Genesis and applications of the Cerro Rubio kaolin deposit, Patagonia (Argentina)

At Cerro Rubio area, the stratigraphic position and the origin of kaolinization have been a matter of controversy. Most of the residual kaolin deposits of Patagonia, Argentina are related to a paleoweathered surface developed over the rhyolitic Bahia Laura Group during the Upper Jurassic–Lower Cretaceous. In the nearby areas and in the same type of rocks, there are Au–Ag epithermal deposits that show argillic alteration, therefore determining the origin of the alteration (weathering or hydrothermal) is essential in exploring new areas for either gold or kaolin. The source rocks are tilted tuffs where the ash-shards and biotites were transformed to kaolinite. A positive cerium anomaly as well as the high δ18O isotopic composition of the kaolinite of 23–24‰ suggest that the kaolinite was formed under weathering conditions. Field and fossil evidence indicate that the source rocks were Middle Jurassic in age. All these evidences suggest that the Cerro Rubio is part of the Paleoweathered surface of Patagonia where almost all the kaolin deposits of Argentina occur.