The use of alternative methods for differentiation of banded iron formations and iron ore in the body N4WS, serra norte – carajÁs mineral province

Abstract

The use of non-traditional geophysical methods is becoming increasingly common in activities involving iron ore, as the increasing ore demand intensified the competition in the international market. This motivated us to integrate the physical properties of the rocks to better understand the relations of the iron ore with the proto-ore and host rocks. The work was conducted in N4WS body, Serra Norte, Carajás Mineral Province (CMP), located in the state of Pará. The Carajás Mineral Province hosts some of the largest world-class iron ore deposits in the world, operated by Vale S.A. The results of airborne magnetic data showed that the mineralized bodies previously mapped are not directly linked to the high gradients observed in the amplitude of the analytic signal. This response is related to the proto-ore, constituted by jaspilites with low values of K, eU and eTh. An unsupervised classification of these properties permitted to map individualized ore bodies. Measurements of the magnetic susceptibility and gamma radiation emission in drill holes were satisfactory. There was a clear differentiation between iron ore, jaspilites and mafic rocks, mainly in the magnetic susceptibility parameter. The gamma ray results from radioelements separated iron formations and associated mineralization from the adjacent mafic rocks. The use of the unsupervised classification k-means was useful for distinguishing between jaspilites within the same package and to show anomalous areas not previously mapped. The integration of rock physical properties, geological data and airborne geophysical data produced excellent results. There was a direct correlation between what was measured and what was observed in situ at the surface. Thus, it was possible to individualize the lithotypes in the N4WS using the physical properties. This confirms the feasibility of using these methods as an alternative to the currently used tools for iron ore exploration, with the potential to increase the efficient use of human and financial resources investments.