The San Sebastian mine is located approximately 56 miles northeast of the city of Durango, Mexico, on concessions acquired in 1999. Access to San Sebastian is via Mexico Highway 40, approximately 7 miles east of Guadalupe Victoria, and then approximately 14 miles of paved rural road through the towns of Ignacio Allende and Emiliano Zapata. The processing plant, located near Velardeña, Durango, Mexico, was acquired in April 2001.
Our concession holdings cover approximately 308 square miles, including the Francine vein, the Don Sergio vein and multiple outlying active exploration areas. Production from the Francine vein was from a high-grade silver vein with significant gold credits. Production from the Don Sergio vein was from a high-grade gold vein with some silver credits. Mineral concession titles are obtained and held under the laws of Mexico, and are valid for 50 years with the possibility of extending another 50 years. There are work assessment and tax requirements that are variable and increase with the time that the concession is held.
Several intermediate sulfidation epithermal veins occur within the Saladillo Valley and include the Francine, Profesor, Middle and North vein systems. These veins are proximal to each other and are hosted within a series of shales with interbedded fine-grained sandstones interpreted to belong to the Cretaceous Caracol Formation. The Don Sergio, Jessica, Andrea and Antonella veins located in the Cerro Pedernalillo area, about 4 miles from Francine, are end member low sulfidation epithermal veins hosted by the same formation with the addition of dioritic intrusive rocks.
Underground development along the Francine vein started in May 2001, and reached full production during the second quarter of 2002. Mining of economic ore on the upper Francine vein was completed during the first quarter of 2005. The mine has been placed on care and maintenance as exploration continues on the property, including the Hugh Zone, which is located 2300 feet below historic mining. Mining of economic ore on the Don Sergio vein was completed in the fourth quarter of 2005 and reclamation of this portion of the mine site was completed during 2006. San Sebastian’s life-of-mine production over four years was 11.2 million ounces of silver and 155,937 ounces of gold.
The Francine vein strikes northwest and dips southwest, and is located on the southwestern limb of a doubly plunging anticline. The vein ranges in true thickness from more than 13 feet to less than 1.5 feet, and consists of several episodes of banded quartz, silica-healed breccias and minor amounts of calcite. The vein is oxidized to a depth of approximately 328 vertical feet and the wall rocks contain an alteration halo of less than 7 feet next to the vein. Mineralization within the oxidized portion of the vein contains limonite, hematite, silver halides and various copper carbonates. Higher-grade gold and silver mineralization is associated with disseminated hematite and limonite after pyrite and chalcopyrite, copper carbonates including malachite and azurite and hydrous copper silicates including chrysocolla. Native gold occurs associated with hematite and limonite. Mineralization in the sulfide portion of the Francine vein contains pyrite, chalcopyrite, sphalerite, galena, native silver, argentite and trace amounts of aguilarite. Hugh Zone mineralization contains chalcopyrite, sphalerite, galena, argentite, acanthite, tetrahedrite, polybasite, stephanite, freibergite, and pyrargyrite.
Access to both underground workings has been through ramps from the surface connecting one or more levels. Ore has been mined by the cut-and-fill stoping method and extracted from the stopes using rubber-tired equipment and hauled to the surface in trucks. Run of mine ore has been hauled in trucks by contractors to our processing facility near Velardeña, which is approximately 68 miles from the San Sebastian mine and 72 miles from the Don Sergio mine. The mill, which was constructed in 1994 and is capable of processing approximately 550 tons per day, is a conventional leach, counter-current decantation and Merrill Crowe precipitation circuit. The ore has been crushed in a two-stage crushing plant consisting of a primary jaw, a secondary cone crusher and a double-deck vibrating screen. The grinding circuit includes a primary ball mill and cyclone classifiers. The ground ore was thickened, followed by agitated leaching and four stages of counter-current decantation to wash solubilized silver and gold from the pulp. The solution bearing silver and gold was clarified, deaerated and zinc dust added to precipitate silver and gold that is recovered in plate and frame filters. The precious metal precipitate was smelted and refined into doré, and was then shipped to a third-party refiner. Processing of economic ore was completed during the fourth quarter of 2005, and the mill was placed on care and maintenance at that time. On March 6, 2009, Hecla sold the Velardeña mill to ECU Silver Mining Inc.