In the Concepcion del Oro region, Cretaceous-age sedimentary rocks are folded into a set of anticlines and synclines. The stratigraphy, consisting mostly of calcareous shale interbedded with limestone and sandstone of the Caracol formation, is steeply dipping. There are also significant amounts of thicker bedded limestone in the area. The Cerro de Oro mineralized zone is located midway between a large syncline that passes a through the town of Melchor Ocampo and a paired anticline about three kilometers to the north.
A granodiorite porphyry intrudes the earlier sedimentary rocks and outcrops in the central parts of the mineralized zone. The outcropping granodiorite contains mineralization ranging from quartz veinlet type to fracture type stockwork.