La ParrillaWed, 10/21/2015 - 15:42
The La Parrilla silver mine is located 65km southeast of Durango in the western part of the Mexican Altiplano situated within the municipality of Nombre de Dios. Operations at La Parilla include production from four different underground mines and a small open pit. According to First Majestic Silver’s technical report for La Parrilla, the mine’s regional geologic setting is dominated by a core of igneous rocks of dioritic composition intruding a Cretaceous sedimentary sequence of calcareous rocks. This intrusive stock caused structural conditions favorable for subsequent emplacement of mineralization along faults and breccia zones, as well as replacement and skarn deposits into bed and contact zones. The La Parrilla district is mineralized with concentrations of silver, lead, and zinc, associated with gangue minerals such as quartz, calcite, and other minor elements.
La Parrilla consists of underground silver-gold-lead-zinc mines with a processing facility that was originally constructed in 1956. In 1960, the mining claims were acquired by Minera Los Rosarios, which ran the mine until 1999 when operations were shut down due to low silver prices. In 2004, First Majestic Silver acquired the mining rights and the plant from Minera Los Rosarios while in 2006, it successfully negotiated the acquisition of the mineral rights surrounding the original mine, then held by Grupo Mexico. The main underground operations today are Rosario-La Blanca, San Marcos, Quebradillas, and Vacas. The Vacas mine began production in the second semester of 2013 at a rate of 300 t/d, producing sulfide ore with silver grades ranging from 200-240 g/t. The open pit has been developed on oxide ore situated atop the active Quebradillas underground mine. The underground stoping method used for mining the near-vertical veins and orebodies of the operations of La Parrilla is overhand cut and fill.
The ore processed from the La Parrilla mining district consists of oxides and sulfides, which both have silver as their principal economic component. The ores also contain significant amounts of lead and zinc, and minor amounts of gold. Oxide ores are processed by cyanide leaching to produce doré metal; sulfide ores are processed by differential flotation to produce a silver rich lead concentrate and a zinc concentrate. The mine underwent a fifth major development project that further expanded the mill to 2,000 t/d from the previous level of 850 t/d. The expansion was deemed commercially effective on March 1, 2012, when the new parallel 1,000 t/d flotation and 1,000 t/d cyanidation circuits also became fully operational. At the new run rate, La Parrilla is expected to produce approximately 3.3-3.4 million ounces of silver equivalent annually.