Geology setting and metallogenesis of the Alta Floresta Province, southern Amazon Craton (Brazil)

The Alta Floresta Province consists of Paleoproterozoic plutono-volcanic sequences (2.01-1.75 Ga) originated from a series of successive magmatic arcs that accreted to the southwestern margin of the Central Amazon Province. The geologic framework of the eastern sector of the province is organized into: 2.8-1.97 Ga deformed metamorphic and metamorphosed granitic basement; 1.97-1.78 Ga I-type plutono-volcanic and volcano-sedimentary sequences; 1.78-1.77 Ga post-orogenic and anorogenic plutono-volcanic units; and Mesoproterozoic (~1.3 Ga) to Quaternary sedimentary sequences. The deposits are clustered into four main groups: (i) disseminated Au±Cu(±Mo); (ii) structurally-controlled vein-type Au±Cu(±Mo); (iii) disseminated Cu+Mo; and (iv) structurally-controlled vein-type Au+Zn+Pb±Cu. Ore zones in groups (i) to (iii) are represented by pyrite±chalcopyrite±molybdenite, whereas group (iv) consists of pyrite+sphalerite+galena±chalcopyrite. In most deposits, mineralization is contained within muscovite-chorite-quartz-rich or silica-rich zones. The fluid regime of groups (i) and (ii) is mainly represented by CO2-rich fluids, whereas group (iv) by two-phase aqueous fluids with heterogeneous degree of filling. Pyrite and molybdenite Re-Os and pyrite Pb-Pb systematics constrain the mineralization age in the 1.84-1.77 Ga range, which overlaps with the ages of porphyritic granitoids, and in a regional scale, to the Colíder and Teles Pires suites ages. These deposits represent magmatic-hydrotermal systems and are considered to share broad similarities with porphyry-epithermal deposits.