Summary:
The Alta Floresta Gold Province (“AFGP”) is located in the south-central portion of the Amazon Craton (Almeida, 1978; Almeida et al., 1981), a crustal segment north of South America that would have stabilized at 1.0 Ga, which is surrounded by the mobile Neoproterozoic mobile belts of Tucavaca (in Bolivia), Araguaia-Cuiabá (Central Brazil) and Tocantins (northern Brazil) (Almeida et al., 1976; Cordani et al., 1988; Tassinari & Macambira, 1999). As the AFGP covers an area of approximately 430,000 km2, it represents one of the largest cratonic regions on the planet, comprising two Precambrian shields: Central Brazil (or Guaporé) and Guiana shields, that are separated by the Paleozoic Solimões-Amazonas(Tassinari) basin (Macambira, 1999; Dardene &Schobbenhaus, 2000; Tassinari et al., 2000).
The Alta Floresta Gold Province (AFGP) is mostly comprised of plutono-volcanic sequences generated in paleo- and mesoproterozoic continental arcs, in addition to deformed and metamorphic units in restricted greenschist facies to its central and northwestern portions. The units that comprise the province, especially its eastern segment, are essentially represented by oxidized calcium-alkaline plutonic and volcanic rocks, of medium to high potassium (K), meta- to peraluminous, belonging to the magnetite series (type I granites). of volcanic, sub-volcanic and alkaline granitoids (type A granites).
According to Assis (2015), in general, these units can be grouped into four main sets:
I. Deformed and metamorphized granitic basement (2.81 to 1.99 Ga);
II. Felsic plutono-volcanic and volcano-sedimentary sequences belonging to the magnetite series (type I granites; 1.97 to 178 Ga);
III. Post-collisional and anorogenic plutono-vucanic units (1.78-1.77 Ga); and IV. Clastic sedimentary sequences (~1.37 Ga).
The basement of this portion of the province corresponds to heavily razed areas and lacks outcrops. The basement unit is currently divided into two main complexes: (i) Bacueri-Mogno 2.24 Ga (Pimentel, 2001), not exposed in the eastern segment of the AFGP; and (ii) Cuiú-Cuiú 1992 ±7 Ma (Souza et al., 2005). The first main complex comprises pyroxene-rich orthoamphibolites, orthogneisses, paragneisses (garnet-silimanite-cordierite-biotite gneiss, illimanite-biotite gneiss and illimanite gneiss), enderbitic plutonics, banded iron formations, calc-silicate-quartzite-granite, quartzite-granitic rocks, metagabbro-norite and metapyroxene that exhibit mylonitic foliation and/or medium- to high-dip gneiss banding that are oriented east-west to east-southeast-west-northwest (Souza et al., 2005; Silva & Abram, 2008). Pimentel (2011) obtained isochronic Sm-Nd ages of 2.25 Ga and ?Nd(t) of 2.4 for amphibolite in this complex, corresponding, therefore, to the oldest age in the region. The Cuiú-Cuiú Complex, the second main complex, however, outcrops near the cities of Peixoto de Azevedo and Novo Mundo, and consists essentially of granitic to tonalitic gneisses, migmatites intruded by calcium-alkaline foliated granitoids of tonalitic to monzogranitic composition (Paes deBarros, 2007), in addition to shales, mafic and ultramafic rocks and banded iron formations (Dardenne & Schobbenhaus, 2001). The Matupá Gold Project area is part of the granitic bodies of the Matupá Intrusive Suite, which has an intrusive geological relationship to the gneiss basement of the Cuiú-Cuiú complex and to the Diorite/Gabbro bodies, the oldest regional event.
The Matupá Intrusive Suite are mostly identified from soil due to few available outcrop exposures or by diamond drilling. These rocks were intruded by quartz feldspar porphyries and late fine-grained mafic to intermediate dykes. These sequences are in contact with volcanic and pyroclastic rocks of the Colíder Group located north of Guarantã do Norte city.
The lithology of the basement rocks in the Project area includes biotite-tonalitic gneisses representative of the Cuiú-Cuiú complex. Among the most significant lithologies in the properties, particularly surrounding the X1 Deposit and parts of the Alto Alegre block, are medium, in equigranular and porphyritic biotite-granodiorites (potassium feldspar porphyries up to 3 cm in size) of light gray color, essentially isotropic, and may locally present incipient to little penetrative foliation when close to zones of regional magnitude shear or smaller shear zones reflecting them. The porphyritic biotite-granodiorites are composed of quartz, plagioclase, potassium feldspar phenocrysts (pink microcline), biotite and magnetite.
The Diorite/Gabbro bodies, the oldest regional event, present greater spatial expression, are phaneritic, magnetic, fine to medium grained, isotropic, and are mainly composed of plagioclase and hornblende, but locally phenocrystals of local plagioclase are also observed.
The X1 Deposit occupies a topographic high point (hill) and is hosted by the Matupá Intrusive Suite near the contact with the mafic/ultramafic Flor da Serra Suite. The extents of the deposit have dimensions of 400 m east-west and 250 m north-south.