Deposit Geology
The Cerro Blanco deposit is a classic hot springs-related, low-sulphidation quartz-adularia-calcite vein system. It is localised along a complex fault intersection created during late Miocene-Pliocene tectonic extension within the active Central American volcanic arc. Local igneous activities that drove the Cerro Blanco hydrothermal system include a vesicular andesite dike swarm and mineralization stage rhyolite / dacite flow dome eruption and cryptodome intrusion.

The Cerro Blanco vein systems are best developed (widest and most continuous) within the 300 to 500 m elevation ranges. Principal host rocks include a lithic tuff – calcareous shallow marine-volcaniclastic sequence and, to a lesser extent, the overlying volcaniclastic-hydrothermal breccia sequence of probable Pliocene age. Vein zones often appear to transition to barren calcite beneath the ±300 m elevation in the northern half of the deposit. To the south, high-grade quartz-adularia-calcite vein zones continue at least another 100 m down to 200 m elevation. Some veins remain open at depth.

Mineralization
The Cerro Blanco gold deposit occurs within a large hydrothermal alteration zone covering an area about 5 km long and 1 km wide. This zone exhibits the effects of strong, pervasive hot spring type hydrothermal alteration.

Gold mineralization is hosted within a broadly north-south striking sequence of westerly-dipping siltstones, sandstones, and limestones (Mita Group) that are capped by silicified conglomerates and sediments with contemporaneous dacite / rhyolite flow domes or cryptodomes (Salinas Unit). The Salinas rocks are synmineral and believed to have accumulated progressively in a low-relief graben characterised by a shallow groundwater table. The Salinas conglomerate was presumably derived by erosion of the flanking horst blocks as relief was created during active faulting. The topographic inversion required to explain the current prominent position of the graben fill is ascribed to the silicic character of the Salinas unit and its consequent resistance to erosion.

The west and east sides of the Cerro Blanco ridge consist of flat agricultural plains characterised by Quaternary basalts, interbedded with boulder beds and sands. These rocks also appear down-faulted to lower elevations, implying major post-mineral extensional movements on such faults; and they may be neotectonic (active).

The current gold resource occurs under a small hill and is confined within an area about 400 m x 800 m. The gold deposit is characterised by both high-angle and low-angle banded chalcedony veins, locally with calcite replacement textures. High-angle mineralised faults and discontinuous stockwork zones host some of the highest gold grades. Gold-bearing structures in the Cerro Blanco project area extend 2 km to the northwest of the gold deposit and occur largely confined within the hydrothermal alteration zone. Exposures are poor and locally covered by alluvium and post-mineral rocks. Gold-bearing structures extend at least 1 km south and southwest of the deposit under valley fill and post-mineral rocks. Geothermal well MG7, located about 0.5 km east of the deposit, encountered a 27 m zone averaging 6.3 g Au/t and 22 g Ag/t at a depth of 634 m. The upper 6 m of this zone averages 23.9 g Au/t and 79 g Ag/t

Gold and silver occur almost exclusively in quartz-dominated veins of low-sulphidation epithermal origin and in low-grade disseminated mineralization within the Salinas conglomerates and rhyolites.

Deposit types
The low sulphide content and near absence of base metals in the Cerro Blanco veins confirm it as a classic hot springs-related low-sulphidation epithermal deposit. In common with most low-sulphidation deposits, it appears to be linked to compositionally bimodal, basalt-rhyolite volcanism, the hallmark of intra- and backarc rift settings worldwide. The hydrothermal system seems likely to have been initiated during rhyolite dyke and cryptodome emplacement, at the base of the Salinas unit, with the rhyolitic magma and magmatic input to the mineralising fluid both being derived from the same deep parental magma chamber.

Adularia-sericite epithermal gold-silver deposits characteristically occur as banded fissure veins and local vein / breccias which comprise predominantly colloform banded quartz, adularia, quartz pseudomorphing carbonate, and dark sulphidic material termed ginguro bands. Examples of adularia-sericite epithermal gold-silver deposits include Waihi and Golden Cross, Pajingo, Vera Nancy, Cracow, Hishikari, Sado, Konamai, Tolukuma, Toka Tindung, Lampung, Chatree, Cerro Vanguardia, Esquel, El Peñon.

