Summary:
The Pau-a-Pique deposit is hosted by a mica-rich mylonitic zone in the sheared contact between the footwall Fortuna Formation and the hanging wall Mesoproterozoic igneous basement. The metasediments comprise metaconglomerates and arkosic metasandstones, while the basement includes diorites, tonalites, and granodiorites. These units were affected by the D2 shearing (Melo et al., 2022), and the igneous rocks were transformed into schistose layers of biotite, quartz, chlorite, muscovite, epidote, calcite, ilmenite, rutile, magnetite, apatite, and titanite. Toward the center of the shear zone, the biotite transitions into gray muscovite in zones with subsequent hydrothermal alteration and high-grade gold mineralization. The sheared metasediments in the hanging wall are described as centimetric to metric layers of muscovite with quartz, magnetite, rutile and ilmenite (Melo et al., 2022).
A silicified breccia occurs to the southwest of the Pau-a-Pique orebody, with no gold mineralization. It is uncertain whether it is related to an earlier rifting-related hydrothermal event, during the deposition of the Aguapeí sediments, a late D3 event, or a later Neoproterozoic event (Melo et al., 2022).
Mineralization
The Pau-a-Pique ore zone is a 3- to 15-m-wide schistose layer with biotite and muscovite, along with multiple generations of quartz veins. The gold mineralization includes disseminated coarse pyrite with associated swarms of quartz veins. Gold occurs as inclusions in the pyrite and native gold within the quartz veins or disseminated in the mylonite. Gangue minerals comprise biotite, muscovite, magnetite, albite, chlorite, calcite, apatite, ilmenite, and rutile.