Stoping from Pit Walls While Developing the Underground Mine at St. Lawrence Columbium
• The free-world production of columbium ore concentrates ~as doubled in the last five years. St. Lawrence Columbium and Metals. Corporation has contributed largely to this expansion, its production rate increasing from 720 tons of concentrates per year in 1961 to 2 200 tons in 1965. ' To follow the normal market development, the Company initiated an engineering study aimed at establishing the most economical mining methods, thus permitting it to increase its milling rate from 1,000 tpd in 1964 to 2,000 tpd in 1967 and possibly to 3,000 tpd in 1968. The results of this study pointed out the advantages to be gained in converting from an open pit to an underground operation. This paper describes how the mining engineering department has successfully developed "stopes" from the walls of its No. 2 open pit, in order to assure continuity of its operation during the interval required to develop its underground mine.