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 ........

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 hi ........

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