11 th SGA Biennial Meeting Let’s Talk Ore Deposits 26-29 th September 2011 Antofagasta, Chile 873 Metallogenesis of Eastern Guiana Shield in Brazil Evandro L. Klein CPRM/Geological Survey of Brazil, Belém, Brazil Lucia T. Rosa-Costa CPRM/Geological Survey of Brazil, Belém, Brazil Abstract. The Eastern Guiana Shield in Brazil contains orogenic and paleoplacer Au, sedimentary and supergene Fe and Mn, magmatic Cr, Ti, Sn, Nb-Ta, and paleoplacer diamond deposits. It also holds potential for Cu, Zn, Ni, PGE, and thorianite deposits. Although the tectonic evolution of this shield spans from 3.32 to 0.61 Ga, the most active tectonic and metallogenic period was between 2.26 and 1.95 Ga. The internal structure of this area is quite complex and at least three tectonic domains are recognised: an Archean block intensively reworked during the Rhyacian, and two Rhyacian domains that represent continental arcs. Ore deposits formed at ~2.26- 2.21 Ga (Fe, Mn, Cr, Cu-Au, and paleoplacer gold and diamond); 2.11-1.93 Ga (widespread orogenic gold); 1.75 Ga (Sn, Nb-Ta); 0.61 Ga (Ti); 0.05-0.02 Ga (supergene Fe-Mn). Keywords. Guiana Shield, Archean, Paleoproterozoic, metallogeny 1 Introduction The most recent review of the metallogeny of Guiana Shield is found in Dardenne and Schobbenhaus (2003). In the last decade, new geological, geochronological and Nd isotope studies have been produced allowing for a better understanding of the geological evolution of the eastern portion of the Guiana Shield (see review in Rosa-Costa et al. 2009). In addition, some new metallogenic studies have been conducted at deposit and district scale (Melo et al. 2003; Faraco et al. 2006; Galarza et al. 2006; Nunes et al. 2007; Klein et al. 2009; Klein and Fuzikawa 2010). This work summarises the different types of ore deposits of the Brazilian portion of Eastern Guiana Shield (i.e., State of Amapá and NW-Pará State) and attempts to integrate the ore genesis within the evolution of the distinct tectonic domains of this part of the shield. 2 Tectonic domains The Eastern Guiana Shield in Brazil in subdivided into three tectonic domains (Rosa-Costa et al. 2006; Klein et al. 2011). The Lourenço Domain occupies the northern portion of the Eastern Guyana Shield in Brazil (Fig. 1). It is composed of gneisses and diorite to granodiorite of 2.18-2.16 Ga interpreted to have formed in juvenile magmatic arc (Nogueira et al. 2000). These plutonic rocks are associated with discontinuous strips of metavolcano-sedimentary sequences. Younger rocks include granitoids and charnockite of 2.10-2.05 Ga (Faraco et al, 2009 and references). The Amapá Block represents an Archean crust (Fig. 1) that has been reworked during the Rhyacian period. Its basement is composed of 2.85-2.60 Ga associations of granite-gneiss-migmatite with remains of older crust (3.32 Ga), and of charnockites of 2.66-2.63 Ga. This basement records granulite facies metamorphism at 2.10-2.08 Ga and has been intruded by pre-orogenic layered mafic-ultramafic rocks, by several generations of orogenic granitoids between 2.22 and 1.99 Ga, and by anorogenic granites of 1.75 Ga. Greenschist to granulite facies supracrustal rocks occur as disrupted and elongated NW-SE trending sequences composed of mafic-ultramafic volcanic rocks, and chemical and clastic sedimentary rocks (Rosa-Costa et al. 2006). The Paleoproterozoic Carecuru Domain is composed of gneisses, calc-alkaline granitoids dated at 2.19-2.14 Ga, narrow and discontinuous belts of metavolcano- sedimentary rocks, and remnants of Archean granulite gneiss (Fig. 1). The association is interpreted to have formed in magmatic arc setting. Younger units comprise syn- to post-collisional granitoids of 2.10-2.03 Ga (Rosa-Costa et al. 2006 and references). In the southern portion of the domain crops out the 612 Ma old Maraconaí Alkaline Complex. It comprises peridotite, pyroxenite and subordinate syenite and alkali granite (Lemos and Gaspar 2002) and it is hosted in basement units. 3 Ore deposits 3.1 Lourenço Domain The Lourenço Domain contains orogenic(?) gold and sedimentary iron deposits (Fig.1). The gold deposits are hosted in 2.15 Ga old granitoid and gneisses and in supracrustal sequences. Mineralisation took place at ca. 2.00 Ga and is associated with silicification, saussuritisation, chloritisation and sulphidation of the host rocks (Nogueira et al. 2000). Sedimentary iron deposit and occurrences are associated with magnetite- bearing quartzite and itabirite. The ore was probably deposited prior to 2.26 Ga and underwent supergene enrichment in the Eocene-Oligocene period. 3.2 Amapá Block Orogenic gold deposits of the Amapá Block are associated with the metavolcano-sedimentary Vila Nova Group (>2.26 Ga) (Fig. 1). The main gold deposit of this domain is Amapari. The gold-sulphide ore is hosted in a N-S trending shear zone that affected amphibolite facies pelitic schists, BIF and carbonate rocks, and subordinate skarns produced by the intrusion of a 1.99 Ga old granite. Mineralisation was produced by low-salinity aqueous-carbonic fluids of metamorphic origin at 270 to >420°C (Melo et al. 2003; Nunes et al. 2007). Ore