Petrography of auriferous conglomerates in the Fortuna formation of the group Aguapei in Pau-A-Pique deposits in the Mato Grosso district, in the centre of Brazil

Gold anomalies in the Pau a-Pique deposits are present in anastomossed shear zones near the contact between the Group Aguapei conglomerates and the Tonalito Alvorada. These high-strain zones are subparallel to the regional shearing NW - SE, and they have a brittle-ductile structures. The gold ore is exploted from veins and disseminations in the conglomerates that were affected by hydrothermal alteration. The main hydrothermal minerals in the mineralized layer are quartz, tourmaline, pyrite, biotite, chlorite and white mica. These hydrothermal minerals present textures that indicate their post-tectonic growth due the circulation of mineralizing fluids in the late shearing stages. (author)