The geology of the Curipamba Project is characterized by the predominantly volcanic and volcaniclastic rocks of to the Macuchi Group of Middle Paleocene–Eocene age.

The El Domo deposit is a gold-rich, polymetallic VMS deposit. Mineralization is largely flatlying, stratiform and stratabound and occurs in one main massive sulphide lens, a directly overlying talus, or breccia zone, and a number of smaller, mineralized lenses primarily in the footwall of the main lens. The geology is complicated by a number of sub-vertical faults that offset the strata by up to approximately 50 m vertically. The deposit has a lateral extent of approximately 1,300 m by 1,100 m.

Mineralization can be divided into five types, where sphalerite, chalcopyrite, and pyrite are the principal sulphide minerals:
1. Massive sulphides with indistinct texture. In some places, a fragmental texture can be seen within the sulphides, suggesting that they may be formed by the replacement of lapilli tuff.
2. Sulphide-altered lapilli tuffs and peperites.
3. Transported sulphide fragments within polymictic lapilli tuffs.
4. Sulphide “pseudo”-fragments within polymictic lapilli tuffs.
5. Rare, thinly laminated siliceous chert with banded sulphides.

Gold was identified within sphalerite + galena + barite mineralization, where it occurs as minute inclusions in sphalerite. Accessory minerals include galena, tennantite/tetrahedrite, covellite, chalcocyanite, and barite, with barite being the principal gangue mineral.

Mineralization at El Domo is broadly zoned with an upper “cap” of barite, enriched variably in silica sphalerite, galena, and gold. This cap is underlain by a massive sulphide zone with local zoning of zinc-rich mineralization along the hanging wall contact and a copper-rich base. Vallejo et al. (2016) describes the vertical zonation of massive sulphides well-developed where the stockwork grades over a few metres into massive pyrite which is irregularly replaced by abundant chalcopyrite. The copper-rich zone is overlain by the zinc-lead zone dominated by coarse grained low-iron sphalerite, and associated skeletal galena with subordinate pyrite. The contact between the copper and zinc-lead zones is polymetallic and marks the replacement of the zinc-lead assemblage by the copper-rich one.

Mineralization in the grainstone shows evidence of at least two mineralization events. The sulphides include breccias which appear to have been caused by some form of collapse (possible anhydrite dissolution), while interstitial spaces were infilled by sphalerite and, in some cases, chalcopyrite. The sulphide mineralization occurs in veins of quartz with pyrite and some proportions of chalcopyrite, sphalerite, and minor galena.

The sulphide and precious metal compositions have numerous unusual features, usually associated with high temperature systems that have achieved boiling just prior to theirexpulsion on or near the seafloor. The exceptionally high gold recorded in many of the upper zones in all of the occurrences, together with the anomalous antimony, arsenic, mercury, and bromine contents of some of the minerals, can only be achieved by this process, which enables exceptionally efficient gold precipitation. Gold is conserved in the vapour phase of a hydrothermal fluid, and thus may be deposited over a much wider area than the base metals. At Curipamba, gold is generally associated with baritic exhalite.

The mineralization at El Domo shares most of the features of a VMS deposit. VMS deposits are major sources of Zn, Cu, Pb, Ag, and Au, and can contain trace metals such as Co, Sn, Se, In, Bi, Te, Tl, Ga, and Ge.

Deposits of this type are spatially and chronologically related to submarine felsic and/or mafic volcanism and are characterized by an underlying stockwork or feeder zone related to major hydrothermal alteration, which is typically more prominent in the footwall than in the hanging wall, and massive or semi- massive mineralization formed on or near the seafloor.

Most ancient VMS deposits still preserved in the geological record formed mainly in oceanic and continental nascent-arc, rifted-arc, and back-arc settings. The crustal composition exerts a major control on the mineral contents of VMS deposits, with Cu-Au-(Zn) deposits forming mainly on the primitive crust and Zn-Cu-Pb-Ag deposits on continental crust.

The principal mining method is conventional open pit mining (drilling, blasting, loading, and hauling) at a production rate of 1,750 tpd. The open pit mine design consists of a single pit with a mining sequence optimized through four main phases to maximize grade, reduce stripping ratios, and maintain the processing plant at optimum capacity.

