Magnetic mineralogy and properties of the Peٌa Colorada iron ore deposit, Guerrero Terrane: implications for magnetometric modeling

A wide range of physical and magnetic parameters have been used to characterize the iron ores and lithologies of the Peña Colorada Mine, southern Mexico, including saturation magnetization, Curie temperature, density, magnetic susceptibility, remanence intensity, Königsberger ratio, and hysteresis parameters. Rock magnetic properties are mainly controlled by variations in magnetite content, deuteric oxidation, and hydrothermal alteration. Magnetite grain sizes in iron ores range from 4 to >20 μm, which suggest the predominance of multi-domain (MD) states over single-domain (SD) and pseudo-single-domain (PSD) states. Curie temperatures are 580±5°C, characteristic of magnetite. Hysteresis parameters indicate that most samples present PSD to MD behavior. AF demagnetization and isothermal remanent magnetization (IRM) acquisition curves show that natural remanent magnetization (NRM) and laboratory remanences are carried by MD magnetite in iron ores and PSD–SD magnetite in the host rocks. The variation of NRM intensity and susceptibility suggests that the carriers of remanent and induced magnetization are the same in all cases, Ti-poor titanomagnetites. The Königsberger ratio falls in a narrow range between 0.1 and 4, indicating the presence of MD and PSD magnetites. There is a clear correlation among the magnetic parameters measured with high- and low-temperature oxidation states in both types of iron ore and host rock. A large dipolar magnetic anomaly is observed over the deposit. Data for susceptibility, intensity and direction of the NRM provide constraints for modeling of the magnetometric anomalies by quantifying the relative contributions of induced and remanent magnetization components and allowing better control of the geometry of source bodies.