Gênese e evolução de mesocavidades e espeleotemas em testemunho de sondagem N4WS-1495 ao longo de formações ferríferas bandadas, Serra Norte, Província Mineral de Carajás – PA

Abstract

Carajás Mineral Province adds natural cavities generated on jaspilite lateritic yoke and associated rocks, beginning on a microscopic scale by successive physicochemical conditions generating interconnected mesocavities subsequently suffered landslides and rainfall causing chemical complex crystalline forms generically known as speleothems. Mesocavities studies on drill core on subsurface conditions have not been performed to date, what has prevented a broader approach to the understanding of cavities and speleothems in these conditions. Thus, this work focused on petrographic study of speleothems along mesocavities formed in subsurface provide a better understanding of genesis and evolution of speleothems type coraloide in N4WS-1495 borehole, which used geological parameters, mineralogical and petrographic by means of XRD methods, MEV and optical microscopy. These parameters allowed define catalysts that possibly in contact with water, accelerated the dissolution of silica and promoted the formation of meso cavities and subsequently generation of speleothems. The silica-temperature and high alkalinity, in the presence of Na and K, assigned by hydrothermal alteration processes during the intrusion of granites Serra dos Carajás and mafic dike, dissolved and generated meso cavities. In relation to dissolved iron in the opaque bands, requires low-oxygen, high concentrations of carbon dioxide and high pH. Continuous process of dissolution of siliceous and opaque bands led caves to interconnect, either by solubilization and / or brittle features, and now stockspeleothems type coralloid at depths greater than 440 meters. These have speleothems related to genesis of a compound exudation of water supersaturated in gel of iron hydroxide which precipitated finding geochemical stability. Have concentric texture, marked by alternation of iron and silica concentrations, possibly due to seasonality of the surface environment that hit the banded iron formations (BIF's) in the subsurface.