Initially, open pit mining will be used, followed by a combination of open pit and underground mining. Underground development will start in Year 9 of the production schedule proposed in the PEA at a target rate of 1,000 tpd, using variations of room and pillar methods.

The El Domo VMS deposit has two structural domains: the Eastern sector, which contains the deepest mineralized zone, below the andesite unit, and the Western sector, which encompasses the mineralized zone underneath the tuff unit. The tuff unit is mostly composed of incompetent rocks, and will be mined by open pit methods. Material will be drilled and blasted, then loaded by backhoe excavators into haul trucks dispatched to the crusher, waste dumps, or stockpiles.

The UG mine design includes a 2 km long 5.0 m wide x 5.3 m high main ramp which will be driven at a grade of -12% on straight sections and -10% on curves (with a curve radius of 20 m). The main ramp is located on the central axis relative to the mineralized lenses and has a favourable lithology for mining. The portal for the main ramp is located close to the processing plant.

Cross-cuts, with a cross-section of 5.0 m x 5.3 m, will be excavated from the main ramp to access mineralization. From the cross-cuts, drifts with a 3.0 m x 3.0 m cross-section will be driven at a grade of +/-15%, from which the deposit will be mined by the room and pillar method.

The Project considers the construction of a surface plant for backfill to supply the mine. The
backfill will be pumped from the surface to the production workings by pipes. The backfill plant will have a capacity of 350 m3/d, which will be used to backfill the voids produced by the operation, thus preventing the collapse of adjacent workings and, in turn, allowing the mineralization to be mined upwards in steeply dipping zones.

Mining will be carried out by the room and pillar method in the flatter portions of the deposit. This method is suitable for the mineralized lenses at the Project that lie in a nearly horizontal plane as a result of their geomechanical properties A variation of room and pillar with backfill will be used in the steeper portions of the deposit.

To mine the North, Central, and South mineralized zones, cross-cuts will be excavated from the base of the main ramp towards the zones, from which drifts will be opened to each the base of the zones.

Room and pillar mining uses the same drilling and blasting techniques utilized in drifting using a drill jumbo. The room and pillar stope design has a cross-section of 5.0 m wide x 3.0 m high. This will create a pillar 4.0 m wide, resulting in an 80% mining recovery. Geotechnical studies will be required to determine the optimum pillar size.
Mucking of mineralized material is carried out by scooptram to a truck loading station in the main cross-cut.

All open pit and underground mining will be carried out using contractor personnel and equipment with oversight by owner’s personnel. The open pit contractor operations will include pit and dump operations, pit dewatering, and road maintenance. The underground contractor operations will include all development and production activities.

Mineralized material from the open pit mine, underground mine, or run of mine (ROM) stockpiles will be delivered to the primary crusher dump hopper by trucks or FELs. A stationary grizzly over the dump hopper will ensure that the feed passing through to the primary jaw crusher will not exceed 600 mm in size.

The multi-stage crushing circuit will produce a product suitable for feed to the grinding circuit, which, in closed circuit with cyclones, will produce a product with a P80 of 75 µm. Cyclone overflow will be thickened in a flotation feed thickener to enable control of flotation feed density. The underflow from the cyclones will be returned to the grinding mill. A crushed mineralized material stockpile will provide feed for the grinding circuit when the crushing circuit is not operating.

The plant will process 612,500 tpa through conventional comminution and flotation circuits to produce saleable copper, zinc, and possibly lead concentrates. The potential to produce a lead concentrate is being evaluated in on-going test work. In addition, future test work will be aimed at optimizing the process flow sheet and reagent scheme to maximize the recovery of valuable metals while minimizing costs of consumables and reagents.

The processing plant will consist of the following unit operations:
• Crushing and grinding
• Flotation
• Concentrate thickening and filtration
• Tailings thickening and disposal

Underflow from the flotation feed thickener will be diluted to the desired density with process water and then be conditioned with flotation reagents prior to flotation. Initial flotation will recover the majority of sulphide minerals and precious metals into a rougher concentrate. The rougher concentrate will be reground to improve liber ........