The alteration and mineralization in the UZ at Marmato evolved through early stage, higher temperature propylitic alteration to later, lower-temperature intermediate argillic alteration, with most of the gold and silver being deposited in the later stage.

The gold-silver and base metal association in the UZ at Marmato is typical of the intermediate sulfidation epithermal type. The veins lack distinctive epithermal textures and the mineralization has a relatively high depth and temperature of formation, which straddles the deep epithermal to mesothermal transition as defined by the original classification of Lindgren (1922) and by estimates of formation temperature of 300°C (Heald et al., 1987). The Marmato deposit lacks known shallow and surface epithermal features such as lithocaps, sinters and crustiform banded veins.

Mineralization is interpreted to be genetically related to the host porphyritic rocks, as shown by the inter-mineral timing of the porphyry phases cross-cutting earlier stages of propylitic alteration, the latemineral timing of the final dacite P5, and miarolitic cavities lined with propylitic-stage minerals. The veins and veinlets are structurally controlled and did not form a multi-directional porphyry stockwork or breccia related to hydro-brecciation. In this model, the host stocks might be considered as latemineral intrusions with respect to a postulated porphyry gold-copper-molybdenum centers.

Gold mineralization occurs in veins and veinlets with dominant NW and W-NW trends. The deposit mainly comprises sulfide-rich veinlets and veins composed of minor quartz, carbonate, pyrite, arsenopyrite, Fe-rich sphalerite (i.e. marmatite), pyrrhotite, chalcopyrite and electrum in the epithermal Upper Zone, quartz, pyrrhotite, chalcopyrite, bismuth sulfide, telluride minerals and free gold in the mesothermal MDZ. Pervasive early propylitic alteration is over-printed principally by phyllic and intermediate argillic alteration related to the gold mineralized veins of low to intermediate sulfidation epithermal type, with weak and patchy potassic (biotite) alteration at depth.

The Marmato deposit lacks known surface epithermal features, such as lithocaps, sinters and crustifome-banded streaks. The veins can be found from the surface (1,700 meters above sea level [masl]) and there is evidence of their continuity up to the 900 masl, on course there is a continuity that goes from 50 m for secondary veins or splays to 600 m for the main veins.

The current significant mineralized zones in title #014-89m, are located in the NW sector of the title, covering an approximate area of 30 Ha, with a distribution towards depth, approximately from elevation 1,200 m to 600 m, emphasizing that gold mineralization remains open at depth.

The mineralization in the current mine consists of three distinct phases, a first phase characterized by the mesothermal vein/veinlet mineralization which defines the MDZ, followed by an epithermal low to (subsequent) intermediate sulfidation style generally found in the UZ (SRK, 2019).

TCL recognized two principal deformation stages within the Marmato stock (TCL, 2010):

• Syn-mineralization W-NW to E-SE compression that reactivated some basement structures as well as generating a range of second-order shear and extensional structures along N-NW to W trends, as well as N-NE trending thrust faults.
• Continued post-mineralization compression into the late-Pliocene, (approximately 2 Ma) that resulted in uplift due to renewed thrusting along the main terrane boundaries, forming thrust bounded intermontane basins such as the Cauca-Patia depression.

TCL outlined four principal trends of auriferous structures within the Marmato area:

• NW trending steep to sub-vertical faults/fractures.
• W-NW trending steep to moderately inclined structures.
• W trending structures that tend to have moderate to relatively low angle dips.
• E-NE to NE trending structures that show a range of dips.

TCL reported that kinematic indicators show that gold mineralization accompanied a phase of W- NWE-SE orientated compression. The N-NE trending reverse faults and conjugate fractures reflect this compression component. Within this tectonic framework the E-W faults should be predominantly dextral strike-slip and the W-NW faults should be predominantly sinistral strike-slip. CGM interprets the rotation of some of these structures to be the result of rotation during progressive compressional deformation event, however CGM also noted that there are pre-gold mineralization and post-gold mineralization phases of fault movement on a number of faults and veins (J. Ceballos, 2019, pers. comm.)

The mine is currently developed and mined to the 1,000 m elevation. A transition occurs from narrow vein mineralization to large porphyry mineralized areas (gold associated with pyrrhotite veinlets). Mineralization is generally vertical with veins widths ranging from more than 1 m to several m. Porphyry mineralized areas also have a vertical mineralization trend and can be up to approximately 100 m in width.

The production schedule targets a total production of 1,500 t/d or 525,000 t/y (based on 350 days per year) to the mill. A gradual ramp up is planned for 1,100 t/d (385,000 t/y) in 2020, 1,250 t/d (437,500 t/y) in 2021, 1,400 t/d (490,000 t/y) in 2022 and 1,500 t/d in 2023. The Transition accounts for 400 t/d while the remaining UZ production comes from the veins. LoM for the Veins is 12 years for a total of 3.81 Mt at 4.37 g/t Au. LoM for the Transition zone is 11 years for a total of 1.33 Mt at 3.56 g/t Au.

