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Pitarrilla, Mexico

  • Pitarrilla Technical Report

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Location and History

The Pitarrilla project is located on the eastern flank of the Sierra Madre mountain range in the central part of Durango State, Mexico. The major city of Torreon lies approximately 150 kilometers (93 miles) east of the project. Road access is good, with paved highways extending to within 20 kilometers (12 miles) of the center of the property. Silver Standard, through a subsidiary, holds a 100% interest in the mineral rights to the approximately 128,500-hectare Pitarrilla claim block. The company also holds significant surface rights in the area.

Geology and Metallurgy

To date, five zones of economically significant silver mineralization have been identified on the property, with four of these zones being closely associated with a rhyolite flow-dome complex that caps a 600-meter-thick package of Tertiary-age andesite, dacite and rhyolite volcanic rocks. This succession of volcanic rocks unconformably overlies folded marine sedimentary rocks of Cretaceous age, and is intruded by a complex system of rhyolite sills and dikes. These rhyolite intrusive bodies, which can be more than 100 meters thick, are a key rock type at Pitarrilla because most mineralization is either hosted in the rhyolites or in the enclosing brecciated host rock.

There are now two types of mineralization at Pitarrilla. The first is finely disseminated microscopic grains of silver minerals in iron-stained rhyolite intrusive and volcanic rocks. The second is disseminated massive sulphide mineralization containing variable amounts of silver, iron, zinc, lead and copper sulphide minerals. Copper sulphide values generally average between 0.2% and 0.5% but can range up to 17% in individual samples. Lead and zinc values each can locally exceed 20%.

In 2007, diamond drilling was focused on outlining Breccia Ridge mineralization, and a significant outcome of the program was the confirmation of massive sulphide mineralization located in feeder zones below Breccia Ridge. The drill density was increased such that the majority of the resources were classified as measured and indicated. Only resources in these categories can be considered in a feasibility study. Another major accomplishment in 2007 was the collaring of a 3,000-meter decline to provide access to the Breccia Ridge sulphide mineralization. By the end of the year, the ramp was 300 meters long and is scheduled to reach target depth by the third quarter of 2008.

This past year was very successful in expanding the known resource at Pitarrilla and in improving the overall quality of the defined resources. In April 2007 resources were increased, and again in November 2007. Measured and indicated resources increased to 383.1 million ounces of silver, which represents an increase of 64% over last year; while the inferred resources increased slightly, to 193.2 million ounces of silver. This was achieved through the completion of over 73,000 meters of drilling in 110 holes. The indicated and inferred contained zinc resource at Breccia Ridge now stands at 1.375 billion and 1.300 billion pounds, respectively; and the indicated and inferred contained lead resource stands at 500 million and 657 million pounds, respectively.

In-fill and step out drilling at Breccia Ridge confirmed the continuity of the mineralization intersected the previous year. Significant 2007 Breccia Ridge holes include PD-221 which intersected 1,676.2 feet with 3.1 ounces silver per ton (510.9 meters with 105.2 grams silver per tonne), including 233.6 feet with 8.2 ounces silver per ton (71.2 meters with 281.6 grams silver per tonne), 1.72% zinc, 1.30% lead and 5.57% copper; and hole PD-226 which contained an impressive 725.1 feet averaging 3.6 ounces silver per ton (221.0 meters averaging 124.6 grams silver per tonne), including 35.1 feet with 20.8 ounces silver per ton (10.7 meters with 712.4 grams silver per tonne), 5.34% zinc and 6.08% lead.

Project Scope and Plans

The 2008 exploration program at Pitarrilla calls for continuation of an aggressive drilling program to complete the step-out drilling on Breccia Ridge and locate new zones of mineralization. At present there are two diamond drills working on the property. A pre-feasibility study has been initiated to estimate the project economics of developing the Breccia Ridge Sulphide Zone, which will form the foundation of a feasibility study. The underground ramp will be extended to access the mineralization for metallurgical sampling and definition drilling. Metallurgical studies will continue with the objective of optimizing the ore processing flow sheet.

For details on the reserves and resources of the San Agustin Project,view the current Resource Summary (312 kb pdf).