Santa Cruz Regional Exploration Properties
The Santa Cruz regional projects include Falcon, Verde, Azul, and Puntudo properties. Many of the properties within the regional exploration package were strategically located by CVSA using satellite imagery in Patagonia, suggesting large alteration systems. The amount of subsequent exploration on these has varied, but in many cases anomalous gold mineralization has been identified. Extorre is re-examining all of these systems with a view of identifying gold and/or silver targets at a size threshold lower than that used by CVSA in the first instance.
By the end of 2010, the company completed sufficient drilling ( +10,000 metres) to trigger a "back-in" decision by CVSA. On March 19th, 2011 Cerro Vanguardia ("CVSA") advised the Company that it elected not to exercise its back-in right on the the Santa Cruz Projects (namely Verde, Azul, Falcon and Puntudo properties). Extorre now owns 100% of the projects and CVSA retains only a 2% net smelter return.
Santa Cruz Province - Project Location Map
Falcon
Falcon is located about 80 km north of Cerro Vanguardia mine in Santa Cruz province. Gold mineralisation on this property is associated with tectonic and carapace breccias in a 12 square kilometre rhyolite flow dome setting. Gold is hosted in strongly brecciated brittle fracture zones developed in the rhyolite flow-dome and at its brecciated contact with the host tuffs and volcaniclastics. Gold appears to be associated with finely banded chalcedonic to fine crystalline quartz veinlets cutting the breccias and filling open spaces within the breccias. Powdery hematite is a common feature of the mineralization. Pyrite is locally present and visible gold has been reported. The hydrothermal alteration comprises silicification of the rhyolite breccias, and local argillic alteration.
Work completed includes reconnaissance geological mapping and rock chip sampling. Better rock chip assay results include:
- 2 metres at 7.1g/t Au, 87 g/t Ag,
- 2 metres at 2.2 g/t Au, 10 g/t Ag, and
- 23 metres at 1.8g/t Au including 2 metres at 17.3 g/t Au.
Magnetic and IP surveys were conducted to define structures underneath cover, and to better delineate drill targets.
Diamond drilling commenced in Q4, 2010 and by year end, 620 metres were drilled to test for potential large low grade gold deposits. Diatreme breccias were encountered, and assays are awaited.
In February, 2011 Extorre announced results from reconnaissance drilling on the Falcon property, located 80 kilometres to the northwest of Cerro Moro, and 6 kilometres to the northeast of Mariana Resources' Dos Calandrias project. Four of five initial holes intercepted broad zones of gold - silver mineralization. See Extorre press release dated February 22nd, 2011 for more details on these results.
Verde
Silver mineralisation on this property, in western Santa Cruz Province, relates to at least 30 structures with epithermal vein quartz and alteration zones proximal to a volcanic sinter. Strike lengths of veins range from 100 to 700 metres and widths from 0.7 to 3.0 metres. Work by CVSA included geological mapping and extensive rock chip sampling which gave strongly anomalous silver values. The values above 15g/t silver are shown on the map. The sinter zone is shown in red, and felsic volcanics in yellow.
Exeter has conducted a program to confirm values, conducted more detailed mapping and sampling, in addition to magnetic and IP surveys to outline structures under extensive cover.
Drilling in Q4, 2010 targeted testing high grade veins at depth, and also major structures delineated by geophysics under cover. A total of 1580 meters was drilled and at end 2010, with some 1700 samples are in various stages assaying and processing. The total metreage drilled on the Verde property to end 2010 is 3623.74 meters which includes 42 RC holes for 2044 meters in the previous 2006 reverse circulation drilling program.
Puntudo
The Puntudo Project is located some 250 kilometres west of the Cerro Moro Project in Santa Cruz, Argentina. Extorre is operating two drill rigs on the property to test structures that are the potential extensions to the high grade silver system on the Joaquin property to the north. Potential extensions to both the La Marocha and the La Negra trends have been defined on the basis of exploration that included geological mapping, geochemistry and ground magnetics.
Puntudo Project Location Map with Ground Magnetics
Historic Work Completed at Puntudo
In 2010, work at Puntudo focused on the central Puntudo Hill area and structural extensions, where economic tenure gold-silver intersections have been drilled. The data was re-interpreted and drill targets were outlined. Additional exploration potential was evident from silver gold drill intersections on adjacent properties owned by third parties, and a complete regional evaluation was completed.
