Los Gatos Silver-Zinc-Lead Project

The Los Gatos silver-zinc-lead project is located in the Municipality of Satevo, Chihuahua, Northern Mexico.

Minera Plata Real (MPR), a joint venture between Sunshine Silver Mining (SSMRC) and Dowa Metals (DOWA), is the project developer and operator. SSMRC holds 51.5% stake in the JV, while Dowa holds the remaining 48.5%.

The underground Los Gatos silver-zinc-lead project is expected to produce approximately 50,000 tonnes per year (tpa) of zinc concentrate and 30,000tpa of lead concentrate. Its mine life is estimated to be 11.5 years.

The project is expected to involve a pre-production development cost of $316m (£253.78m), which is financed through a $210m term loan from Dowa. The remaining $106m was received as equity contribution commitments from the JV partners.

Construction of the project was started in mid-October 2017 and is expected to be completed in the third quarter of 2019. The project is expected to be fully commissioned by the beginning of 2020.

Los Gatos silver-zinc-lead project location and geology

The Los Gatos silver-zinc-lead project area lies approximately 120km south of the state capital of Chihuahua City. It is accessible via the Federal Highway-24 from the capital city and can be reached in approximately two hours.

The mining concessions of the project are identified on the north-western portion of the town of San Jose Del Sitio, covering and area of 103,086.8ha.

The Cerro Los Gatos deposit lies in the transition zone between the Sierra Madre Occidental volcanic province and the Mesozoic Chihuahua basin. The region comprises a thick sequence of tertiary volcanic rocks dissected by a strong North-Northwest bearing fault system.

Cerro Los Gatos mineralisation

Mesozoic-aged sedimentary rocks of the Chihuahua Platform make up the oldest rock formations in the area. The mineralisation is commonly related to skarn, limestone replacement, and Mississippi Valley type deposits.

A series of west-northwest trending veins form the mineralised section, hosted in volcanics on the footwall side of a listric normal fault contact.

Silver mineralization occurs as acanthite (argentite) and native silver, detected in thin sections as proustite, while lead occurs primarily as galena and lead oxide minerals, disseminated in quartz vein materials.

Zinc occurs as sphalerite and zinc silicate minerals, disseminated in quartz vein material and as replacement in the andesitic and dacitic flow units.

Cerro Los Gatos reserves

As of January 2017, the mineral reserves of Los Gatos were estimated to be 9.8Mt grading 247g/t silver (Ag), 4.8% zinc (Zn), and 2.3% lead (Pb).

Mining method and ore processing

Transverse and longitudinal longhole stoping methods, along with selective drift-and-fill method, will be applied at the underground mine. The mining will be initially performed at the Central Zone (CZ), which will be mined using the drift-and-fill method.

The North-West Zone (NWZ) will be concurrently mined with the CZ using the longhole stoping method. At the NWZ, transverse longhole mining will be employed at portions thicker than 9m, while longitudinal longhole will be used for portions less than 9m-wide.

Load, haul dump machines (LHD) and dedicated underground trucks will load and transport ore/waste from the underground workings via an internal ramp system and portal.

The processing facility will operate at 2,500tpd and will produce lead, zinc, and silver at 92% operational availability. Jaw crushers adjacent to the underground mine portal will crush the run-of-mine (ROM) material, which is then conveyed to semi-autogenous grinding (SAG) and ball milling circuit.

The resultant material will be forwarded to the flotation circuit consisting of lead flotation, followed by zinc flotation. The rougher flotation concentrates will be reground to 80% finer than 25μm for both lead and zinc sections prior to cleaner flotation to remove the sulphides for further upgrading.

Lead sulphide will be recovered in a rougher flotation bank to produce a concentrate that will be cleaned in three stages to meet smelter specifications. The lead flotation tailings will be conditioned for zinc sulphide flotation.

The zinc flotation circuit also comprises a rougher bank and five stages of cleaning to produce smelter-grade zinc concentrates. The final lead and zinc concentrates will be thickened, filtered, and stored prior to loading in trucks for shipment.

Los Gatos silver-zinc-lead project infrastructure

Access to the project is through a paved road from Chihuahua, while a portion of the road from San José del Sitio will be rerouted to avoid interference with a nearby river.

Power will be supplied through a new 66km-long, 115kV utility transmission line originating from the San Francisco de Borja substation.

Raw water required for the operations will be supplied by groundwater pumped from dewatering wells.

Workers will be accommodated at a 500-person temporary accommodation camp.

Contractors involved

Tetra Tech prepared the Cerro Los Gatos project feasibility study. M3 Engineering was engaged as the engineering, procurement, construction management (EPCM) contractor, while Cementation Mexico was awarded the mine development contract.