Pista is a prospect located near the main orebodies of the Coringa gold deposit, in southeastern Tapajós Gold Province, near to Novo Progresso town, State of Pará, Brazil. The detailed petrographic investigation of drill core samples indicates that an alkali feldspar granite is the main host rock to the mineralization. This rock consists of perthite k-feldspar, quartz and albite. In addition, a set of pyroclastic rocks, consisting of alkali feldspar rhyolitic ignimbrite and lapilli-tuff, and hydrothermal breccia have also been recognized. These rocks were affected by different stages of hydrothermal alteration. Seven types of alteration have been recognized: albitization, propylitic, sericitization, silicification, carbonatization, argillic and hematitization. Sericitization and silicification are the most significant ones, and are related with the Au-sulfide mineralization. Adularia, associated with quartz veinlets and sericite, has been observed in strongly sericitized and brecciated zones. The mineralization occurs in two styles, disseminated and fissure-filling, and includes pyrite, sphalerite, galena and chalcopyrite. Analyses by SEM-EDS showed hessite particles (Ag2Te) containing up to 6.6% Au and sphalerite with Au contents between 1.5 and 3.25%, indicating that Au is associated with Ag and Zn. Quartz veinlets contain fluid inclusions that occur in clusters, intra- and transgranular trails and in isolation. Preliminary microthermometric analysis allowed the recognition of three different fluid types: (1) aqueous-carbonic fluid (fluid I), with low-salinity, from 3.0 to 8.0 wt.% NaCl equiv., and CO2 contents from 0.06 to 0.7 (mol% CO2); (2) aqueous fluid (fluid II), with low-salinity, from 6.0 to 9.7 wt.% NaCl equiv. Both fluids are probably of magmatic origin and formed by boiling. There is also an (3) aqueous, low salinity fluid (Fluid III), with 0.2 to 3.0 wt.% NaCl equiv., and homogenization temperatures ranging from 190 to 310ºC, resulting from meteoric water inflow. The host rock types, the polymetallic nature of the mineralization, the occurrence of adularia in the hydrothermal alteration, and the presence of low salinity aqueous-carbonic and aqueous fluids allow us to suggest that Pista is part of a magmatic–hydrothermal mineralized system, possibly a low- or intermediate-sulfidation epithermal system.
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