Juanicipio is a high-grade silver-gold-lead-zinc project in Mexico. It is owned by Minera Juanicipio, a joint venture (JV) between Fresnillo (56%, operator) and MAG Silver (44%).
Underground development at Juanicipio began in 2013. A resource estimate and preliminary economic assessment was prepared in 2017 and the Juanicipio mine development was approved by the JV partners in April 2019.
The mine began production in October 2020 and is expected to produce an average of 11.7 million ounces (Moz) of silver and 43.5 kilo-ounces (koz) of gold a year, once fully operational. Fresnillo is anticipated to continue mining operations at the site until 2038.
The pre-operative capital investment in the project is estimated at $440m.
Juanicipio project location and geology
The Juanicipio project is located in the Fresnillo district of Zacatecas state in Mexico. The 7,679ha site is situated 14km from Fresnillo mine.
Juanicipio comprises two major vein systems, namely the Valdecañas principal vein and the Juanicipio vein. Largely open at depth, the Valdecañas system constitutes dilatant zones at the east and west extremes, along with numerous en echelon vein splays and cross-veins. The Juanicipio vein, which is open to the west and to depth, contains silver-gold epithermal structures.
The Valdecañas vein system shows conventional metal zonation of an upper precious metal zone known as the Bonanza Zone, grading downwards into a deeper base metal zone known as the Deep Zone.
Mineralisation in the Bonanza Zone comprises precious metal-rich, banded, or brecciated quartz pyrargyrite-acanthite-polybasite-galena-sphalerite veins. Mineralisation in the Deep Zone contains base metal-rich, brecciated, or banded quartz-galena-sphalerite-chalcopyrite veins with low pyrargyrite and acanthite.
Juanicipio Project resources
The total indicated resources were estimated to be 12.83Mt graded at 427g/t of Ag, 2.10g/t of Au, 2.11% of Pb, 3.68% of Zn, and 0.13% of Cu as of October 2017.
The total inferred resources stand at 12.13Mt graded at 232g/t of Ag, 1.44g/t of Au, 2.46% of Pb, 4.68% of Zn, and 0.27% of Cu.
Mining at Juanicipio
The Juanicipio Project comprises an underground mine and a flotation plant, which is expected to be commissioned in mid-2021.
The mine is accessed through twin underground declines. The upper footwall access drift has been driven from the Valdecañas vein, from which three internal spiral footwall production ramps are being extended to depth. The original access decline was twinned to provide capacity for hauling additional ore and waste to enable a processing capacity of 4,000tpd.
The underground mine development also includes cross-cuts across the Valdecañas vein. The first cross-cuts were made from the easternmost footwall ramp. The surface construction of the project involves the installation of the processing facility and ancillary infrastructure.
The project employs long-hole stoping as the primary mining method, with waste rock backfill at a production rate of 4,000tpd. The ore is delivered to the surface processing plant after underground crushing, truck hauling, shaft hoisting, and conveying.
The ore from the vein will be crushed underground and conveyed from the underground crushing station to the process plant area via the underground conveyor ramp. The conveyor ramp will provide access to the Valdecañas underground mining infrastructure and act as a fresh air entry for the ventilation system.
Processing at Juanicipio
The ore from development and initial production stopes will be processed at the Fresnillo beneficiation plant until the commissioning of the Juanicipio beneficiation plant. The Fresnillo beneficiation plant produced 394,000oz of silver, 610oz of gold, 138t of lead and 174t of zinc during the quarter ending September 2020.
The Juanicipio beneficiation plant will have a throughput rate of 4,000tpd, which will be attained by ramping up operations over a three-year period. It will include a semi-autogenous grinding (SAG)/Ball mill comminution circuit and sequential flotation to produce a silver-rich lead concentrate, a zinc concentrate and a gold-rich pyrite concentrate.
The SAG/Ball mill will produce feed to the flotation circuit. Separate concentrates of lead, zinc, and pyrite will undergo thickening, filtering and stockpiling before being transported by trucks directly to customers or for onward shipment.
The plant and tailings storage facility will be constructed in a newly acquired open, flat ground.
An engineering, procurement and construction management (EPCM) contract was awarded to an affiliate of Fresnillo for the construction of the processing plant, as well as to oversee the mine construction and development.
AMC Mining Consultants was appointed by MAG to prepare the resource estimate and preliminary economic assessment.