Diagenetic evolution of sandstones and conglomerates of the Camaquã District, of Rio Grande do Sul, and its relationship with the Cu-Pb-Zn mineration

Abstract

The sulfide mineralizalion of lhe Camaquã mines (Cu) and of the Santa Maria deposit (Pb-Zn), State of Rio Grande do Sul, southem Brazil, is associated with red bed type deltaic alluvial fan conglomerates and sandstones, from the Brazílian - Pan African Event. The sulfide mineral development was controlled by the diagenetic evolutíon, as follows: a) - the Eodiagenetic Stage, comprises mechanical infiltratíon of clays, intense alteratíon of intrastratal detrital silicates and oxides, precipitatíon of hematite and quartz as silcrete beds. In transitional reduced lateral facies framboídal pyrite was also formed; b) - the Mesodiagenetic Stage is characterized by secondary quartz and feldspar overgrowths, changes of the detritic clays, neoformation of chlorites and illites, pyrite formation and intense calcite cementation. This event was followed by the generation of secondary porosity, late euhedric quartz growth, late feldspathic alteratíon, and ankerite precipitation. Fe-Cu-Pb-Zn sulfídes precipitated in the secondary porosity or replaced earlier phases; c) - the Telodiagenetíc Stage is characterízed by the development of a paleo-oxídation/cemenlation zone with supergene enrichment of Cu and Ag. The syntectonic remobilization of the Meso and Telodiagenetic sulfides produced lhe veins ai the Camaquã mines.