The dacite and andesite porphyry stock which hosts the Marmato deposit extends for some 18 km long by 3 to 6 km wide, is elongated north to south and is one of a number of porphyry stocks in the district. The mineralization, comprising the veins, grade shells, grade shell deeps and mineralized porphyry is hosted within a mineralized corridor some 0.5 to 1.5 km wide, with a drill defined strike length of approximately 1.3 km. The mineralized corridor is intersected by a predominantly NW-SE trending fault network (as interpreted by the Company during 2012), with a cross-cutting fault towards the north forming a hard boundary with a lower grade porphyry unit (or “barren porphyry”).

The mineralization is described as being of the epithermal intermediate sulphidation type. Gold-silver mineralization is hosted by a sheeted pyrite veinlet system associated with intermediate alteration within the porphyry. Gold is associated with sulphides and is mostly free.

The updated drilling database indicates that the veins typically range between 0.5 metres and 5 metres wide and extend for 250 metres to 1000 metres along strike and 150 metres to 750 metres down dip. This is supported by underground mining which has confirmed that individual vein structures have good geological continuity and can extend for 100 to 800m along strike and 100 to at least 300m down dip.

The broad zones of veinlet mineralization (‘grade shells’) modeled during the 2012 update typically vary from 10 to 230 metres wide, reaching up to 340 metres wide in areas of significant veinlet accumulation, whilst extending with good geological continuity for between 200 metres and approximately 950 metres along strike, and between 100 metres and 900 metres down dip. At depth within the central portion of the deposit SRK has noted a zone of elevated grades which has been referred to as the higher grade (>2.0 g/t) “deep zone”. This zone is indicated to be continuous along strike for approximately 350 metres and has a confirmed down dip extent that range that reaches up to 500 m, with a thicknesses that varies between 35 and 150 metres.

Current mining in the mineralized material zones specifically targeting the veins, splay, and halo materials. The mineralized zone currently being mined by GCM extends from Level 16 to the deepest level at Level 21. Mining is conducted using modified sublevel stoping mining method with 25 m high stopes that vary in length and width depending on the vein. The minimum stope width is 1 m. The stoping is completed using jackleg drills operating on hydraulic backfill from the processing plant that fills the stopes. No cement is mixed in the hydraulic backfill material. The mine typically has 20+ stopes in various forms of development or production. The multiple stopes are used to meet production needs and to balance grade fed to the plant.

The Marmato process plant operates at approximately 1,200 t/d and recovers about 87% of the gold and 40% of the silver from ore that averages approximately 2.5 g/t Au and 9.5 g/t Ag. The plant was upgraded in 2016 and the discussions that follow are based on the current configuration of the plant.

The process plant flowsheet includes crushing, grinding, gravity concentration, gold flotation, cyanidation of the flotation concentrate, Merrill- Crowe precipitation and refining of the precipitate and gravity concentrate to produce a final gold/silver doré product.