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Location: 108 Km S from Medellín, Colombia
Calle 7 sur No. 42 - 70, Oficina 2101, Edificio ForumMedellínColombia
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The La Cumbre Project is located along the eastern margin of Colombia’s physiographic Western Cordillera. The region is underlain by a highly complex basement known as the Romeral Terrane, which may be characterized as a tectonic mélange. The basement took form when Middle to Upper Mesozoic-aged volcanic and sedimentary oceanic rocks collided with, and were accreted to, the northern Andean paleo-continental margin, beginning in the Early Cretaceous. The resulting suture is known as the Romeral fault system and the mélange can be traced for over 1,000 km along the northern Andes.The La Cumbre and surrounding area is underlain by four principal rock units. These include: 1) a basement complex consisting of mafic and ultramafic oceanic volcanic rocks and granitoid intrusive rocks belonging to the Romeral Terrane, 2) stratified clastic sedimentary rocks of the Amaga Formation, 3) basalt-andesite through felsic volcanic and pyroclastic rocks of the Combia Formation, and, 4) dioritic to monzonitic hypabyssal porphyritic intrusive rocks.The Dos Quebradas, El Centro and La Cumbre porphyry gold deposits are associated with three Miocene intrusive centers in a north-south trend that have a strike extension of approximately two kilometers at elevations between 1,600 meters above sea level (MASL) and 1,050 MASL.The Dos Quebradas, El Centro and La Cumbre porphyry gold deposits are copper-poor porphyry gold systems in which intermediate argillic alteration locally extensively overprints an early potassic assemblage and its associated quartz veinlet stockwork. Gold in these deposits occurs in altered dioritic intrusions and in the diorite-basalt contact zones. The highest gold and silver grades occur in the early diorite phases characterized by potassic (mainly biotite with subordinate K-feldspar) and potassic-calcic alteration that is characterized by addition of traces of actinolite and garnet to the potassic assemblage. Significant amounts of quartz ± sulfide veinlets and greater than 3% hydrothermal magnetite are common in these early phases.The intrusions that host mineralization consist of several phases of diorite and later andesitic dike phases exhibiting characteristic alteration zoning, possibly because of telescoped porphyry and epithermal systems and progressive leaching of gold by overprinting argillic alteration.La Cumbre is a discrete porphyry gold center in which the average gold content reaches economic tenor even though the quartz-veinlet intensity is relatively low. The La Cumbre porphyry gold center is truncated to the north and west by the structural corridor of La Amarilla.Gold values in the early diorite are highest where hydrothermal biotite and fine-grained chalcopyrite reach maximums. Gold grades are lower in the inter-mineral phases; they still have potassic alteration with a lower density of veinlets compared with the early intrusive phases. Sulfide contents in early intra-mineral phases are normally lower than 1% but up to 3% and include pyrite, and locally trace amounts of chalcopyrite, bornite, and molybdenite.Late inter-mineral intrusive phases present moderate to strong intermediate argillic alteration with an average sulfide content of 3% to 5% composed mainly of pyrite with traces of molybdenite and chalcopyrite. The late inter-mineral phases are devoid of potassic alteration and quartz veins. Post mineral dikes exhibit argillic alteration (kaolinite) with subordinate chlorite and epidote.Gold and copper grades in basaltic wall rock follow potassic biotite and potassic calcic (biotiteactinolite) alteration. A-veinlet densities reach up to 50 veinlets per meter. Most artisanal mining activity in the Quinchia area follows centimetric fault gouge along faults in tuffaceous volcanic rocks with strong intermediate argillic alteration. Gold occurs with the fault gouge that contains fine-grained pyrite.The intrusions that host mineralization consist of several phases of diorite and later andesitic dikes exhibiting characteristic alteration zoning, possibly because of telescoped porphyry and epithermal systems.Mineralization at La Cumbre was discovered through follow up drilling of surface geochemical anomalies by Kedahda in 2006. The mineralization was best tested in the central part of La Cumbre where four holes were drilled along an east-west section. Hole DD008 intersected 210 m of 0.80 Au g/t and 0.15% Cu from surface to a vertical depth of 150 m. Drilling to the south of this section confirmed the mineralization at surface which continued as a low-grade zone to 520 m depth in hole DD018.
