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

A wide range of physical and magnetic parameters have been used to characte rize the iron ores and lithologies of the Pena Colorada Mine, southern Mexi co, including saturation magnetization, Curie temperature, density, magneti c susceptibility, remanence intensity, Konigsberger ratio, and hysteresis p arameters. Rock magnetic properties are mainly controlled by variations in magnetite content, deuteric oxidation, and hydrothermal alteration. Magneti te grain sizes in iron ores range from 4 to >20 mum, which suggest the pred ominance of multi-domain (MD) states over single-domain (SD) and pseudo-sin gle-domain (PSD) states. Curie temperatures are 580 +/- 5 degreesC, charact eristic of magnetite. Hysteresis parameters indicate that most samples pres ent PSD to MD behavior. AF demagnetization and isothermal remanent magnetiz ation (IRM) acquisition curves show that natural remanent magnetization (NR M) and laboratory remanences are carried by MD magnetite in iron ores and P SD-SD magnetite in the host rocks. The variation of NRM intensity and susce ptibility suggests that the carriers of remanent and induced magnetization are the same in all cases, Ti-poor titanomagnetites. The Konigsberger ratio falls in a narrow range between 0.1 and 4, indicating the presence of MD a nd PSD magnetites. There is a clear correlation among the magnetic paramete rs measured with high- and low-temperature oxidation states in both types o f iron ore and host rock. A large dipolar magnetic anomaly is observed over the deposit. Data for susceptibility, intensity and direction of the NRM p rovide constraints for modeling of the magnetometric anomalies by quantifyi ng the relative contributions of induced and remanent magnetization compone nts and allowing better control of the geometry of source bodies. (C) 2000 Elsevier Science Ltd. All rights reserved.