At near surficial levels, many are capped by eruption breccias and sinter deposits. Eruption (phreatic) breccias, which form by the rapid expansion of depressurized geothermal fluids, are characterised by intensely silicified matrix and generally angular fragments including sinter, host rock and local surficial plant material. Although sinter deposits formed distal to fluid upflows commonly associated with eruption breccias, sinters tend to be barren with respect to gold but may be anomalous in other elements such as boron, arsenic and antimony.

Cerro Blanco shows all the characteristics of a completely preserved, non-eroded epithermal deposit. The occurrence of hot springs (sinters, silicified reeds, pisoliths) directly above the presumed feeder veins at Cerro Blanco implies a high water table and swampy conditions (cf. McLaughlin, California). In areas of high topographic relief, outflow springs (sinter) are usually found several kilometres from the upflow zones. The widespread occurrence of lacustrine and fluvial clastic sediments in the Salinas Group and accretionary lapilli, typical of water-rich pyroclastic surges, supports this interpretation. Sedimentation probably kept up with subsidence. Mudstone dykes and geopetal structures—open fractures filled by horizontally bedded chalcedonic and sulphide-rich sediment—reinforce the interpretation. The hydrothermal breccia in the south part of the South Ramp may be a diatreme.

Mine Operations
Approach Mining is to be carried out using conventional open pit techniques with hydraulic shovels, wheel loaders, and mining trucks in a bulk mining approach with 5 m benches. An Owner-operated mining operation is planned, with outsourcing of certain support activities (e.g., explosives manufacturing and blasting).

Open Pit Geotechnical Design Parameters:
- Final Vertical Bench Height - 20.0 m;
- Bench Face Angle - 74.0 degrees;
- Average Catch Berm Width - 10.0 m;
- Horizontal - 15.8 m;
- Vertica - 20.0 m;
- Inter-ramp Slope Angle (Crest-to-Crest) - 51.8 degrees;
- Rise:Run - 1.27.

Ramp & Road Design
The ramps are designed specifically for the primary hauler, the CAT 775F, in accordance with the SME Standard of 2 and 3.5 times the ramp width of the vehicle operating width. The operating width of the CAT 775F is 5.7 m. The ramp is wide enough for vehicle operation as well as the establishment of a safety berm on the pit side and a drainage ditch on the wall side. The safety berm is designed to be at least half the height of the tallest tire (CAT 775F) to be used on site.

Production Drilling & Blasting
Drill and blast specifications are established to effectively drill and blast a 5 m bench with a single pass. For this bench height, a 171 mm blast hole size is proposed with a 5.0 m x 5.0 m pattern with 1.5 m of subdrill. These drill parameters, combined with a high energy bulk emulsion with a density of 1.2 kg/m3, result in a powder factor of 0.32 kg/t. Blast holes are planned to be initiated with electronic detonators and primed with boosters. At this stage of the study, some assumptions were made concerning the type of explosives to use in relation with the high temperature of the groundwater and the rock. The operation will begin with bulk emulsion, and as the pit is deepening under the water table, specialized high-temperature package explosive will be used. This will be clarified in the next phase.

Grade Control
The grade control program will consist of establishing dig limits for mill feed and waste in the field to guide loading unit operators. A high-precision system combined with an arm geometry system will allow shovels to target small dig blocks and perform selective mining. The system will give operators a real-time view of dig blocks, mill feed boundaries, and other positioning information.

Pre-Split
Pre-split drill and blast is planned to maximise table bench faces and to maximise inter-ramp angles along pit walls. The pre-split consists of a row of closely spaced holes along the design excavation limit of interim and final walls. The holes are loaded with a light charge and detonated simultaneously or in groups separated by short delays. Firing the pre-split row creates a crack that forms the excavation limit and helps to prevent wall rock damage by venting explosive gases and reflecting shock waves. As a best practice, it is recommended that operations restrict production blasts to within 50 m of an unblasted pre-shear line. Once the pre-split is shot, production blasts will be taken to within 10 m of the pre-shear and then a trim shot used to clean the face. Pre-split holes spaced 2 m apart will be 20 m in length and drilled with a slightly smaller diameter of 165 mm (6.5 inches).

Loading
The majority of the loading in the pit will be done by three 7 m3 hydraulic excavators. The excavators will be matched with a fleet of 70-ton payload capacity mine trucks. The hydraulic excavators will be complemented by two production front-end wheel loaders (FELs) with an 8.2 m3 bucket.

