Geologia do depósito de Au Cavalo Branco (Botuverá - SC)

Abstract

Cavalo Branco is a quartzvein gold deposit located in the Botuvera region (SC, Brazil). The deposit is genetically related to the emplacement of a small diorite pluton in a conjugated fracture of a shear zone affecting metapelitic hornfels from the Brusque Group, formed by granitic plutons emplaced around the deposit. The mineralizing fluid that formed the gold quartz vein has generated potassic, phyllic and propilithic hydrothermal zones around the vein. Gold, with small amounts of pyrite, chalcopyrite and galena, has crystallized during the development of the phyllic zone. A shear zone reactivation has deformed part of the gold bearing quartz vein and provided the rising of pink granite veins. New hydrothermal fluids related with the reactivation displaced gold and sulfides from the sheared portion of the deposit and promote carbonatization and chloritization of the host rocks. Recrystallized gold shows silver (23,20%) and copper (0,51%) grades a little higher than primary crystallized gold (19,95% e 0,01%, respectivelly). Recrystallization has not changed the sulfide compositions. Primary mineralization has the same characteristics of periplutonic granitogenic gold veins. Although the shear reactivation has changed gold composition and the alteration style of the host rocks, these changes are not considered enough to justify the classification of the deposit as “orogenic”. The facies of the diorite that formed the deposit and the pink granite dykes emplaced during the shear reactivation were not yet known in the Botuvera region.