Detection of Mineralogical Changes in Pyrite Using Measurements of Temperature-Dependence Susceptibilities

Detailed measurements of temperature-dependence susceptibilities were employed to detect mineralogical changes in pyrite samples from Song County, Henan Province. The results indicate that pyrite converts to pyrrhotite in either an argon or an air atmosphere through two possible processes: (1) Magnetite firstly appears around the powder of pyrite by oxidation caused by oxygen adsorbed on the powder below 400°C, and then the newly formed magnetite reacts with sulphur atoms, released from the pyrite lattice, and converts to pyrrhotite at higher temperature. (2) Pyrite directly changes to pyrrhotite by desulphidation, and this reaction is the main source of pyrrhotite in our experiments. During heating in an argon atmosphere, magnetite began to form at 380°C, while pyrrhotite did not form until 535°C. When pyrite was heated to 535~560°C, the Curie temperature of the newly formed pyrrhotite was not stable, and the Curie temperature might tend to be stable, when pyrite was heated above ~560°C. The type of the newly formed magnetic minerals, when pyrite was heated in an argon atmosphere, depended only on the maximal temperature, not on the stay time at the maximal temperature. The amount of the newly formed magnetic minerals was controlled by both these factors.