The Gramalote Ridge and Trinidad deposits are considered to be examples of structurally-controlled intrusive-related gold deposits.

Intrusive-related gold deposits have many synonyms, including Intrusion-related gold systems, gold porphyries, and plutonic-related gold quartz veins. The deposit model that follows is abstracted from Lefebure and Hart (2005).

The deposit shows a number of the features of intrusive-related gold deposits, including:

• Alteration and mineralization are structurally controlled, restricted to small haloes along veins, sheeted veins and stockworks arrays;
• Sulphides content is less than 5%;
• Some evidence indicates that the host rock is directly related to fluids evolved from the cooling pluton, including pegmatite, aplite and K-feldspar alteration (Rodríguez, 2009).

The QP is of the opinion that exploration programs that use a structurally-controlled, intrusive-related gold model are applicable to the Project area.

The Project is located in the northern portion of Colombia’s Central Cordillera. The terrane primarily comprises a metamorphic basement complex and the Antioquia Batholith. The Cajamarca–Valdivia basement terrane (Cediel and Ciceres, 2000 and Cediel et al, 2003) consists of early Paleozoic metamorphic rocks; as well as ophiolitic, oceanic, volcanic, and intrusive rocks.

In the general Project area, the main compositional types within the Antioquia Batholith are tonalite and granodiorite, with subordinate monzonite and gabbro. Alaskitic, felsitic and andesitic dikes have intruded the complex. Age dating conducted by AngloGold suggest the gold mineralization is associated with the last stages of batholith crystallization.

Gramalote Ridge is situated between two west–northwest-trending macro-scale curved lineaments that splay off the Palestina fault to the east, and transect the Antioquia Batholith, termed the Nus River and the El Socorro lineaments. Differential movement along the Nus and El Socorro lineaments is thought to have generated north–northwest, north–south and northeast-striking tensional dilation within the tonalite, reflected in the formation of stockwork style sheeted quartz and quartz carbonate veinlets.

Gramalote Ridge

The Gramalote Ridge deposit has dimensions of 1,300 by 1,500 by 700 m. The mineralization has been drill tested to a depth of about 650 m.

Mineralization at Gramalote Ridge is hosted in uniform medium-grained tonalite with minor amounts of granodiorite and aplite dykes.

Alteration is structurally-controlled and occurs as both broad zones and narrow selvedges around veins. At Gramalote Ridge, vein selvedges range from a few millimetres up to as much as 10 cm. The broader alteration zones mimic the vein selvedges and progress from an outer quartz–sericite zone to inner carbonate and potassic zones.

Gramalote Ridge mineralization occurs within several zones that periodically coalesce both along strike and down-dip. Zones vary in width from 10–150 m in true width with vertical to sub-vertical dips to the south–southeast. The deposit remains open at depth and along strike.

Anomalous gold grades are associated with three overprinting, texture-destructive alteration assemblages including potassic, quartz–sericite and sericite–carbonate. The magnetite-destructive alteration characteristics of these zones is clearly defined from airborne and ground magnetic surveys over the tonalite host rock, which is weak to moderately magnetic.

The mineralization is vein hosted, either in sheeted veins or in local stockworks, and is structurally-controlled.

Three stages are identified and associated with vein and alteration types:

• Quartz–calcite–pyrite is an assemblage of fine-grained quartz and calcite with very fine-grained pyrite. This vein type generally does not host gold;
• Quartz–pyrite–chalcopyrite–gold is the most important gold host, typically associated with K-feldspar (potassic) selvedge. The gold occurs in fractures in pyrite together with chalcopyrite;
• Quartz–calcite–white mica is commonly barren but can show moderate gold grades. The veins are typically identified through the selvedge of white mica.

Veinlets have been classified into seven types. Anomalous gold mineralization is associated with Type 1 (Quartz ± pyrite), Type 2 (Quartz + carbonate + pyrite + chalcopyrite) and Type 5 (Coarse pyrite + quartz) vein types, with Type 1 and Type 2 the most prevalent.

Mineralization in saprolite and saprock (oxide) is weathered insitu and does not show evidence of significant transport or displacement. Weathered mineralization is limited to the areas directly above fresh mineralization and represents a small percentage of the mineralization. Saprolite/saprock thickness is variable from 5–50 m, with an average thickness of 21 m for Gramalote Ridge overall and about 15 m thick above mineralization.

The silver to gold ratio is approximately 1:1.

The primary mineralization consists of pyrite and chalcopyrite. Secondary minerals include rutile and a titaniferous mineral.

Free gold occurs as argentiferous gold coeval with several tellurides and bismuth sulphosalt minerals.

Trinidad

The Trinidad deposit has dimensions of approximately 1,500 m by 500 m. Mineralization has been drill tested to a depth of about 300 m.

The Trinidad mineralization is hosted in similar rock types to those described for Gramalote Ridge.

