Between 1995 and 2000, the British Geological Survey and the Government of Ecuador carried out regional-scale surveys in the Cana Brava area which included an airborne magnetic survey, geological mapping, and rock and stream sediment sampling. The regional airborne magnetic survey (1 km line spacing) outlined a series of structures and large scale geological features including a 5 km-wide east-northeast trending magnetic low which passes directly through the Cana Brava property. This magnetic low may be due to magnetite destruction associated with hydrothermal alteration along a coincident structure. The Giron Fault is not evident in the magnetic data, however a mapped regional east-northeast trending fault lies on the north side of this magnetic low. Lineaments related to major structures and twin concentric rings/faults that may represent caldera structures are evident from regional topographic maps, and this is supported by regional volcanogenic studies.
Industry exploration work on the property was first reported in the early 1990's and consisted of satellite imagery analysis to define exploration targets for field follow-up. During 1994, Rio Tinto Zinc Corporation explored for epithermal gold and porphyry copper deposits and carried out a stream sediment geochemistry survey. Iamgold Corporation carried out regional exploration throughout the district in 2000 and the western part of the Cana Brava property was covered by a soil geochemistry survey (100 m spaced samples on 100-200 m spaced grid lines) as part of this program. They reported anomalous copper, molybdenum and gold coincident with epithermal alteration.
Cornerstone Exploration Program
Cornerstone acquired the Cana Brava property in 2007, but work was suspended for a prolonged period resulting from the Mining Moratorium enacted in April 2008. Immediately thereafter the Cana Brava mining title was erroneously revoked by the Ecuadorian Government, however this decision was appealed and the mineral rights were restored in November 2012 (see November 14th news release).
Exploration work on the Cana Brava property prior to the Mining Moratorium has consisted of data compilation, reconnaissance geological mapping, prospecting and rock sampling.
Geology and Mineralization
On the west side of the Cana Brava property, hydrothermal breccia (Cana Brava Breccia) outcrops over a large area measuring 1 km by 0.5 km. These breccias are interpreted to represent the uppermost part of a mineralized porphyry system. Goethite and hematite are extensively developed as disseminations and stockwork veins within the breccias which are often silicified with fine quartz veinlet networks and granular silica. Vuggy silica occurs in breccia clasts and structural zones. Clasts and blocks of dacite quartz feldspar porphyry are common.
Silicic ribs are characteristic of the Cana Brava property and are generally 1-2 m wide, but 10-20 m widths are recorded. They are extensively developed on the west side of the property over an area measuring 2.5 km by 2 km centered on the Cana Brava Breccia. The ribs often display a breccia texture with angular clasts of silicified quartz feldspar porphyry and iron oxide stockwork. They have a pronounced northeast trend sub-parallel to the two main regional faults.
Alteration typical of porphyry and high sulphidation epithermal systems, including advanced argillic, argillic and propylitic alteration, accompany mineralized hydrothermal breccia and silicic ribs at both the Cana Brava Breccia and the East Zone.
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