Rock magnetic properties of iron ores and host rocks from the Peña Colorada mining district, western Mexico

Abstract

The Peña Colorada iron-ore deposit consists of several ore-bodies distributed over an area of about 5 km 2 in the northwestern sector of the state of Colima, in western Mexico. The mineralized area shows the general shape of an irregular long tubular body of variable thickness (from a few meters to several tens of meters) and a width of 500 to 1000 m. It has a NW-SE regional strike. The iron ore has been locally classified in two types: ‘normal’ (massive) and ‘amorphous’ (disseminated), with distinct mineral and textural associations. Both types of ore are related and changes occur gradually from one to another in vertical or horizontal directions. The amorphous ore shows the effects of several periods of hydrothermal activity, which has resulted in lower quality and quantity of iron-ore. There is a marked correlation among the natural remanent magnetization intensity, low field susceptibility, stability parameters, hysteresis loops, and temperature dependent susceptibility curves with high and low temperature oxidation states in both types of iron-ore and host rocks characteristic of the area. The variations may be mainly interpreted in terms of the oxidation state of the titanomagnetites present in the iron ores.