MINERALIZATION AND ALTERATION IN EL REAL PROSPECT, GUERRERO, SOUTHERN MEXICO

The El Real silver deposit is located 240 Km SW of Mexico City in Guerrero, Mexico. It is in an old district that was worked initially by the Spaniards in the 18th century. The historical production is unknown but other important veins occur in the district: Santa Ana, Puerta del Sol, Las Josefinas, El Platano, San Nicolas del Oro, Jimotla. The main vein, Montana de Plata, is a 600 m long vein-like brecciated structure containing high-grade silver ore (average of 1680 grams per tonne at the surface). It is controlled by a regional-scale north-south fault system linked to the suture zone between two of the components of the Guerrero terrane (Arcelia and Teloloapan subterranes). The ore bodies are hosted in a complex of rhyolitic domes and dikes of Tertiary age, which represents the continuity of the Sierra Madre Occidental from northern Mexico. The structure is a north-south, dextral strike-slip normal fault that dips 60° to the west. It has an average width of 6.0 meters. The breccia consists of subangular to subrounded fragments of porphyritic rhyolite cemented by sulfides, quartz and sericite. Sulfides include pyrite, arsenopyrite, acanthite, proustite, sphalerite and galena. The breccia is surrounded by an extensive phyllic halo consisting of quartz, sericite, illite and pyrite. The vertical interval between the deepest known mineralization and the top of the exposed orebody is approximately 600 meters. Microthermometric measurements of primary and psudeosecundary fluid inclusions indicate maximum homogeneization temperatures of 223°C and salinities up to 8.3 % eq NaCl. The characteristics of this epithermal system are compatible with a low sulfidation system hosted in volcanic rocks. Fluid inclusions data and the elevation difference between mineralized horizons suggest mineral continuity of the ore band on two different levels. This encourages the exploration on this almost virgin district.