Rock magnetism and magnetic surveys in the iron ore deposit of El Encino, Mexico

In this study, we report results of petrophysical properties such as bulk (low field) magnetic susceptibility, remanent magnetization, Kِenigsberger ratios, density, unblocking temperature spectra, isothermal remanent magnetization acquisition, and thermomagnetic analysis from surface and borehole samples of rock units and iron ore bodies in the iron mining district of El Encino, Jalisco, southwestern Mexico. Iron mineralization consists mainly of magnetite (from 65% to 90% volume) and hematite. It is associated with granodioritic intrusions and volcanic units in a mid-late Cretaceous volcano-sedimentary sequence. The magnetite in the iron ore has generally large grain size and a multidomain behavior. Stable remanent magnetization components associated with pseudo- or single domain behaviors are also observed. Iron ore bodies and associated intrusives show large dipolar magnetic anomalies. For the iron ore bodies examined, either the induced or the remanent component is responsible for the magnetic anomaly response. Data on bulk susceptibility, remanent intensity, and direction provide important constraints for modeling the magnetometric anomalies i.e., by quantifying the relative contributions of induced and remanent magnetization components; and thus permitting a better control of the geometry of source bodies.