La Parrilla silver mine is located in the state of Durango in Mexico. The underground mine is 100% owned by First Majestic Silver Corporation and covers an area of 69,867ha. It began operations in October 2004.
The mine produced 1.5 million ounces (oz) of silver (Ag) in 2010. The production at the end of the second quarter of 2011 was 395,716oz of Ag.
The mine is expected to last until 2024. Ongoing exploration activities are, however, expected to extend the mine’s life beyond 2024.
Geology and reserves of La Parrilla
The mine is located in the western part of Mexican Altiplano, an extensive volcanic mountain range stretching across the US and Mexico. The plateau features narrow, fault-controlled ranges separated by flat-floored basins located 1,900m to 2,100m above sea level.
Proven and probable reserves at the mine as of June 2011 are estimated at 5.2 million metric tons (mt) grading at 202g/t. Measured and indicated reserves are 1mt grading at 146g/t. Inferred resources are estimated at 8mt grading at 177g/t.
Mineral deposits occur between a diorite intrusive stock and Cretaceous sedimentary rocks of limestone, shale and mudstone. The mineralisation includes silver, lead and zinc concentrates and occurs in vein-fault zones, breccias and replacement bodies of the diorite intrusive stock.
Mining and processing
The mining complex includes four underground mine structures – Los Rosario, La Rosa, San Jose and Quebredillas, as well as an open pit mine above the Quebradillas mine. The processing mill of the mine is surrounded by these four structures.
The open pit mine at Quebradillas consists of near surface mineralisation including estimated reserves of 1.77mt of ore grading at 102g/t. Recovered ore is trucked from the mine to the process plant. The mine is expected to operate till 2017.
Mining is carried out by conventional drill and blast methods. Trackless, diesel-powered mining equipment is used to carry out the mining operations.
These include load-haul-dump loaders, dump trucks, electro-hydraulic drill jumbos and other support equipment. Ore is processed at the cyanidation and flotation plants.
Mine development, exploration and production are carried out by mining contract firms. The process plants are operated by First Majestic.
Each of the four underground mines is accessed through various adits, declines and shafts. First Majestic is currently constructing a shaft which will link all the mines. The new shaft will consolidate all the operations of the mine, improve efficiencies and reduce costs.
The shaft is being constructed at the Los Rosario mine and is expected be completed by 2012. The project also includes construction of an underground rail system to move ore and waste from the shaft.
The recovered ore consists of oxides, sulphides and small quantities of lead, zinc and gold. Oxide ore is processed using cyanide leaching which yields doré metal. The sulphide ore is processed using differential floatation to create a silver-rich lead and zinc concentrate.
Expansion of La Parilla silver mine
First Majestic commenced a $35m expansion programme in December 2010 to increase production of the mine from 850tpd to 2,000 tons a day (tpd).
The expansion will double the mine’s annual production to three million oz of Ag. It involves construction of a new ball mill, addition of a crushing area, expansion of the floatation and cyanidation circuits and installation of new thickeners and filters.
First Majestic completed the first phase of the expansion programme in September 2011. The floatation circuit commenced operations at the rate of 787tpd, increasing total output to 1,254tpd. The cyanidation circuit was 60% complete by September 2011. Both the circuits are expected to be fully operational by the end of December 2011.
First Majestic is exploring the San Marcos, San Nicolas and Vacas prospects of the mine.
The San Marcos prospect has been drilled to a depth of 10,122m in 43 drill holes. The Vacas prospect has been drilled to a depth of 15,217m in 46 drill holes.
The company plans to drill another 1,600m in four drill holes at the San Marcos and Vacas prospects in 2011.