Aranzazu Copper-Gold-Silver Mine, Zacatecas

Aura Minerals reopened its wholly-owned Aranzazu copper-gold-silver mine in the Zacatecas State of Mexico, in October 2018.

The Aranzazu mine was owned and operated by various companies since 1962, before Aura Minerals acquired it in June 2008.

Formerly known as the El Cobre project, the Aranzazu mine, however, was put under care and maintenance in January 2015, due to unfavorable market conditions.

Aura Minerals completed a feasibility study for the mine re-opening, based on revised mineral resource estimate and mining design, in July 2018.

The feasibility study predicted 70,416 tonnes (t) of copper, 122,149 ounces (oz) of gold and two million ounces (Moz) of silver production in concentrates over a mine life of 5.5 years, with an estimated investment of $92.5m.

Aura Minerals completed the first shipment of copper concentrates from the Aranzazu underground mining operation in October 2018, while the construction of a new tailings disposal system (TDS) is scheduled for completion by the end of the year.

Aranzazu mine geology and mineralization

The Aranzazu poly-metallic mine encompasses 11,182ha in the Concepcion del Oro district, an intrusive complex in northern Zacatecas that hosts copper-gold-silver mineralization in exoskarn, endoskarn, quartz monzonite, hornfels, and marble.

The 250m-wide and 600m-deep Aranzazu ore body has a strike length of 1.5km and comprises seven mineralization zones, namely BW, Glory Hole Footwall (GHFW), Glory Hole Hangingwall (GHHW), Arroyos Azules (AA), Mexicana South and North, and Cabrestante.

Glory Hole Footwall (GHFW) and Glory Hole Hangingwall (GHHW) are the two biggest mineable ore bodies in the property.

Aranzazu copper-gold-silver reserves

The Aranzazu mine was estimated to hold 4.6 million tonnes (Mt) of proven and probable reserves grading 1.72% copper, 1.17 g/t gold and 19.2 g/t silver, as of January 2018.

Mining method for Aranzazu mine

Aranzazu is an underground mining operation employing both longitudinal and transverse long hole open stoping (LHOS) methods with delayed backfill.

The underground mine is accessed by two main (5m x 5m) ramps and the stopes are designed to be 15m and 10m-wide with the sub-level intervals ranging between 20m and 30m.

The blasted ore in deep underground workings is removed and transferred to haul trucks for transportation to the mill, using remotely-operated load-haul-dump (LHD) units.

Ore processing

The run-of-mine (RoM) ore is trucked to the 2,600tpd processing facility, where it undergoes screening, crushing, grinding, cyclone overflow, floatation, and concentrate dewatering and thickening for the production of final concentrate products.

The processing facility houses a static slotted grizzly screen with 15-inch openings, two vibrating screens with 4 inches and 9.5mm-wide slotted openings respectively, a 250hp primary jaw crusher, a 300hp secondary cone crusher, a 400hp tertiary cone crusher, and three 500hp primary single-stage ball mills.

Tailings from the processing plant are disposed to a tailings storage facility.

Infrastructure facilities for the Aranzazu mine

The underground mine is ventilated by two 2.35m-diameter axial mine fans. Water from the bottom of the mine is pumped to a central clarifier sump with the clean water further pumped to surface storage ponds. The pumping system for the mine has the capacity to discharge 45 litres of water a second.

The mine receives electricity supply from existing 4.16kV substations on the surface, while a new 13.6kV substation has been planned to supply power to new mining zones at GHFW and GHHW.

The mine site is accessed from the city of Zacatecas via existing paved roads connecting the Highway 54 located 5km away.

Contractors involved with Aranzazu mine restart

Farshid Ghazanfari Consultancy was engaged for the geological study for the feasibility of the Aranzazu mine reopening, whereas Call & Nicholas was responsible for geotechnical modeling.

Jacobs Engineering Group provided process and metallurgy consultancy services.

Wood PLC provided the design for the new tailings disposal facility (TD5).

Altura Environmental Consultants was contracted for providing environmental and permitting services.

Anthem Capital provided financial modeling and valuation services.