The Strong and Harris Copper-Zinc-Silver Project is located in Arizona. (Credit: omid roshan on Unsplash)
Induced Polarisation anomaly of the mine and other mines. (Credit: Excelsior Mining Corp.)
A Preliminary Economic Assessment (PEA) report for the project was published in October 2021. In picture, chalcocite. (Credit: Robert M. Lavinsky (1972–) /Wikipedia)

The Strong and Harris Project is a copper-zinc-silver deposit located in the US state of Arizona. It is held by Excelsior Mining via wholly owned subsidiaries Excelsior Mining Arizona and Excelsior Mining Holdings.

Excelsior acquired the property in 2019. Although exploration works at the property began in 1964, it has no history of production.

A Preliminary Economic Assessment (PEA) report for the project was published in October 2021. It estimates an average annual production of 62 million pounds of copper and 82 million pounds of zinc.

The project is expected to have a mine life of around seven years. Initial capital cost was estimated to be $328m, with a payback in 3.1 years.

After filing the PEA report, the company announced plans of a drill programme with the aim of expanding the mineral resource base, metallurgical test work as well as completion of a feasibility study.

Strong and Harris Location and Site Access

The Strong and Harris Copper-Zinc-Silver Project is located approximately 65miles east of Tucson in Cochise County, Arizona.

The project is situated on the east side of the Little Dragoon Mountains in an alluvium-covered valley.

The project is accessible via the Interstate 10 (I-10) freeway and can be reached through the unpaved Johnson Road.

Overall, the Strong and Harris Project consists of 35 patented mining claims, 113 unpatented claims, and two fee land parcels covering approximately 2,255 acres of land in sections 13, 14, 23, and 24 of Township 15S, Range 22E.

Geology and Mineralisation

The Strong and Harris copper-zinc-silver deposit is situated in an alluvium-covered valley.

The alluvium-covered valley sits on mineralised Paleozoic rocks which include the Carboniferous Escabrosa Limestone, the Carboniferous Black Prince Limestone, the Permian Earp Limestone, the Permian Colina Limestone, and the Carboniferous to Permian Horquilla Limestone.

A thin mafic sill, locally known as Peabody Sill, intrudes the Horquilla Limestone in the project area.

The mineralisation was identified as a sub-type of a copper-skarn system. The copper-zinc-silver mineralisation is characterised by sulphide minerals and accompanied by calc-silicate alteration of the carbonate host-rock .

The minerals are also hosted within quartz +/- calcite +/- feldspar veins. The most favourable sites for copper-zinc-silver mineralisation are within the sub-units of the Earp Formation.

The deposit is oxidised to different levels and it decreases with the increase in depth resulting in oxide, transitional, and sulphide zones.

Strong and Harris Mineral Resources

The estimated resources of the property are entirely classified as inferred in the technical report.

The inferred mineral resource estimate totals 76.16Mt containing 794Mlbs copper at a grading of 0.52%, 500.2Mlbs copper oxide at a grading of 0.33%, 858.4Mlbs zinc at a grading of 0.56%, and 9.51Moz silver at a grading of 0.12oz silver/tonne.

Mining and Processing

The project is expected to employ traditional open pit with high-grade underground mining to recover the remaining sulphides at the bottom of the pit.

The project will use 100-ton capacity haul trucks, wheel loaders and other equipment for mining and hauling ore. The mineral resources will be processed via heap leaching and concentration, depending on the oxidation zone.

Copper, zinc and possibly silver will be produced from the sulphide mineralised material, while copper and potentially zinc from the oxide mineralized material.

Oxide mineralised material will be processed via sulfuric acid heap leaching. Solvent extraction process will be used to extract copper and zinc from this material.

The sulphide mineralised material will be subjected to two-stage crushing, then grinding, followed by a two-stage flotation approach to produce copper concentrate (incorporating silver credit) and zinc concentrate.

Project Infrastructure

The key infrastructure of the Strong and Harris Copper-Zinc-Silver Project will consist of an access road, an administrative building, a tailings dam facility, explosives silos, magazines, and growth media stockpiles.

A leach pad, a processing plant, and a waste storage area are also a part of the infrastructure of the project.

An existing 115kV transmission line crosses the project area from the southeast to the northwest. A new transmission line will be constructed to connect the existing line in the northwest.

A substation will supply power to the site and will be located in the plant area.

Contractors Involved

The 2021 PEA of the Strong and Harris Copper-Zinc-Silver Project was prepared by Mine Development Associates, a division of RESPEC.

SRK Consulting also supported in the preparation of the 2021 PEA, while McPhar Geophysics conducted an Induced Polarisation and Resistivity (IP/Res) survey.