The deposits discovered by Orosur to date in the San Gregorio project area are considered to be typical of mesothermal vein-style, or orogenic-style gold deposits.

The deposits located along the east-west to northwest trending SGFS are, from west to east, the Santa Teresa deposits, the Polvorín deposit, the Ombú deposit, the San Gregorio deposit and the Arenal deposit. Zapucay and Argentinita deposits lie along the extension of the one fold and thrust fault system to the east, with similar age of SGFS.

Gold mineralization at SGGP has occurred as infill of brittle fractures within favourable host rocks such as zones of silicification and mafic units. Brittle fracture has occurred within these zones in response to local extensional tectonics created by the intersection of different trending faults, faults with dikes and changes in the attitude of the fault itself. Intense brittle fracture, silicification and quartz veining are apparent in higher grade zones. At least 3 phases of fracturing and veining can be recognised from drill core.

The gold deposits are generally hosted within basement granulite and amphibolite facies within the upper plate of a large thrust fault that defines the contact with the younger granites to the north. Pyrite is the dominant sulphide, and gold grade is directly proportional to the pyrite content. The gold at all deposits is fine, and visible gold is rare. Other potentially deleterious elements are in low concentrat ........

Open pit mining is performed by conventional open pit methods, using drill and blast techniques to break the rock, and then load it by excavator on to 50 tonne trucks to be transported to appropriate destinations. Historically, mining and hauling from satellite pits around San Gregorio was performed by contractors with smaller mining equipment to match the equipment size, to the size of the pits. Over the past years, contractor mining of satellite pits and ore haulage became a significant cost item for the Corporation. So, during 2012, Orosur decided to acquire its own fleet of smaller mining loading and hauling equipment. Total capital expenditure to acquire this fleet was approximately US$4.5M and was funded by a leasing contract to be repaid in 36 months.

Underground mining at Arenal started in April 2013. Mining is performed according to conventional Inclined Room and Pillars (IRP), and Transverse Stopping methods. That includes development drifting, long-hole drilling, charging & blasting and finally ore mucking out.

The TS method consists of primary and secondary stopes. Primary stopes measure 50m long by 20m high by 20m wide. Secondary stopes have the same maximum dimensions, but include a 6m internal pillar. An 8m wide pillar is located between the primary and secondary stopes. The pillars allow backfill material to consist solely of waste rock, without requiring any cement. The primary stopes have a drill drift driven along both side of the stop ........

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