The mineralisation observed at surface and in the drill core along the trend of the Alpala deposit is considered as a classic porphyry Cu-Au system and exploration has been guided with this as the primary target. Exploration is also assessing the potential for surrounding economic porphyry deposits within a 1 to 2 km radius of the Alpala deposit, as well as the potential for discovery of epithermal and skarn deposits peripheral to these porphyry systems throughout the Cascabel Project area.

These mineralised systems are hosted within a linear belt (Andean Porphyry Belt) that extends from southern Chile right through to Ecuador and Colombia to Panama. The Andean Porphyry Belt is host to the largest concentrations of Cu in the world, including numerous deposits that are in active mining operations.

Major host rock types of the Alpala deposit consist of gabbroic and basaltic basement rocks, overlain by Cretaceous siltstones and minor sandstones that are unconformably overlain by a sequence of Tertiary volcanosedimentary and andesitic lavas. The volcanic and volcano-sedimentary sequences that host the deposit were previously mapped as the Macuchi Unit (Vallejo., 2007), a volcanic arc of tholeiitic and calc-alkaline composition which was formed on oceanic crust during the Eocene.

Drilling has defined a northwest trending, steeply northeast dipping corridor known as the Greater Alpala Trend. This trend is centred upon a syn-mineralisation causal quartz-diorite intrusion (QD10) cut by a series of intra-mineralisation, late-mineralisation, and post-mineralisation stocks, dykes and breccias of diorite, hornblende diorite, quartz diorite, tonalite and granodiorite. Intrusions have been emplaced episodically such that each subsequent intrusion has introduced mineralising fluids (notably as porphyry-type quartz and quartzsulphide veins) into the Alpala porphyry system, and/or remobilised existing mineralisation or contributed to localised overprinting and destruction of the pre-existing mineralisation.

Thin-section petrography reveals the presence of very fine-grained quartz in the groundmass of the intrusions, which suggests compositions that range from quartz diorite to tonalite. However, the intrusive rock types have been classified on observations made by the field geologist using a 20 times magnification hand lens (Garwin et al., 2017).

Two of the Alpala intrusions have been dated by the sensitive high-resolution Ion Micro Probe (SHRIMP) U/Pb zircon radiometric dating method, which indicates an approximate age of 39 Ma for the intrusions (Garwin et al., 2017).

Intrusions are typically emplaced with a stock-like geometry that is moderately elongate in a northwest direction. Intrusions often hold typically vertically and laterally extensive northwest trending, steeply dipping dyke extensions beyond their stock margins.

Due to the multi-episodic nature of the complex, several dykes appear rootless or ‘hanging’ in section view, however, these are seen to connect to the main stock or stocks in three dimensions or have been intruded and truncated by younger stocks.

The geometry of the various lithologies and intrusive bodies at Alpala is now well-understood and has been modelled from the completed drilling, demonstrating extensive sub-vertical continuity and highly complex intrusive relationships.

The majority of the Cu and Au mineralisation at Alpala was added to the system by the QD10 intrusion with supplementary additions through time with the injection of the intra-mineralisation QD15, IM, IM BX, IMF T intrusive phases, with only very minor metal addition from late-mineralisation and post-mineralisation intrusions as the system waned.

The equigranular to sub-porphyritic, hornblende-bearing intrusions at Alpala are narrow, taper upwards, and are geometrically similar to grade models of Cu, Au and Ag mineralisation. Mineralisation occurs as a prolate body approximately 2,400 m northwest by 1,200 m northeast and 2,800 m in vertical extent, defined at a Cu equivalent (CuEq) shut-off criteria of greater than 0.15% CuEq and/or greater than 0.55% B-type quartz veins.

The Alpala deposit geological, structural and mineralisation all display a clear anisotropy which is prolate in a sub-vertical sense, dipping approximately 78° towards northeast, and oblate in plan (striking northwest). Recognition of this geometry, in the field and in various datasets, has played a critical role in the path to discovery of the Alpala deposit.

The porphyry related vein types and mineralisation paragenesis at Alpala indicate a systematic progression in time and have been described by SolGold using the nomenclature originated by Gustafson and Hunt (1975).

Understanding of the intrusive phase relationships within the Alpala deposit was advanced following a detailed review of drill core in 2014, which focused on identifying the different vein types and their paragenesis. This work resulted in advances in the recognition of inconspicuous intrusive contacts and clearly showed that each intrusive phase contains a specific set of veins and resultant Cu and Au grades.

The most important vein types recognised in the Alpala deposit are:
- Prismatic quartz showing unidirectional solidification texture (UST), cut by a chalcopyrite rich C-vein;
- Intrusive contact between late QD20 and early D10, showing truncation of early B-veins and a late CDvein that crosscuts the contact;
- Chalcopyrite vein and late-stage bornite along fracture surface;
- Magnetite bearing B1 quartz vein stockwork with clots of chalcopyrite (Cp);
- Late-stage pyritic D-vein with selvedge’s of quartz-sericite.

