Horizontal Cut-and-Fill Stoping at Falconbridge Nickel Mines, Limited

THE property of Falconbridge Nickel Mines, Limited, is in Falconbridge township, approximately thirteen miles northwest of Sudbury. From the mine and townsite, a gravel road leads to Sudbury and a branch line of the Canadian National railway to Sudbury Junction. The ore deposit is at the southeastern corner of the 'Sudbury Basin'. It lies in a sheet-like mass, striking in an east-west direction, between norite to the north and greenstone to the south. The general attitude of the ore-body is vertical, but with frequent variations in dip of as much as 10° to the north or south. The deposit is very irregular in outline, the width varying from a few feet to eighty or ninety feet. In the vertical plane, rolls are frequently encountered. Gouge is very often present at one or both ore contacts. The norite to the north shows much jointing. The chief ore minerals are pyrrhotite, pentlandite, and chalcopyrite. The nickel content of the ore is usually double the copper content, average assays ranging from 2 to 2.5 per cent nickel and 1 to 1.5 per cent copper. The ore is of three main types: massive, breccia, and disseminated. The breccia ore, the most common type, consists of sulphides containing rounded inclusions of highly-altered country rock, which, in places, are so large that sorting is necessary in the stopes. In the norite, the breccia ore may grade into disseminated sulphides, which frequently are sufficiently concentrated for profitable mining. In places in the breccia ore, concentrations of solid sulphide masses occur. Until early in 1935, all mining at Falconbridge was by shrinkage scoping, but this method was found to be less and less suitable as greater depth was attained. When mining had reached the 1,000-foot level, ore drawn from large shrinkage stopes was found to have been diluted as much as fifty per cent by sloughing of the wall-rocks, caused by increased rock pressure and insufficient support. It was apparent that this method of stoping was un-suitable and -Mr. E. J. Martin was engaged to superintend the introduction of a method of cut-and-fill stoping.