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Yauricocha mine, Peru

6th July 2018

By: Thabi Shomolekae

Creamer Media Senior Writer

     

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Name: Yauricocha mine.

Location: The Yauricocha mine is located in the Alis district, Yauyos province, in the Department of Lima, Peru.

Holding and Controlling Company: Sierra Metals owns 82% of Sociedad Minera Corona, which, in turn, owns 100% of the Yauricocha mine.

Brief Description: Yauricocha is an underground polymetallic mine.

It exploits a series of carbonate-replacement orebodies and veins.

Brief History: The silver of Yauricocha was initially documented by Alexander von Humboldt in the early 1800s. The Valladares family filed the claims for the Yauricocha mine in 1905 and mined high-grade silver ore for 22 years. Cerro de Pasco Corporation acquired the Yauricocha claims in 1927.

Cerro de Pasco started mining operations at Yauricocha in 1948, until the Peruvian military government nationalised Cerro de Pasco Corporation and Yauricocha became a production unit of State-owned Centromin Peru for 30 years. The Yauricocha unit was privatised and purchased by Sociedad Minera Corona in 2002. Sierra Metals acquired 82% of the total equity of Corona in May 2011.

Yauricocha has produced 13.6-million tonnes of mineralised material containing 63-million ounces of silver and 378 000 t of lead, 117 000 t of copper and nearly 618 000 t of zinc since 1973. Since 1979 Yauricocha has averaged 413 000 t/d of production.

Products: Silver/lead/zinc/copper/gold.

Geology/Mineralisation: Yauricocha is a carbonate replacement ore deposit. This type of deposit is found on continental margins of orogenic belts and on the inner side of principal arcs where carbonate rocks representing miogeoclinal or stable platform depositional environments are widespread. The deposits are associated with magmatic intrusions that are believed to be a result of subduction.

The carbonate replacement ore deposits of the Yauricocha district are spatially and genetically related to the Yauricocha stock, a composite intrusive body of granodioritic to quartz monzonitic composition that has been radiometrically dated at about 7.5-million years old. The stock intrudes tightly folded limestone and lutite beds of the Late Cretaceous Jumasha and Celendín formations, and the overlying Casapalca formation.

Mineralisation of the Yauricocha deposit is formed principally of pyrite, quartz, enargite, chalcopyrite, bornite and covellite in the core and central parts of the bodies. Loose masses of friable pyrite, galena, sphalerite and minor amounts of chalcopyrite in a gangue of limestone, clay and quartz occur in the periphery of the bodies. Native gold is associated with the sulphide minerals.

Mineralogical zoning of the district is marked, with the core comprising enargite located within the Jumasha limestone near the contact with the France Chert. To the west are rich bodies of bornite and chalcopyrite, with a predominance of enargite. Further to the west rich bodies of lead, zinc, silver and gold occur. The same zoning is observed at a smaller scale inside the orebody.

Reserves: Total proven and probable reserves as at November 13, 2017, were estimated at 8.92-million tonnes grading 48.3 g/t silver (Ag), 1.2% copper (Cu), 0.77% lead (Pb), 2.43% zinc (Zn) and 0.52 g/t gold (Au).

Resources: Total measured and indicated mineral resources as at November 13, 2017, were estimated at 13.21-million tonnes grading 62.3 g/t Ag, 1.52% Cu, 0.92% Pb, 2.79% Zn and 0.65 g/t Au.

Total inferred mineral resources as at November 13, 2017, were estimated at 6.63-million tonnes grading 43.0 g/t Ag, 1.19% Cu, 0.47% Pb, 2.16% Zn and 0.55 g/t Au.

Mining Method: Underground mining, using the sublevel block caving and cut-and-fill mining methods.

Major Infrastructure and Equipment: Mining at Yauricocha is conducted using various extraction methods; principally sublevel caving and overhand cut-and-fill stoping.

During cut-and-fill stoping the mine uses timber in square sets to maintain the level open for safe access (mostly through breasting) and then fills the lower level after mining the upper level.

About 93% of the ore and waste material is extracted through the Klepetko tunnel located at Level 720. The tunnel has a section of 3 m x 3 m, is 4 km long and is equipped with 20 trolley locomotive hauling ore cars of 110 ft3 to 160 ft3 capacity.

As a result of the potential of the orebodies at depth, the company is sinking a hoist raise to extract ore from deeper levels of the lead oxide, copper and polymetallic orebodies to the 720 haulage level. The new access will serve the Mascota, Cuye, Catas, Antacaca, Rosaura and Antacaca Sur orebodies in the Mina Central. Given the depth of current production below the surface, development drilling to convert the mineral resource to a mineable reserve is performed on an ongoing basis from underground workings.

The Chumpe mill treats ore produced by the Yauricocha mine using crushing, grinding and flotation. The ores are complex, carrying zinc, lead, copper, silver and gold values.

Three types of ore have been historically treated - polymetallic (PM), containing payable silver, lead, copper and zinc; copper ore, containing payable copper and silver; and lead oxide, containing payable silver and lead. Gold occurs in the ores and is partially recovered, until recently it has not been tracked in the mill. Impurity elements, such as arsenic and antimony, are routinely monitored. Currently the mine is processing limited quantities of copper ore. The Chumpe mill is operating only two milling circuits, one treating polymetallic ore and one treating lead-oxide ores. Current production of copper ore is being processed through the PM circuit.

The plant produces lead, copper and zinc concentrate in the polymetallic plant; and copper and lead oxide concentrate in the lead oxide circuit. The sulphide lead concentrate from the oxide plant is combined with the sulphide lead in the polymetallic circuit.

Prospects: Sierra Metals is planning to expand the Yauricocha mine through sustainable growth stages from 3 000 t/d to 3 600 t/d in 2019, and to 5 500 t/d in 2021.

Contact: Sierra Metals investor relations Mike McAllister.

Contact Details:

Sierra Metals

Tel +1 866 493 9646

Email info@sierrametals.com

Website https://www.sierrametals.com/

Edited by Sheila Barradas
Creamer Media Research Coordinator & Senior Deputy Editor

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