Dec 21 2012
Cornerstone Capital Resources Inc. announced today results from prospecting and geological mapping surveys carried out on its wholly owned Caña Brava property located in south-central Ecuador.
Highlights:
- Two large high sulphidation (HS) epithermal gold-silver zones defined by extensive hydrothermal breccia and silicic ribs developed within an advanced argillic alteration lithocap
- West Zone (Caña Brava Breccia) is developed over a 2.5 km by up to 2 km area and is coincident with a 3 km by 1 km multi-element soil geochemistry anomaly
- East Zone shows a similar HS system measuring 1.75 km by 1 km which is open in most directions
- 334 rock samples collected with multiple samples returning anomalous gold (18 samples > 1 g/t Au, 36 samples > 0.5 g/t Au) and silver (13 samples > 100 g/t Ag, 35 samples > 30 g/t Ag)
- Base metals and epithermal pathfinder elements are strongly anomalous throughout the Caña Brava Breccia
- Porphyry gold-copper target identified below the Caña Brava Breccia
Brooke Macdonald, President of Cornerstone, stated "Exploration results to date on the Caña Brava property show good potential for significant epithermal gold and silver mineralization with strong indications of porphyry style mineralization at relatively shallow depths. Currently we are seeking a partner to help fund additional exploration surveys in order to develop drill targets. It is noteworthy that despite the excellent potential, no drilling has ever been carried out on the property".
The 1,150 hectare Caña Brava property is located near the community of Gualel in the province of Loja, 100 km south southwest of the city of Cuenca. The project area is situated in the Ecuadorian Andes on the east side of the Cordillera Occidental at elevations ranging from 2,950 m to 3,650 m above sea level. Access from Cuenca is provided by paved roads and a secondary gravel road to Gualel, from which trails provide access to the property. Maps showing the location, geology and exploration results for the Caña Brava property can be viewed at http://cornerstoneresources.com/i/pdf/NR12-27CanaBrava.pdf.
Regional Geology and Mineralization
The Caña Brava property is underlain by Tertiary age sequences of mafic and felsic volcanic flows, tuffs and sediments which are intruded by granodiorite and diorite batholiths and stocks. Structurally the area is bounded by two major north-northeast trending regional faults, the Giron Fault which cuts directly through the property, and the Catamayo Fault located approximately 15 km to the east. Cross cutting transverse faults developed within this north-northeast structural trend commonly control the emplacement of intrusions and development of associated porphyry and epithermal alteration and mineralization. Caña Brava is located in the southwestern part of a northwest oriented belt of epithermal precious metal prospects and deposits.
Property History
Between 1995 and 2000, the British Geological Survey and the Government of Ecuador carried out regional-scale surveys in the Caña 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 Caña 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 Caña 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 Caña Brava property in 2007, but work was suspended for a prolonged period resulting from the Mining Moratorium enacted in April 2008. Immediately thereafter the Caña 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 Caña 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 Caña Brava property, hydrothermal breccia (Caña 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 Caña 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 Caña 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 Caña Brava Breccia and the East Zone.
Results and Discussion
During the prospecting and geological mapping programs at the Caña Brava property, Cornerstone collected a total of 334 representative rock chip samples with 18 returning > 1 g/t Au, 36 returning > 0.5 g/t Au and 66 returning > 0.2 g/t Au. One sample assayed 64.5 g/t gold with high silver value (42.5 g/t Ag). In addition, 13 samples assayed > 100 g/t Ag, 35 samples assayed > 30 g/t Ag and 59 samples assayed > 10 g/t Ag. There is strong correlation between gold and silver assay results and base metal and epithermal pathfinder element values are strongly anomalous throughout the Caña Brava Breccia area to the west.
Historical soil sampling surveys show a 3 km by 1 km multi-element (Au-Ag-As-Sb-Hg-Cu-Mo) anomaly associated with the Caña Brava lithocap, and Cornerstone's rock sampling program has confirmed gold-silver-copper mineralized zones associated with hydrothermal breccia and silicic ribs. Furthermore, recent work has provided a much better understanding of the nature and controls of alteration and mineralization.
Two mineralized HS epithermal zones have been identified on the Caña Brava property extending over 2.5 km by up to 2.0 km on the Caña Brava Breccia and 1.75 km by 1 km on the East Zone. Economic grade gold and silver assay results from samples collected from outcrop throughout the altered and mineralized zones strongly suggest potential for precious metal epithermal deposits as well as copper-gold porphyry deposits at depth. The East Zone is exposed as intermittent outcrop over an area of 1.7 km by 1 km and is defined by silicic ribs and hydrothermal breccia possibly related to another porphyry system centered on the Fierro Urco lithocap located 2.5 km northeast of the property. The silicic ribs and breccia are associated with advanced argillic alteration and are strongly anomalous in precious and base metals, as well as epithermal pathfinder elements.
Qualified Person
Yvan Crepeau, M.Ba., P.Geo, President Cornerstone Ecuador SA and a qualified person in accordance with National Instrument 43-101, is responsible for supervising the exploration program and has reviewed and approved the technical information contained in this news release.
Assaying
All samples were delivered by Cornerstone employees for preparation at Acme Analytical Laboratories (ACME) facility in Cuenca. Rock samples are prepared by crushing 1 kg to 80% passing 2 mm (10 mesh), splitting 250 g and pulverizing to 85% passing 0.06 mm (150 mesh) (ACME code R150). Prepared samples are then shipped to ACME in Vancouver, Canada where samples are assayed for a multi-element suite (ACME code 1F-MS, 15 g split, Aqua Regia digestion, ICP-MS finish).
Quality Assurance / Quality Control (QA/QC)
The ACME preparation facility in Cuenca was audited by Cornerstone. ACME is an ISO 9001:2008 qualified assayer that performs and makes available internal assaying controls. Certified blanks and standards are systematically used as part of Cornerstone's QA/QC program. Rejects and 100 g pulps for each rock sample are stored in Cuenca for future use and controls.
Source: http://www.cornerstoneresources.com/