MINERALIZATION
The mineralized vein at Los Ricos South, which is up to approximately 30 m wide, has had at least three quartz vein formation and metal precipitation events (Nebocat, 2004). The vein strikes across the Property for 3.5 km, following a northwest-southeast trending fault, and dips approximately 65° to 70° to the west.

In 1923, the Cinco Minas Company retained an independent consultant named George Garrey to carry out and deliver a report on his geological examinations of the underground workings (Garrey, 1923). Garrey (1923) examined the underground workings and reports the chief gangue mineral is quartz, but whereas crystalline quartz is plentiful and colourless, cream colored, milky or occasionally even amethyst, the bulk of the quartz is a dense fine-grained grey, yellowish of greenish porcelain quartz intermixed with chalcedonic quartz of a slightly later origin. This quartz is associated with less grey, brown and white calcite. Some of the calcite was deposited contemporaneously with the quartz, but most of it post-dates the latter. The contemporaneous calcite is more abundant in the vein near surface than at depth. Comb quartz and open vugs in the quartz vein were more abundant in the upper workings near surface. Siderite, rhodochrosite and adularia were also noted as rare occurrences, whereas kaolinite was also present near secondary enriched oxidized mineralized materials. Chlorite and possibly epidote were also in evident in association with the quartz, or in partially replaced rock fragments.

The chief sulphide minerals are galena, chalcopyrite, sphalerite, pyrite, covellite, bornite and silver sulphides. The higher-grade sulphide zones are generally associated with finegrained galena and minute specks of chalcopyrite. Coarse-grained sulphides generally carry low metal values. Recognizable silver sulphides are rare, however, specks of pyrargyrite were observed in the high-grade sulphides that might have been tetrahedrite, argentite or other silver sulphide minerals. Native silver flakes and specks were observed coating fractures in high-grade sulphide mineralized zones.

There appear to have been either several periods of vein deposition or a long period of mineralization interrupted periodically by faulting and brecciation of the quartz. The mineralization appears to have formed relatively early. The location of the mineralized shoots, which appear to rake at 65° to 70° northwestwards, seems to have been controlled by:
• segregation of the minerals during deposition from the original primary solutions;
• periods of movement and brecciation that followed the first period of mineralization; and
• formation of the diagonal slips or cross-faults that confined or diverted the later primary mineralizing solutions into these breccia-filled channels.

The portions of the quartz vein between the various mineralized shoots show little evidence of brecciation of the original quartz. The richest mineralized shoots appear to have been associated with the greatest width of quartz and the portions of the veins showing the greatest number of periods of brecciation.

DEPOSIT TYPES
Los Ricos (Cinco Minas) is a classic Neogene (previously Tertiary) age, volcanic-hosted and low-sulphidation epithermal precious metal deposit.

Epithermal deposits of Au (±Ag) are a type of lode gold deposit that comprises veins and disseminations formed at or near (=1.5 km) the Earth’s surface (Hedenquist, 2000; Taylor, 2007; Figure 8.1). The deposits occur in association with hot springs and young volcanic centres. The host rocks are volcanic and volcaniclastic sedimentary, sedimentary and metamorphic rocks. The mineralization is dominated by Au and Ag, but Cu, Pb and Zn may also be present in variable amounts.

Epithermal Au deposits are classified on the basis of the sulphidation state of the sulphide mineralogy as belonging to one of three sub-types (Hedenquist, 2000; Taylor, 2007):
• Low-Sulphidation: previously called adularia-sericite, these low-sulphidation subtype deposits are considered to be formed by near-neutral pH fluids, as a result of being dominated by meteoric waters but containing some magmatic C and S.
• High-Sulphidation: previously called quartz-(kaolinite)-alunite, alunite-kaolinite, enargite-Au, or high-sulphur deposits, these highly acidic deposits generally occur proximal to magmatic sources of heat and volatiles and form from acidic hydrothermal fluids containing magmatic S, C and Cl.
• Intermediate-Sulphidation: some deposits with mostly low-sulphidation characteristics have sulphide mineralized assemblages that represent a sulphidation state between that of high-sulphidation and low-sulphidation deposits.

MINING METHODS
The Los Ricos South Project will consist of both open pit and underground mining operations. Underground mining will generally follow open pit mining, although there will be an overlap of three years. The entire duration of mining activity will be 11 years.

