Geology of Paleoproterozoic Gneiss-and Granitoid-Hosted Gold Mineralization in Southern Tapajós Gold Province, Amazonian Craton, Brazil

Abstract

Vein-quartz gold mineralization in Southern Tapajós Province is hosted by arc-related, calc-alkaline tonalitic orthogneisses (Cuiú-Cuiú Complex, 2033-2005 Ma) and post-collisional, calc-alkaline, K-rich granitoids (Creporizão Intrusive Suite, 1997-1957 Ma). The deposits are structurally controlled and form typically tabular bodies that parallel the hosting structures, and are characterized by quartz veins surrounded by halos of strongly altered wall rock, which are usually narrow and show weak to prominent ductile fabric. Steeply dipping fault-fill veins and shear veins account for 80% of the structural style, followed by breccia veins and lesser stockworks and veins hosted in low-angle reverse-oblique faults. Hosting structures vary from ductile-brittle to brittle in nature, and together with structural and textural evidence provided by the veins, indicate a wide range of depth of emplacement for the mineralization, from shallow to mid-crustal. Quartz and sericite are the main alteration minerals and pyrite is ubiquitous. We modify current structural models for the Tapajós Province, proposing the NW-SE-trending strike-slip event that affected the Creporizão Suite, and transposed the gneissic banding of the Cuiú-Cuiú Complex as the second (D2) major structural event in the province, occurring broadly coeval with the emplacement of the late-stage plutons of the Creporizão Suite (~1.97-1.95 Ga). Emplacement of low-angle fault-hosted veins, shear veins, and fault-fill veins that show evidence of plastic deformation (i.e., most of the deposits in Southern Tapajós Province) are related to this structural phase.