The Guanajuato mine complex (GMC) is an underground silver-gold mining operation located in the Guanajuato state of Mexico. Fully owned by Minera Mexicana el Rosario, a subsidiary of Great Panther Mining, the mine complex has been in production since 2006.
The exploration activities in the Guanajuato mining district dates back to 1548 when silver mineralization was discovered by the Spanish colonists in the La Luz area. They controlled the mining district until 1816 and the mines were turned over to the Sociedad Cooperativa Minera Metalurgica Santa Fe de Guanajuato (the Cooperative) in 1939. Guanajuato was acquired from the Cooperative by Great Panther for approximately $7.25m in 2005.
The Guanajuato mine complex that comprises the Guanajuato and the San Ignacio underground mines produced a total of 591,000 ounces (oz) of silver and 11,588oz of gold in 2019, while an updated mineral resource technical report for the mine complex was filed by Great Panther in December 2020.
Project location and geology
The Guanajuato silver-gold mine is located approximately 380km northwest of Mexico City in the Guanajuato state of Mexico. The total project area of the Guanajuato mine complex is estimated to be approximately 10,355ha.
The Guanajuato mine lies in the southern portion of the Mesa Central physiographic province, within the central part of the Guanajuato mining district. The Mesa Central is dominated by Cenozoic volcanic and volcanoclastic rocks with faulted Tertiary age volcanic rocks, juxtaposed alongside the Mesozoic basement stratigraphy, Tertiary intrusive units, and Quaternary conglomerates.
The San Ignacio mine is underlain by a monotonous package of basalt and andesite volcanic rocks of the lower Cretaceous La Luz andesite with subtle to well-developed pillow structures of locally flattened basalt.
Mineralisation and reserves
The mineralisation at the Guanajuato and San Ignacio mines occur as fissure-hosted low-sulphidation epithermal gold-silver-bearing quartz veins and stockwork. The mineralisation at Guanajuato occurs along regional scale faults of which the Veta Madre is the largest with a strike length of approximately 25km.
The San Ignacio mine hosts sixteen epithermal veins with silver grades ranging from 82g/t to 248g/t while gold grades range from 1.80g/t to 3.39g/t.
The measured and indicated mineral resources at the Guanajuato mine were estimated to be 433,953 tonnes (t) grading 249g/t silver and 1.64g/t gold as of July 2020, while that at San the Ignacio mine were estimated to be 387,898t grading 142g/t silver and 2.56g/t gold.
The Guanajuato mining complex utilises the cut and fill underground mining method with a 3.5m x 3.5m access ramp at the bottom of the vein, from which mining drifts are developed along the ore zone. The sub-levels off the access ramp are developed between 20m and 35m apart.
The mining operations at the San Ignacio mine began in the third quarter of 2013 with the bulk mining operations concentrated at the Nombre de Dios zones with the lesser operations carried out at the Melladito and Intermediate zones including an initial development in the Melladito South zone. The main ramp measures 4.5m x 4.5m with a slope of 12%
The underground mining fleet comprises jack-leg drills, a 16ft Jumbo including 3.5 yard and 4.0-yard Scoop-Trams for ore handling, along with 10t and 18t trucks for ore transport.
The processing plant at the Guanajuato mine complex has a capacity of approximately 779 tonnes per day (tpd). Silver and gold are recovered as sulphide concentrate components containing pyrite, electrum, and silver sulphide.
The run-of-the-mine (ROM) ore undergoes crushing in a PettiBone jaw crusher and the over size is fed to a Metso secondary cone crusher. The crushed ore is fed into three twin Denver ball-mills and mixed with water before being fed to a series of Gmax G10 hydro-cyclone classifiers.
The fine ground slurry is fed to the primary rougher flotation cells to produce a primary concentrate. The concentrate undergoes two-stage cleaning before being fed to the primary and secondary cleaner flotation cells. The concentrate material is passed on to an automatic filter press with 30 plates to produce a final concentrate with an average water content of 8%.
The concentrate from the secondary cleaner flotation cells is sent to a settling tank before being introduced to the thickening circuit which produces a material containing 50% to 70% solids by weight. The product is then filtered in a Clever filter press with 30 plates to produce a filtered concentrate with 12% average humidity. The concentrate is then sampled, weighed, stored, and made ready for shipment.
The mining areas of the Guanajuato complex are easily accessible via a system of modern roads from all nearby population centres. The San Ignacio property located approximately 8km northwest of the City of Guanajuato is accessible via a paved road through the towns of Santa Ana and Cristo Del Rey.
The electrical power requirement for the Guanajuato Mine Complex is provided by state-owned Federal Electricity Commission (CFE Comision Federal de Electricidad) through a 13.2kV transmission line.
The process and potable water requirement for the mining complex is sourced from the water storages in the historical underground workings.
Great Panther entered into an off-take agreement with Switzerland-based physical metal traders IXM Group in December 2019 for the entire gold-silver concentrates production from the Guanajuato mine complex during 2020 and 2021.
Kav Drilling was appointed as the drilling contractor for the underground drilling surveys at Guanajuatito, Los Pozos, Santa Margarita and Valenciana ore zones in 2020.