A thermomagnetic analysis of rocks (20-700 degrees C.) : the design and construction of measuring apparatus, and its application to rocks from the Whiteshell area

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Coles, Richard Leslie
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As a preliminary study, relating to the regional magnetic anomalies in Manitoba and Northwestern Ontario, a reconnaissance sampling survey has been made over the flank of a regional anomaly in the Whiteshell area of Southeastern Manitoba. Thermomagnetic curves and Curie transition temperatures have been determined for 70 samples over the 14 mile traverse. The Curie temperatures are closely grouped about a mean of 573*C. It is considered improbable that the magnetic minerals found at the surface are directly related to a possible Curie level at the bases of the regional magnetic anomalies. The design and construction of the recording thermomagnetic balance is described. A commercial electrobalance is coupled with an air-cored coil system and furnace to provide sub-saturation thermomagnetic curves between 20* and 700*C., in air. The heating and cooling cycle may be completed in about one hour. Indications are that rapid heating to 610*C. produces no significant changes in Curie temperatures, but heating to 700*C. may cause a decrease in Curie point, for the magnetic phases present in these rocks. This latter effect is considered not to be due to the present of air.