There are two different mining methods, separated into two distinct zones as follows:
- The first zone is the mineralized vein material between 950 m elevation to 1,300 m elevation, referred to as the Veins. This is the current mine and will be mined using the current conventional cut and fill stope method.
- The second zone is the wider porphyry material between 950 m elevation and 1,050 m elevation, referred to as the Transition Zone. A modified longhole stoping method will be used in this area. The stope size is 15 m wide by 15 m high with varying length of up to 26 m. These stopes are mined in a primary-secondary sequence with paste backfill for the primary stopes and unconsolidated waste rockfill for the secondary stopes. Where waste rock is unavailable, hydraulic sand fill will be used to fill the secondary stopes.

Mining Operations
Stoping
CAF stopes are mined using stopers and jacklegs. Once the level access is driven, raises (tambores) are driven on either side of the stope. A sublevel is driven laterally and used as a drilling platform, where 1.7 m to 2.3 m slices are drilled up into the back. After blasting and bolting, the stope is mucked out either using slushers for higher grade stopes or skid steer loaders/microscoops for lower grade blocks. Once the stope is mucked out, concrete barricades are built on either side of the stope and filled with unconsolidated hydraulic fill.
- Drilling and blasting
- Mucking or slushing to a raise and removing the mineralized material from the raise and hauling by train along the production level
- Sand backfill
- Repeat the cycle on top of the sandfill
Transition stopes are 15 m by 15 m and will be mined using a modified longhole stoping method in two sections. The first section is from Level 21 up to Level 20 and the second section is from Level 22 to Level 21 with a pillar in between. The Transition will be mined in a primary-secondary sequence. The stope is drilled from a top access using a jumbo fitted with an adapter for long hole drilling. A slot will first be drilled and blasted, before the rest of the stope is slashed into the slot. The material will be mucked from the bottom using a remote scoop. The primary stopes will be backfilled using pastefill and the secondary stopes are filled with waste rock.

Development
Development in the Veins is completed using jacklegs. Level accesses are 2.2 m by 2.2 m, sublevels vary depending on the width of the vein. The apiques will be extended down to level 22. A 3.5 m by 3.5 m ramp is used to access the Transition stopes. The level access and transverse drifts are the same size as the ramp. Development for the Transition zone is done using a jumbo.

Haulage
All is hauled using rail haulage on the level. The main haulage level is Level 18. Material from Levels 16 and 17 is brought to Level 18 via an orepass. Material on Level 19 is hauled up using the incline and material below Level 19 is brought up via the shaft hoist. 10 tonne trucks will be used in the transition zone to haul ore to the orepass, which is then loaded to rail carts and brought to the apiques.

Backfilling
Backfilling is completed using unconsolidated hydraulic backfill from the plant. Currently, approximately 55% of the mill tailings are returned to the mine as backfill. There are four tailings pipelines going underground to different levels with each pipeline having a capacity of 290 m3/d. The plant’s backfill capacity is 715 m3/d. One limitation of the backfill system is the lack of a surge tank, so there is limited catch up possibility should a delay occur. Waste rock generated underground that is not hauled out is used as backfill.

Current Operations
Crushing Circuit
RoM ore is hauled by rail from the mine and dumped into a hopper where a slusher is used to move the material to a 5 m by 7 m feed hopper that feeds a vibrating grizzly to remove the -3/8 inch material, prior to feeding the primary jaw crusher. The discharge from the jaw crusher is conveyed to a doubledeck vibrating screen fitted with a 7/8 inch upper deck and a 3/8 inch lower deck. The screen oversize from the top deck is conveyed to a Nordberg 1352 Omnicone which is operated in closed circuit with the vibrating double-deck screen. Ore retained on the second deck is conveyed to a Nordberg HP300 cone crusher, which is also operated in closed circuit with the vibrating screen. The -3/8 inch screen undersize discharges to the fines bin. The -3/8 inch undersize from the vibrating grizzly is further classified in a spiral classifier. The classifier oversize is fed directly into the primary ball mill and the classifier undersize is thickened and then pumped to the primary hydrocyclones. The crushing circuit has an operating capacity of 1,600 t/d.

Grinding
Crushed ore (-3/8 inch) is fed from the fines bin and then transported on a conveyor fitted with a belt, scale to the 9.5 ft by 14 ft primary ball mill (600 hp). The cyclone underflow discharges to the 7.5 ft by 10 ft secondary ball mill (300 hp), which is operated in closed circuit with the cyclones and the overflow advances to the flotation circuit.

Expansion Plans
Install a refurbished 15.5 ft by 22 ft ball mill (3000 hp) to replace the current primary ball mill (600 hp) and secondary ball mill (300 hp)

CGM operates a 1,200 t/d process plant to recover gold and silver values from material produced from current Marmato mining operations in the UZ and plans to expand this facility to a 1,500 t/d capacity in the next couple of years. In addition, CGM is evaluating the development of the MDZ, which is below the current mining operations and the construction of a new 4,000 t/d plant to process material solely from the MDZ.

Marmato Process Plant (Current Operations)
Gravity Concentration Circuit
The primary ball mill discharges to a Knelson gravity concentrator to recover coarse gravity recoverable gold. The tailings from the gravity concentrator is pumped to the cyclones. The cyclone underflow discharges to the secondary ball mill (300 hp), which is operated in closed circuit with the cyclones and the overflow advances to the flotation circuit. The gravity concentrate is combined with the flotation concentrates prior to advancing to the regrind and cyanidation circuits ........