Hauling
Haulage will be performed with 70-tonne class mine trucks. The truck fleet productivity was estimated in Talpac software. Several haulage profiles were digitised in Deswik with haul routes exported to Talpac to simulate cycle times. Cycle times have been estimated for each period and all possible destinations, as there are several waste storage areas.

Primary Crushing
Mineralised material from the open pit, at maximum lump size of 1,067 mm, will be transported to the plant by 70-tonne capacity rear dump trucks. The trucks will tip directly into either side of the ROM pocket. However, if the trucks are not permitted to directly tip into the ROM pocket, then the truck load will be dumped onto the ROM pad. The ROM pad will be primarily utilised for emergency storage and blending if required. ROM material will be reclaimed to the ROM pocket by a front-end loader.

A rock breaker will be installed to assist in breaking down oversize material retained above the gyratory crusher in the ROM pocket. Mill feed material will be crushed by the gyratory crusher and then withdrawn from the ROM discharge pocket by a variable speed apron feeder. The crushed material will be transported via the stockpile feed conveyor to the crushed stockpile. The stockpile feed conveyor will be fitted with a weightometer to monitor the primary crusher throughput and to control the apron feeder variable speed drive.

The crushing circuit will be serviced by a single dust collection system consisting of multiple extraction hoods, ducting, and a baghouse. Dust collected from this system will be discharged onto the stockpile feed conveyor and then finely sprayed with water for dust suppression.

Crushed Stockpile
The crushed material will be conveyed to the crushed material stockpile. The stockpile will have a live capacity of approximately 10,000 t (equivalent to 13 hours of mill feed). Three reclaim apron feeders located underneath the stockpile will be installed with variable speed drives (VSDs) to control the reclaim rate feeding the grinding circuit. A single apron feeder will be capable of providing the total plant throughput of 627 t/h and will feed the mineralised material to the SAG mill feed conveyor.

Grinding
Reclaimed material from the crushed stockpile will feed a 10.97 m diameter x 6.71 m EGL SAG mill via the SAG mill feed conveyor. The SAG mill will be installed with a 16,000 kW induction motor and a VSD to control the speed of the SAG mill. A belt-scale on the SAG feed conveyor will monitor the feed rate. Process water will be added to the SAG mill to maintain the slurry discharge of the SAG mill at a constant density of 70%. SAG mill discharge will pass over a screen to remove grinding media scats and a small amount of pebbles. The SAG discharge screen undersize will report to the cyclone feed pump box, combining with ball mill discharge. The SAG mill discharge will have an average transfer size (T80) of 419 µm. SAG discharge screen oversize will be conveyed to the SAG mill feed conveyor.

Slurry from the cyclone feed pump box will be transferred to a cluster of 18 (16 operating / 2 standby) 500 mm hydrocyclones for size classification. The cyclone overflow, at a final target product P80 of 53 µm, will be transferred to the pre-leach thickener. The hydrocyclones have been designed for a 300% circulating load.

Cyclone underflow will feed a 7.92 m diameter x 12.80 m EGL overflow ball mill with a VSD-controlled 16,000 kW induction motor. Ground slurry will overflow from the ball mill into a trommel screen attached to the discharge end of the ball mill. The trommel screen oversize, consisting mainly of grinding media scats, will discharge into a trash bin for removal from the grinding circuit, while the undersize will flow into the cyclone feed pump box.

Process Plant Description
The overall process flowsheet includes a single-stage gyratory crusher and a SAG and ball (SAB) grinding circuit with a ball mill in closed circuit with hydrocyclones to achieve the final product size. The hydrocyclone overflow stream will flow by gravity to two vibrating trash screens operating in parallel ahead of a pre-leach thickener. The thickened slurry is pumped to a pre-oxidation circuit and then to a leach circuit where sodium cyanide, lime slurry, lead nitrate, and oxygen are added for gold and silver leaching. A CIP carousel circuit will adsorb dissolved gold and silver onto activated carbon. A Zadra elution circuit will be used to recover gold and silver from loaded carbon to produce doré. A cyanide destruction circuit using SO2 and air will reduce the WAD cyanide level in the tailings stream to less than 1 ppm. The tailings stream will be thickened and filtered to produce a filter cake and transported to a tailings storage facility.