The use of geophysical methods in permafrost investigation: Iron ore deposits of the central part of the Labrador Trough,Northeastern Canada

A brief summary of our knowledge of permafrost is presented. The general properties and the thermal regime of permafrost encountered in the Schefferville area are discussed. The factors influencing the occurrence or disappearance of permafrost are discussed individually. Attempts to determine the mechanical and thermal properties of frozen rock materials, with the aim of relating these to geophysical results and to the various blasting responses appear to represent the best approach. In addition to the mapping of topography, drainage patterns, distribution and type of vegetation, snow cover and installation of thermistors, electrical resistivity surveys, borehole geophysical techniques and seismic refraction method are now recognized as important tools in predicting and outlining permafrost zones where blasting and handling procedures of iron ore are very expensive and difficult. Examples and results of such studies carried out on the Timmins 1, Timmins 4, and Fleming 3 deposits are presented. As the mining operations will move northwards into the Timmins, Barney, Goodwood, Leroy and Kivivic groups of deposits, an increasing percentage of the mining activities will be located in permafrost; consequently, it is of the utmost importance to develop a technique permitting a rapid and accurate prediction of permafrost zones in order to reduce prohibitive costs of operation. The delineation of permafrost in a particular deposit has many practical applications such as the demarcation of areas where trenching and test pitting is planned, prediction of ground conditions for test and tonnage drilling, delineation of areas of open cast walls which will be affected by permafrost and consecutive importance in slope design, operational planning of areas where free digging is possible during dirt (overburden) stripping and economic planning of mining operations, particularly with respect to drilling and blasting costs. Additional important applications include the delineation of areas of potential water problems during operations due to the presence of permafrost in the wall rocks and broad outline of the blasting patterns and choice of charge distributions to be used.