OPEN PIT MINING
The Los Ricos South Property contains several gold vein systems, some of which were partially mined in the past. The deposits are near surface and lend themselves to conventional open pit mining methods. For this PEA production plan, three different open pits will be developed over the life of the Project to support the processing operation.

The topography across the Project site is quite hilly and mining will generally occur in pits located along various hillsides.

The excavation of the open pits will require the removal of three different materials, all of which are tracked separately in the production schedule.
• Overburden: consists of loose material overlying some of the deposits, which will be stripped and hauled to nearby waste rock storage facilities.
• Waste Rock: is barren or low grade material, also placed into nearby waste rock storage facilities.
• Process Plant Feed: is mineralized material above cut-off grade that will be hauled to the process plant facility.

The design of the open pit layouts and the mining schedule requires several steps. These are: 1. Run pit optimizations to select the optimal pit shells to be used for mine design.
2. Design an operational pit (with ramps and benches) based on the optimal pit shell.
3. Design pit phases as needed to moderate the mining sequence.
4. Develop a life-of-mine mine production schedule, based on supplying 5,000 tpd (1.82 Mt per year) of mineralized feed to the process plant.

UNDERGROUND MINING
The dominant mining method for the two mines is longitudinal retreat sublevel Longhole Stoping (“LHS”) with Paste Fill (“PF”). In the LR mine, around backfilled Old Workings, mining uses transverse access instead of longitudinal. Approximately 25% of the mined tonnes from the entire underground portion of the Project are mined using transverse access. The CC mine uses longitudinal retreat for all extracted tonnage.

Extraction of mineralized material from the underground portion of the Los Ricos South Project will use two mining areas: Los Ricos (“LR”) and Cerro Colorado (“CC”). The LR mine will target the Los Ricos and Rascadero veins, while the CC mine will target the Cerro Colorado 1 and Cerro Colorado 2 veins. The East vein was determined to have insufficient tonnes above cut-off grade (“COG”) to support underground mining under present conditions. Figure 16.10 shows the two mining areas, with the open pit mining areas superimposed on the underground development.

The LR mine is expected to produce 87% of total recovered tonnes from the entire underground portion of the Los Ricos South Project. The CC mine is significantly smaller and lower-grade; however, it does provide an NPV benefit to the Project, and also de-risks the production plan for the underground by providing a separate, albeit lower-rate, feed source. Figures 16.11 and 16.12 show longitudinal projections of the LR and CC mines, respectively.

Initial mine development for the LR underground will start in YR 4, with underground production beginning in YR 5 and lasting until the end of YR 11. The CC underground will begin development in YR 5, with underground production beginning in YR 6, lasting until midway through YR 9. Nominal production from the combined underground operations is 2,000 tpd, with the CC mine operating at approximately 600 tpd and the LR mine operating between 1,500 tpd to 2,400 tpd.

Mined tonnage in the underground portion of the Project is derived from two sources: in-situ stopes (virgin rock), and excavation of historical workings that have been backfilled with lowergrade mineralized material (“Old Workings”).

Mining Methods
Production in the CC mine uses entirely longitudinal retreat LHS mining. Production in the LR mine uses a combination of longitudinal retreat and transverse access LHS mining. Transverse mining exists only in areas surrounding Old Workings that are to be extracted concurrently with in-situ adjacent stopes. Both mines use PF as backfill for all underground stopes.

Longitudinal retreat access involves driving an access through mineralized material along the strike of the vein to the end of a group of stopes. Where filling is required for sequencing, a top and a bottom access (nominal level spacing of 20 m) are required. Where filling is not required (e.g. certain crown pillar areas or isolated stopes), only a bottom access is required. The stope is drilled off using downholes (or upholes where no top access exists), loaded, and blasted, and mineralized material is recovered from the bottom access using an LHD. Once loading is complete, a wall is built to seal the bottom access of the stope, and then the stope is filled with PF. After a curing period (nominally 14 days), the cycle repeats on the next stope in the sequence. Longitudinal retreat mining progresses from the bottom of a mining area to the top, working on top of PF.

