ROCK MAGNETIC-PROPERTIES OF IRON-ORES AND HOST ROCKS FROM THE PENA-COLORADA MINING DISTRICT, WESTERN MEXICO

The Pena Colorada iron-ore deposit consists of several ore-bodies dist ributed over an area of about 5 km(2) in the northwestern sector of th e State of Colima, in western Mexico, The mineralized area shows the g eneral 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 100 0 m. It has a NW-SE regional strike. The iron ore has been locally cla ssified 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 vertica l or horizontal directions. The amorphous ore shows the effects of sev eral periods of hydrothermal activity, which has resulted in lower qua lity and quantity of iron-ore. There is a marked correlation among the natural remanent magnetization intensity, low field susceptibility, s tability parameters, hysteresis loops, and temperature dependent susce ptibility curves with high and low temperature oxidation states in bot h types of iron-ore and host rocks characteristic of the area. The var iations may be mainly interpreted in terms of the oxidation state of t he titanomagnetites present in the iron ores.