Metalogênese da jazida aurífera Cuadrazón, Cerro Frontino, Cordilheira Ocidental, Colômbia

Abstract

At Cuadrazón mine, gabbro, pyroxenite and diorite are found, hosting polymetallic veins. This is an elliptical stock, oriented towards N30E and N80E, resulting from the emplacement of multiple magmatic pulses into the continental crust, associated with the Western Mountain range arc; these outcrop to the north-west of the Colombian Andes and constitute the Cerro Frontino Gabbro stock. These plutons exhibit an internal texture consistent with magmatic differentiation and the mixing of magmatic pulses that intruded into sedimentary rocks, generating skarn. Strain mechanisms in the gabbro’s petrographic texture indicate that: I) the emplacement of these plutons was influenced by magmatic and solid-state flows; II) the plastic deformation is consistent with a non-coaxial shear regime; III) the structural framework of the polymetallic quartz veins in the Cuadrazón deposit is consistent with simple shear and partitioning into synthetic conjugates. The veins consist of a quartz-carbonate gangue, and sulphides of Fe, Cu, Pb, Zn, Fe oxides and gold. These veins are thought to be the products of several hydrothermal pulses and are controlled by a shear system with a strike ranging from 068°–097° to 250°–270°, with a dip of around 60°, mainly to the west, consistent with the strike of the dominant regional structures to the north of the Cordilheira Ocidental. The deformation associated with this structure is recorded in features such as planar slippage, folding and fracturing in quartz, carbonate and sulphides, indicating that the shear zone was reactivated after the formation of the veins. These shear structures have been interpreted as a structural subdomain recording deformation and kinematics related to regional structures, whose activation and reactivation occur under the influence of the same tectonic context, which is consistent with the geotectonic history of the formation of the Western Cordillera during the Neogene. The gabbro hosting the veins shows evidence of propylitic alteration (chlorite + epidote + pyrite + carbonates) and sericitic alteration (sericite + quartz + pyrite) in halos, as well as chloritisation and silicification (quartz enrichment). The aqueous fluid inclusions revealed a high-salinity system (up to 20.16 wt% NaCl eq.), with high-temperature entrapment conditions (Th between 307.9 and 321 ºC) and correspond to approximately 1 kbar at a depth of 350 m beneath an active tectonic system. These physico-chemical characteristics (with salinity varying within the same temperature range) suggest a mixture of magmatic and meteoric (and/or basin-derived) hydrothermal fluids, which resulted in the precipitation of the ore and indicate a boiling process. Fluid migration was facilitated by the activation of simple shear zones under a rupture regime, and this condition, combined with the characteristics of the deposit, shows that the mineralisation develops under special tectonic conditions compatible with low- to intermediate-sulphidation epithermal deposits, influenced by skarn-type systems.