known. To date, no extensive reconnaissance or geochemical work has been carried out. In order to promote future exploration, the author searched among spanish historical documents for clues of previous mining operations. Through the research a total of twenty three (23) sites were relocated which reveal a predominantly gold placer mining operation in the region. Furthermore, the data clearly denotes two zones of mineral occurrence: a northern gold-rich deposit zone and a southern copper dominant area. The extensive hydrothermal processes and contact metamorphism associated with the Rio Blanco Stock and its proximity to the southern hydrothermal alteration belt and San Lorenzo Batholith appear to account for this mineral differentiation.