Geologia e Metalogênese do Depósito Au-Ag (Pb-Zn) do Coringa, Sudeste Província Mineral Tapajós, Pará.

Abstract

The Tapajós Mineral Province (TMP) is located in the south-central portion of the Amazonian Craton and is considered one of the main metallogenic provinces of Brazil. A significant part of the province comprises felsic volcanic and volcanoclastic rocks and granites, which formed predominantly in two intervals, 2.02 to 1.95 Ga and 1.91 to 1.87 Ga, belonging to several stratigraphic and lithodemic units. Fieldwork, petrography, and high-resolution airborne geophysics allowed us to produce a new map at the 1:100,000 scale for the southeastern portion of the TMP, where the gold and silver (Cu-Pb-Zn) Coringa deposit is located. We identified two new geological units: (1) the volcanic and pyroclastic rocks of the Vila Riozinho Formation, previously attributed to the Iriri Group, including a facies defined here of this formation, which comprises a group of rocks with the largest magnetic content in the region (Vila Riozinho Formation - magnetic pyroclastic facies), and (2) the Serra Alkali Feldspar Granite, which intruded into the Vila Riozinho Formation (VRF). These units are the host rocks of Coringa deposit. The FVR rocks represent a magmatic arc with high K calcalkaline to shoshonitic affinities. There are similarities in the patterns of LILE and HFSE and the multielementar diagrams with the granitic rocks from Creporizão Intrusive Suite (CIS). The contemporaneousness between these units reinforce a possible petrogenetic correlation and converge to the hypothesis of similar sources, of probable remelting of arc rocks. Isotopic data revealed similar behavior between VRF, SAFG and Maloquinha Intrusive Suite expose similar behavior and present negative εNd values; however, it indicates rocks derived from enriched sources (ancient crustal rocks). Therefore these units had the same source during tectonic setting and crustal evolution of TMP. It is a transcurrent post-collisional stage that followed the collision of the Cuiú-Cuiú Magmatic Arc related to the Orosian volcano-plutonic event (2033-2005 Ma). Based on available geochronological information these units can be associated with a volcano-plutonic event that occurred in the Orosirian period, at about 1.98 Ga. The Au-Ag (Cu-Pb-Zn) Coringa deposit, occurs essentially in veins and veinlets whose match the regional trend (NNW-SSE). The host rocks are volcanic and pyroclastic rocks of the Magnetic Pyroclastic Facies (MPF) from the Vila Riozinho Formation (ignimbrites, tuffs, and breccia), and the Serra Alkali Feldspar Granite, with a predominance of the supracrustal rocks The hydrothermal processes affected all lithotypes associated with mineralization, producing distal alteration (carbonate-chlorite-epidote), intermediate-proximal alteration (sericite-pyrite) and proximal alteration (chlorite-hematite). The mineralized veins are generally composed of quartz + pyrite + chalcopyrite + galena + sphalerite + electrum + chlorite + sericite. Gold grains occur as inclusions or fractures in pyrite. The fluids presents low salinity, rich in H2O and poor in CO2, with evidence of mixing (magmatic-meteoric), and the presence of adularia and Mn-carbonate are outstanding features of this deposit. All characteristic converge to confirm an intermediate- sulfidation epithermal deposit as a genetic model to Coringa deposit.