Newmont Overseas Exploration Limited, Surinam

The Chega Tudo gold deposit is located in the Gurupi belt of northern Brazil. Gold mineralization in the Mina Velha (upper level) and Mandiocal (intermediate and lower levels) orebodies is hosted in highly strained Paleoproterozoic (2148–2160 Ma) felsic to intermediate metavolcanic rocks and schists that record greenschist facies metamorphism. The orebodies are broadly concordant with the regional northwest-oriented foliation, and mineralization comprises thick quartz vein sets and small quartz-carbonate-sulfide veinlets and enclosing hydrothermally altered host rocks. The hydrothermal mineral assemblage is postpeak metamorphism, syn- to late tectonic, and includes quartz, calcite, chlorite, white mica, pyrite, subordinate chalcopyrite, and traces of sphalerite and galena. Free-milling gold occurs in sulfide-poor veins in the upper and lower zones of the deposit, whereas refrac-tory gold was deposited in fractures of pyrite and quartz in the more gold-enriched intermediate (±lower) level. Fluid inclusion and stable isotope (O, H, C, and S) data indicate that the two styles of gold deposition were produced by a combination of fluid immiscibility, fluid-rock reactions (sulfidation, carbonatization), and prob-ably mixing, occurring in two discrete stages within a single mineralizing event associated with fluid flow within and around an active shear zone under fluctuating pressure conditions