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Hermosa zinc/lead/silver project, US – update

Aerial view of the Hermosa gold project

Photo by South32

17th May 2024

By: Sheila Barradas

Creamer Media Research Coordinator & Senior Deputy Editor


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Name of the Project
Hermosa zinc/lead/silver project.

Santa Cruz County, Arizona, in the US.

Project Owner/s

Project Description
Hermosa is a polymetallic development comprising the zinc/lead/silver Taylor sulphide deposit, the zinc/manganese/silver Clark oxide deposit and an extensive, highly prospective land package, with the potential for further polymetallic and copper mineralisation.

A prefeasibility study (PFS) has tipped the deposit to be the first development of a multidecade operation, establishing the project as a globally significant producer of metals critical to a low carbon future. The deposit is being designed as South32’s first ‘next-generation mine’, with automation and technology used to minimise its impact on the environment and target a carbon-neutral operation, in line with South32’s goal of achieving net-zero operational carbon emissions by 2050.

The PFS is based on a dual-shaft underground zinc/lead/silver mine development using longhole open stoping and a conventional sulphide ore flotation circuit, producing separate zinc and lead concentrates, with silver by-product credits. The PFS estimates average production of 111 000 t/y of zinc, 138 000 t/y of lead and 7.3-million ounces a year of silver, with the current resource supporting a mine life of 22 years and a nameplate capacity of 4.3-million tonnes.

The deposit, located adjacent to and up-dip of the Taylor deposit, has the potential to underpin a second development stage at Hermosa. The deposit has a mineral resource estimate of 55-million tonnes averaging 9.08% manganese, 2.31% zinc and 78% g/t silver. A scoping study has confirmed the potential for a separate, integrated underground mining operation producing battery-grade manganese, as well as zinc and silver.

Potential Job Creation
Not stated.

Net Present Value/Internal Rate of Return
Not stated.

Capital Expenditure

Planned Start/End Date
According to the PFS production schedule, first ore is expected in the 2027 financial year, with a single-stage ramp-up to nameplate production expected in the 2030 financial year.

Latest Developments
The US Forest Service (USFS) has initiated the federal permitting process for the project.

Under the umbrella of the National Environmental Policy Act, the USFS has launched the scoping process, inviting public input and commentary on South32’s project plans to identify the scope of environmental analysis, and explore potential impacts as part of the environmental-impact statement.

While all Hermosa’s mining will be done on private land and require several state permits to begin initial development, a federal permit is required to fully develop the project.

The scoping process is specifically focused on the scope of the environmental analysis, alternatives that meet the purposes and requirements of the project, and on receiving information that will help the USFS understand and analyse environmental effects of the project’s proposed expansion of ancillary infrastructure on Forest Service lands.

Federal authorisation is expected to take more than two years, and will include multiple rounds of public feedback and discussion.

Key Contracts, Suppliers and Consultants
Fluor (process plant and on-site infrastructure); SRK Consulting (geological and technical reviews); Stantec (mining studies); NewFields (hydrogeology studies); Montgomery & Associates (dewatering and tailings); Black and Veatch, and BQE (water treatment design); and CPE (off-site roads).

Contact Details for Project Information
South32, email

Edited by Creamer Media Reporter


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