Lo Increible 4A and 4B properties are located in the El Callao area of the State of Bolivar in Venezuela. They total 2,217 hectares and are immediately north and adjacent to Crystallex International Corporation's La Victoria property in the El Callao district. In addition to Crystallex, Gold Fields Limited, Hecla Mining and CVG-Minerven all have producing gold mines and are actively exploring for gold in the area. The properties are held under mining contracts, granted by the Corporacion Venezolana de Guayana ("CVG").
Medoro intends to initiate an aggressive exploration and resource definition program on its properties, with a view to fast-track the development of these resources.
HistoryThe Lo Increible 4A and 4B properties encompass 2,217 hectares, contain numerous gold showings and occurrences, four of which have been partially drilled and contain inferred mineral resources. The Lo Increible 4A and 4B properties include more than 80 small mine workings and excavations along a 7 kilometre strike length of the Lo Increible Shear Zone. The concessions are in the El Callao mining district, the most prolific gold producing region in Venezuela, with a recorded output of six million ounces since 1870.
Notwithstanding El Callao district's impressive production history and Lo Increible's numerous surface workings, little modern exploration had taken place until Bema Gold began working in the Lo Increible district in late 1993.
GeologyLo Increible 4A and 4B concessions are located within the Pastora-Botanamo Province of the Guyana Shield. The Pastora-Botanamo province consists of a greenstone belt assemblage of mafic and felsic metavolcanics, metasedimentary, and igneous intrusive rocks. Extrusion of the volcano-sedimentary pile occurred between 2,300 – 2,050 Ma. The oldest rocks consist of tholeiitic mafic metavolcanics rocks of the Carichapo Group (El Callao and Cicapara Formations), overlain by intermediate felsic volcanic rocks and tuffs of the Yuruari Formation (Pastoria supergroup, 2300 – 2250 Ma).
The regional stratigraphy in the El Callao Mining District comprises a single volcano-sedimentary cycle of the Pastora Botanamo Province. Sub-aquaeous extrusion of mafic volcanic rocks evolved through intermediate and felsic volcanism, and eventually the epiclastic deposition of sedimentary formations. This whole package of rocks was then intruded by mafic and felsic dykes and sills, and late granitoid stocks and plutons.
The El Callao Formation is the main host for gold mineralization in Venezuela. The age of the gold mineralization is believed to be pene-contemporaneous with late granitoid intrusion, which ranges from 2,100 – 1,800 Ma.
The principal deposit types in the El Callao district lode-gold shear-hosted quartz-carbonate veins and disseminated gold with sulphides. Although Lower Proterozoic in age, the deposit types comprise "typical" Archean greenstone-hosted shear and vein gold mineralization similar to other Archean greenstone hosted lode gold deposits worldwide. The lode gold deposits are related to steeply dipping planar shear zones of brittle to ductile deformation and the regional faults are a manifestation of brittle deformation within zones of high strain. The shear zones are regional structures, generally sub-parallel to the volcanic stratigraphy.
The Lo Increible Shear is a complex zone of splays and bifurcating faults along a minimum 15 kilometre strike length, and cuts across the Lo Increible 4A and 4B concessions for at least seven kilometres. Geological and structural mapping of the workings and outcroppings along the Lo Increible mineralized belt indicate deformation processes brittle-ductile shearing events. Intense brittle-ductile shearing has been focused along lithological contacts as a result of intrinsic competency contrast, both at formational contacts and within formations.
The overall trend of the system is north-east through the concessions. At its widest the zone of deformation is 1.5 kilometre wide comprising multiple shear and vein systems. Gold mineralization occurs in shear - vein systems, associated with intense hydraulic brecciation, silica injection and flooding, carbonate alteration in the form of calcite, dolomite, and ferroan dolomite, sericitization, and the deposition of sulphides, in particular pyrite and arsenopyrite.
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