INDEX AND PROBABILITY MAPS OF OCCURRENCE OF IRON ORE DEPOSITS: A PROPOSED GEOPHYSICAL APPROACH DEVELOPED IN CURRAL NOVO DO PIAUI ́ (PI) STATE – BRAZIL

ABSTRACT. This article shows the results of the development of a procedure called TC-ASA index which is based on the contrast of magnetic and radiometric prop-erties between host rocks and the mineralization, being interpreted as the probability of occurrence and defining ambience where iron formation to occur. It consists in subtracting the values of total count (TC) from the analytic signal (ASA), which are products of gammaspectrometry and magnetic methods, respectively. This index was applied to the actual data referring to the iron formations of Curral Novo do Piauı́, where the main mineral is magnetite, thus characterized by high magnetic susceptibility and often associated with metabasic rocks. These rocks often present low concentration of radioactive elements, enabling the identification of geolog-ical environment with potential for occurrence of iron ore. The use of this procedure allowed for the reduction of the exploration area, providing a fast target se-lection for geological mapping, geochemistry and ground geophysics. In addition, it supplies with important elements that will assist mining companies in setting strategic priorities