Mapeamento geológico de calcário em uma localidade do município de Forquilha-CE

Abstract

The present work aims to conduct a geological mapping of limestone in a locality of the municipality of Forquilha, in the state of Ceará, Brazil. The study area is part of an agricultural limestone company in the region and belongs to the Sobral Geological Sheet (SA.24-Y-D-IV), within the geological context of the Independência Unit of the Ceará Group, part of the Ceará Central Domain in the northern portion of the Borborema Province. Limestone is one of the most widely used rocks in various industries, such as cement, lime, crushed stone production, metallurgy, chemical industry, and the production of soil acidity correctives. This study is essential due to the importance of this rock in the regional economic scenario, as well as its potential to assist in the exploration and development of mining in the region. The methodology used in this work consists of three stages. The pre-field stage involved gathering bibliographic information about the region and creating pre-field maps. The field stage was carried out through traverses in the study area to identify the existing lithologies, collect samples, and take structural measurements. The post-field stage consisted of performing macroscopic and petrographic analyses and compiling the data for the creation of the geological map and the final report. Fieldwork indicated the presence of different lithologies, highlighting marble, schist, gneiss, and quartzite. The region's carbonate rock, commercially characterized as limestone, was identified as marble due to signs of metamorphism observed in the rocks. The marble in the region shows a massive structure and a homogeneous composition, with foliation oriented at 094° Azimuth and dipping at 27°. A set of fractures oriented at 231° Azimuth with a dip of 65°was identified. Petrographic slide analysis showed a predominant presence of calcium carbonate (calcite and/or dolomite), with crystal sizes ranging from 0.5 to 1.5 millimeters, featuring planar, concave, and convex contacts indicative of a metamorphic texture. Additionally, opaque minerals and muscovite were identified. In greater detail, cleavage patterns characteristic of calcite and dolomite in two directions with an approximate cleavage angle of 74° were observed. Based on the tests performed, it was found that the region's marble could be used as cladding stone, as the obtained results meet the technical standards required for this application. However, this possibility should be carefully considered, as the standard is not specifically intended for carbonate rocks, and the region shows a family of fractures.