Summary:
Deposits found at El Bagre is best described as a structurally controlled mesozonal gold-silver sulphide-bearing quartz vein lode deposits, with veining emplaced in shear zones within competent intrusive host rocks.
Mesozonal veins occur in rock assemblages of Archean, Proterozoic, and Phanerozoic age, commonly hosted in metamorphosed mafic volcanic flows (greenstone-hosted type) and sedimentary rocks (slate-belt or turbidite-hosted type). In other cases, the veins are located within the contact aureole of granitic intrusions in various host rocks, as is the case at the Properties. Gold mineralization can have a variety of forms and may occur in shear zones, discordant quartz veins or quartz-vein sets (e.g., stockworks) as well. as stratabound zones. Although free gold does occur in quartz veins in some deposits, much of the gold occurs in association with pyrite and/or arsenopyrite in the altered wallrocks surrounding the veins.
Local Geology
Locally, the El Carmen plutonic body corresponds to a leucocratic tonalite, of medium to coarse grain and phaneritic texture, composed of quartz, plagioclase, amphibole, and biotite.
Inside the underground operations, close to the vein contact, the intrusion shows a mylonitic texture, orientated quartz crystals, and chloritization of biotite. In vein exposures, it is common to find xenoliths with phyllic alteration.
Mineralization
Auriferous quartz-sulphide veins are hosted within the El Carmen – El Cordero stock (Leal-Mejía, 2011). The numerous veins trend north-northwest to north-northeast, the most important of which include the El Carmen and La Ye systems, which can be traced over five kilometres. Mineralization is hosted in the structurally controlled quartz veins and is often associated with late, brittle reactivation of the fault zones.
The veins consist of a milky white quartz containing native gold and up to 20% mixed sulphides, dominated by pyrite with occasional galena, and chalcopyrite. Sulphide and native gold distribution within the veins is patchy. The veins average approximately one metre in thickness and range from half a metre to four metres in length. Related wall rock alteration includes haloes of moderate to pervasive sericite ± chlorite and carbonate replacing feldspar within the host intrusive.