Central is a gold deposit of the Cuiú-Cuiú goldfield, located in the Tapajós Gold Province,
Amazonian Craton. The deposit is hosted in a NW-SE-trending structure and the mineralized
zone is followed by 800 m along the strike and 450 m along the dip, and is 50-70 m thick. The
ore bodies are hosted in a monzogranite dated at 1984±3 Ma and ascribed to the Parauari
Intrusive Suite. Resources are estimated in 18.6 t Au. The hydrothermal alteration is
predominantly of the fissure-filling type and sericitization, chloritization, silicification,
carbonatization and sulfidation are the main alteration types. Pyrite is the predominant sulfide
mineral, whereas chalcopyrite, sphalerite and galena are subordinated phases occurring in
fractures and rims of pyrite. Gold particles occur in fractures of pyrite and contain subordinate
amounts of silver. Three types of fluid inclusions are hosted in quartz veins and veinlets. Type
1 is the least abundant and is composed of one- (CO2vapor) and two-phases (CO2liq-CO2vapor)
inclusions; Type 2 comprises two- (H2Oliq-CO2liq) and three-phases (H2Oliq-CO2liq-CO2vapor)
inclusions; Type 3 is the most abundant type and consists of two-phases (H2Oliq-H2Ovapor)
inclusions. CO2 is the volatile phase in CO2-bearing inclusions (types 1 and 2) and these
inclusions were produced by phase separation of an aqueous-carbonic fluid. The density of
this fluid is low to moderate (0,33 - 0,80 g/cm³), as is the salinity (11.15 - 2.42 wt.% NaCl
equiv.). The homogenization temperatures show a peak at 340ºC. Type 3 inclusions have
NaCl as the main salt component, the global density varies from 0.65 to 1.11 g/cm³, and the
salinity ranges from 1.16 to 13.3 wt.% NaCl equiv. The homogenization temperature shows
bimodal distribution, with peaks at 120-140ºC and 180ºC. Fluid inclusion and mineral (quartz,
chlorite, calcite) isotopic compositions show δ18O and δD values of +7.8 to +13.6 ‰ and -15
a -35 ‰, respectively. Pyrite shows δ34S values of +0.5 to +4.0 ‰ and δ13C values ranging
from -18 to -3.7 ‰ were obtained in calcite and CO2 inclusion fluids. The fluid δ18OH2O and
δDH2O values plot in the field of metamorphic waters with a weak shift towards the meteoric
water line. However, considering the absence of known metamorphic event at the time of
mineralization at Central, the fluids are interpreted as belonging to a magmatic-hydrothermal
system. Accordingly, the aqueous-carbonic fluids were exsolved from felsic magmas related
to the latest phases of evolution of the Parauari Intrusive Suite and the carbonic and aqueouscarbonic
fluid inclusions were trapped in this phase, predominantly at 340°C. The continuous
exsolution lead to progressive decrease in the CO2 contents of the magmas and to increasing
predominance of aqueous fluids. At this time, the fluids might have interacted with meteoric
waters and most of the low-temperature aqueous inclusions were trapped. It is possible that
part of the aqueous fluid inclusions (those with the highest trapping temperatures) represent local mixing of the different fluid sources. These observations allow to interpret Central as a
magmatic-hydrothermal gold deposit related to the final stages of evolution of the Parauari
Intrusive Suite.
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