Zinc, St. Louis, 1970, vol. II, pp. 423–48, AIME, New York
5. G. Steintveit:ibid. World Symposium on the Mining and Metallurgy of Lead and Zinc, St. Louis, 1970, vol. II, pp. 223–46, AIME, New York