The Sorby Hills silver-lead-zinc project is a high-grade open-pit project being developed in the Shire of Wyndham-East Kimberley, Western Australia.

Pacifico Minerals holds 75% stake in the project, while Henan Yuguang Gold Lead holds the remaining.

An updated pre-feasibility study of the project was released in March 2019, which projected a pre-production capital expenditure of A$95.4m ($66.78m). The project is expected to produce 249,000 tons (t) of lead and 9.3 million ounces (Moz) of silver, over its estimated mine life of eight years.

The Western Australian Environmental Protection Authority extended the Sorby Hills project commencement timeline from 2019 to April 2024.

Pacifico proposes to start the second phase of infill and expansion drilling program in the first half of 2019 and complete the project’s definitive feasibility study (DFS) by late-2020.

Sorby Hills silver-lead-zinc project cation, geology, and mineralization

The Sorby Hills silver-lead-zinc project is located approximately 50km from Kununurra, in the Kimberley region of Western Australia. Discovered in 1971, the project is located within five mining leases (M80/196-197 and M80/285-287) that encompass an area of 12,612ha.

The deposits are formed in lower Carboniferous carbonates, which are part of the Burt Range Formation located on the eastern flank of the Pincombe Range.

The mineralization is much similar to the carbonate-hosted mineralization of Mississippi Valley-Type deposits. The mineralization is hosted within 13 discrete carbonate hosted silver (Ag), lead (Pb), and zinc (Zn) 7-10m thick pods. The pods formed a 7km-long linear north-south belt along the northern margin of the Burt Range Formation.

The mineralization occurs as sediment replacement deposit and is identified along the flat-lying contact between an upper siltstone and a lower dolomite. It is primarily a lead-dominant system with high silver content along with a high downdip potential for zinc.

Sorby Hills silver-lead-zinc project reserves

The JORC-compliant mineral resources of Sorby Hill, as of March 2019, are estimated to be 29.98 million tons (Mt) of ore containing 3.7% of lead (Pb) and 43g/t of silver.

Mining and processing

Conventional open-pit mining, using excavators and haul trucks, will be used to mine the three Sorby Hills pits.

The major mining fleet will encompass two Komatsu PC1250 excavators, two Caterpillar D9 dozers, and four Caterpillar 777G haul trucks, which will be supported by support equipment such as water trucks for dust suppression, service vehicles, pit dewatering pumps, and lighting equipment.

The processing plant at Sorby Hills will have a capacity of one million tons per annum (Mtpa) and will employ conventional milling and flotation processes along with a dense media separation (DMS) plant.

The ore will be passed through a single-stage primary crusher and then through a beneficiation plant before passing through the DMS plant, which may use either conventional DMS processes or ore sorting technology.

The resultant product will pass through a lead-only flotation circuit, comprising roughening and scavenging units, and a two-stage cleaning process to produce a high-grade silver-lead concentrate that will have a recovery rate of 91% lead and 87% silver.

The concentrate will be filtered, packed in sealed containers, and transported by road to the Wyndham Port.

Infrastructure facilities at Sorby Hills

Major infrastructure at the project include the processing plant, administration and maintenance buildings, tailings storage facility, waste dumps, and evaporation area.

The produced concentrates are proposed to be transported to the port through the Weaber Plains road.

Grid power fed by the Argyle dam will be the source of power for the project. Workers are proposed to be accommodated in Kununurra and transported to the site daily.

Contractors involved

CSA Global prepared the updated mineral resources estimate for the Sorby Hills project, while Lycopodium, an engineering consultant based in Perth, Australia, reviewed the project PFS.