The Cuiabá Gold Deposit is located in the northern part of the Quadrilátero Ferrífero, Minas Gerais State, Brazil.
A. Polished slab of non-mineralized Cuiabá BIF. The light quartz–carbonate bands (1) alternate with dark carbonate–quartz bands (2). The bands define the original compositional layering (Fonte Grande Sul orebody, level 5).
B. Marked banded texture in ores. light quartz–carbonate bands (1) and sulfide bands (3) (Serrotinho orebody, level 4).
C. Widespreadly recrystallization of pyrite over light and dark quartz carbonate layers (Balancão orebody, level 5).
D. Mineralized Cuiabá-BIF showing isoclinal folding of sulfide mesobands (Fonte Grande Sul orebody, level 5).
E. Sheared ore showing the boudinage of more competent quartz–carbonate, chert-rich layer. Sulfide is mostly pyrrhotite. Boudin neck areas are filled by quartz and sulfides (stope of Fonte Grande Sul orebody, level 5).
F. Large pyrite porphyroblast with inclusions of gold (Au), pyrrhotite (po), arsenopyrite (asp), and gangue minerals (quartz and carbonate, dark color) (Fonte Grande Sul orebody, level 5).
G. Replacement structures in hand specimen. sulfide layers (3) alternate with light quartz–carbonate layers (1) and dark quartz–carbonate layers (2). Locally, late quartz vein crosscuts the layers (4). Note the replacement of dark quartz–carbonate layer (1) by sulfides (3) (Canta Galo orebody, level 5).
H. Fully developed euhedral pyrite grain with inclusions of carbonate. Note that the replacement of ankerite takes place along grain boundaries (Canta Galo orebody, level 5).
I. Hand specimen of upper mafic metavolcanics showing sulfidation processes along discrete shear zones (Balancão Footwall orebody, level 5).
J. Quartz vein-type gold mineralization. Sulfides (with gold inclusions) occur along the mylonitic foliation and around quartz remobilization (Galinheiro Quartzo orebody, level 5).
Source: The Archean BIF-hosted Cuiabá Gold deposit, Quadrilátero Ferrífero, Minas Gerais, Brazil Luiz Cláudio Ribeiro-Rodrigues, Claudinei Gouveia de Oliveira, Gunther Friedrich.