Contribuição ao estudo hidrogeológico na área de ocorrência das cavidades naturais da Serra Norte, província mineral de Carajás- PA

Abstract

The present research, monograph level, corresponds to a structural and hydrogeological study of speleological banded iron formations (BIF's) belonging to the Serra Norte of Carajás- PA, in partnership with a major project of research to natural cavities, PROCAV. Study involved preparation of geological, drainage and topographical strain ellipsoid, and the hydrological characterization of structures related to BIF's. Methodology included, first, analysis of deformation ellipsoid maps, highlighting the model Riedel, in which geological structural information were collected, such as features, potentially open (faults, fractures and joints). Results show that faults, fractures and joints occur in three preferred directions: NW-SE, NE-SW and N-S. This arrangement coincides both with leading open fractures systems (anti-Riedel) as to the direction the caves in the study area. This indicates, above all, that the formation of these cavities has a strong tectonic control. In addition, the relationship with topography, expressed in the altitudes map is very important because along the edges of Serra Norte plateau, where the altitude becomes greater than 700 meters, is also presence of cavities. With contribution also represented in Normal climatological Isohyets map outlining the areas refills and hydrological discharges, able to contribute strongly to development of cavities, due the fact dissolution of BIF's, achieved primarily through acidification, followed by basification of water and soil pH. Resulting in the extension of micro porosities and later enlargement of them, resulting in caves and speleothems, sometimes rich in pure iron, related to water as main agent. PROCAV work, together with hydrogeology is highlight of speleological heritage of Brazil, as well as, being aimed at a cave discoveries, are able to enrich the bank caving information on hydrogeological vision in a unique way.