The Colombia Buriticá Gold Mine is fully owned by Continental Gold Colombia Branch, which is a branch of Continental Gold. Continental Gold is in turn wholly owned by Zijin America.
Zijin America’s ownership structure is as follows:
• 68.77% owned by Gold Mountains (H.K.);
• 22.74% owned by CLAI Gilding (BVI) Investment Limited, an independent third party (connected to the Company only through its minority stake in Zijin America);
• 7.26% owned by ZLCFL-Cayman International Investment Cooperation Limited, an independent third party;
• 1.23% owned by Longyan Xinjing Investment Partnership (Limited Partnership), which serves as an employee shareholding platform for the Zijin Mining Group.
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Summary:
Geology and Mineralogy
The northern Andean Cordillera in Colombia was uplifted by the subduction of multiple oceanic plates, with major accretionary events forming volcanic-magmatic belts during the Jurassic, Cretaceous, and Tertiary periods. The Buritica Project lies within the Miocene-age Middle Cauca Belt, known for hosting numerous polymetallic porphyry and epithermal deposits. The region’s geology is dominated by the Cretaceous Barroso Formation, consisting of pillow basalts, andesitic pyroclastics, dolerites, and mudstone layers. The area is intruded by Cretaceous Santa Fe Batholith tonalites and the Buritica Intrusive Complex (‘‘BIC’’), with radiometric dating (U/Pb) indicating an age of 7.7±0.1 million annum (‘‘Ma’’).
The Buritica Project hosts two major Au-Ag vein systems: the Yaragua and the Veta Sur. Yaragua trends ENE (75°–80°), is nearly vertical, and measures 1,350 metres (‘‘m’’) in length, 1,660 m in depth, and 220 m in width, with 24 high-value mineralised veins (‘‘HVMs’’) commonly 0.5–1.0 m wide. Veta Sur strikes NE (40°–50°), is also steeply vertical, spans 1,300 m in length, 1,600 m in depth, and 300 m in width, with 28 HVMs showing similar geometry to Yaragua. In addition to vein-style mineralisation, 4 low-grade pillar-like mineralised systems (‘‘BMZs’’) have been defined. These BMZs are hosted vertically within Yaragua and Veta Sur and are irregular in shape, with diameters of 100 to 150 m and vertical extents of 300 to 600 m.
The area is transected by N-S to NNW-trending faults, including the Tonusco Fault system east of Yaragua and Veta Sur, which cuts off intrusive complexes and hydrothermal alteration zones, indicating post-intrusion and post-mineralisation activity. These faults were likely active during ore formation and persisted into the post-ore stage.
Mineralisation is primarily hosted within the BIC, composed of diorites and hydrothermal/intrusive breccias, though some Au-Ag veins extend into wall rocks of the Cretaceous Barroso Formation. Au, Ag, and copper (‘‘Cu’’) are economically recoverable based on metallurgical tests, with zinc (‘‘Zn’’), lead (‘‘Pb’’), and sulphur potentially recoverable. Arsenic levels do not significantly impact Au recovery.
Deposit Type
The Buritica Project is the northernmost significant Au-Ag deposit known to date in the Miocene Middle Cauca belt, where the La Colosa porphyry style deposit has defined 28 million troy ounces (‘‘Moz’’) of gold, the Nueveo Chaquiro porphyry style deposit has achieved 3.6 million tonnes (‘‘Mt’’) of copper and 5.6 Moz of gold, and the Marnato is recognised as an epithermal gold deposit.
The CGL Colombia believes that Buritica deposit is a low-intermediate sulphuration epithermal vein-type gold- silver deposit but it shares many characteristics with porphyry gold deposits. Overall, BMZ gold- mineralisation is typically associated with areas of increased veinlet density or disseminated mineralisation with similar mineralogy found in the HVM, and the BMZ shells have a relationship to the orientation of the epithermal vein systems which crosscut the porphyry system.
The characteristics of the mineralisation at the Buritica Project are summarised as follows:
- The mineralisation is mainly hosted in porphyry intrusion system, with mineral zoning related to porphyry ore-forming process, where the porphyry style mineralisation has not well developed in Buritica Project area.
- Later stage mineralisation is dominated by Au and Ag and controlled by fault structure appearing vein-like shape, with ratio of Ag/Au of 2.8 to 6.3.
- Au-Ag mineralisation is usually associated with high grade of sphalerite, chalcopyrite and galena.
- Fluid inclusion, isotope studies, and rock geochemistry (Lesage et al, 2013, Aerne and Kretz, 2014) suggest a magmatic source for the gold bearing fluids with late stage mixing from meteoric waters.