Preliminary Magnetic Studies of the Helen Mine 'Kill Zone' Soils, Wawa, Ontario, Canada

English Abstract:

As part of a larger study on using magnetic properties to examine mining-related pollution in Canada, the present-day distribution of iron-oxides emitted from the closed Helen Mine iron sintering plant near Wawa (Ontario, Canada) has been investigated. In this area, the vegetation cover has been severely disturbed, thus providing an excellent setting to investigate variations in magnetic properties. A total of 50 sites were sampled on cross-sections perpendicular (X-X’) and parallel (Y-Y’) to the dominant wind direction in order to investigate magnetic properties as a function of both wind direction and distance from the source. The in-situ surficial magnetic susceptibility (measured using a Bartington MS2D) decreased away from the source. Remanence and hysteresis measurements (2G Cryogenic Magnetometer, Magnetic Measurements VFTB) suggest that the primary magnetic mineral was magnetite; however, a biplot of IRM_-100mT/SIRM vs ARM_40mT/SARM indicated minor greigite. The laboratory analysis also showed that the highest susceptibility was not observed at the surface but in the subsoil. Similarly, magnetic spherules were not observed in magnetic extracts from the topsoil samples (0-5cm) but samples from the subsoil (5-10cm) contained magnetic spherules (2µm-10µm). EDS analysis shows that the spherules contain high weight percentages of Fe (up to 85%) and O (up to 48%), with some samples showing minor concentrations of other elements (e.g. Al, Ti, Mg). The vertical distribution of magnetic spherules and susceptibility could be due to vertical migration or to post-mining soil development.