The mine plan uses the block cave mining method which is considered to be the appropriate method due to the size, grade, ground conditions and depth of the Alpala deposit. High level studies have highlighted some areas of the deposit that may be mined using other bulk underground methods, such as sublevel caving, but that these are small and not material to the plan at this early stage of study.

The mine plan considered in this Pre-Feasibility directly relates to the first 30 years of production. In this plan, the highest value material is targeted. Column heights are up to 700 m and a relatively even draw across each footprint ensures even cave propagation.

This approach is in line with SolGold’s corporate strategy which is to maximise extraction of the Alpala deposit while still optimising the economics of the project. Targeting the high value material in the first phase ensures and optimises the project economics. Mining the lower value second phase later maximises extraction without compromising the economics of the project.

The main lateral mine access needs to be suitable for personnel and material movement and also accommodate the Material Handling System (MHS). A secondary function of the development will be to provide ventilation flow.

The lateral access design for Cascabel includes twin declines running parallel to each other developed from a boxcut at the surface. The declines are 50 m from centreline to centreline and based on the 5.5 mW x 5.8 mH profile (main access decline) and 6.5 mW x 6.0 mH (conveyor decline) with a pillar of 44 m/46 m between them. The 6.5 m span in the Conveyor Decline will allow for the installation, and ongoing servicing of the materials handling conveyor system in the conveyor decline. A separation of 44 m will be kept between the inside walls of the two declines. Both declines have a nominal gradient of 15.6% (1:-6.4), which is suitable for both the conveyor and the running of haul trucks.

The cave footprint is focussed on the 300 mRL with the layout consisting of an undercut, extraction and haulage level. All levels have ventilation drives which connect to internal shafts forming part of the primary ventilation network.

The extraction level has an “El Teniente” layout with crosscuts (or Extraction Drives) spaced 32 m centre to centre. Drawpoints are spaced at 20 m. There are tip points for the loader to transfer ore from the cave to passes which report to the haulage level below. Turning bays are designed at the start of each crosscut for efficient movement of the loaders. Ventilation drives connect to internal shafts forming part of the primary ventilation.

The extraction level has a Haulage Level running underneath it which will be utilised for material handling during the production Phase of each level.

The haul drives allow trucks to transfer the ore from ore passes to the level crushers where the crushed ore will be transferred to the main decline conveyor via transfer conveyors.

These drives also form part of the ventilation circuit for the level development. The drives have a profile of 5.5 mW x 5.8 mH and currently are designed without gradient.

In addition to the initial access shaft and the access and conveyor declines, the Pre-Feasibility design includes 7 shafts for ventilation (5 exhaust shafts and 2 intake shafts). Each of these shafts is 5.0 m in diameter to suit the ventilation requirements for the steady-state operating mine. The early access shaft will also become a source of fresh air intake once all early access requirements are completed, and the decline development reaches the footprint.

All 7 shafts are mined in two set of legs; first legs are established to the 910 L underground level 910 (910 FAD drive and 910 RAD drive) and second legs are established to 255 L (255 FAD drive and 255 RAD drive).

The mine scheduling was undertaken with a base case mine production rate of 25 Mt/y. The 25 Mt/y base case was in-line with the material handling system assumptions provided by Wood. Further analysis is recommended to best optimise the production rate.

Ore production at the maximum 25 Mt/y rate is achieved 8 years and 7 months from the project start.

The mine plan assumes that development and production activities will be undertaken with a rubber tired, diesel-powered and battery electric mechanised mining fleet. It is proposed that the production haulage fleet consist of Battery Electric truck from reputable suppliers, such as Sandvik.

The number equipment owned by the Mine Contractor(s) for development activities and to set up the cave are quite sporadic over the mine life. The largest requirement is at the start of the project for the initial access and set up of the 300 mRL footprint, then there is another spike in requirement from around Year 13 of the project when the second cave on the 300 mRL footprint is established.

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The flowsheet design is conventional, and assumes a flotation-leach approach.

The grinding circuit is designed at the 80th percentile.

The flotation circuit is capable of recovering the copper, gold and silver associated with chalcopyrite. The remaining gold and silver associated with sulphides (pyrite) in the cleaner scavenger tailings is capable of being recovered for further processing in a cyanide leach plant.

The concentrate production rate is expected to be up to 795 kt/y from 25 Mt/y process plant feed. The concentrate quality will vary from month to month based on ore variability, mine planning as well as the geometallurgy.

The total copper, gold and silver production to concentrate is expected to be 2,837 kt, 6.75 Moz and 19.43 Moz during the LOM based on the flotation testwork completed to date.

The total gold and silver production to doré is expected to be 862 koz and 2,283 koz during the LOM based on the limited testwor ........