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

The Alta Floresta Province consists of Paleoproterozoic plutonic-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 plutonic-volcanic and volcano-sedimentary sequences; 1.78-1.77 Ga post-orogenic and anorogenic plutonic-volcanic units; and Mesoproterozoic (similar to 1.3 Ga) to Quaternary sedimentary sequences. The ore 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. Groups (i) to (iii) are characterized by pyrite-chalcopyrite-molybdenite, whereas group (iv) consists of pyrite-sphalerite-galena-chalcopyrite-digenite. 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. Re-Os on pyrite and molybdenite and Pb-Pb on pyrite geochronology systematics constrain the mineralization age between 1.84 - 1.77 Ga. This overlaps with the ages of porphyritic granitoids, and in a regional scale with ages of the Colider and Teles Pires suites. These deposits represent magmatic-hydrothermal systems and are considered to share broad similarities with porphyry-epithermal deposits.