Weathering conditions evaluation of banded iron formations of Bonito Mine (Northeastern Brazil) based on coupled cluster-correspondence analysis

Abstract

This research was focused on weathering conditions regarding Banded Iron Formations (BIF) ore exploitation at Bonito Mine. The database is stemmed from an exhaustive drilling program at the mining site. Therefore, hundreds of iron ore samples were assayed for Fe2O3, SiO2, Al2O3, P and Mn grades, and qualitative geotechnical data such as weathering grades, physical ore type, voids, and coring depth levels were collected from drilling core samples. A previous petrographic study has shown that there are four BIF types: amphibolitic itabirites, martitic itabirites, hematitic itabirites, and magnetitic itabirites. In order to enhance this study, a multivariate model using geochemical and geotechnical data under a systemic approach was employed. This approach was conceived to account for the whole available information, both quantitative and qualitative, through the Correspondence Analysis and Cluster Analysis grounded appropriate methodology. This innovative strategy disclosed the presence of two groups of samples, denoted in the sequel Cluster 1 and Cluster 2. Cluster 1 is characterized by the Fe-poorer/High-Al BIF ores describing an association of magnetitic itabirites, martitic itabirites to amphibolitic itabirites which are conditioned to depths deeper than 70 meters and they usually stand as slightly weathered rocks or fresh rocks. Cluster 2 encompasses Fe-richer/Low-Al BIF ores composed of martitic, magnetitic and hematitic itabirites which are described as moderate to highly weathered porous friable ore materials. The proposed multivariate modeling strategy can deal with a wide range of miscellaneous geological issues.