Estudio de la relación entre las anomalías magnetométricas terrestres y los tipos de alteraciones hidrotermales presentes en la concesión minera “Caña Brava”, provincias de Loja y El Oro – Ecuador

Abstract

This work presents a study of the relationship between magnetic anomalies and hydrothermal alterations in “Caña Brava” mining concession, located in both Loja and El Oro provinces in Ecuador. The concession area is covered by volcanic and volcanoclastic rocks, which are attributed to Saraguro Group (Late Eocene-Early Miocene) affected by intrusive bodies (Middle Miocene). Magnetic survey was used to make a total magnetic field, reduction to pole and first vertical derivative maps. Interpretation show three main magnetic domains: Domain 1, high magnetic anomalies associated with fresh intrusive bodies and/or potassic alteration. Domain 2, low magnetic anomalies associated with argillic, advanced argillic and philic alterations. Domain 3, moderate anomalies related to magnetite bearing rocks with propylitic alteration, or deep intrusive bodies with strong magnetism. Through TerraSpec analysis and study of thin sections hydrothermal alterations were characterized. Advanced argillic alteration shows kaolinite-pyrophyllite-dumortierite in Soroche creek area, kaolinite-dickite-alunite association in Caña Brava creek area and alunite-pyrophyllite-kaolinite-dickite association in the Northeast area. Argillic alteration has abundant illite in Soroche creek area, where it was characterized. Phyllic alteration presents a sericite-quartz-tourmaline association; this alteration was found in both the Soroche and Caña Brava creek areas. Propylitic alteration is the most extensive in the concession area and was characterized in the Soroche and Caña Brava creek areas, it shows a chlorite-epidote mineral association. The relationship between hydrothermal alteration, magnetometry and geochemical zonation patterns suggest the presence of an epithermal high sulfidation system with transition to a porphyry copper type system at depth in the area of the concession, which should be proven by further exploratory drilling.