The El Roble massive sulfide mineralization is classified as the ‘mafic-type volcanogenic massive sulphide type’.

Atico geologists and other workers use four major rock classifications to described the geology of El Roble license areas. The lowest unit is a submarine mafic volcanic unit up to several kilometers thick. Whole rock (NaO, K2O, MgO, FeO) analyses reported by Ortiz et al. (1990) place the basalt flows in the tholeiitic field. The mafic volcanic unit is overlain by a “black chert unit” up to 30 m thick and turn these grades upwards into a pelagic sedimentary unit, locally termed the “grey chert” up to 120 m thick. The entire package is topped by a sandstone-mudstone, turbidite unit several kilometers thick. The massive sulfide deposits are hosted in the black chert and grey chert units always occurring within meters of the uppermost mafic volcanic contact. The succession of basalt flows, black to grey chert and overlying pelagic sedimentary rocks and sandstone-shale turbidites sequence has been intruded by andesite and latite dikes which post date and disrupt the massive sulfide mineralization.

Mineralization
The El Roble deposit consists a series of massive sulfide lenses, separated by faulting and are the dismembered fragments of once coherent, single, massive sulphide body. The mineral deposit that comprises the El Roble Project consists of mafic-type volcanogenic massive sulfide (VMS) mineralization for which there are numerous exam ........

The El Roble Mine consists of an underground mine with surface infrastructure. Access is by paved primary and secondary highways from Medellin, Antioquia. The mine produces ores that are processed at the local process plant, concentratres are shipped to Buenaventura, Colombia on the Pacific coast for storage and eventual shipping to overseas smelters.

The workings are all underground. The principal mine adit is located within a kilometer of the process plant at the nominal 1,850 Level (1,850-m MASL). The 1880 Level serves as a ventilation intake as well as access for all personnel and materials; additionally, it is the main haulage access to transport ore and waste to the surface. A secondary access is located at the 2000 Level (2,000-m MASL), this access is the primary ventilation exhaust for the mine.

Ore is hauled from underground in highway dump trucks and dumped to covered surface stockpiles, the stockpiles are sampled and the material blended to meet the plant feed grade needs.

Mining Method
Various stoping methods have been used at El Roble successfully. Early in the mine's life blasthole open stoping was done successfully. Large, stable voids were excavated in the massive sulfides with no backfill palced immediately after mining. This method was used from abpve the 2200 Level to the 2000 Level. As large voids were not filled, eventually massive wall failures resulted in collapsed stopes and accesses.

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