For transverse access, an access drift is driven in waste rock parallel to the strike of the vein, offset 10 m from the vein, and transverse cross-cuts are driven from the access through waste rock and into the mineralized material on 15 m centres. For the LR mine, this method is only used in areas around previously mined-out stopes that have been backfilled with lower-grade mineralized material. In cases where economic mineralized material exists on both sides of the Old Workings, this method is mirrored to the opposite side. Extraction of a stope using transverse mining is slightly different from the extraction sequence used for longitudinal mining. With the exception of the very top level in the crown pillar, all transverse mining requires an overcut and an undercut, since filling with PF is necessary to the sequence. Extraction of the top level is expected to be lower as backfilling will not be possible. All longhole drilling for transverse mining is expected to be with upholes, as the mining method progresses top-down to avoid excavating the entirety of the old workings and leaving an open void over 250 m tall above the initial in-situ transverse stopes. Mapping from the level above will be used to improve drill hole target accuracy.

Primary Crushing
The proposed crushing circuit will reduce the run of mine mineralized feed from a nominal top size of 600 mm to a product of 80% passing (P80) 150 mm for the SAG mill feed material. The front end crushing circuit includes, but is not limited to, the following equipment:
• ROM feed hopper.
• Rock breaker for oversize feed.
• Vibrating grizzly apron feeder.
• Jaw crusher.
• Associated conveyor belts.
• Belt scale and belt magnet.

The feed material will be hauled from the open pits and underground mine and dumped at the ROM delivery area adjacent to the crusher. The ROM surge bin will have a capacity of 100 t with a vibrating grizzly feeder that feeds the primary jaw crusher.

The 150 kw jaw crusher, 762 mm x 1219 mm (30 in x 48 in.) will process a nominal 278 tph of material based on the utilization factor noted in Table 17.1 The jaw crusher discharge will be conveyed to the crushed feed stockpile.

Crushed Feed Stockpile and Reclaim
The stockpile will provide production surge capacity to ensure a steady rate to the SAG mill and process facility. The equipment in this area includes:
• Crushed Feed Stockpile: 4,500 t live capacity.
• Reclaim Apron Feeders (3): variable speed.
• Associated conveyor belt feed system with belt scale, self-cleaning magnet.

The apron feeders will discharge onto the SAG mill feed conveyor to feed crushed material to the primary grinding SAG mill unit. The apron feeders will reclaim the material from the 4,500 t stockpile and ensure a controlled feed rate to the SAG mill of 226 tph. Feed control to the feeders will be ensured by the inline belt scale.

Grinding Circuit
Based on the preliminary testwork and recovery rates, the grinding circuit final product size will have a design P80 of 74 µm. The feed rate to the primary SAG mill will be a nominal 226 tph. The grinding circuit is a two (2) stage process with the SAG mill / screen / pebble crusher and the ball mill in closed circuit with classifying cyclones.
The equipment in this area includes:
• SAG mill – 7.3 m diameter x 2.74 m long (24 ft x 8.8 ft) – 2.3 MW installed power.
• Pebble Crusher – 260 kw installed power.
• Ball Mill – 5.12 m diameter x 7.04 m long (16 ft x 22 ft) – 2.6 MW power installed.
• Mill Discharge pumpbox with associated cyclone feed pumps.
• Cyclone classification – six (6) operating 6gMAX20 units.
• Grinding circuit control – flow meters, density meters, variable speed pumps.
• Grinding area sump pump(s).
• Sampling system – raw feed and leach feed.

Recycled water from the pre-leach belt filter(s) will be added to the SAG mill feed to ensure a slurry density with the mill of 74%. Any oversize material (from the classifying screen) will be sent to the pebble crusher via conveyors and recirculated to the SAG mill feed belt. The screen undersize will feed the ball mill pump box to allow to be pumped and classified at the cyclone cluster. The cyclone overflow, P80 = 74 µm will flow to the pre-leach thickener. Grinding media will be added to the mills are required to maintain power draw and grinding of the material to the desired size.

The process plant flowsheet design comprises conventional crushing, a semi-autogenous mill with a pebble crusher, and a closed circuit ball mill circuit with cyclones to ensure product (P80) size feed to the leaching circuit. The classified material will be thickened in a pre-leach thickener to increase the slurry density and decrease the slurry volume. The thickener underflow will be filtered in belt filters and repulped with SART discharge solution prior to entering the leach tankage. The thickener overflow water will be recirculated to feed the grinding circuit. After the required leaching retention time, the discharge slurry (and loaded solution) will be filtered in pressure filters. The reason for this is twofold – wash and recover pregnant solution for recovery within the Merrill Crowe system, and also produce “dry” stackable tailings that is less than 16% moisture and less than 2 ppm cyanide in the pore water. At the Los Ricos site, water recovery and management are ve ........