Gold deposits of the Tapajos and Alta Floresta Domains, Tapajios-Parima orogenic belt, Amazon Craton, Brazil

The Tapajos region is one domain of a major Paleoproterozoic orogenic belt, named Tapajos-Parima and is. discussed in the context of the evolution of the Amazon Craton. The orogenic belt is. composed of a back-arc sequence, f our volcano-plutonic arcs, intra-arc sedimentation and is limited to the ea st by the cratonic rocks of the Central Amazon Province. The evolution and timing. of the main events is established by zircon, baddeleyite, and titan ite SHRIMP U-Pb geochronology of 29 rock samples, while lead and argon isot opes are used to study the age and source of the gold mineralization. Based on the mesoscopic nature of the orebodies, and, in some cases} on microthe rmometric and stable isotope data, the Tapajos gold deposits are classified as (1) orogenic and (2) intrusion-related, and may be grouped into four de posit-type categories: (1) orogenic, turbidite-hosted: disseminated and qua rtz-pyrite veinlet deposits, hosted by metaturbidites (lower greenschist-fa cies, Jacareacanga Group) and emplaced in ductile structures; (2) orogenic, magmatic arc-hosted: disseminated and pyrite-quartz--carbonate vein deposi ts,, hosted by metamorphic rocks (Cuiu-Cuiu Complex) and formed under a duc tile-brittle regime, with the Ouro Roxo deposit as a type example; (3) intr usion-related, epizonal quartz-vein deposits: vertical to subvertical quart z-pyrite veins and pyrite disseminations filling extensional brittle faults ; and (4) intrusion-related, epizonal, disseminated/ stockwork deposits, th e type-example being the Serrinha deposit. Gold mineralization of type 3 is similar to that of Korean-type, while type 4 mineralization shows some sim ilarities to porphyry-type deposits. Galena Pb-Pb and muscovite Ar-Ar data indicate an age of similar to1,860 Ma for the intrusion-related gold minera lization. Preliminary Pb isotope data on K-feldspar indicate that the fluid source was more likely to have been from within the Jacareacanga, Cuiu-Cui u and Tropas units than the Creporizao, Maloquinha, and Iriri units. This s tudy shows the existence of two main types (orogenic and intrusion-related) of gold deposits, which are related to specific tectono-magmatic events th at occurred during a limited period of time in the orogenic belt evolution. This information may be useful as a guide for gold exploration along the o rogenic belt.