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Sierra Metals Peru

Peru Exploration

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Yauricocha’s exploration projects have been grouped based on proximity to the mine area and include the Central Mine Area, Near Mine Target Areas and Regional Early Stage Exploration Areas. Brief descriptions of each area have been provided below.

Central Mine Area

Cuye

The Cuye deposit is located in a tongue of limestone within the Mascota intrusive stock and the France Chert, in the extreme northern part of the mineralized zone of the Yauricocha mine. This deposit is closely associated with the Mascota intrusive stock in the upper levels.  It is of very irregular, tubular or pipe-like form that tends to expand at depth following the principal E-W system of fracturing.  Its dip is not constant but varies from north to south.  Its length is greatest in Level 575 and decreases towards the surface.  Furthermore, its mineralization varies with depth, with the upper part Cu-Pb-Zn mineralized and grading to Cu at depth.

The mineralization is coated with residual silica that contains Au and Ag, and a thin supergene enrichment is observed down to Level 360.  Mineralization consists of pyrite-silica and pyrite with enargite and tetrahedrite in the central part, and galena, sphalerite, chalcopyrite and pyrite in the peripheral zones with increments of chalcopyrite, hematite, magnetite and possibly gold below Level 770.  The mineralization is banded and appears to follow the strike of the limestone and probably reflects its original stratification.  The mineralization also occurs in bands that follow the E-W fracture system.  In the upper levels, on Level 465, its contact with limestone is often sinuous with local brecciated areas of little width.

Catas

The main Catas deposit lies SE of the Cuye deposit and is located at the contact of the Jumasha limestone and the France Chert.  It is a large deposit, both horizontally and vertically.  It extends from the surface to below Level 720 and at Level 520 it reaches its greatest extent and occurrence of major mineralization. The Catas Principal deposit occurs in fractured and brecciated Jumasha limestone in contact with the France Chert and an intrusion, following the strike of the stratigraphy with persistent fracturing related to the NW-SE and E-W sets.

Mineralization consists principally of friable and/or massive pyrite, sphalerite, galena and minor amounts of chalcopyrite and bornite, with massive pyrite and/or breccia comprising the core of the deposit.  Soft masses of friable pyrite, galena, sphalerite with some chalcopyrite in a gangue of limestone form an irregular covering around this core.  Drilling done by SIMSA during 1998 and drilling done from Level 920 by Minera Corona during 2005 intercepted the Catas deposit in a manner that determined the deposit persists to depth, increasing in size and defined as a Cu-Au deposit of chalcopyrite, pyrite, hematite and magnetite.  Certain areas of the deposit have cores of sphalerite.

Near-Mine Target Areas

Purisima

This area is underlain by lutite and hosts an outcropping silicified, stratabound disseminated deposit.  The deposit has been mapped over an area of 250 m x 15 m and extends under cover.  Centromin drilled the deposit during 1986-1987; the deepest hole, only 30 metres deep, bottomed in mineralization and averaged 2.17 g/t gold (“Au”) and 17.7 g/t silver (“Ag”) over the 30 m.  The target here is an open-pitable gold deposit averaging an estimated 2-3 g/t Au and 16-18 g/t Ag.

Adrico

This area lies within the Victoria target area but outside the veined area.  Mineralized breccias hosted by granodiorite contain pyrite, and surface rock-chip sampling has yielded gold contents up to 15.0 g/t, with an average grade of 2.16 g/t Au.

Victoria

This area is underlain by granodiorite that hosts copper-silver veins in E-W trending faults near the operating mine and the veins are similar to the Cuye ore body of the central mine area. The Cuye ore body produced 1.2 million tonnes of ore at average grades of 2.5% copper (“Cu”) and 90.6 g/t Ag, mined by Centromin and others, but the body has an additional 100,000 tonnes in reserve, and is open laterally and to depth.

The Victoria vein was mined during 1969-1976 and 1994-1996 by Centromin, but only to a shallow depth, and it produced 23,807 tonnes averaging 81 g/t Ag, 0.43% lead (“Pb”), 2.04% Cu and 0.65% zinc (“Zn”).  The vein is open to depth and along strike.

San Juan

This area is underlain by a sequence of calcareous red lutites, pure limestones and reddish arenaceous limestone that hosts breccias containing polymetallic mineralization.  It is located about 2 km NE of the Victoria-Adrico target.

Carmencita

This area is underlain by limestone that hosts chimney-type, lead-oxide mineralization.

Regional Target Areas

Ipillo

This area hosts polymetallic veins within an intrusive granodiorite.  During 1991-1997, Centromin mined the Poggi 1 vein and produced 70,786 tonnes of ore at average grades of 97 g/t Ag, 2.28% Pb, 0.53% Cu and 5.89% Zn.  Abundant veins and veinlets occur over an area of 2 km2 and stockworks of veins occur in large portions of the veined area.  The potential for open-pitable stockwork deposits as well as vein-hosted deposits is considered to be high by the mine’s staff.

Éxito Sur

This area is at the contact between the Jumasha limestone and an intrusive granodiorite, the setting where many of the mine’s deposits occur.  Éxito Sur lies 1 km south of the inactive Éxito mine, where Centromin produced 258,634 tonnes averaging 63 g/t Ag, 2.87% Pb, 0.13% Cu and 9.73% Zn between mid-1991 to 1998.  Subsequently, Minera Corona produced 277,244 tonnes averaging 63 g/t Ag, 2.14% Pb, 0.18% Cu and 12.06% Zn from 2004-2008.

At Éxito Sur, extensive manganese mineralization occurs on the surface that has been explored by drifting and drilling only to shallow depths. The manganese mineralization is inferred to indicate massive polymetallic mineralization at depth. The current programme will include deeper holes to test this concept.

Yauricocha Fault

This fault is a major regional fault that trends NNW-SSE for several kilometers and is a major ore-controlling fault in the Yauricocha mine.  Exploration along the fault to the southeast of the mine is designed to test this portion of the fault for additional deposits.  The primary targets are dilational areas along the fault, similar to the mineralized areas in the Central Mine Area. 

Yanamachay/Silacocha

These early stage targets have no prior exploration work however, ancient workings are known and the the Company believes there is potential for mineralization. The targets are replacement polymetallic mineralization at the contacts of granodiorite with limestone of the Jumasha Formation and intercalated limestone, arenites and lutites of the Oyon/Chimu Formation.