Hydrothermal alteration, mineralization and fluid inclusions in the Pista and Fofão prospects: implications for the genetic model of the Coringa polymetallic deposit, SE Tapajós Mineral Province, Amazonian Craton, Brazil
Journal of the Geological Survey of Brazil
Hydrothermal alteration, mineralization and fluid inclusions in the Pista and Fofão prospects: implications for the genetic model of the Coringa polymetallic deposit, SE Tapajós Mineral Province, Amazonian Craton, Brazil
Autor Correspondente: Rafael Guimarães Corrêa-Lima | [email protected]
Palavras-chave: Pista and Fofão epithermal gold mineralization, Tapajós, Brazil
Resumos Cadastrados
Resumo Inglês:
Pista and Fofão are prospects located near the main orebodies of the Coringa polymetallic deposit,
in southeastern Tapajós Mineral Province of the Amazonian Craton. In both prospects, the minerali
-zation is hosted in an Orosirian alkali feldspar granite, which is associated with coeval volcanic rocks
at Pista. The paleo-hydrothermal system comprises an early post-magmatic stage, characterized by
albite and K-feldspar alterations. Silicified and brecciated zones, sericitization of wall-rocks, both with
adularia, as well as carbonatization (siderite and Mn-siderite rich stage) are the proximal ore alteration
zones. Chlorite – hematite – rutile – epidote veinlets represent weak and distal zones of hydrothermal
alteration. The mineralization is polymetallic (Au and subordinate Ag, Zn, Pb, and Cu) and occurs as
dissemination and filling fissure veinlets. The gold occurs as inclusions in with silver-tellurides, inclu
-sions in pyrite and free gold in sphalerite and hematite within quartz veinlets. Fluid inclusions trapped
in quartz veinlets show H2O, H2O-CO2-NaCl and CO2 only inclusions. Microthermometric data indicate
an H2O-CO2-NaCl fluid, likely of magmatic derivation, with low-salinity (5.4 ± 1.3 wt. % NaCl equiv.) and
moderate density (0.36-0.94 g/cm3) trapped between 264 and 370ºC, and a low-salinity aqueous fluid
(≤11.2 wt % NaCl equiv.) trapped at 280 to 360ºC, possibly evolved from effervescence followed by
isothermal mixing with an external heated H2O-NaCl fluid, probably meteoric. After this, the fluids
were continuously diluted and cooled. This stage is represented by the liquid-rich H2O-NaCl fluid inclusions
of low salinity (up to 5.3 wt. % NaCl equiv.) and relatively low trapping temperature (177 to 113°C). The
petrographic and fluid inclusions data suggest that the Au, Ag and base metals precipitation resulted
from fluid mixing and dilution, which led to the breakdown of Au(HS)2. We interpret the Pista and Fofão
prospects as part of a magmatic-hydrothermal mineralized system, with some characteristics compa
-tible with those of low- to intermediate-sulfidation epithermal systems, despite the absence of some
typical textures from these systems.