Cerro Lindo is a Kuroko-style VMS deposit with economic grades of Zn, Cu, Pb, and Ag.

Mineralization is hosted by a pyroclastic unit composed of ash and lapilli-type polymictic tuffs with subrounded, well classified fragments. Some lapilli have centimetre-scale, pencil-like shapes, due to development of an incipient schistosity.

Eight styles of mineralization were identified at the Cerro Lindo deposit:
1. Pyritic, homogeneous, primary massive sulphide (SPP): This unit includes almost exclusively pyrite, less than 10% barite, and minor interstitial chalcopyrite. Its structure is equigranular, generally coarse grained (3 mm to 6 mm), but with fine-grained areas (0.4 mm to 2 mm)

2. Copper-rich, baritic homogeneous primary sulphides (Cu-SPB): This unit contains more than 50% total sulphides (including barite), and more than 10% barite. Barite is associated with sulphides because it was deposited from the same solution at the same time as the sulphides. Its structure is homogeneous, and it is composed of barite, pyrite, pyrrhotite, chalcopyrite, and brown sphalerite. Sulphides typically occur as intergrowths and patches, and brown sphalerite is included in chalcopyrite grains. There is less pyrite than in the Zn-SPB unit (described below). The Cu-SPB is generally found within or near the contact with Zn-SPB and SPP.

3. Zinc-rich, banded, baritic primary sulphides (Zn-SPB): This unit comprises more than 50% of total sulphides (including barite), and more than 10% barite. The Zn-SPB unit contains variable proportions of pyrite, barite, yellow sphalerite, and galena. It is typically banded and has a coarse grain size (3 mm to 6 mm).

4. Semi-massive sulphides (SSM): This unit contains between 20% and 50% sulphides, which are mostly represented by barren pyrite as disseminations, patches, stringers, and stockworks. This mineralization is generally fine grained as compared to massive sulphides. SSM forms a variable envelope, 20 m to 80 m thick, around the massive sulphide bodies. The sulphide proportion decreases outward. It is better developed in the footwall.

5. Pyritic oxidized sulphides (SOP): This unit comprises bornite and covellite, and is mostly located in the OB2 mining production area.

6. Baritic oxidized sulphides (SOB): This unit comprises bornite, covellite, and oxidized zinc, and it is also located in the OB2 mining production area.

7. Leached massive sulphides (SLB) and leached semi-massive sulphides (SSL): These units are located near surface in the OB2 mining production area.

8. Mineralized volcanic rocks (VM): This unit contains rhyolite and dacite rocks with some chalcopyrite and sphalerite disseminated in veinlets or patches, located on the edge of the mineralized zones.

Cerro Lindo contains 19 mining production areas within the mineralization domains. The mineralized lenses exhibit an irregular elongated geometry. Their longest axis (nearly 500 m) has a northwest-southeast horizontal trend (azimuth 135°). The mineralized bodies are approximately 300 m thick (occurring between 1,600 MASL and 1,980 MASL) and 100 m wide. They are the largest near the edge of the Topará Ravine, beyond which they diminish in size toward the southeast. The mineralized bodies generally dip to the southwest at 65° on average.

The majority of these bodies show three types of mineralization. The upper part features the massive mineralization of barite, sphalerite, galena, and pyrite (SPB). The lower part includes massive pyrite (SPP), with two different general grain sizes, one fine grained with a higher chalcopyrite content and the other coarse grained and largely barren. In the lateral portions, mineralization is semi-massive, contains 20% to 50% sulphides, and occurs as disseminations, patches, and stockworks. The base of the system exhibits a cluster of small veins of pyrite, pyrrhotite, and to a lesser extent, chalcopyrite. The mineralization at Cerro Lindo is generally coarse grained, which may be related to recrystallization due to the contact metamorphism, and this improves metallurgical recovery.

The massive sulphide frequently presents a marked banding, which may be related to tectonic deformation. In the contact with the adjacent batholiths, there is a noticeable predominance of remobilized sulphides elongated in banding that runs parallel to the volcanic contact with the intrusives. The rigidity of the batholiths likely fostered the generation of areas of greater sulphide deformation and mobilization.

Recently, a new domain termed mineralized volcanic (VM) has been identified, which differs from the other lithologies because it does not contain massive sulphides. The mineralization is scattered or occurs as patches in the volcanic rock and consists of mainly tetrahedrite, freibergite, sphalerite, and galena. Typical metal concentrations in VM are up to 15% Fe; 1% Zn, and greater than 0.25% Cu, 0.50% Pb, and 30 ppm Ag.

Significant barite is present mainly in the upper portions of the deposit. A secondary enrichment zone, composed of chalcocite and covellite, formed near surface. Silver-rich powdery barite remains at surface as a relic from sulphide oxidation and leaching.

The lead content is usually low and is mainly associated with high grade zinc zones, and locally with late quartz veins or small volcanic enclaves. These enclaves represent approximately 2% to 3% of the deposit volume, and commonly measure 0.5 m to 10 m in diameter. Silver grades correlate well with copper and lead.

