Gênese das mineralizações associadas ao magmatismo ácido na região do Garimpo do Papagaio, noroeste da Proví­ncia Aurífera de Alta Floresta (MT)

Abstract

The Alta Floresta Gold Province is situated on the southern portion of Amazonian Craton and forms an elongate region with WNW-ESSE direction where auriferous deposits are associated with Paleoproterozoic plutonovolcanic magmatism. The area of research covers the Papagaio artisanal gold mining, located in Paranaíta, Mato Grosso. During geological mapping, plutonic to subvolcanic rocks bodies of granodioritic and granitic compositions were identified, as well as dacitic and rhyolitic volcanic and pyroclastic rocks. These lithotypes belong to the calc-alkaline series of medium to high potassium, meta-to peraluminous corresponding to type I granites of volcanic arc in an active continental margin. U-Pb ages showed that magmatism in the region has crystallized in the range of 1.80-1.78 Ga with inherited zircons up to 2.1 Ga, showing evidence of a deeper and older crust during subduction. εNd (t) data showed the contribution of crustal and mantle material in the source with T DM age between 2.15-2.02 Ga. These data revealed that volcanism in the area belongs to the Colíder Suite, corresponding to a magmatism that was active for approximately 16 Ma and evolved from dacitic to a rhyolitic composition. The mining prospect occurs on gold mineralization with copper, zinc and low levels of lead, preferably confined in veins that cut potassic, seritic and propylitic alteration halos. The existing veins in the region evolve systematically into six types: (I) Barren quartz vein associated with potassic alteration halo; (II) Quartz vein with ore minerals, sometimes associated with sericitic halo; (III) Sulphide vein with a well developed sericitic alteration halo in the salbands; (IV) and (V) Late quartz and carbonate veins; (VI) system of quartz veins newer and unrelated to deposit evolution. The first three types are similar to A-B-D system described in porphyry deposits, while the newer ones have characteristics of a shallower and epithermal environment. Gold occurs mainly in the central zone of the type II veins, in paragenesis with chalcopyrite + sphalerite + pyrite ± galena ± magnetite. The quartz of the veins underwent different intensities of recrystallization due to subsequent hydrothermal pulses and cathodoluminescence images showed that aquocarbonic fluid inclusions represent primary fluids with important participation in metalliferous content transportation. The results of D, O and S stable isotope in hydrothermal quartz, sericite and pyrite show that fluids are magmatic with meteoric contributions. In this context, the Papagaio artisanal mining developed on a continental magmatic arc, from the intrusion of hydrated and oxidized granite bodies that mark the final magmatic event of the Colíder Suite. It represents a porphyry deposit that was superimposed by epithermal intermediate-sulfidation characteristics as a result of hydrothermal telescoping, resulting from the lowering of the magma chamber.

Gold in Paleoproterozoic (2.1 to 1.77 Ga) Continental Magmatic Arcs at the Tapajós and Juruena Mineral Provinces (Amazonian Craton, Brazil): A New Frontier for the Exploration of Epithermal–Porphyry and Related Deposits

“…The supracrustal sequences at the Tapajós, particularly those from the last orogenic event, reveal remarkably well-preserved volcanic textures and structures from deformation and metamorphism [70]. Large nested volcanic calderas (up to 50 km in diameter) over or close to large E-W lineaments have been identified in the Tapajós and Xingu areas [15,46,71], as well in the Juruena Domain [62,72].…”

“…1.89-1.87 Ga and ca. 1.97 to 1.95 Ga subduction-related calc-alkaline andesites to rhyolites have been separated from A-type rocks in several localities in the Tapajós Domain [3,15,46,56,[59][60][61] and the Juruena Domain [53,62,63].…”

“…1.79 Ga; [11]) and volcanic rocks of the Colíder Group (ca. 1.81-1.78 Ga; [58,62,79,80,82]. The Colíder Group comprises rhyolite, rhyodacite, quartz trachyte, ignimbrites, laminated ash-tuffs, epiclastic rocks, and minor andesite [74,77].…”

“…The Colíder Group comprises rhyolite, rhyodacite, quartz trachyte, ignimbrites, laminated ash-tuffs, epiclastic rocks, and minor andesite [74,77]. These units are often crosscut by 1.79-1.78 Ga mafic to felsic dikes emplaced in variable crustal levels, including gabbro, diabase, andesite, dacite, and rhyolite [23,29,62,79].…”

“…HS = Field of high-sulfidation hydrothermal fluids; LS = Low-sulfidation fluids, and T = Alunite of the 1.87 Ga Tapajós high-sulfidation fluid. Data source: [this paper, [8,15,20,35,62,76,100,101]]. Nine 40 Ar-39 Ar spectra for alunite yield ages between 1869 ± 2 Ma and 1846 ± 2 Ma.…”