Geology of Ecuador
Ecuador’s main physiographic elements broadly coincide with geological domains. The flat-lying western Costa forearc and the eastern Oriente foreland areas bound the Andean mountain chain that splits into two segments, the Western (Occidental) and Eastern (Oriental) cordilleras. These two cordilleras in Ecuador are separated by the Inter-Andean Depression.
Volcanic and magmatic arcs within Ecuador span the Jurassic to Quaternary periods
Some of the oldest exposed rocks in Ecuador are of Palaeozoic to Precambrian age that outcrop as a fault-bound inlier along the western side of the Eastern Cordillera.
A Jurassic volcanic arc broadly coincides with the eastern side of the Eastern Cordillera and extends the full length of Ecuador but terminating in northern Peru. This Jurassic arc hosts several porphyry copper-gold and epithermal gold deposits at Mirador, Mirador Norte, Panantza-San Carlos, Warintza, and Fruta de Norte in southeast Ecuador.
Magmatism retreated ocean-ward during the Cretaceous, with a Cretaceous arc running the length of Peru and encroaching northward and terminating in southernmost Ecuador. This Cretaceous belt is not known to be a major porphyry belt other than for a short segment of the belt in coastal central Peru where it hosts the Los Pinos and Almacen deposits and Ellana, Tingo, Puquio, Anita de Tibilos and Chavez N2 prospects. The northern end of this Cretaceous arc includes the large Tangula batholith which lies just south of the Bramaderos property, and which is a member of the coastal batholiths further south in Peru.
During the Late Cretaceous, several allochthonous (i.e. transported from a distance) oceanic terranes were accreted to the Ecuadorian margin and form the basement to the forearc (i.e. the Costa forearc) of the presently active Quaternary volcanic arc that runs along the Inter-Andean Depression. In southwest Ecuador, the allochthonous Amotape terrane, which is a distinct tectonic block that extends into northern Peru, accreted to the Ecuadorian margin during the Palaeozoic to earliest Cretaceous. The El Oro Massif is a micro tectonic block at the northern edge of the Amotape terrane which imparts an east-southeast structural trend that is anomalous relative to the main north-northeast trend of Ecuador.
The stratigraphic sequence that dominates the Bramaderos property forms part of the Cretaceous-age Celica-Lancones Basin in southwest Ecuador and northwest Peru. This extensional basin formed over the Amotape Block and its suture with the Andean margin. The basin hosts large VMS deposits at Tambo Grande in Peru and was deformed in the Late Cretaceous.
During the subsequent Palaeocene to Eocene epochs, extensive volcanic rocks of the Sacapalca Formation erupted east of the Cretaceous arc and along the southerly extension of the Inter-Andean Depression.
Superimposed on these older volcanic arcs is a zone of Miocene magmatism which runs north-south along the full length of Ecuador, and which hosts numerous porphyry and high-sulphidation deposits and prospects. The Miocene Belt is quite wide in east-west dimension in central-south Ecuador where intrusions of diorite, quartz diorite and granodiorite form the ESE-trending Cangrejos-Zaruma intrusive belt controlled by a deep-seated or crustal scale fracture system along the northern edge of the Amotape terrane.
The Miocene epoch was an exceptionally metallogenically fertile period in southern Ecuador and northern Peru. A belt of magmatic-related gold-copper and copper-gold deposits, mostly porphyry-related systems, of Miocene age extend from around 3oS in Ecuador down to 8.5oS in Peru. The Miocene belt is less prolifically mineralized north and south of this latitude range. This interval of high copper-gold fertility is genetically related to the subduction of the Inca Plateau beneath this sector of the Andean margin during the Miocene. The inland deflection of contours on the Wadati-Benioff Zone (depth to zone of seismicity related to the subducting plate) is a consequence of buoyant and flat subduction of the Inca Plateau segment of the plate, resulting in widespread compressional tectonics in the over-riding plate which, a key factor in porphyry copper-gold metallogenesis.