As is typical of Kuroko-style VMS deposits, Cerro Lindo is characterized by a distinct mineralization zonation.

Cerro Lindo has been operating since 2007, with production rates of approximately 7 Mtpa in the recent years. The mine is mechanized, using rubber-tired equipment for all development and production operations. Mining is carried out in ten separate orebodies, using bulk longhole stoping methods, with up to 30 m high stopes, in a primary, secondary, and tertiary sequence. Stopes are backfilled with a low-cement content paste fill made from flotation tailings in the surface paste plant and distributed to the underground via two vacuum filter trains.

The highest operating level is the 1970 m level, the lowest operating level is the 1550 m level, and the ultimate bottom level is planned to be the 1490 m level.

The mine is accessed through fifteen portals that service adits, drifts, and declines. The main ore flow is directed via the grizzly installations on the 1830 m level that feed the jaw crusher located on the 1820 m level. From the crusher discharge, the ore flows up to the surface stockpile areas via an inclined conveyor and out at the 1940 m level from where it continues to flow to the plant via inclined surface conveyors.

MINE METHOD
The stoping methods employed at Cerro Lindo include the bulk Sublevel Longhole Stoping (SLS) method, which accounts for the majority of the production, and the Cut and Fill (C&F) method, utilized where necessary such as for the mining of sill pillars which require a more conventional method for economic extraction. The SLS stope dimensions are typically 20 m to 30 m in height by 25 m long and vary in width. Dimensions can vary given the orebody geometry or local geotechnical conditions which necessitate extra care in keeping stopes of a size to permit effective ground control and stoping productivities.

RPA considers the mining methods and stope dimensions appropriate for the style of mineralization at Cerro Lindo. SLS has been extensively used at the mine and the current mine designs follow a similar approach. RPA also notes that there is on-going investigations into using C&F mining methods to extract pillars where possible.

The SLS method can vary with production drilling being completed in a fan pattern using downward drilling or uppers drilling. The production drill holes vary in size from 102 mm in diameter for the downward drilling to 76 mm in diameter for uppers drilling to optimize stoping results in terms of size of fragmentation and overall stoping productivity.

MINE DESIGN
The mine design includes access via 5.0 m by 4.5 m ramps driven at various gradients to access the stope areas and other infrastructure (sumps, electrical substations, refuge stations, storage areas, etc.). A fleet of 35 t and 52 t haul trucks operated by contractors move the muck to the grizzlies located on the 1830 m level. The ore is crushed at this level and conveyed to the surface stockpiles.

CRUSHING
Crushing is carried out in three stages with the first stage occurring underground, where a primary jaw crusher, fed via a stationary grizzly, crushes ore to less than 100 mm. Crushed ore is conveyed to the coarse ore stockpiles located at the processing plant. When the primary crusher requires maintenance, ore is trucked directly to surface where it is stockpiled prior to being crushed in a mobile primary crusher, which discharges onto the coarse ore stockpile feed conveyor.

Coarse ore is reclaimed from the stockpile and fed to two parallel crushing circuits, each consisting of secondary and tertiary crushing. Reclaimed ore is screened, with the oversize reporting to the secondary crushers, while the undersize is directed to the fine ore bins. Secondary crusher product is screened, with the screen oversize reporting to the tertiary crushers and the undersize being directed to the fine ore bins. The tertiary crushers are in closed circuit with the tertiary screens, with the screen undersize directed to the fine ore bins. Ore is crushed to 80% passing (P80) 4 mm, and the two fine ore bins provide approximately 16 hours of storage capacity.

GRINDING
Fine ore is fed from the fine ore bins to two parallel ball mill circuits, each in closed circuit with high frequency classifying screens, at a rate of approximately 900 tph. Each grinding circuit also includes flash flotation, producing bulk (copper and lead) concentrate. The first grinding circuit is the original single-stage ball mill circuit installed in 2007 and capable of processing 5,000 tpd, while the second circuit, consisting of two identically sized ball mills in series, can process approximately 15,000 tpd. Grind size for the circuits is P80 150 µm to 170 µm.

The Cerro Lindo processing plant is located on a ridge adjacent to the Mine, situated at an altitude of 2,100 MASL to 2,200 MASL. The processing plant commenced operations in 2007 with a processing capacity of 5,000 tpd, however, it has since been expanded to a name-plate capacity of 21,000 tpd. Processing consists of conventional crushing, grinding, and flotation to produce separate copper, lead, and zinc concentrates. Tailings are thickened and filtered for use as backfill or trucked to the dry stack tailings storage facility.

FLOTATION
Flotation consists of bulk rougher and scavenger flotation to produce a copper-lead concentrate, which is then cleaned and combined with the flash flotation bulk concentrate prior to being separated into copper and lead concentrates. The bulk flotation tails form the feed to zinc rougher and scavenger flotation to produce a zinc concentrate, which is then cleaned. The three concentrates are thickened and filtered, and then deposited in ........