Abstract
The Crixas gold deposit is located in central Goias State, approximately 400 km northwest of the capital Brasilia. It is owned in joint venture by INCO Gold Ltd. and Anglo American Ltd. The indicated reserves are 7 million metric tons with a grade of 10 to 12 g/metric ton. The discovery was made in the late 1970s with mining commencing in the fall of 1988.The hosting Crixas greenstone belt is underlain by a typical Archcan metamorphosed volcanic-sedimentary sequence and is surrounded by granite-granite gneiss terrane. The Crixas gold deposit is located at the contact of the metavolcanic and metasedimentary sequences. Gold ore occurs within an upper and lower ore zone. The upper ore zone consists of an outer shell of ferroan dolomite-chlorite-biotite schist, an inner shell of sericite-chlorite schist, and magnetite-chlorite schist which in turn surrounds a core of massive arsenopyrite-pyrrhotite-chalcopyrite. The lower ore zone consists of a quartz-cemented graphitic pelite breccia.The upper and lower ore zones are interpreted to represent metasomatically altered parent lithologies. Metasomatism postdates a maximum regional metamorphism of epidote-amphibolite facies or biotite-garnet grade. Carbonatization, sericitization (base leaching), silicification, and sulfidization are indicated to have operated during the development of the ore deposit. Gold deposition is believed to have occurred as the result of reduction of f (sub S 2 ) through the formation of Fe-rich carbonate, silicate, and sulfide phases.The style of deformation within the deposit is typical of a high-strain environment. Regional structural data provide strong evidence that the high strain is related to low-angle thrusting. The age of the thrusting or the time of mineralization is not known; however, low-angle thrusting is related to a Brasiliano cycle event (550-450 Ma).
Published Version
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