Mapeamento geológico e caracterização petrográfica das brechas hidrotermalizadas ricas em Óxido de Ferro e Sulfeto da localidade de Croatá — Pio IX — Pi

Abstract

The region of Croatá lies in the SE portion of the sheet Pio-IX (SB.24-YA-VI), and has one of the main ore mineral occurrences of the sheet. The host rock to mineralization corresponds to alkali-feldspar granite, pink, with medium to coarse grained, which is found strongly brecciated and hydrothermally altered. These alterations are represented by changes both in texture, color, and the mineralogical and chemical composition of the host rock. Among the changes is to potassic, propyl, hematite and sulfides, which must be passed between them is progressive. The potassic alteration is characterized by formation of potassium feldspar that occurs disseminated and banded and/or shafts that represents the initial stage of hydrothermal alteration, amendment propyl is predominantly shaped by alteration epidote for to feldspar that occur disseminated and in veins, reflecting a more advanced stage of hydrothermal alteration; in tarnishing the rock is composed mainly ofpyrite occurs disseminated and in veins in millimetric to centimetric stockworks standard type, with the gaps and feldspar granite is cut by fractures filled with hematite, occupying an area of approximately 1500 meters but may be extended, since it has a setting in sub-surface. This phase precedes the tarnishing oxide phase seems to indicate high activity of reduced sulfur, hydrothermal solutions common to high temperatures associated with granitic rocks; The hematitic is represents one of the main stages of hydrothermal alteration, as well as one of the latest, since it overlaps the other phases of amendments. It is marked by microvenules late hematite, which evolves into a massive gap hematite, similar to a veie with a width of about 10m and a length about 200m. All these loopholes hydrothermalized develops along the zone of brittle-ductile shear of NE-SW direction which occurs pararei the axial surface of the mega-fold of the central part of the leaf - Pio-IX. However, these gaps can also be found in the region along sinistrai faults in a NW-SE.