Geology and Mineralisation
The property is underlain by Jurassic age volcanics of the Bahia Laura Gp including variably welded rhyolitic tuffs, rhyolite flows and local vitrophyres of the Chon Aike Fm and minor air fall tuffs. In the north part of the area and forming the peak of Puntudo is a heterolithic breccia unit, interpreted by Mincorp geologists to be of diatreme origin. Principal structural trends on the property are NW and NE.
The gold mineralized zone at Puntudo forms a prominent elongate zone trending WNW as an annular structure rimming a rhyolitic flow dome, and extending in a south easterly direction for some six kilometres. The flow dome is interpreted to have formed on the northern margin of a large volcanic caldera.
Where it crops out, this favourable breccia structure varies from a few metres wide, to approximately 20 metres wide at La Quebrada and Rico Sectors to 200 metres wide at Puntudo Sector where it may be represented as a diatreme. Hydrothermal breccias have a matrix of iron oxide and silica comprising at least five separate stages of silicification.
Exploration
Exploration has been conducted by both CVSA and Exeter. Exeter's work has included detailed mapping, induced polarization surveying, ground magnetics and drilling.
Gradient Array Resistivity
Exeter have collected a total of 375 composite rock chip samples, each covering an area of about 3 to 10 square metres, and channel rock chip sampling.
Exeter composite rock chip channel sample across the Quebrada Sector gave 25 metres @ 1.7 g/t Au, 127 g/t Ag, and 2.4% Pb. These results confirm CVSA rock chip channel sampling, which had yielded 26.5 metres grading 1.9 g/t gold. Two separate composite rock chip channel samples, taken at the Quebrada North prospect gave 2.5 metres @ 74 g/t Au and 192 g/t Ag and 2 metres @ 8.1 g/t Au.
Exeter also confirmed results from the Rico Sector, located approximately two kilometres northwest of the Quebrada zone. Sampling by CVSA had returned 21 metres grading 3.5 g/t gold and Exeter sampling gave 5 metres grading 31 g/t gold and 29g/t silver. A separate rock chip channel sample by Exeter at Rico gave 14 metres @ 2.0 g/t.
A third zone, the Puntudo zone, located 900 metres to the northwest of the Rico zone is a large area of breccia, now considered a sinter zone. Initially a total of 28 large composite samples, collected by CVSA and Exeter over an area of 10,000 square metres in the Puntudo zone, averaged 0.5 g/t gold. Follow-up composite rock chip and rock chip channel sampling has confirmed values to be less than 1.0 g/t Au with a single sample returning 24 g/t Au.
Channel sampling by Exeter discovered a new zone of silicification ("Quebrada South"), 1.6 kilometres southeast of La Quebrada Sector, that returned 1.2 g/t gold, 57 g/t silver and 0.15% lead over a width of 4.5 metres.
Outside of the main mineralized structure, Exeter discovered further mineralization consisting of silica veining in rhyolitic volcanics. Individual samples returning assay values up to 17 g/t gold. This new zone is some 2 kilometres south of the Puntudo zone.
Drilling Results
Follow-up drilling over the 4 kilometre long Puntudo structure was completed in May 2005, comprising 21 reverse circulation percussion drill holes for a total of 1,719 metres, with down hole depths varying from 36 to 140 metres. This programme was to further test significant auriferous intersections highlighted in the December 2004 and January 2005 drilling, where previously best results received included; 20 metres at a grade of 3.6 g/t gold, including 4 metres at a grade of 9.2g/t gold intersected in CPRC24 and 20 metres at a grade of 3.7 g/t gold, including 8 metres at a grade of 9.6g/t gold intersected in CPRC27. New high grade intersections include; 2 metres at a grade of 12.1 g/t gold intersected in CPRC43 as displayed on the following cross section.
And 2 metres at a grade of 42 g/t gold intersected in CPRC50 as displayed on the following cross section:
Following the successful second tier drilling at the Rico prospect deeper drilling was performed to test the mineralisation at greater depths, where CPRC41 intersected significant mineralisation as displayed in the following cross section, which has assisted in the interpretation of southeast plunging ore shoots, as discussed further below.
The Puntudo structural zone has now been tested by a total of 55 reverse circulation percussion drill holes for a total of 3898 metres. Interpretation of all data now suggests that it would appear that targets for high grade mineralisation are located within broad zones of low grade mineralisation. In particular, high grade gold intercepts appear to relate to southeast plunging ore shoots within the Puntudo structural corridor, as displayed on the following long section:
All assays quoted above were calculated at a 0.5 g/t gold cut-off with no cutting of high grades.