Discovery of Direct-Shipping Iron Ore by Geophysical Methods in Northern Canada
MAURICE SÉGUIN, Kungliga Tekniska Hogskolan, lnstitutionen For Geodesi, Stockholm, Sweden.
The primary aim of all ground geophysical work has been, of course, to locate orebodies. As with any geophysical method, its success depends on a proper mastering of the types of surveys and equipment used and their application to the physical properties associated with the orebodies. The Schefferville deposits are iron ores subjected to enrichment by the process of leaching. Although some ore types are porous and low in density, most of the ore zones have had a net increase in density brought about by enrichment. In the course of their formation, the magnetic characteristics of the rocks have usually changed, as much of the magnetite was altered to relatively nonmagnetic iron oxides and hydrous iron oxides. All drift-covered areas underlain with iron-formation are potential ore-producing areas. From these first two physical properties and a determination of the thickness of the overburden, a combined gravity-magnetic-seismic and/or resistivity survey allows for the detection and sorting out of iron-formation and potential ore zones from the country rocks. If the iron-formation possessed relatively uniform physical and chemical properties, the problem of locating areas underlain with ore, using geophysical methods, would be greatly simplified. Unfortunately, the iron-formation is a complex assemblage of rock types, each having different physical and chemical characteristics. In spite of t his, qualitative and semi-quantitative correlation between the results of the surveys and the geology and structure of the area could be established. ln addition, a semi-quantitative to quantitative correlation of the values of the residual gravity anomalies with the specific gravity, the iron content, the porosity factor, the dimensions of the underlying orebodies and the values of t he ground magnetic intensity above a reference lithologic unit, with the per cent weight Fe30 4 recovery and the susceptibility, led to the discovery of a direct-shipping iron ore deposit in the Schefferville mining district of Canada.
Density, Deposits, Gravity, gravity anomalies, iron ore, magnetite, quartzite, Schefferville Area, iron ore, Iron ores, Ore, Ores