The Ixtaca gold-silver project is estimated to contain 73.1Mt of proven and probable reserves. Image courtesy of Almaden Minerals.
Coarse and mid-size ore from secondary crushing unit will be sorted by an XRT ore sort machine to remove waste rocks. Image courtesy of Almaden Minerals.
A closed circuit ball mill will be used to grind the crushed ore to a size of 75 microns. Image courtesy of Almaden Minerals.

The Ixtaca gold-silver project is a precious metals project under development in the Puebla state of Mexico. Almaden Minerals is developing the project with an estimated initial capital cost of $174m.

The pre-feasibility study (PFS) for the gold-silver project was completed in May 2017, while the feasibility study (FS) was completed in December 2018. Construction is expected to be started in the fourth quarter of 2019, while plant start-up is expected in the second quarter of 2021.

The project is expected to produce an average of 90,800oz of gold and 6.14Moz of silver through its anticipated mine life of 11 years.

Ixtaca gold-silver project location, geology, and mineralisation

In 2010, Almaden discovered the Ixtaca epithermal gold-silver deposit, which is located within the Tuligtic property. Almaden owns the property through its subsidiary Compania Minera Gorrión.

The gold-silver project is hosted within the Trans Mexican Volcanic Belt (TMVB), a tertiary to recent intrusive volcanic arc that runs east-west across Mexico.

“The project is expected to produce an average of 90,800oz of gold and 6.14Moz of silver through its anticipated mine life of 11 years.”

The project is regarded as a low-sulphidation epithermal vein system and hosts extensively clay altered and silicified volcanic rocks. It is made up of high-grade vein swarms comprising barren limestone.

Gold and silver mineralisation is formed as zones of high-grade vein and veinlets in the carbonate basement units. It also hosts quartz-calcite veins, which outcrop in limestone approximately 100m below the exposed sinter.

Gold-silver reserves at Ixtaca project

The proven and probable mineral reserves at the Ixtaca project are estimated to be 73.1Mt, grading 0.59g/t Au and 36.3g/t Ag. The mine is estimated to contain 1.39Moz of gold and 85.2Moz of silver.

Mining at Ixtaca

Conventional open-pit mining, involving drilling and blasting followed by loading and hauling, will be applied at Ixtaca. Mill feed is estimated to be 7,650tpd for the first four years, which will be increased to 15,300tpd from the fifth year.

Mining operations are categorised into direct mining and general mine expense (GME). Direct mining activity will be conducted by the mining contractor while Almaden proposes to undertake GME operations.

Ore processing at Ixtaca gold-silver project

Almaden acquired the 7,000tpd Rock Creek mill plant in Alaska for $6.5m for Ixtaca operations. The mill was placed under care and maintenance after being operated for just three months.

The plant will employ conventional methods of ore processing along with flotation and leaching methods to produce gold and silver doré bars.

Run-of-mine (ROM) ore will be passed through a three-stage crushing unit and the crushed ore will be transported to the grinding circuit by an over land conveyor. The ore will be ground to a size of 75 microns by ball milling in a closed circuit with cyclones, while the underflow will be screened.

Undersize from the screening unit will be further processed in semi-batch centrifugal gravity separators to produce a gravity concentrate, which will be subject to intensive cyanide leaching, with the cyclone overflow treated in a flotation unit to produce a flotation concentrate.

The concentrate will be forwarded to the carbon-in-leach (CIL) circuit for extracting gold, followed by agitated tank leaching to perform silver leaching. Gold and silver from the CIL-loaded carbon will be recovered through a carbon desorption process, while the Merrill Crowe process will recover gold and silver from the pregnant solution from the agitated leach circuit.

Infrastructure facilities at Ixtaca

The gold-silver project is accessed through a paved road along the Highway 119 from Apizaco.

Raw water will be collected from the water storage and freshwater dams, as well as stored in a freshwater storage tank.

Power supply for the mine will be sourced from the Apizaco substation of Comisión Federal de Electricidad (CFE). A new 27km-long, 115kV transmission line will be constructed to connect the substation.

Contractors involved

Almaden engaged Moose Mountain Technical Services for the preparation of the feasibility study for the project. Other consultants involved in the PFS preparation included APEX Geoscience, Giroux Consultants, and SRK Consulting (US).

Auramet International was appointed as the financial adviser to securing financing, while Dynamic Engineering Services was contracted for deconstructing the Rock Creek mill.