Aspectos lito-estruturais das minas de ferro N4E e manganês do azul, Serra dos Carajás-Pará

Abstract

The areas of iron (N4E) and manganese (Azul) mines in the Serra dos Carajás region were investigated with emphasis on structural geology, aiming to define the geometric arrangement of the various ore bodies and the kinematic framework, as well as their relationships with the regional structuring. The iron mine (N4E) is subdivided into two segments called Aba Leste and Aba Sul. The lithotypes occurring in this area are represented by friable itabitite (soft hematite HM, hard hematite HD), metajaspilite, metavolcanic rocks and canga. . Most of the rock units are distributed in the form of lenses and discontinuous and wedged bands, with a general orientation N-S on the East Rim and E-W on the South Rim, drawing a “J” with concavity facing northwest. The analysis of the structural elements present in the rocks of the N4E mine, in line with the information available for the Serra Norte region, allowed the characterization of three sets of main structures: the oldest set comprises the mylonitic foliation, the shear zones with oblique riding character, stretch lineation and associated folds; the second set refers to the NW-SE, E-W and N-S ductile transcurrent shear zones that cut and limit the body of N4; the last set corresponds to the folds and crenulations present throughout the entire ore body. These sets of structures are interpreted in the context of a single deformational event. The lithotypes that make up the manganese mine (Blue) are classified into three types: Protomines, Surface Deposits and Subsurface Deposits. Mining is currently being carried out in the central part of the deposit, between the LT00 and LT800E lines, where the ores related to surface and subsurface deposits were identified. The first includes pisolites (PIS), blocks (BL), platelets (PLT) and manganese breccias (BLM), and the second encompasses manganeseiferous mudstones (PM), granulated manganese material (MMG) and massive manganese material (MMM). The various types of manganese ore are wavy, defining synformal and antiformal structures oriented in the E-W direction and associated with strongly inclined thrusts to the north. The N4E and Azul mines are located on the northern edge and in the central-north region of the divergent macrostructure of Serra dos Carajás, respectively. Such a regional geometric arrangement is interpreted as a positive flower structure associated with an E-W sinistral binary. In this sense, the lithostructural units of the two studied areas must be understood as fractions of an inverted transcurrent volcano-sedimentary basin.