Alteration is similar to that described for Gramalote Ridge.

Mineralized zones at Trinidad are 10–80 m thick and are continuous along strike for up to 1,500 m and down dip for >500 m. As at Gramalote Ridge, such zones periodically coalesce both along strike and down-dip. The deposit remains open at depth and along strike, especially to the west

Saprolite/saprock thickness is variable, with an average thickness of 31 m overall, and about 33 m thick over the mineralization.

Mineralization is associated with stockwork veinlets and alteration along their margins. Veinlets have been classified into seven types, and gold mineralization is associated with Type 1 (quartz with fine pyrite), Type 2 (quartz with Fe carbonate) and Type 5 (quartz with granular pyrite) veins.

The 2020 PEA is based on mining of the Gramalote Ridge deposit only. No mining is envisaged for the Trinidad deposit in the 2020 PEA.

A conventional open pit truck and shovel operation is planned. A SMU size of 10 m x 10 m x 10 m was used was used for benchmarking the mineral resource model. No additional dilution factor or mining loss was applied to the grades in the mine plan.

The Gramalote Ridge pit will have four phases, consisting of three phases in the main pit, and a small satellite pit that will have a single phase.

The main ramps were designed to 30 m width for two-way access, and are assumed to have a 10% gradient. The lowest benches will have a 15 m wide ramp, and will be single-lane. Pit benches are assumed at 10 m intervals, with pre-split drilling at 20 m depths, drilling two benches at a time.

The mine planning strategy includes the use of stockpiles for oxide and sulphide materials. Three stockpiles are planned:

• High-grade sulphide stockpile; approximate 6.5 Mt capacity; =0.66 g/t Au material for the initial years, variable thereafter to optimize head grade;

• Low-grade stockpiles; approximate 46.3 Mt capacity; =0.29–=0.66 g/t Au material;

• Oxide stockpiles; approximate 4.5 Mt capacity; =0.25 g/t Au material.

All stockpile areas will have access ramps that are 30 m wide and a maximum 8% grade as well as a temporary slope angle of 30º.

A waste rock storage facility (WRSF) is planned to be situated in the El Topacio and El Banco basins, towards the westernmost end of the project site. This facility will be developed in four construction stages. The WRSF will have a maximum total capacity for about 320 Mm3 of material but the current mine plan only produces 288.4 Mt of waste.

The mining plan considered a maximum sinking rate of eight benches per phase per year. Pre-stripping is estimated at 8.6 Mt for the period prior to the first year of production. This is scheduled to be mined in a nine-month period using the mining equipment. Any mill feed material mined during pre-stripping activities will be stockpiled.

Waste moved during this period (5 Mt) will be used during the construction of the mineplatforms and mine roads.

The average mining rate will be between 45–52 Mt/a for the first seven years and will then reduce significantly over the final years of mining, for an 11-year mine life. The strip ratio is forecast at 1.93:1.

Mining operations assume that lower-grade material will be stockpiled, and treated at the end of the mine life, and high-value cut-backs will be mined early in the LOM to increase the plant feed grade during the initial years of production.

Year-1 and the first half of Year 1 will be restricted to pre-stripping activities. The second half of Year 1 will be the ramp up period for the process plant. From Year 2 and thereafter, the mine will be operating at approximate full capacity.

Mining will be completed in four phases, mining nearly 100% sulphide material. Oxide material will be stockpiled and processed at the end of the mine life.

The mine will operate 365 days a year, 24 hours a day distributed in two 12-hour shifts with an assumed 15 days lost due to weather conditions.

Mining will be carried out with an Owner-operated fleet.

Standard open pit mining equipment has been selected, with conventional drilling, blasting, loading and hauling envisaged.

Initial access to the excavation areas will be executed using a contractor with a small fleet of articulated trucks, excavators and the required support equipment.

The Owner equipment was selected based on a standard open pit mining operation with conventional drill, blast, load and haul activities. The equipment selection considered bulk excavation of mill feed material and waste using hydraulic shovel/excavators and front-end loaders.

The proposed plant will process ROM mill feed material at a rate of 11 Mt/a to produce doré bars, using conventional equipment and processes. The process plant will consist of primary crushing, two-stage grinding with flash flotation, conventional froth flotation, flotation tailings pumping, concentrate regrinding, concentrate leach, CCD thickening, carbon-in-pulp (CIP), carbon desorption, gold recovery by zinc precipitation (Merrill Crowe), and cyanide destruction of CIP tailings slurry before the tailings are pumped to the tailings management facility (TMF).

The primary crusher facility will consist of a dump pocket with two truck dump positions. A rock breaker will be provided to break up any oversize rock. Mineralized material will feed into a gyratory crusher from the dump pocket, and then discharge into a chamber below the crusher. From this chamber the crushed mill feed material will be withdrawn by an apron feeder which will control the material loading onto a coars ........